Cameratechnologybasics

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The Basics of Camera Technology The Basics of Camera Technology Marketing Communication Group Product Information Department Business Planning Division B&P Company Sony Corporation Preface With the development of technologies and endeavors to reduce production costs, various advanced functions, originally available only on high-end video cameras, have been introduced to a wider range of professional video cameras, designed to target larger markets with their versatility. Thus, it has become imperative for those involved in the marketing and sales activities of such video cameras to understand these functions, as well as become familiar with the meanings of the related terminology. Having considered this background, we have created “The Basics of Camera Technology” a useful document that provides comprehensive explanations of all the camera terminologies we consider to be significant. These terms have been carefully selected and placed into five categories: Optical System, CCD Mechanism, Camera Functions, VTRs, and Others. This allows readers to quickly find relevant information according to the terminology in question. We hope this document will be helpful in your business. Marketing Communication Group Product Information Department Business Planning Division B&P Company Sony Corporation Table of Contents Optical System Angle of View..................................................................... 2 Iris ..................................................................................... 6 Chromatic Aberration......................................................... 3 Light and Color.................................................................. 7 Color Conversion Filters .................................................... 3 MTF (Modulation Transfer Function)................................. 8 Color Temperature ............................................................ 4 Neutral Density (ND) Filters .............................................. 8 Depth of Field .................................................................... 4 Optical Low Pass Filter ..................................................... 9 Flange-Back/Back Focal Length........................................ 4 Prism ................................................................................. 9 Flare .................................................................................. 5 White Shading................................................................. 10 F-number ........................................................................... 5 Zoom ............................................................................... 11 Focal Length...................................................................... 6 CCD Mechanism EVS/Super EVS............................................................... 14 Readout Mechanism ....................................................... 18 Field Integration and Frame Integration Mode ................ 15 RPN (Residual Point Noise) ............................................ 19 HAD SensorTM.................................................................. 16 Spatial Offset Technology ............................................... 20 IT/FIT CCD ...................................................................... 16 Variable Speed Electronic Shutter .................................. 21 On Chip Lens................................................................... 17 Vertical Smear................................................................. 22 Picture Element ............................................................... 18 Camera Functions Adaptive Highlight Control ............................................... 24 Gain................................................................................. 31 ATW (Auto Tracing White Balance)................................. 24 Gamma ........................................................................... 32 AWB (Auto White Balance) ............................................. 24 Genlock ........................................................................... 32 Black Balance.................................................................. 25 H/V Ratio......................................................................... 33 Black Clip......................................................................... 25 Intercom (Intercommunication) System .......................... 33 Black Gamma .................................................................. 25 Knee Aperture ................................................................. 33 Black Shading.................................................................. 26 Knee Correction .............................................................. 34 Center Marker.................................................................. 26 Lens File.......................................................................... 34 Clear Scan/Extended Clear Scan (ECS) ......................... 26 Level Dependence .......................................................... 34 Color Bars........................................................................ 27 Limiter ............................................................................. 35 Crispening ....................................................................... 28 Linear Matrix Circuit ........................................................ 36 Cross Color Suppression................................................. 28 Low Key Saturation ......................................................... 36 Detail Level ...................................................................... 29 Mix Ratio ......................................................................... 37 TM ................................................................ 30 Multi Matrix ...................................................................... 38 Dynamic Contrast Control (Automatic Knee Control) ...... 30 Pedestal/Master Black .................................................... 38 Electric Soft Focus........................................................... 31 Preset White.................................................................... 39 File System...................................................................... 31 Reference File................................................................. 39 DynaLatitude 1 The Basics of Camera Technology Optical System Triax................................................................................. 44 Scene File ....................................................................... 40 TruEyeTM (Knee Saturation Function) Processing ........... 44 Skin Tone Detail Correction ............................................ 41 Turbo Gain....................................................................... 45 Sub-carrier Phase Control/Horizontal Phase Control ..... 41 V Modulation.................................................................... 45 Tally ................................................................................ 42 White Balance ................................................................. 46 Tele-Prompter ................................................................. 42 White Clip ........................................................................ 47 TLCS (Total Level Control System) ................................ 43 Zebra ............................................................................... 47 ClipLinkTM/Index Picture/Automatic Logging Function .... 50 SetupLogTM ...................................................................... 51 EZ Focus......................................................................... 50 SetupNaviTM ..................................................................... 51 Camera Functions VTRs CCD Mechanism Return Video ................................................................... 40 EZ Mode ......................................................................... 51 VTRs Others SDI .................................................................................. 61 Camera Control System.................................................. 54 Sensitivity ........................................................................ 62 Camera Control Unit (CCU) ........................................ 54 Synchronization Signal (Sync Signal).............................. 62 Master Setup Unit (MSU)............................................ 54 VBS/BS Signal................................................................. 63 Remote Control Panel (RCP)...................................... 55 Vertical Resolution........................................................... 63 Camera Command Network Unit (CNU)..................... 55 Color Signal Forms ......................................................... 56 RGB ............................................................................ 56 Y/R-Y/B-Y ................................................................... 56 Y/C .............................................................................. 56 Composite................................................................... 56 Decibels (dB) .................................................................. 56 Dynamic Range .............................................................. 57 HD/SD (High Definition/Standard Definition) .................. 57 Horizontal Resolution...................................................... 57 Interlace/Progressive ...................................................... 58 Minimum Illumination ...................................................... 59 Modulation Depth............................................................ 59 NTSC/PAL ...................................................................... 60 PsF (Progressive, Segmented Frames).......................... 60 RS-170A ......................................................................... 61 S/N (signal-to-noise) Ratio.............................................. 61 The Basics of Camera Technology 2 Others Additive Mixing................................................................ 54 C 2003 Sony Corporation. All rights reserved. Reproduction in whole or in part without written permission is prohibited. Sony, BETACAM, DVCAM, DynaLatitude, HAD sensor, Memory Stick, Trinitron and TruEye are trademarks of Sony. Some of images in this document are simulated. All other trademarks are the properties of their respective owners. Optical System Optical System CCD Mechanism The Basics of Camera Technology Camera Functions VTRs Others Optical System Angle of View When shooting a landscape with a camera, as in figure A, Angle of view becomes narrow when a telephoto lens is there is a certain range that will be displayed on a picture used. On the other hand, angle of view becomes wider with a monitor. Angle of view indicates the displayable range of the wide-angle (that is why it is called "wide-angle"). image (plane) measured by the angle from the center of the Consequently, the wider the angle of view is, the wider the lens to the width of the image in the horizontal, vertical, and displayable range becomes. diagonal directions. These are called, the horizontal angle of The angle of view depends on image size, so lenses view, vertical angle of view, and diagonal angle of view, intended for 2/3-inch and 1/2-inch CCD cameras have differ- respectively. ent focal lengths. Monitor Horizontal Angle of view Video Camera Figure A Angle of view can be derived from the following equation. w = 2tan-1 y/2f w: Angle of view y: Image size (width of the image in horizontal, vertical, or diagonal direction.) f: Focal length Focal length Angle of view Image size CCD Figure B 2 The Basics of Camera Technology able in lenses with longer focal lengths, and results in deteri- 'refracted' or gets bent. The amount of refraction depends on oration of the edges of the image. the light's wavelength, which determines its color. Recent technology has made it possible to effectively reduce This also holds true for lenses used in a video camera lens. chromatic aberration of a video camera lens. This is The difference in refraction from color to color directly results achieved by combining a series of converging and diverging in each color light (in a color camera RGB) forming focus on lenses with different refraction characteristics to compensate a different image plane. For example, if one color is in focus for the aberration. The use of crystalline substances such as on the CCD imager, the other colors will be slightly out of fluorite has been practiced to offset the aberration and focus and look less sharp. This phenomenon is more notice- accordingly the locus of the image reproduced. CCD Mechanism When light passes through glass, the path it follows is Optical System Chromatic Aberration Camera Functions Red light's focal point Green light's focal point VTRs Blue light's focal point Color Conversion Filters be possible to balance the camera for all color temperatures temperature. For example, Sony professional video cameras using the R/G/B amplifier gains, this is not practical from a are designed to be color balanced at 3200 K (white balance: signal-to-noise ratio point of view, especially when large gain refer to “White Balance” ). This is the color temperature for up (refer to “Gain” ) is required. The color conversion filters indoor shooting when using common halogen lamps. How- reduce the gain adjustments required to achieve correct ever, the camera must also provide the ability to shoot under white balance. color temperatures other than 3200 K. For this reason, a number of selectable color conversion filters are placed Relative energy before the prism (refer to “Prism” ) system. These filters optically convert the spectrum distribution of the ambient color 3200 K temperature (illuminant) to that of 3200 K, the camera's operating temperature. For example, when shooting under an illuminant of 5600 K, a 5600 K color conversion filter is used to Converted area convert the incoming light's spectrum distribution to that of approximately 3200 K. 5600 K Your question now may be, "why do we need color conversion filters if we can correct the change of color temperature electrically (white balance)?". The answer is quite simple. White balance (refer to “White Balance” ) electrically adjusts the amplitudes of the red (R) and blue (B) signals to be equally balanced to the green (G) by use of video amplifiers. 400 500 600 Wavelength (nm) 700 We must keep in mind that using electrical amplification will result in degradation of signal-to-noise ratio. Although it may The Basics of Camera Technology 3 Others All color cameras are designed to operate at a certain color Optical System Color Temperature The color reproduced by a camera largely depends on the Since, cameras cannot adapt automatically to the color tem- color of the light source (or the illuminant) under which the perature of the light source, it is essential to select the appro- camera is used. This is sometimes difficult to understand priate color conversion filter (refer to “Color Conversion because the human eye is adaptive to changes in the light Filters” ) for the shooting environment in order to obtain accu- source's color and the color of an object will always look the rate color reproduction. The combination of electronic White same under any light source: sunlight, halogen lamps, can- Balance (refer to “White Balance” ) with appropriate color dlelight etc. conversion filter selection will create more accurate color reproduction. The color of light source is defined by using heated carbon (black body absorbing all radiation without transmission and reflection) as a reference. When heating a piece of carbon, it will start glowing and emitting light when it reaches a certain absolute temperature (expressed in Kelvin or (K)). The spectral distribution of the light emitted from the light source is determined by its corresponding absolute temperature, Light Source Skylight Noon Sunlight Sunrise and Sunset 12 V/100 W Halogen Lamp Candlelight Color Temperature (approx.) 12000 K - 18000 K 4900 K - 5800 K 3000 K 3200 K 2900 K known as color temperature. Depth of Field When focusing a lens on an object, there is a certain distance range in front of and behind the object that also comes into focus. Depth of field indicates the distance between the closest and furthest object that are in focus. When this distance is long, the depth of field is "deep" and when short, the depth of field 1)The larger the iris F-number (refer to “F-number” ) (stopping down the amount of incident light), the deeper the depth of field. 2)The shorter the focal length of the lens, the deeper the depth of field. 3)The further the distance between the camera and the subject, the deeper the depth of field. is "shallow". Needless to say, any object outside the depth of field (range) will be out of focus and look blurred. Thus depth of field can be controlled by changing these fac- Depth of field is governed by the three following factors: tors, allowing the camera operator creative shooting techniques. Deep depth of field Shallow depth of field Flange-Back/Back Focal Length Flange-back is one of the most important matters to consider eras, on the other hand, do not require this system. In a 3- when choosing a lens. Flange-back describes the distance CCD camera, the flange-back additionally includes the dis- from the camera's lens-mount reference plane (ring surface tance that the light travels through its prism (the distance the or flange) to the image plane (such as CCDs) as shown in the light travels in the glass material, converted to the equivalent figure below. It is necessary to select a lens with the appro- distance in air, plus the rest of the distance between the lens priate flange-back for the given camera. Flange-back is mea- mount and CCD surface). sured differently depending on whether the camera uses In today's camera systems, flange-back is determined by the glass materials in its light path (like a prism: refer to “Prism” ) lens-mount system that the camera uses. 3-CCD cameras or not. 3-CCD cameras use this system to separate incom- use the bayonet mount system, while single CCD cameras ing light into their three primary color components, which are use either the C-mount or CS-mount system. The flange- then captured by each associated CCD. Single CCD cam- back of the C-mount and CS-mount systems are standard- 4 The Basics of Camera Technology Similar to flange-back is back focal length, which describes three flange-back standards for the bayonet mount system, the distance from the very end of the lens (the end of the cyl- 35.74 mm, 38.00 mm, and 48.00 mm. inder that fits into the camera mount opening) to the image plane. The back focal length of the camera is slightly shorter Optical System ized as 17.526 mm and 12.5 mm respectively. There are than its flange-back. Back focal lenght CCD Mechanism Flange-back with a color shade. numerous diffused reflections of the incoming light inside the In order to minimize the effects of flare, professional video lens. This results in the black level of each red, green and cameras are provided with a flare adjustment function, which blue channel being raised, and/or inaccurate color balance optimizes the pedestal level and corrects the balance between the three channels. On a video monitor, flare between the three channels electronically. VTRs causes the picture to appear as a misty image, sometimes light passes through the camera lens. Flare is caused by Camera Functions Flare Flare is a phenomenon that is likely to occur when strong F-number The maximum aperture of a lens indicates the amount of light diaphragm within the lens (refer to “Iris” ). The lens iris ring is that can be gathered by the lens and directed to the camera also calibrated in F-stops. These calibrations increase by a imager. A larger physical diameter lens will receive light over factor of 2 , so lenses normally carry calibrations of 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22. Since the amount of incoming expressed as an F-number (or F-stop), where the numerical light is proportional to the cross-sectional area, the bright- value of the F-number (F) is mathematically calculated by ness of an image is in inverse proportion to the second power dividing the focal length (refer to “Focal Length” ) (f) by the of the F-number. Simply put, as the value of the F-number effective aperture of the lens (D), as below: increases by one stop, the brightness will decrease to one F = f/D half. This reciprocal relationship means that the smaller the Fnumber, the "faster" the lens, and the higher the sensitivity it It is important to know that the F-number or F-stop is a key will provide on a camera. The maximum aperture F-number factor that affects the depth of field of the scene shot by the is labeled on the front of the lens, and is an important distin- camera (refer to “Depth of Field” ). The smaller the F-number guishing factor when comparing lenses. In lenses used with or F-stop becomes, the shallower the depth of field will TV cameras, a mechanism is required to reduce the sensitiv- become, and vice versa. ity of the lens and camera, and this is achieved by a variable f: Focal length Lens D: Effective aperture F2.8 F2.0 F1.4 Incoming light The Basics of Camera Technology 5 Others a wider area, and therefore is more efficient. The aperture is Optical System Focal Length Focal length describes the distance between the lens and the Video camera lenses usually consist of a series of individual point where the light that passes through it converges on the lenses for zooming and aberration-compensation purposes optical axis. This point is where the lens is in focus and is (refer to “Chromatic Aberration” ), and thus have a virtual called the focal point. To capture a focused image on a CCD focal point called the principal point. imager, the focal point must coincide with the CCD imager plane by controlling the focus of the lens. Focal length Focal point Iris The amount of light taken into a camera and directed to its and closing these diaphragms, the diameter of the opening imager is adjusted by a combination of diaphragms inte- (also called aperture) changes, thus controlling the amount of grated in the lens. This mechanism is called the lens iris and light that passes through it. The amount of the iris opening is functions just like the pupil of the human eye. By opening expressed by its F-number (refer to “F-number” ). F = 4.0 6 The Basics of Camera Technology F = 11.0 white (or transparent). This can be explained with a prism retina of the human eye reacts to light when we view objects. (refer to “Prism” ), in which the light that passes through it is Technically, light consists of various electromagnetic waves separated into its individual light components - typically, the each with a different wavelength. The human eye is only colors of the rainbow. sensitive to electromagnetic waves whose wavelengths fall Coming back to our main subject, the reason we see each between approximately 380 and 760 nanometers. This object with a different color is because each object has differ- range of electromagnetic waves is called the visible spec- ent light-reflection/absorption characteristics. For example, a trum, and indicates the range of light that the human eye can piece of white paper reflects almost all light colors and thus see. To the human eye, each wavelength is viewed as a dif- looks white. Similarly, a pure blue object only reflects the ferent light color. blue light (spectrum) and absorbs all other light colors. The Light emitted from a typical light source (sunlight, fluores- light colors that each object reflects are governed by the cence/halogen lamps) is a combination of a variety of differ- characteristics of the surface of the objects. CCD Mechanism The human eye is sensitive to light. Or in other words, the Optical System Light and Color ent light colors, although the light source may seem to look Camera Functions VTRs It's Green... Others Only a green spectrum is reflected on the leaves. Other colors are absorbed. The Basics of Camera Technology 7 Optical System MTF (Modulation Transfer Function) Modulation Transfer Function (MTF) is an important index ter. When choosing a television lens, it is equally important that indicates a lens's capability of reproducing the contrast to inspect the characteristic of the MTF at the low to mid fre- of picture details. MTF is measured as the lens's contrast quencies in addition to the lens's final resolving power. This reproducibility, which is the capability of resolving the fine is because the low to mid frequency areas of a lens usually black and white vertical lines on a resolution chart. Since represent the main frequency areas used in the NTSC or PAL lenses are typically less sensitive to higher spatial frequen- video signal (refer to “NTSC/PAL” ). It is essential to have a cies (narrower black and white lines), the contrast reproduc- high response (close to 100%) in this area, otherwise the ibility attenuates as the frequency increases. The MTF curve video picture will not be reproduced with sharp contrast. The indicates this change, shown below as a graph with the spa- figure below shows an example. Lens B is capable of resolv- tial frequency on the horizontal axis and contrast reproduc- ing the image at higher spatial frequencies (detailed areas of ibility on the vertical axis. Note that the MTF value changes the image) and may often be misevaluated to having more until it reaches a point where the lines can no longer be resolving power than Lens A. However, up to point X, Lens A resolved. This point indicates the final resolving power of the has the higher resolving power, which can be of more impor- lens, or the narrowest black and white lines that can be tance in most camera applications. resolved. Needless to say, the higher the value of contrast When choosing a lens, both its MTF curve and final resolving reproducibility, the more faithfully contrast is reproduced at power must be considered with care depending on the appli- the given spatial frequency. This means that lenses with cation. higher MTF values at each frequency reproduce contrast bet- MTF Lens A can produce higher image quality. 100 Lens A Higher Contrast Reproducibility Lens B Point X Lens B can produce higher image quality. 33 100 lines/mm Higher Resolving Power Neutral Density (ND) Filters When shooting outdoors, the camera is often subjected to not affect the color temperature (refer to “Color Temperature” extreme highlights. In some cases, these highlights cannot ) of the incoming light since attenuation is uniform over the be handled even with the smallest iris opening of the lens. entire spectrum. ND filters may also be used to intentionally For this reason a few types of selectable ND filters are placed select a wider iris (refer to “Iris” ) opening. As the depth of before the prism (refer to “Prism” ) system with the color con- field (refer to “Depth of Field” ) is in reverse proportion with version filters (refer to “Color Conversion Filters” ). These ND the iris aperture (opening), the camera operator can inten- filters attenuate the magnitude of incoming light to allow tionally defocus objects in front of and behind the object that brighter images to be handled. The use of ND filters does is being shot using the appropriate ND filter. 8 The Basics of Camera Technology Due to the physical size and alignment of the photo sensors An optical low pass filter is placed in front of the CCD prism on a CCD imager, when an object with fine detail, such as a block and only allows light with relatively lower frequencies to fine striped pattern is shot, a rainbow-colored pattern known pass through it. Since this type of filtering may also reduce picture detail, the characteristics of an optical low pass filter pen when the frequency of the lens's incoming light exceeds are determined with special care - to effectively reduce Moire, the CCD's spatial-offset frequency (refer to “Spatial Offset but without degrading the camera's maximum resolving Technology” ) determined by the spacing between each power. photo sensor. In order to reduce such Moire patterns from appearing, optical low pass filters are used in CCD cameras. CCD Mechanism as Moire may appear across the image. This tends to hap- Optical System Optical Low Pass Filter Prism length. For example, in the figure below, green is not “Additive Mixing” ), 3-CCD video cameras process color reflected by any of the prisms and thus is directed straight to video signals by first separating the incoming light into the the green CCD. Red is not reflected at the surface of the sec- three primary colors, red, green, and blue. This is done by ond prism, but gets reflected at the third, and through one the camera's prism system, which is an arrangement of three more reflection within the second prism, it is directed to the prisms. The prism system utilizes the different reflection red CCD. Camera Functions As explained in the section titled Additive Mixing (refer to characteristics that light has depending on its color or wave- VTRs Others Prism CCD Incoming light CCD CCD Camera Color separation system of a 3-CCD camera The Basics of Camera Technology 9 Optical System White Shading White Shading is a phenomenon in which a green or spectral characteristics of the prism. This effect is seen as magenta cast appears on the upper and lower parts of the the upper and lower parts of the screen having a green or screen, even when the white balance (refer to “White Bal- magenta cast even when the white balance is correctly ance” ) is correctly adjusted in the center of the screen adjusted in the center. (shown below). White shading is seen in cameras that adopt a dichroic layer White shading is more commonly due to the lens having an (used to reflect one specific color while passing other colors uneven transmission characteristic and is seen typically as through) in their color separation system. In this system, the the center of the image being brighter than the edges. This is three primary colors (red, green, and blue) are separated corrected by applying a parabolic correction waveform to the using color prisms (refer to “Prism” ). The three-color prisms variable gain amplifiers used for white balancing. use a combination of total reflection layers and color selective reflection layers to confine a certain color. For example, the Another cause of White Shading is uneven sensitivity of the blue prism will confine only the blue light, and will direct this photo sensor in the CCD array. In this case, the White Shad- to the blue CCD imager. ing phenomenon is not confined in the upper and lower parts However, the color-filtering characteristics of each prism of the screen. slightly change depending on the angle that the light enters Sony high-end professional BC cameras are equipped with (angle of incidence) each reflection layer. This angle of inci- circuitry that automatically performs the proper adjustment to dence causes different light paths in the multi-layer structure suppress the White Shading phenomenon. of the dichroic coating layer and results in the change of the Red-reflecting dichroic coating Green cast Magenta Cast Blue-reflecting dichroic coating 10 The Basics of Camera Technology Technically, 'zoom' refers to changing a lens's focal length changing the zoom position. In the telephoto position, less (refer to “Focal Length” ). A lens that has the ability to contin- light is reflected from the subject and directed through the ually alter its focal length is well known as a zoom lens. lens, and thus the iris must be adjusted accordingly. Optical System Zoom Zoom lenses allow the cameraperson to change the angle of Since chromatic aberration (refer to “Chromatic Aberration” ) in turn changes the area of the image that is directed to the and other light-diffusion characteristics change when the CCD image. For example, by zooming-in to an image (the focal length is changed, high-quality zoom lenses use a lens's telephoto position), less of the image will be directed to series of compensation lenses (which account for the higher the lens and thus that area of the image will appear to be purchasing cost). magnified. Zooming-out (wide angle position) means that more of the image is directed to the imager and thus, the The correlation between the zooming ratio and angle of view image will look smaller. It also must be noted that the can be described as shown in the figure below. CCD Mechanism view (refer to “Angle of View” ). Changing the angle of view amount of light directed to the imager also changes when Camera Functions 4.8 mm 8 mm 400 mm 48 mm VTRs 665 mm 120 mm 200 mm Correlation between zooming and angle of view Others The Basics of Camera Technology 11 Optical System CCD Mechanism CCD Mechanism The Basics of Camera Technology Camera Functions VTRs Others CCD Mechanism EVS/Super EVS EVS (Enhanced Vertical Definition System) and Super EVS ing the same high vertical resolution. However, since the first are features that were developed to improve the vertical reso- 1/60 seconds of accumulated charges are discarded, EVS lution of a camera. Since Super EVS is an enhanced form of sacrifices its sensitivity to one-half. EVS, let's first look into the basic technology used in EVS. Super EVS has been created to provide a solution to this EVS has been developed to provide a solution when drop in sensitivity. The charge readout method used in Super improved vertical resolution is required. Technically, its EVS sits between the Field Integration and EVS. Instead of mechanism is based on Frame Integration (refer to “Field discarding all charges accumulated in the first 1/60 seconds, Integration and Frame Integration Mode” ), but reduces the Super EVS allows this discarded period to be linearly con- picture blur inherent to this mode by effectively using the trolled. When the period is set to 0, the results will be the electronic shutter. same as when using Field Integration. Conversely, when set As explained in Frame Integration, picture blur is seen due to to 1/60, the results will be identical to Frame Integration. And the longer 1/30-second accumulation period. EVS eliminates when set between 0 to 1/60, Super EVS will provide a combi- this by discarding the charges accumulated in the first 1/60 nation of the improved vertical resolution of EVS but with less seconds (1/30 = 1/60 + 1/60), thus keeping only those visible picture blur. Most importantly, the amount of resolu- charges accumulated in the second 1/60 seconds. Just like tion improvement and picture blur will depend on the selected Frame Integration, EVS uses the CCD's even lines to create discarding period. This can be summarized as follows: even fields and its odd lines to create odd fields - thus provid- When set near 0: less improvement in vertical resolution, less picture blur. When set near 1/60: more improvement in vertical resolution, more picture blur. Each photo site Field Integration • High in sensitivity but low in resolution. • No discarded electrons. Odd Even Odd Super EVS • Advantages of both Field Integration and Frame Integration (Technically inbetween the two). • The electric shutter is operated at a different timing in alternated lines. Even Electrons are NOT discarded completely. Odd Even Discarded electron Effective electron 14 The Basics of Camera Technology EVS (Frame Integration) • High in resolution but low in sensitivity. • Shutter speed is set to 1/60s for NTSC or 1/50s for PAL. • Electrons are to be discarded to the overflow drain of the CCD. CCDs usually have about the same number of vertical pixels This method is known to provide high vertical resolution but as the number of scanning lines that the TV system does. has the drawback of picture blur since images are captured For example, in the NTSC (refer to “NTSC/PAL” ) system, across a longer 1/30-second period. there are 480 effective TV scanning lines and therefore The Field Integration method reduces this blur by shortening CCDs used in this system have about 490 vertical pixels. the accumulation intervals to match the field rate, 1/60 sec an even field or an odd field, this would mean that the charge tant to keep in mind that only half of the total scanning lines accumulation would drop to one-half due to the shorter accu- are displayed at a time (known as a field). This also means mulation period. Field Integration avoids this by combining that the CCD should readout only half the number of its verti- the charges of two vertically adjacent photo sites and reading cal samples to create a picture field. There are two readout them to the vertical register in pairs. Each pair represents methods used - the Frame Integration method or the Field one pixel on the interlaced scanning line as the aggregation Integration method, which is most commonly used today. of two adjacent vertical pixels. Odd and even fields are crebined. Although this method is most commonly used, it must accumulates the charge for one full frame (1/30 second/two be noted that less vertical resolution is provided compared to fields) before it is readout to the vertical register. To create the Frame Integration mode. This is simply because the pic- even fields, the charges of the CCD's even lines are readout, ture information of two adjacent pixels is averaged in the ver- and for odd fields, the charges for the odd lines are readout. tical direction due to the physically enlarged sensing area. A X X D Pixels B, D, ETC X Charge Integration X Time Frame Integration 1 frame A B C D E + + + + X X X X Charge Integration Time A+B A+B B+C C+D B+C C+D D+E D+E Field Integration CCD Read Out Modes The Basics of Camera Technology 15 Others E Pixels A, C, E, ETC X B C VTRs Field Odd Even Camera Functions ated by altering the photo sites of which charges are comIn the Frame Integration method, each pixel in the CCD array CCD Mechanism (NTSC). However, if every other line was read out to create In interlace TV systems (such as NTSC or PAL), it is impor- Optical System Field Integration and Frame Integration Mode CCD Mechanism HAD SensorTM The HAD (Hole Accumulated Diode) sensor is a diode sensor The Hole Accumulated Layer also plays an important role in which incorporates a Hole Accumulated Layer on its surface. eliminating lag. The amount of lag in CCDs is determined by This layer effectively reduced dark current noise, which is the efficiency of transferring the electrons accumulated in the caused by electrons randomly generated at the Si-Si02 photo sensor to the vertical shift register. In CCDs without a boundary layer. The Hole Accumulated Layer pairs up holes Hole Accumulated Layer, the bottom (potential) of the photo- with the electrons generated at the CCD surface, reducing sensing well tends to shift and, as shown in (a), an amount of the number of electrons (amount of dark current noise) that electrons will remain in the well even after readout. However, enter and accumulate in the sensor. The reduction of dark with the HAD sensor, since the Hole Accumulated Layer current noise results in a reduction in fixed pattern noise, a clamps the bottom of the photo-sensing well to the same high signal-to-noise ratio (refer to “S/N (signal-to-noise) potential, the accumulated electrons will fall completely into Ratio” ), and low dark shading. the vertical register (b). Thus, electrons will not remain in the photo-sensing well after readout. Surface direction Depth direction Surface direction 0V 0V Potential fixed due to HA layer Lag V-Regi Potential N-Substrate Sensor ROG Depth direction OFGC (a) CCD without HAD sensor structure Potential N-Substrate Sensor V-Regi ROG OFGC (b) HAD sensor IT/FIT CCD CCDs are categorized into two types, depending on the light. Smear appears as a vertical line passing through the CCD's structure and the method used to transfer the charge highlight, often seen when shooting a bright object in the accumulated at each photo site to the output. dark. This phenomenon is due to electric charges, accumu- The IT (Interline-Transfer) CCD takes a structure such that lated in highly exposed photo sites, leaking into the vertical the column of photo-sensing sites and vertical registers are register before the transfer from the photo sites to the vertical arrayed alternately. The photo-sensing sites (so-called pix- register occurs. els) convert the incoming light into electrical charges over a 1/60-sec period (1/60 secfor NTSC, 1/50 sec for PAL) (refer The FIT (Frame Interline Transfer) CCD was primarily to “NTSC/PAL” ). After this period, the accumulated charges designed to overcome this drawback. The upper part of this are transferred to the vertical shift registers during the vertical device operates exactly like an IT CCD, having a separate blanking interval. The charges within the same line (the sensing area and charge shifting registers. The bottom part same row in the CCD array) are then shifted down through operates as a temporary storage area for the accumulated the vertical shift register in the same sequence and read into charges: immediately after the charges are transferred from the horizontal register, line by line. Once a given line is read the photo-sensing area to the horizontal registers (during the into the horizontal register, it is immediately read out (during vertical blanking interval), they are quickly shifted to this fully the same horizontal interval) so the next scanning line can be protected storage area. Since the charges travel through the read into the register. vertical register over a very short period, the effect of The only significant limitation in the IT imager structure is an unwanted charges leaking into the vertical register from the artifact called vertical smear (refer to “Vertical Smear” ), photo sites is much smaller, especially when the CCD is which appears when the CCD is exposed to an extreme high- exposed to highlights. 16 The Basics of Camera Technology due to the use of a HADTM sensor and On Chip Lens technol- due to its complexity, usually costs more than an IT CCD. ogy (refer to “HAD SensorTM” and “On Chip Lens” ). However, it most be noted that in recent Sony IT CCDs, the vertical smear has been reduced to an almost negligible level Vertical shift register Optical System The FIT structure thus offers superior smear performance but Photo sensor CCD Mechanism IT CCD Temporary storage area Camera Functions Horizontal shift register VTRs FIT CCD Others On Chip Lens As compared to the human eye's ability to see in the dark, CCD cameras have a limitation in sensitivity (refer to “Sensitivity” ). Many technologies have been developed to improve sensitivity - the On Chip Lens being one of the most significant. On Chip Lens (OCL) technology drastically enhances the light-collecting capability of a CCD by placing a microlens above each photo sensor so that light is more effectively On-Chip-Lens directed to them. The combination of Sony HAD-sensor technology and OCL has achieved tremendous improvement Al Al Si Si in image-capture capability, even under extremely low-light conditions. Since each micro-lens converges the incoming light to each photo-sensing area, less light leaks into the CCD's vertical register, greatly reducing vertical smear (refer to “Vertical P+ N+ 2nd P-Well Hole Accumulated Layer N+ P+ 1st P-Well Smear” ). N-Substrate Sensor C.S (Channel R.O.G stop) V-register (Read out gate) Sensed light The Basics of Camera Technology 17 CCD Mechanism Picture Element CCD specifications are indicated with the number of horizontal and vertical picture elements they have within their photosensitive areas. A picture element contains one photo sensor to sample the intensity of the incoming light directed to it. The number of picture elements within the CCD's sensing area is the main factor, which determines the resultant resolution of the camera. It must be noted that certain areas along the edges of the CCDs are masked. These areas correspond to the horizontal and vertical blanking periods and are used as a reference for absolute black. Thus, there are two definitions in describing the picture elements contained within the CCD chip. CCD picture element 'Total picture elements' refers to the entire number of picture elements within the CCD chip, including those which are masked. 'Effective picture elements' describes the number of Masked picture element picture elements that are actually used for sensing the incoming light. Effective picture element Readout Mechanism CCDs are the most popular imaging devices used in today's Figure C describes the structure of an Interline Transfer (refer video cameras. In brief, CCDs convert incoming light directed to “IT/FIT CCD” ), with the photo sensors used for the light-to- through the camera lens into electrical signals that build a charge conversion and the charge readout mechanism (to video signal. Since the mechanism of a CCD is very similar build the video signal) shown. The photo sensors, also called to the human eye, it is worthwhile to take a look at the how pixels, convert the incoming light into electrical charges. The the human eye works and compare this to a CCD. As figure light conversion and charge accumulation continues over a A shows below, in the human eye, an image (= light) is period of 1/60 seconds. After the 1/60-second period, the directed to and formed on the retina, which consists of sev- electrical charges at each photo sensor are transferred to the eral million photosensitive cells. The retina then converts the vertical shift registers during the vertical blanking interval. light that forms this image into a very small amount of electri- The charges within the same lines (the same row in the CCD cal charges. These are then sent to the brain through the array) are then shifted down through the vertical shift register, brain's nerve system. This is the basic mechanism of how during the next 1/60-second accumulation period, and read people see. into the horizontal register, line by line at a frequency of Coming back to the mechanism of a CCD, the CCD has 15.734 kHz (NTSC format: refer to “NTSC/PAL” ). Once a photo sensors that work exactly like the retina's photosensi- given line is read into the horizontal register, it is immediately tive cells. However, the electrical charge readout method is readout (during the same horizontal interval) so the next quite different. scanning line can be read into the horizontal register. 18 The Basics of Camera Technology Optical System Figure A: Mechanism of human eyeball Retina Brain cells Pupil CCD Mechanism Light to electricity conversion Figure B: Mechanism of CCD camera CCD Picture monitor Vertical shift register Photo sensor Camera Functions Lens VTRs Others Horizontal shift register Figure C: CCD Readout mechanism RPN (Residual Point Noise) RPN stands for Residual Point Noise. This term refers to a directions. On the other hand, compensation technology white or black spot seen on a picture monitor due to a defect electrically offsets the unwanted level shift, reducing the in the CCD. Generally, these spots consist of up to several blemishing effect. numbers of destroyed pixels in the horizontal and/or vertical Distinct causes of dead pixels and blemishes are still under direction, which cannot reproduce colors properly. investigation however. Until now, it has primarily been These spots can be categorized into two types - dead pixels believed that cosmic rays cause damage to the CCD pixels and blemishes. While dead pixels can no longer reproduce during high-altitude transportation in an aircraft. This is colors, blemishes can; they just cannot reproduce colors based on the statistics of greater numbers of cameras trans- properly due to an unwanted level shift of the charges accu- ported by air, exhibiting more RPN. mulated in their pixels. Sony has developed concealment and compensation technologies to counter dead pixels and blemishes, respectively. Concealment technology intelligently interpolates dead pixels using adjacent picture data in the horizontal and vertical The Basics of Camera Technology 19 CCD Mechanism Spatial Offset Technology Spatial Offsetting is a method used to improve the luminance amount of signal charges accumulated in each photo sensor horizontal resolution of CCD cameras. Use of this technique is shown in 1 through 7 as signal level. If displayed on a allows a higher resolution to be achieved than theoretically video monitor, the green CCD signal levels would appear as expected with the number of picture elements that each CCD shown in A' and the red and blue signal levels would appear imager has. As shown in (a), the red and blue CCD chips are as shown in B'. fixed to the prism block with a one-half pitch offset in horizon- These represent the resolution without spatial offsetting tal direction in respect to the green CCD chip. Thus, the being used. number of samples (picture elements) within a line to create The luminance signal, which is defined in TV standards as an the luminance signal is double, giving a higher resolution addition of R/G/B signals with certain weights on each signal, than when spatial offset is not used. is equivalently provided by adding A' and B' in spatial offset- This can also be explained by examining the outputs of the ting. This is shown in C'. As a result, the resolution is greatly three CCD chips. When shooting a subject (for better under- improved. standing, imagine a black triangle written on a white sheet of Furthermore, when Spatial Offsetting is done, unwanted arti- paper) with a CCD camera using spatial offset, the image is facts caused by the CCD clock signal will be decreased and projected on the green, red, and blue CCDs as shown in (b). thus contribute to reproducing sharper picture images. A and B in (c) are enlargements of areas A and B in (b). The "Picture insertion" 1/2P P 1/2P CCD(R) CCD (R and B) P CCD(G) CCD(B) 1/2P CCD(G) P: pitch (a) A V Resister Photo sensor B CCD(G) CCD(R/B) A' B' HALF PICTURE ELEMENT C' (b) (c) Spatial Offsetting 20 The Basics of Camera Technology tion period to be shortened using the electronic shutter func- tube camera. This function is similar to mechanical shutters tion. The electronic shutter operates in such a manner that used in film cameras and can be used in the very same way. when a certain shutter speed is selected, for example, 1/500 When activated, it allows the camera to capture objects mov- second, electrons accumulated only during this period are ing at high speeds with less picture blur. output to the vertical register. All electrons accumulated To understand how this function works, it is worthwhile review- before this period are discarded. The result is that movement ing the mechanism of an IT CCD (refer to “IT/FIT CCD” ). capture only within the short shutter period will be captured Incoming light is converted to electrons (electrical charges) at less, effectively reducing the picture blur of fast-moving each photo sensor, where they are accumulated over a certain objects. period and then transferred to the vertical shift register. When It is also important to note that shortening the accumulation the electronic shutter is set to OFF (1/60 second, 1 field), elec- period results in a drop in sensitivity, which must be compen- trons are accumulated over the entire field period (1/60 sec- sated for by using a wider iris opening. Higher shutter speed ond) and then readout to the vertical register. However, if is sometimes used for the purpose of getting shallow depth of there is fast movement in the picture during this accumulation field (refer to “Depth of Field” ) with a wider iris (refer to “Iris” ) period, picture blur will be seen. opening instead of using neutral density filters (refer to “Neutral Density (ND) Filters” ). Generated electrons VTRs Vertical shift register Camera Functions To avoid this blur, CCD cameras allow the electron accumula- ment of an electronic shutter, which was not available in any CCD Mechanism The use of CCDs in video cameras has enabled the develop- Optical System Variable Speed Electronic Shutter 1/60 Horizontal shift register Shutter period Discarded electrons (a) Mechanism of IT CCD 1/60 Shutter period Shutter period Output electrons (b) Principle of electronic shutter The Basics of Camera Technology 21 Others Output 1/60 CCD Mechanism Vertical Smear Vertical Smear is a phenomenon peculiar to CCD cameras, constantly leak into the vertical register while it shifts down to which occurs when a bright object or light source is shot with the horizontal register. the camera. This phenomenon is observed on the video The amount of smear is generally in proportion to the inten- monitor as a vertical streak above and below the object or sity of the light from the subject or light source and the area light source as shown below. A most notable example is that these occupy on the CCD. Thus, in order to evaluate when the headlights of a vehicle are shot with a CCD camera smear level, the area must be defined. in the dark. Smear in recent Sony CCD cameras has been drastically Smear is caused by the direct leakage of incoming light into reduced to a level that is almost negligible due to the use of the vertical shift register or the overflow of the electrical the HAD sensor (refer to “HAD SensorTM” ). charges accumulated in the photo sites. The reason that smear is observed as a vertical streak is because electrons Vertical smear 22 The Basics of Camera Technology Vertical smear is reduced by the use of HAD sensor Optical System Camera Functions CCD Mechanism The Basics of Camera Technology Camera Functions VTRs Others Camera Functions Adaptive Highlight Control Conventional cameras only have a single knee point/slope Input signal level (refer to “Knee Aperture” and “Knee Correction” ) characteristic. In contrast, the Sony ADSP (Advance Digital Signal white clip Processing) system has multiple knee point/slope characteristics. The camera intelligently monitors the brightness of all areas of the picture and adapts the knee point/slope for opti- Multiple knee point/slope mum reproduction. A typical example is shooting an interior scene, which includes a sunlit exterior seen through a window. This function applies only to video levels in excess of the knee point, the middle and low luminance parts remaining unchanged. Knee point 1 . . . . . . . . . . . . . . . Knee point n Normal On ATW (Auto Tracing White Balance) ATW stands for Auto Tracing White Balance. This feature can must be changed accordingly. If Auto White Balance was be considered an extension of AWB (refer to “AWB (Auto used, the operator would have to activate it each time a small White Balance)” ) but with much more convenience. While change was seen in the color temperature. Auto White Balance is used to set the correct color balance The use of Auto Trace White Balance eliminates this need, for one particular shooting environment or color temperature since the white balance will be automatically reset according (refer to “Color Temperature” ), Auto Tracing White Balance to the change of color temperature. In other words, the white corrects the color balance automatically and dynamically with balance will automatically follow the change of color tempera- any change in color temperature. ture. For example, imagine shooting a scene that moves from It must be noted however, that while Auto Tracing White Bal- indoors to outdoors. Since the color temperature of indoor ance can be convenient, it does have limitations in the accu- lighting and sunlight is obviously different, the white balance racy of white balance adjustments. AWB (Auto White Balance) Unlike the human eye, cameras are not adaptive to the changes in color temperature (refer to “Color Temperature” ) Auto White Balance is often mistaken with Auto Tracing White of different environments. For this reason, all professional Balance (ATW) (refer to “ATW (Auto Tracing White Balance)” cameras allow 'White Balance' adjustments to make a 'white' ), a feature equipped in consumer video cameras. While object always look white (refer to “White Balance” ). Auto ATW is 'completely' automatic and constantly adjusts the White Balance is a feature that allows white balance to be white balance in accordance with the change of the lighting automatically adjusted simply by the press of a switch. This environment, AWB is designed to set the correct color bal- feature comes in handy when there is not time for manual ance for only one particular environment. Therefore, the adjustments or for operators not familiar with white balance. operator must activate it each time a small change is seen in 24 The Basics of Camera Technology paper - that occupies more than 70% of the viewfinder dis- nient, however, AWB achieves much more accurate color play, and then pressing the AWB button located on the cam- reproduction as compared to ATW. AWB is achieved by fram- era body. ing the camera on a white object - typically a piece of white To ensure accurate color reproduction from a camera, it is Most cameras provide an Auto Black Balance function, which imperative that the camera reproduces a true black when the automatically closes the lens iris and balances the R, G, and lens iris is closed, otherwise a colorcast may be seen. This B black levels when activated. requires accurate matching of the R, G, and B black levels. All cameras have a circuit to prevent the camera output sig- which electronically 'clips off' signal levels that are below a nals from falling below a practical video level, which is speci- given level called the black clip point. The black clip point is fied by the television standard. This is known as Black Clip, set to 0% video level. Camera Functions Black Clip CCD Mechanism Black Balance Optical System the color temperature. This may sound somewhat inconve- Black Gamma cast station (different broadcast stations will have their own signal levels can be adjusted using the Black Gamma fea- stipulations on the black level). VTRs In high-end Sony cameras, the gamma curve near the black This feature is achieved without affecting the gamma curve of the mid-tone and high tones areas. Adjusting black gamma to obtain a steep gamma curve near the black signal levels allows more contrast to be seen in dark parts of the picture, Output level ture. thus resulting in better reproduction of picture detail. near the black signal levels also results in the increase of Gamma OFF Cross point noise, and black gamma must be adjusted with care. Conversely, black gamma can be adjusted to reduce noise in dark picture areas but with the drawback of less contrast being seen. Reproduction of black is extremely important to obtain the desired color reproduction of entire images, accurately and 3.5 to 4.5 faithfully. Thus, professional video cameras, especially those Input level used in broadcast stations, are required to have this capability to reproduce faithful black level stipulated by each broad- Standard video gamma Gentle gamma curve near the black signal levels The Basics of Camera Technology 25 Others However, it must be noted that using a steep gamma curve Camera Functions Black Shading Black Shading is a phenomenon observed as unevenness in various secondary factors, such as heat accumulated within dark areas of the image due to the dark current noise of the imaging device. A Black Shading Adjustment function is imaging device. Dark current noise describes the noise available in most professional video cameras to suppress this induced in a CCD by unwanted electric current generated by phenomenon to a negligible level. Center Marker The Center Marker is a mark in the viewfinder that indicates the center of the image being shot. This is especially useful when zooming in to a particular area of the subject. By using the center marker as a reference, camera operators can zoom in to a subject with the desired area accurately framed. This is most convenient when a high magnification lens and high zooming speed is used. Center Marker Clear Scan/Extended Clear Scan (ECS) When computer displays are shot with video cameras, either computer display's vertical frequency. This is done by chang- a white or black, half transparent horizontal bar is seen, run- ing the CCD accumulation period using the electronic shutter. ning from the top to the bottom of the computer screen. This By activating Clear Scan, the electronic shutter speed (CCD phenomenon is due to the difference in the vertical frequen- accumulation period) can be controlled in a linear-like fashion cies of the camera and computer display. In order to eliminate so it can be matched exactly to the computer display's verti- this phenomenon, Clear Scan was developed by applying the cal frequency. In this way, the banding effect mentioned ear- technologies of the CCD's Variable Speed Electronic Shutter lier is effectively eliminated (as shown C). (refer to “Variable Speed Electronic Shutter” ). When the display's vertical frequency is lower (display time Extended Clear Scan is an advanced form of Clear Scan and longer) than the CCD's accumulation period (for example, 1/ is available only on cameras with FIT CCDs (refer to “IT/FIT 60 seconds for NTSC), the CCD will output (readout) the CCD” ). Extended Clear Scan expands the range of available image before the entire computer display is scanned. The shutter speeds down to 30 Hz and 25 Hz, for 59.94i and 50i computer's lines that where not scanned within the 1/60-sec- formats respectively. Thanks to the Clear Scan/Extended ond CCD accumulation period will appear black (as shown Clear Scan functions, almost all monitor scanning frequen- A). Vice versa, if the display's vertical frequency is higher cies are supported. Clear Scan and Extended Clear Scan (display time shorter) than the CCD's accumulation period, are also effective for eliminating the flicker effect when shoot- then the CCD will capture part of the computer scan twice, ing under fluorescent lighting, which may have a different fre- resulting in more light being captured on that part of the CCD quency than that of the standard CCD accumulation period. and a white bar being output (as shown B). Extended Clear Scan can also be used to eliminate the flicker Clear Scan eliminates this phenomenon by allowing the CCD effect when shooting movie screens operating at 48 Hz. readout accumulation period to be synchronized with the 26 The Basics of Camera Technology CRT display CRT display Signal level 0 0 Black bar Optical System Black bar T1 T1 (a-1) f disp < fc.scan White bar (a-3) CCD Mechanism (A) Black bar (a-2) 0 0 White bar T1 T1 (B) White bar (b-2) (a-2) f disp > fc.scan (C) 0 T1 T1 no bar is seen (c-2) (c-3) (a-3) f disp = fc.scan Camera Functions 0 (b-3) VTRs Color Bars Shooting a program usually starts by recording a color-bar duction throughout the entire production chain. They are usu- signal generated in the camera to the top of the tape. For this ally recorded to the source tape at the acquisition stage as a purpose, production cameras have internal color-bar genera- reference to adjust the output encoders of VTRs and other tors. The color-bar signal from the camera can also be used equipment used in subsequent production processes. Adjust- as a reference for adjusting the chroma, phase, and bright- ments are made so that each device outputs the color-bar sig- ness of a monitor. Others Color-bar signals are used to maintain consistent color repro- nal to show the exact same color and brightness as when recorded in the acquisition stage. Vector scopes are used to adjust the color (hue/saturation) while wave-form monitors are used to adjust the brightness. There are a few color-bar definitions in the NTSC TV system (refer to “NTSC/PAL” ). However, all color-bar signals basically look the same (in some cases, additional color bars or blocks are placed below the color bars) when displayed on a picture monitor. There are seven vertical bars - one white bar on the very left, followed with six colored bars to the right. The order of the colored bars from left to right is yellow, cyan, green, magenta, red, and blue. This is the descending order of each color's luminance Color bar level. It is also important to know that each color (including the white bar) is a combination (total: seven combinations) of equally adding the three primary colors, red, green, and blue, and all have 100% saturations. A 75% color bar has the same 100% white bar but the levels of R, R and B for the colored bars is 75%, This maintains the level of the peak to 700 mV but reduces the saturation of the color bars. The Basics of Camera Technology 27 Camera Functions Crispening As mentioned in the section on Detail Level (refer to “Detail Level” ), detail signals are used to raise the contrast at the Crispening level dark-to-light and light-to-dark transitions, making the edges of objects appear sharper both horizontally and vertically. Simply put, detail correction makes pictures look sharper than the actual resolution provided by the camera. However, since detail correction is applied to the entire picture, its use also emphasizes the noise of the picture, especially when the detail level is high. Crispening is a circuit implemented to avoid detail signals being generated around noise. By activating the Crispening function, detail signals with small amplitudes, which are most likely caused by noise, are removed from the signal. As shown in the figure below, in the Crispening process, only detail signals that exceed a designated threshold are utilized for image enhancement. Conversely, the detail signals with small amplitudes are regarded as noise and removed. Crispening allows detail to be adjusted without worrying about its influence over noise. Cross Color Suppression Cross color is an artifact seen across very fine striped pat- have been developed to separate the composite signal into terns when displaying a composite signal feed on a picture its luminance and chrominance components, none have monitor. It is observed as a rainbow-like cast, moving across been complete even with the most advanced technology. the stripes. To understand how cross color occurs, it is Cross Color Suppression technology - incorporated in the lat- worthwhile to review the composite signal (refer to “Color Sig- est Sony professional video cameras - presents a solution to nal Forms” ). the limitations of Y/C separation on TV receivers. Cross A composite signal is formed by combining the chrominance Color Suppression refers to a digital filtering process, which and luminance signals together so their spectrums inter- eliminates any luminance components that may result in leave. In the early days of color broadcast, the composite cross color prior to outputting the composite signal. These signal introduced the benefit of transmitting a color signal frequency components are eliminated from the Y/R-Y/B-Y within the same bandwidth as a black and white signal. How- signals within the camera head by using sophisticated digital ever, a drawback was seen on the TV receiver side. Since all three-line comb filtering (NTSC/fine line/PAL). This allows video signals must be decoded into their R, G, and B compo- the composite signal to be easily separated back into its nents for display on a color video monitor, the composite sig- chrominance and luminance components at the TV receiver. nal first requires to be separated into its chrominance and This results in greatly reduced cross color and dot crawl (dot luminance components (known as Y/C separation). This is noise appearing at the boundaries of different colors) than where the problem occurred. Although many techniques normally observed. Cross Color 28 The Basics of Camera Technology Cross Color Suppression ON detail-correction process. The original signal (a) is delayed raises the contrast at the dark-to-light and light-to-dark transi- by 50 nsec to obtain signal (b) and by 100 nsec to obtain sig- tions, making the edges of objects appear sharper than pro- nal (c). By adding (a) and (c) we have signal (d). The detail vided by the actual resolution of the camera. This process is signal used for enhancement (signal (e)) is obtained by sub- applied electrically within the camera by overshooting the sig- tracting (d) from two times (b). This is further added to (b), nal at the edges. In most professional cameras, image completing the detail correction (f). enhancement is applied to both vertical and horizontal pic- The mechanism for creating the vertical detail signal is basi- ture edges. cally the same as horizontal detail correction. The only differ- In camera terminology, this process is called 'detail'. Detail ence is that the delay periods for creating signals (b) and (c) level refers to the amount of image enhancement, or in other are one horizontal scanning line and two horizontal scanning words, the amount of sharpness added to the picture. lines, respectively. In most professional cameras, this can be altered with the Excessive detail correction will lead to an artificial appear- detail-level control circuitry. ance to the picture, as though objects have been "cut out" It is worthwhile understanding how the horizontal detail signal from the background. is created. (a) Camera Functions For simplicity, let's examine how this is done in an analog improve picture sharpness. In brief, image enhancement CCD Mechanism In all cameras, image enhancement is used as a method to Optical System Detail Level (b) VTRs 1T (c) 2T (d) Others (e) Image enhancement (f) T: 50 – 100 nsec (H detail) H period (V detail) Detail correction The Basics of Camera Technology 29 Camera Functions DynaLatitudeTM DynaLatitude is a feature offered on Sony DVCAM camcord- DynaLatitude functions in such a way that the signal is com- ers for capturing images with a very wide dynamic range or, pressed within the 1 Vp-p range according to the light distri- in other words, images with a very high contrast ratio. For bution of the picture. DynaLatitude first analyzes the light example, when shooting a subject in front of a window from distribution or light histogram of the picture and assigns more inside the room, details of the scenery outside will be difficult video level (or more 'latitude') to light levels that occupy a to reproduce due to the video signal's limited 1 Vp-p dynamic larger area of the picture. In other words, it applies larger range. However, DynaLatitude is a unique technology that compression to insignificant areas of the picture and applies overcomes this limitation so that both dark areas and bright less or no compression to significant areas. areas of a picture can be clearly reproduced within this 1 Vpp range. DynaLatitude OFF DynaLatitude ON Dynamic Contrast Control (Automatic Knee Control) Although many new techniques have been developed for In this way, a scene requiring a wide dynamic range can be highlight control, Dynamic Contrast Control (DCC) is proba- reproduced within a standard video level. The DCC circuits bly one of the most popular. employed in Sony CCD cameras allow a dynamic range of up As with other methods, DCC allows the camera to reproduce to 600%. details of a picture, even when extremely high contrast must Other contrast control methods including DynaLatitude and be handled. A good example is when we try to shoot a per- Adaptive Highlight Control (refer to “DynaLatitudeTM” and son standing in front of a window from inside the room. With “Adaptive Highlight Control” ) are also available on most Sony DCC activated, details of both the person indoors and the professional cameras. scenery outside can be reproduced on a picture monitor despite the large difference in luminance level inside and out- Video output side. The mechanism of DCC is basically the same as knee cor- 100% rection (refer to “Knee Correction” ). The difference is that DCC allows a wider dynamic range by automatically controlling the knee point (and in some cameras, the knee slope) to Knee point a video level optimized for the scene that is being taken. For example, when there are no extreme highlights, the knee point will be adjusted to a point near the white clip (refer to 50% “White Clip” ) so the details of a picture can be reproduced linearly in each area (each video level) with high contrast. On the other hand, when the incoming light far exceeds the white clip level, the DCC circuitry gradually lowers the knee point according to the intensity of the light. 100% 600% Illumination 30 The Basics of Camera Technology Skin Tone Detail (refer to “Skin Tone Detail Correction” ) can Electronic Soft Focus is used in conjunction with Skin Tone be very effective for reducing picture sharpness of specified Detail to create soft images across only the specified color color areas. But it also has limits. It does not really apply pic- range. Optical System Electric Soft Focus ture blur, it simply decreases the detail signal level to apply a cinematic or film-like softness. Original across images with specific colors, most Sony high-end cam- Enhanced eras offer a function called Electronic Soft Focus. This uses Soft Focus the detail signal to reduce, rather than increase, the sharpness of a picture. As shown in the diagram, by subtracting the detail signal from the original signal (as opposed to add- CCD Mechanism In order to further apply a cinematic or film-like softness ing it in image enhancement), Electronic Soft Focus provides a picture that is 'softer' than that achieved with the detail File System Professional video cameras allow a variety of detailed and Depending on their nature and when they are used in the entire setup procedure, adjustment parameters are catego- rimetry for each shooting scenario as well as to compensate rized into appropriate "data files", such as Reference File for technical imperfections in certain camera components. In (refer to “Reference File” ), Scene File (refer to “Scene File” ), order to reduce the burden of repeating an adjustment each Lens File (refer to “Scene File” ) etc. In Sony camera sys- time a shoot is performed, professional cameras provide tems, the Reference File and the Scene File can be stored on facilities that allow these to be saved and recalled as "data removable recording media such as Memory StickTM and files" whenever required. This File System greatly contrib- Memory Card, which enables instant reproduction of shoot- utes to operational efficiency, and has been adopted in all ing conditions for particular scenes as well as the duplication professional video camera systems available today. of camera setup adjustments between multiple cameras. VTRs complex adjustments in order to reproduce the desired colo- Camera Functions switcher turned off completely. Others Gain When shooting with a video camera in low-light conditions, a eral Gain Up values, which are selected by the operator sufficient signal level can often not be obtained due to a lack depending on the lighting. It must be noted that choosing a of light directed to the imager. For such cases, video cameras large Gain Up value will result in degrading the S/N ratio, have a Gain Up function, which electronically boosts the since noise is also boosted. Some cameras have a minus video signal to a sufficient level for viewing on a monitor or Gain Up setting to improve their S/N ratio. recording to a VTR. The Gain Up function usually offers sev- The Basics of Camera Technology 31 Camera Functions Gamma Gamma (γ ) is a numerical value that shows the response It is obvious that the gamma of a picture monitor CRT must characteristics between the image brightness of an acquisi- be compensated for in order to faithfully reproduce pictures tion device (camera) or display device (CRT monitor) and its taken by the camera. Such compensation is called 'gamma input voltage. In order to obtain faithful picture reproduction, correction'. Properly speaking, gamma correction should be the brightness of the picture must be in direct proportion to done within the picture monitor. However, this is done within the input voltage. However, in CRTs used for conventional the camera since it is more economically efficient to perform picture monitors, the brightness of the CRT and the input the correction within the cameras used by the broadcaster, voltage retain a relationship with an exponential function, rather than in the huge number of picture monitors that exist instead of a directly proportional relationship. As shown in in the market. (a), the beam current (which is in proportion to the CRT's The goal in compensating (gamma correction) for the CRT's brightness) versus the input voltage rises as an exponential gamma is to output a signal so that the light that enters the curve, in which the exponent is a factor larger than one. On camera is in proportion to the brightness of the picture tube, the monitor screen, the dark areas of the signal will look as shown in (b). When the light that enters the camera is much darker than they actually are, and bright areas of the proportional to the camera output, it should be compensated signal will look much brighter than they should be. Techni- for with an exponent of 1/γ . This exponent γ ’(1/γ ) is what we cally, this relation is expressed in the following equation: call the camera's gamma. The gamma exponent of a monitor is about 2.2. Thus the camera gamma to compensate for this I=CxEγ is about 0.45 (1/2.2). Although gamma correction in the camera was originally where I is the brightness, E is input voltage and C is a spe- intended for compensating for the CRT's gamma, in today's cific constant. The exponent in this equation is called the cameras, gamma can be adjusted to give the camera image 'gamma' of the CRT. a specific look. For example, a film-like look can be achieved by changing the settings of the camera's gamma. Brightness Brightness Camera gamma Gamma correction CRT’s (a) Input voltage CRT’s gamma (b) Input voltage Genlock In multi-camera systems, it is necessary to synchronize (refer generator to the signal supplied to its Reference IN connec- to “Synchronization Signal (Sync Signal)” ) the internal sync tor. The composite signal used to synchronize the cameras generators of each camera within the system. More specifi- can be supplied from a signal generator, the switcher, or one cally, the frequencies and phases of the V sync, H sync, and of the cameras within the system designated as the master. sub-carrier of each camera output must be synchronized with each other. Otherwise, picture shifts will occur when switching from camera to camera with the switcher system used. Synchronization is accomplished by feeding the same composite signal to each camera as a timing reference. In video technology, this is described as 'genlock', which refers to the camera's function of locking its internal sync 32 The Basics of Camera Technology As explained in the section on Detail Level (refer to “Detail vertical picture edges. It is important to maintain the balance Level” ), detail correction is applied to both horizontal and of the horizontal and vertical detail signals to achieve natural vertical picture edges using separate horizontal detail and picture enhancement. H/V Ratio should thus be checked vertical detail circuitries. H/V Ratio refers to the ratio every time detail signals are added. Optical System H/V Ratio between the amount of detail applied to the horizontal and communications. These are the Engineer's Line (ENG), verbal communication between the camera crew and staff in intended for communication on technical issues between the the studio/OB-van control room is of vital importance. This is studio and the control room, the Producer's Line (PROD), usually done using the Intercom Function, available on all used for communications on how the program should be studio-type camera systems and their counterpart camera built, and the Program Audio Line (PGM), used to feedback control units. In actuality, verbal communication between the the studio content of the show to the camera crew. As with all camera crew and staff in the control room becomes possible other signals, intercom signals are also transmitted between by connecting an intercom system to the camera control unit the camera and camera control unit (refer to “Camera Control which relays the communication line to the camera head. System” ) through the Triax cable (refer to “Triax” ). Intercom systems can have up to three separate channels for Camera Functions Whether the application is for studio or outside broadcasting, CCD Mechanism Intercom (Intercommunication) System VTRs Knee Aperture When knee correction (refer to “Knee Correction” ) is applied to the video signal within a camera, reduction in contrast in the highlight areas cannot be avoided. This is because the highlight contrast - and the detail signals generated to emphasize this contrast - are compressed by the knee correction process which follows. To compensate for this loss in Others contrast, the knee aperture circuit activates to emphasize the edges of only those areas where knee correction is applied (highlights above the knee point). Knee aperture can be adjusted in the same way detail correction can but only for those areas above the knee point. The Basics of Camera Technology 33 Camera Functions Knee Correction When we take a photo against a strong backlight, just like The video level from which signals are compressed is called shooting a portrait picture in front of a sunlit window, we can the knee point. As shown in the figure, the video output still clearly see the subject's face while being able to see the above the knee point is compensated for to give a more grad- details of scenery outside the room. This is because the ual response. Thus some detail (contrast) can still be human eye can handle wide dynamic range (refer to observed in the bright areas above the knee point, broaden- “Dynamic Range” ). However, this is not easily done by video ing the dynamic range of the camera. cameras because of the limited video-level dynamic range specified by the television standard. Therefore if the camera Video output White clip point lens iris was adjusted for correct exposure of human skin tones, the bright areas of the image would not fit into the video-signal range and would be washed out. Vice versa, if 100% the iris was adjusted for the bright areas, the video level of Knee point human skin tones would be very low and would look too dark. In order to obtain an image reproduction like the human eye, as naturally as possible, a function called 'Knee Correction' is 50% widely used on today's video cameras. Knee Correction is a function that compresses the wide dynamic video signals acquired by the imager (CCDs) into the limited video-level 600% 100% range specified by the television standard. Illumination Lens File In general, each camera lens introduces different 'offset' each lens file is assigned a file number designated by the characteristics, which are electronically compensated for on operator, pre-adjusted lens-compensation data can be a lens basis by making appropriate adjustments to the cam- instantly recalled simply by selecting the correct file number. era. However, when multiple lenses are used on the same Simply put, once the setting for a given lens has been made camera, these different characteristics require the camera to and stored as a lens file, all that need to be done to use this be readjusted each time the lens is changed. lens again is to select the file number associated to it. In order to eliminate this burden, most high-end professional Some large studio-type lenses take this a step further by cameras have a so-called Lens File system. With this sys- automatically recalling the correct lens file by registering the tem, camera operators can store lens compensation settings same number in the lens's memory as that used for the asso- for individual lenses within the camera as lens files. Since ciated lens file. Level Dependence Level Dependence is a similar function to Crispening (refer to Dependence allows a different amount of detail correction to “Crispening” ), which is used to prevent unwanted detail sig- be applied under a given threshold. nals generated by noise. While 'Crispening' removes detail Since noise is most noticeable to the human eye in dark pic- signals generated by noise at all signal levels, Level Depen- ture areas, Level Dependence improves the signal quality in dence simply reduces the amplitude of detail signals gener- these areas. Level Dependence is effectively used when the ated in the low luminance areas. In other words, Level picture content has extremely fine details, which could be mistaken for removed noise if Crispening was used. 34 The Basics of Camera Technology Optical System CCD Mechanism LEVEL DEP. Camera Functions Limiter because detail signals are generated in proportion to the dif- Level” ), detail signals are used to raise the contrast at the ference in the luminance levels at the dark-to-light or light-to- dark-to-light and light-to-dark transitions, making the edges dark transitions. of objects appear sharper both horizontally and vertically. The limiter is a circuit to suppress this unwanted effect. It However, when there is large difference in the luminance 'clips off' the top of detail signals that are above a designated level at the dark-to-light or light-to-dark transitions, the detail threshold, thereby preventing excessive detail correction for circuit is likely to generate an over-emphasized picture edge both white and black detail signals. VTRs As mentioned in the section on Detail Level' (refer to “Detail and objects may appear to 'float' on the background. This is Edge Others White limiter level Detail signal Black limiter level Detail signal The Basics of Camera Technology 35 Camera Functions Linear Matrix Circuit All hues in the visible spectrum can be matched by mixing 1.0 the three primary colors, red (R), green (G), and blue (B). The spectrum characteristics of these three primary colors are shown in the figure below. Some areas contain negative 0.75 this means that some colors cannot be matched using any R, G, and B combination. In video cameras, this would result in particular colors not being faithfully reproduced. The Linear Matrix Circuit compensates for these negative light values by electronically generating and adding them to the corresponding R, G, and B video signals. The circuit is placed before the gamma correction (refer to “Gamma” ) so Relative sensitivity spectral response. Since negative light cannot be produced, 0.5 0.25 0 that compensation does not vary due to the amount of gamma correction. In today's cameras, the Linear Matrix Circuit is used to create a specific color look, such as one 400 defined by the broadcaster. 500 600 Wavelength (nm) 700 Ideal spectrum characteristic Low Key Saturation With conventional video cameras, low-light areas can be sub- an optimized level, thus providing more natural color repro- ject to a reduction in saturation. The Low Key Saturation duction. As shown in the figure below, with the Low Key Sat- function offered in Sony's professional video cameras brings uration function, a warmer color is reproduced that is closer a solution to this problem. The Low Key Saturation function to natural human skin. adjusts the color saturation at low-light levels by boosting it to Low Key Saturation OFF 36 The Basics of Camera Technology Low Key Saturation ON pressed. For this reason, pre-gamma correction is effective detail correction (refer to “Detail Level” ) is applied both for enhancing contrast at dark areas of the image. Post- before and after the gamma correction (refer to “Gamma” ) as gamma correction, on the other hand, is used to effectively shown below. The term, Mix Ratio, describes the ratio of the enhance the brighter parts of the image. Unlike H/V ratio amount of detail applied at pre-gamma detail correction and (refer to “H/V Ratio” ), there is no optimum ratio for Mix Ratio. post-gamma detail correction. It is a parameter that is adjusted depending on each opera- The reasons that detail correction is applied twice owes to tor's different preference. the gamma correction's non-linear nature. Gamma correction used in video cameras boosts the contrast at the dark picture areas and those in the white pictures get com- *It should be noted that while the image will appear sharper as the amount of enhancement is increased, noise may also be enhanced. Camera Functions Gamma CCD Mechanism In most professional video cameras, image enhancement or Optical System Mix Ratio DTL VTRs Others The Basics of Camera Technology 37 Camera Functions Multi Matrix Multi Matrix has been developed for further creative control in areas of adjustment, where the hue and/or saturation of each color adjustments of a scene. Unlike conventional color cor- area can be modified. rection or matrix control, in which all color control parameters For example, the hue and saturation of a flower's red petal interact with each other, the Multi Matrix function allows color can be changed, while keeping other colors unchanged. In adjustments to be applied only over the color range desig- addition to such special effects work, this function is also use- nated by the operator. The color spectrum is divided into 16 ful for matching color among multiple cameras, or for reproducing the color characteristics of another camera. R–Y saturation Phase Normal B–Y On Pedestal/Master Black Pedestal, also called Master Black, refers to the absolute than it should do (the image will appear blackish and black level or the darkest black that can be reproduced with heavier). If the pedestal level is set too high on the other the camera. On most cameras, pedestal can be adjusted as hand, the image will look lighter than it should do (the image an offset to the set-up level. Since pedestal represents the will look foggy with less contrast). lowest signal level available, it is used as the base reference By taking advantage of the pedestal characteristics, it is pos- for all other signal levels. sible to intentionally increase the clearness of an image when As shown below, if the pedestal level is set too low due to shooting a foggy scene or when shooting subjects through a improper adjustment, the entire image will appear darker window simply by lowering the pedestal level. 38 The Basics of Camera Technology Optical System Pedestal level CCD Mechanism Normal An image with high pedestal level Camera Functions An image with low pedestal level VTRs Preset White Preset White is a white-balance selection used in shooting “Color Temperature” ), since cameras are not adaptive to the scenarios when white balance cannot be adjusted or when variation of the different spectral distributions of each light the color temperature of the shooting environment is already source, this variation must be compensated for electronically known (3200 K for instance). By selecting Preset White, the and optically. Taking white balance (refer to “White Balance” ) R/G/B amplifiers used for white-balance correction are set to refers to compensating for the different spectral distributions their center value. This means that by simply choosing the electronically. Choosing the correct color conversion filter (refer correct color conversion filter, the approximate white balance to “Color Conversion Filters” ) is also imperative to achieving can be achieved. It must be noted however, that this method accurate white balance - to reduce the amount of white-balance is not as accurate as when taking white balance. adjustments that must be applied electronically. Reference File For broadcasters and large video facilities, it is imperative Reference Files are used to store such user-defined refer- that all cameras are setup to have a consistent color tone or ence settings so they can be quickly recalled, reloaded, or 'look', specified by that facility. This is achieved by using transferred from camera to camera. The parameters that can common base-parameter settings for all cameras that govern be stored in a camera's reference file may slightly differ the overall picture reproduction, such as gamma, detail and between types of cameras. This difference is due to the dif- knee (refer to “Gamma”, “Detail Level”, “Knee Aperture” and ferent design philosophy of what base parameters should be “Knee Correction” ). commonly shared between all cameras. The Basics of Camera Technology 39 Others As mentioned in the section on 'Color Temperature' (refer to Camera Functions Return Video In combination with the Intercom System (refer to “Intercom Return Video. By using Return Video, the camera operator (Intercommunication) System” ) and Tally Systems (refer to can switch the viewfinder to display the output of the camera “Tally” ), Return Video plays a vital role in multi-camera sys- he/she is operating, or the Return Video from other cameras tems. The main purpose of Return Video is to allow a cam- in the system. In most professional cameras, two to four era operator to view images captured by other cameras used return-video signals can be accepted. Return-video signals in the system (or images being aired) by displaying these in are sent from CCU to CCU using a composite video signal the viewfinder of the camera he or she is operating. since picture quality is not required. As shown in the figure below, when Camera 1 is shooting a The use of Return Video allows each camera operator to subject, this same image can be simultaneously displayed on know how other cameras are framing the subject - camera the viewfinders of Camera 2 and Camera 3. This is done by angle, zoom, etc. This allows each camera operator to routing the output signal of each camera to all other cameras always be prepared to go on-air, with seamless switching within the system via their CCUs (refer to “Camera Control achieved from camera to camera. System” ). In camera terminology, this signal is called the Viewfinder image video output Camera 1 CCU Viewfinder image Subject Camera 2 CNU CCU Viewfinder image Video control room Return video signal Camera 3 CCU Return video system Scene File Reference Files (refer to “Reference File” ) store parameter outdoors, indoors, or under other lighting conditions when- data that govern the overall 'look' common to each camera ever demanded. used in a facility. Scene Files, on the other hand, are provided to store parameter settings for color reproduction particular to each 'scene'. Scene Files can be easily created and stored for particular scenes by overriding the data in the Reference File. Scene Files allow camera operators to instantly recall the previously adjusted camera data created for scenes taken 40 The Basics of Camera Technology Latest Sony professional video cameras come equipped with level of a user-specified color to be adjusted (enhanced or a function called Triple Skin Tone Detail, which allows inde- reduced) without affecting the detail signals of other areas. pendent detail control over three specified colors. This Skin Tone Detail Correction was originally developed to enhances the capability of Skin Tone Detail Correction - reduce unwanted image enhancement (detail signals) on enabling one color selection to be used for reducing the detail wrinkles, thus smoothening the reproduction of human skin. level of skin color, and two other selections to be used for Simply by selecting a specific skin color, the detail signal for either increasing or decreasing the detail level of two other that skin can be suppressed. objects. Camera Functions Skin Tone Detail Active Area Width CCD Mechanism Skin Tone Detail Correction is a function that allows the detail Optical System Skin Tone Detail Correction R-Y Y Phase VTRs B-Y Y Saturation As mentioned earlier, genlock (refer to “Genlock” ) is accom- and H-sync phases must be perfectly matched before effect plished by supplying a master sync signal (refer to “Synchro- processing (at the input terminals of the switcher). After the nization Signal (Sync Signal)” ) to the genlock IN connectors effect is processed, the switcher adds an H-sync and burst of each camera within the system. This enables the frequen- signal generated from its own sync generator. For this rea- cies and phases of the V sync, H sync, and sub-carrier of the son, the input signals must also be synchronized with the output signals from all cameras to be synchronized with each switcher's internal sync generator. other. However, when using a switcher in the system to Returning to our main subject, the reason that this system is switch from one camera to another, one other factor must be not complete just by synchronizing the cameras, is because taken into consideration. To understand this, let's briefly the sub-carrier phase and H-sync phase of each camera out- review the mechanism of composite switchers. put varies due to length of the coaxial cable used between In composite switchers, the processing for the creation of the camera and the switcher. Since the sub-carrier phases effects such as MIX and WIPE basically only uses the active and H-sync phases of the two signals must be matched at picture areas of the input signals. Thus, the H-sync and burst the switcher inputs above, this variation in phase must be are removed from the input signals at the switcher input. For compensated for. This is done on the camera (or CCU) using example, a MIX effect is created by simply adding the active the sub-carrier phase control and horizontal phase control. picture areas of the two signals. A WIPE is accomplished by using a key signal, which functions as a switch to determine which parts of the active picture areas of the two signals should be selected for output. In both cases, since the two signals must be combined into one, their sub-carrier phases The Basics of Camera Technology 41 Others Sub-carrier Phase Control/Horizontal Phase Control Camera Functions Tally Tally is a system equipped on professional camcorders and which camera in the studio is being put to air. In multi-cam- studio cameras that is used to alert those involved in the era systems, the camera output to be put to air (or recorded) shoot to the status of each camera. The word 'tally' can be is decided by the staff in the control room from the switcher used to describe the entire tally system, the lamps used to control panel. When a camera is selected for on-air by the indicate the tally signal, or the tally signal itself. In acquisition switcher, the switcher will also send a tally signal to the cam- operations, a tally equipped on a camcorder usually refers to era via the camera control unit controlling that camera. In the REC Tally and is often distinguished from those used in a this way, the camera contributing to the on-air signal will light multi-camera studio system. its tally lamp in red informing both the performers and camera All professional camcorders have a 'tally lamp' on the front of operators which camera is active. There are several tally the viewfinder (for the actor, announcer, etc) and one within lamps on studio cameras. The largest tally lamp is located the camera viewfinder. The primary purpose of this tally is to on the upper-front of the camera body to be easily recog- inform those who will be shot (all performers who will be shot nized by all staff in the studio. There are also tally lamps by the camcorder) that the camcorder is recording (therefore located on the viewfinders attached to the cameras that are called REC tally). When the camcorder is put into 'record' used to communicate with the crew behind the camera, mode, the tally lamps on the viewfinder light in red. including the camera operator. Tally lamps are also provided In multi-camera studio systems, tallies play a different role - on the camera control unit (usually located in the control they inform both the performer and the camera operators room) as well as the video monitors in the control room. Tally REC Tally Tele-Prompter When watching news programs on TV, viewers usually notice ceiling mount camera. Key to this system is the half mirror, newscasters delivering a sequence of stories without refer- which allows the picture monitor screen to be seen by the ring to a script or taking their eyes off the camera. To some, newscaster, but appear transparent to the camera (operator). this may appear as the newscaster having a good memory, The video signal of the script images are fed to this monitor yet in most cases, they are actually viewing scripts displayed from the prompter output located on side of the studio camera. on a system called a tele-prompter. This mechanism allows the newscasters to view the script As shown below, illustrating the traditional tele-prompter sys- while looking straight into the camera lens. tem, a ceiling mount camera above the desk is faced down to All tele-prompter systems today generate the script from a shoot the script. The image from this camera is sent to the computer, displayed on a computer screen viewed through studio camera via the CCU (refer to “Camera Control Sys- the half-silvered mirror. tem” ). In front of the studio camera, there is a device com- The tele-prompter system has been a very helpful tool to prising two parts - a picture monitor facing upwards, and a support newscasters all over the world. half mirror to display the newscaster's scripts captured by the 42 The Basics of Camera Technology Optical System Camera Tele-Prompter CCU Monitor TLCS (Total Level Control System) shooting dark images and sufficient video level cannot be many Sony professional cameras and camcorders. TLCS obtained, even with the widest iris opening, TLCS will acti- has been developed to extend the Auto Iris range of the cam- vate the Automatic Gain Control and boost the signal to the era in a very innovative manner. appropriate level. Vice versa, when shooting bright images With conventional cameras, the Auto Iris range was limited to and the incoming light is excessive even for the smallest iris the smallest and widest opening of the lens iris (refer to “Iris” opening, TLCS will automatically activate the electronic shut- ). TLCS widens this Auto Iris range by effectively using the ter so the video-signal level falls within the 1.0 V signal range. lens iris, CCD electronic shutter, and Automatic Gain Control The overall result is that by activating TLCS, the proper expo- together to achieve proper exposure. sure is automatically set for both dark and very bright shoot- When proper exposure can be achieved within the lens iris ing environments. VTRs TLCS stands for Total Level Control System and is adopted in Camera Functions Tele-Prompter’s mechanism CCD Mechanism Half mirror Studio camera range, TLCS will only control the lens iris. However, when Others An Iris F-stop value for AGC or AE effective point can be pre-set by Advanced menu. Preset F-stop value AE effective point < F5.6 – F16 > AE Control range is equivalent to 2 × F2 stop max. (Up to 1/250 sec. shutter speed) AGC effective point < F1.8 – F5.6 > Auto Iris AGC Control range is equivalent to 2 × F2 stop max. (Upper limit gain value of AGC can be preset by Advanced menu. (0/3/6/9/12 dB) The Basics of Camera Technology 43 Camera Functions Triax Triax is a unique transmission system widely used in broad- The result is a transmission distance of up to 2,000 m with cast camera systems due to its reliability, flexibility, and con- the Triax system (when using a 14.5 mm diameter cable and venience. In brief, Triax is an interface system used for a full rack CCU). The Triax system is state-of-the-art technol- connecting a camera to its associated camera control unit, for ogy - allowing the communication of all signals between the the transmission of signals that must be communicated camera and camera control unit through one simple and flex- between the two devices. ible cable connection. The figure shows the signals commu- In the earlier days of camera systems, multi-core interfaces nicated and their frequency allocations. were used, in which each signal was transmitted through an individual wire bundled within the multi-core cable. Although the multi-core interface was convenient for use in the studio, it also had a serious drawback - a limitation in transmission distance, most notable in outside-broadcasting applications. This was because thin wires had to be used to transmit each of the many signals through one multi-core cable. The Triax system brought an innovative solution to this drawback. Instead of using one wire per signal, the Triax system allows all signals to be communicated between the camera and the camera control through one cable. Each signal is modulated on a carrier signal (frequency) specific to that signal so that signals do not interfere with each other. This allows the signals to be added together and transmitted through the same wire. It also allows bi-directional transmission from the camera to the camera head through the same wire. Since only one wire is used in a Triax cable, this allows a wide diameter wire to be used. Using a wide diameter wire Triax system naturally results in further transmission distances without signal level drop. TruEyeTM (Knee Saturation Function) Processing TruEye processing is an innovative function that has been Since the green and blue channels are compressed using the developed to overcome some of the drawbacks of conven- same red knee slope, the balance between the three chan- tional knee correction (refer to “Knee Correction” ). This nels is maintained, while effectively achieving highlight com- technology makes it possible to reproduce color much more pression for the red channel. naturally even when shooting scenes with severe highlights. The effect of TruEye processing is observed in the color In conventional cameras, knee correction is applied individu- reproduction of highlight areas. As the below photos demon- ally to each R, G, and B channels. The drawback of this strate, with TruEye turned off, the highlight areas are tinged method is that only those channels that exceed the knee with yellow, and when turned on, the correct color balance point are compressed. As shown in the figure (a), let's 'white' is reproduced. assume that only red channel exceeds the knee point at a given time, T1. Since only the red channel will be compressed at the knee point using a preset knee slope, this results in a shift in the color balance between the red, green, and blue channels. This is observed as hue being rotated and saturation being reduced where the knee correction was applied. The TruEye process overcomes this problem by applying the same knee correction to all channels, regardless of whether or not they exceed the knee point. This is shown in the figure (b) where only the red channel exceeds the knee point. 44 The Basics of Camera Technology Optical System Brightness R R CCD Mechanism TruEye ON TruEye OFF G Knee Point B G T1 (a) (b) T1 Knee correction applied Camera Functions B VTRs Turbo Gain Turbo Gain is a function adopted in Sony video cameras and basically an extension of Gain Up (refer to “Gain” ) but offers camcorders that helps shooting in the dark. Turbo Gain is a larger level boost (+42 dB) to the video signal. V Modulation is a type of white shading (refer to “White Shad- lation is caused by the different characteristics of each lens ing” ) that occurs when there is a vertical disparity in the cen- and/or the different optical axis of each zoom position and ter of the lens and prism axis. This causes the red and blue can be compensated for on the camera. Since this compen- light components to be projected 'off center' of their associ- sation data directly relates to the lens, it is automatically ated CCDs, which results in green and magenta casts to recalled as parameters of the Lens File (refer to “Lens File” ). appear on the top and bottom of the picture frame. V Modu- Lens Center Prism The Basics of Camera Technology 45 Others V Modulation Camera Functions White Balance As mentioned in the section on Color Temperature (refer to This relation reverses for a 5600 K light source. “Color Temperature” ), video cameras are not adaptive to the As earlier mentioned, white can only be produced when the different spectral distributions of each light source color. red, green, and blue video channels are balanced (R:G:B = Therefore, in order to obtain the same color under each dif- 1:1:1), and therefore, electrical adjustments must be done at ferent light source, this variation must be compensated for the CCD output. In the latter example (5600 K), the video electrically by adjusting the video amps of the camera. amp of the blue CCD must be adjusted to have a gain smaller For example, imagine shooting a white object. The ratio than 1, making the red, green, and blue signals equal in between the red, green, and blue channels of the camera amplitude. This adjustment is called white balance. In brief, video output must be 1:1:1 to reproduce white. This ratio white balance refers to the adjustment of the video amps of must stay the same under any light source (when shooting a the three CCDs, according to the color of the light source, to white object). However, as in the earlier discussions of Color obtain a 1:1:1 ratio for the red, green, and blue signal levels Temperature, the spectral distribution of light emitted from in order to reproduce white. each light source differs. This also means that the spectral It is most important to note that, once white balance is distribution of the light that reflects from the white object and adjusted, other colors come into balance as well. White bal- enters the camera prism will also change according to the ance should be adjusted frequently when the camera is used light source. As a result, the output of the three red, green, outdoors as color temperature changes rapidly with time. and blue CCDs will vary depending on the light source under which the white object is shot. For example, when the white Note: in the figure, white balance for 3200 K seems to require more adjustment of the video amps than 5600 K. However, the video amps of most cameras are preset to operate on color temperatures around 3200 K, and less gain adjustment is required. object is shot under 3200 K, the signal output from the blue CCD will be very small while that of the red CCD will be very large. Relative energy 3200 K R=G=B B 400 500 600 Wavelength (nm) G R 700 Relative energy White balance B 5600 K 400 500 600 Wavelength (nm) 46 The Basics of Camera Technology G R 700 White balance (3200 K/5600 K) B G R Optical System White Clip All cameras have white-clip circuits to prevent the camera Video output output signals from exceeding a practical video level, even White clip point when extreme highlights appear in a picture. The white-clip circuit clips off or electrically limits the video level of highlights to a level, which can be reproduced on a picture monitor. 100% CCD Mechanism 50% 100% 600% Zebra (refer to “NTSC/PAL” ) - even though the camera can expose viewfinder across highlight areas that are above a designated well above this. White levels above IRE brightness are illegal brightness level. This is particularly useful when manually for broadcast). With this zebra mode, the camera operator adjusting the iris (F-number) of the lens (refer to “F-num- adjusts the iris until the zebra becomes visible in highlight ber”and “Iris” ). Two types of zebra modes are available to areas. The second type, 70-90 IRE zebra, displays a zebra indicate either 100 IRE or 70-90 IRE brightness level. They pattern on highlights between 70-90 IRE, and disappears are used differently, so it is important to know which one to above the 90 IRE level. This is useful to determine the cor- pay attention to. The 100 IRE Zebra displays a zebra pattern rect exposure for the subject's facial skin tones since properly only across areas of the picture which exceed 100 IRE, the exposed skin (in the case of Caucasian skin) highlights are upper limit of legal video (100 IRE is pure white in NTSC likely to fall within the 80 IRE areas. VTRs Zebra is a feature used to display a striped pattern in the Camera Functions Illumination Others ZEBRA OFF 70 100 The Basics of Camera Technology 47 48 The Basics of Camera Technology Optical System VTRs CCD Mechanism The Basics of Camera Technology Camera Functions VTRs Others VTRs ClipLinkTM/Index Picture/Automatic Logging Function The ClipLink feature is a unique system adopted in DVCAM This data can then be transferred to the appropriate DVCAM camcorders that allows shooting data to be effectively used in editing VTR, and the in-point/out-point time codes can be the entire production process. With conventional video cam- immediately used as a rough EDL for the editing process. eras, shot lists (logging time code, etc.) were typically gener- The ClipLink feature also generates a small still image of ated manually using a clipboard, a pencil, and a stopwatch. each in-point, called the Index Picture, which is recorded to This method is not only time consuming but also tends to the DVCAM tape. This provides visual information of each introduce errors, which requires additional work to deliver the shot taken. When used with the appropriate logging soft- correct edit data to the editor at the post-production process. ware, the entire ClipLink data, including the Index Pictures, The ClipLink feature relieves shooting crews from such a the in-points/out-points, and the OK/NG status, can be dilemma. imported. This greatly enhances subsequent editing opera- During acquisition with a ClipLink-equipped camcorder, the tion by relieving the editor from having to review all the tapes in-point/out-point time code of each shot, together with their to pick up and sort the necessary shots before starting edit- OK/NG status, is recorded in the DVCAM Cassette Memory. ing. EZ Focus EZ Focus is a feature employed in the high-end DXC series its widest opening, which shortens the depth of field (refer to cameras and some DSR (DVCAM) camcorders to make “Depth of Field” ) and in turn allows for easier manual focus- manual focusing operation easier (this is not an auto-focus ing. During the mode, video level is managed properly by function). EZ Focus is activated by the touch of a button activating the electric shutter. The lens iris will be kept open located on the control panel of the camera. When activating, for several seconds and will then return to the level of iris the camera will instantly open the lens iris (refer to “Iris” ) to opening before EZ Focus was activated. EZ Focus activated 50 The Basics of Camera Technology Focusing operation White Balance)” ), TLCS (refer to “TLCS (Total Level Control immediately start shooting for unexpected incidents. In such System)” ), and DCC (refer to “Dynamic Contrast Control situations, it is most likely that there will be no time for adjust- (Automatic Knee Control)” ). This is achieved by simply ments. EZ Mode provides a solution. pressing a button located in a position that can easily be EZ Mode is a feature that instantly sets the main parameters accessed when the camera is mounted on the user's shoul- of the camera to their standard positions and activates the der. EZ mode is also fully automatic. auto functions such as ATW (refer to “ATW (Auto Tracing Camera Functions EZ Mode OFF CCD Mechanism In newsgathering, the camera operator must be prepared to Optical System EZ Mode EZ Mode activated SetupLog is a unique feature adopted in high-end DVCAM - therefore making it possible to recall the camera settings camcorders. This function automatically records, or logs, the that were used during any given shoot. SetupLog is particu- camera settings - including the iris opening (refer to “Iris” ), larly useful when the camera must be serviced, since the the gain up setting filter selection (refer to “Gain” ), as well as technician can recall the camera settings that were used basic and advanced menu settings - to a DVCAM tape. Setu- when a recording was not made correctly to examine what pLog data is constantly recorded to the Video Auxiliary data when was wrong. VTRs SetupLogTM area of the DVCAM tape while the camcorder is in Rec mode Others SetupNaviTM SetupNavi is a unique feature adopted in high-end DVCAM TM camcorders. As opposed to SetupLog (refer to “SetupLog ” ), activated by the operator and that the DVCAM tape used to record this data cannot be used for other purposes. which takes a log of the camera settings in real-time, Setup- SetupNavi is particularly useful in the studio to copy setup Navi is specifically intended for copying camera setup data data between multiple cameras. It is also convenient when between cameras using a DVCAM tape as the copy medium. the camera is used by multiple operators or for multiple Activating this feature allows all camera setup parameters, projects, since the exact camera settings can be quickly including the key/button settings, basic and advanced menus, recalled by inserting the DVCAM tape with the SetupNavi service menus, etc to be recorded to a DVCAM tape. It is data. important to note that SetupNavi data is recorded only when The Basics of Camera Technology 51 52 The Basics of Camera Technology Optical System Others CCD Mechanism The Basics of Camera Technology Camera Functions VTRs Others Others Additive Mixing Prior to the development of the color video system, experi- portional to their associated electron beams. To the human ments in colorimetry proved that most hues visible to the eye, these lights are seen as one light beam with the appro- human eye could be composed using the three primary col- priate hue reproduced when viewed from a certain distance. ors, red (R), green (G), and blue (B) (figure A). This fact also The mechanism of a color video camera uses a reverse func- holds true when separating a specific hue - that is, any hue tion as compared to a picture monitor. The light that enters can be separated into a combination/amount of these three the camera's lens is first separated into the three primary col- primary color components. This is called Additive Mixing. ors, R, G, and B using a prism system (refer to “Prism” ) The mechanism of reproducing color on a picture monitor is known as the dichroic mirror. These color light components based on this principle and is a good example to understand are converted into R, G, and B signal voltages at their associ- how Additive Mixing works. ated R, G, and B CCD imagers. The R, G, and B signals are In a video monitor CRT tube, three R, G, and B guns each then processed into the appropriate signal formats to con- emit electrons (electron beams) corresponding to the amount struct the output signal. of the R, G, and B components in the hue that is to be repro- *Note: In the Sony Trinitron®, only one gun is used to emit the three R, G, and B electron beams. duced (figure B). This results in the emission of light from each of the R, G, and B phosphors with their intensities pro Sony Trinitron ® Gun Blue Cyan Magenta White Green Yellow Red Aperture grill RGB stripe phosphors Figure A Figure B Camera Control System In multi-camera studio systems, it is important to know what control knobs and buttons to setup the camera - the later- each device in the system does and how it is used. In addi- mentioned MSU and RCPs. The second key function of a tion to the cameras, multi-camera systems comprise four key CCU is to provide the interfaces for transmitting video and elements - Camera Control Units (CCU), a Master Setup Unit audio between the camera and external devices. For exam- (MSU), Remote Control Panels (RCP) and a Camera Com- ple, the camera output is sent to the switcher system through mand Network Unit (CNU). the output of the CCU. Conversely, the Prompter (refer to “Tele-Prompter” ) signals and Intercom Signals (refer to Camera Control Unit (CCU) In multi-camera systems, one CCU is used for each camera as shown below. The CCU plays two important roles. As its name indicates, the CCU functions as the control interface between the camera and the control panels that provide the 54 The Basics of Camera Technology “Intercom (Intercommunication) System” ) are sent to the camera by supplying them to their associated inputs provided on the CCU. them appropriate for the given camera. Also, any adjust- The MSU provides central control of all cameras used in the ments made during the shoot are made on the RCPs since system. In brief, the MSU provides the control buttons and these are exclusive to each camera. Optical System override the general settings made on the MSU and make Master Setup Unit (MSU) knobs to make all setting changes, including general and detailed, to each camera in the system. The MSU uses a delegation system, meaning that the controls on the MSU Camera Command Network Unit (CNU) The CNU can be considered a control signal router since it is each camera to be centrally setup from a single MSU. The used to route the control signals from each control panel MSU is usually used to make overall or general settings of (RCP, MSU) to the appropriate CCU. Typical CNUs allow the each camera before the shoot. connection of up to 12 RCPs (for up to 12 cameras) and one MSU. This facilitates the connection of the control panels in a large-scale system since the user can connect all remote Remote Control Panel (RCP) CCD Mechanism panel are delegated to the selected camera. This allows panels into a single connector panel. Smaller multi-camera systems can be built without the use of single camera. Therefore, one RCP is used per camera. a CNU. In this case, RCPs must be connected directly to The RCP connects either to the CCU or the later mentioned their associated CCUs, and the control from the MSU must CNU. In a multi-camera system, RCPs are generally used to be daisy-chained between CCUs. Camera Camera Functions The RCP is a remote control panel for dedicated control of a CCU VTRs Camera MSU CCU Camera CCU CNU Camera CCU Others Camera CCU Camera CCU RCP RCP RCP RCP RCP RCP The Basics of Camera Technology 55 Others Color Signal Forms RGB Y/C The RGB signals give most faithful reproduction to both the The Y/C signal is obtained by use of an R-Y/B-Y encoder. original brightness and color of the subject shot with a cam- The R-Y/B-Y signals are modulated on a 3.58-MHz** subcar- era as these signals are obtained directly from the R, G, and rier using quadrature modulation and are combined into one B imagers. Each one of the R, G, and B signals contains chrominance signal (C). The bandwidth of the brightness information on both its brightness and color. Maximum infor- signal is the same as the Y component of the Y/R-Y/B-Y sig- mation on both brightness and color are provided in this form. nal. The bandwidth of the color is equivalent to that of the RY/B-Y signals but slightly distorted due to the quadrature modulator and the band-pass filter used to eliminate high-fre- Y/R-Y/B-Y quency harmonics. The Y/R-Y/B-Y signal is obtained by applying the RGB sig- *In actuality, in NTSC system, an I/Q encoder is used. **3.58-MHz for NTSC, 4.43-MHz for PAL. nals to a matrix circuit, which uses defined coefficients. Information on the brightness of the three RGB signals is converted into one signal called the luminance signal (Y), Composite while information on color is converted into two signals called The luminance (Y) and chrominance (C) signals of the Y/C the color difference signals (R-Y/B-Y). Information on lumi- signal are added to form one signal, which contains both nance is equivalent to that of the RGB signal. The bandwidth brightness and color information. The quadrature modulator of the color (R-Y/B-Y) derived from the RGB signal may be mentioned above uses a color carrier signal with a frequency limited to some extent (around 1.5 MHz) but sufficiently cov- of approx. 3.58 MHz for NTSC and 4.43 MHz for PAL, so the ers the human eye's sensitivity (resolution) to fine detail of resultant chrominance (C) signal's spectrum interleaves with color, which is much lower than that of brightness. the luminance signal's spectrum. This prevents the two signals from interfering with each other when added together to form the composite signal. This method allows the composite signal to be separated back into its luminance and chrominance components for display on a picture monitor. Y B G Light Matrix Circuit Y B-Y R-B Quadrature modulator C R RGB Component Y/C Composite Production of color video signals in camera using an R-Y/B-Y encoder Decibels (dB) In electronics, it is often required to handle signal levels over By rearranging this we have a very wide range. The use of logarithm provides an easier way of expressing both small and large values. It is also v'=vx10db/20 more convenient to know the ratio between a signal's amplitude and one defined signal (e.g., 1.0 V in video electronics) As the relative magnitude is being discussed, by substituting rather than to know the actual amplitude of the signal. For v = 1 the given equation is these reasons, decibels are used to express signal level. v'=10db/20 Decibels are defined with the following equation: The following chart shows some examples of the above caldB = 20log(v'/v) (v:typical signal level) 56 The Basics of Camera Technology culation. ratio dB ratio means a one-tenth drop in amplitude, 6 dB is almost equal to -60 -50 -40 -30 -20 -10 -3 0.001 0.00316 0.01 0.0316 0.1 0.316 0.708 0 +3 +6 +9 +12 +15 +18 0 1.0 1.413 1.995 2.818 3.981 5.623 7.943 a factor of 2, and that conversion from -dB to +dB is given with the reverse proportion. Optical System Here it should be noted that a 20-dB drop in signal level dB The use of decibels also allows easier calculation since multiplication is handled as addition. A typical example is the total gain of a series of amplifiers, which is calculated by adding Dynamic Range light required to produce a 1.0 Vp-p video signal, which is the smallest and largest signal that can be handled by a 100%. This means that an imager with 600% dynamic range device. Although seldom used in camera technology, the has the capability to produce a video signal with six times the term dynamic range is sometimes used to indicate the ratio amplitude of the 1.0 V video standard. Technologies such as between the smallest and largest amount of light that the Knee Correction, DCC, and DynaLatitude are used to com- imaging device can capture. With 2/3-inch CCDs, this is nor- press this amplitude into the 1.0 V range (refer to “Knee Cor- mally 600% while 1/2-inch CCDs have a dynamic range of rection”, “Dynamic Contrast Control (Automatic Knee 300%. The definition in this case is based on the amount of Control)”, and “DynaLatitudeTM” ). Camera Functions In general, dynamic range indicates the difference or ratio of CCD Mechanism each amplifier's gain expressed in decibels. VTRs HD/SD (High Definition/Standard Definition) HD and SD stand for High Definition television and Standard and more pixels per line 1920 as compared to 720 for SD. Definition television systems respectively. High Definition Since high-definition equipment is geared towards high-end television provides much higher picture quality due to the use applications, they are usually designed to provide superior of more effective vertical scanning lines as compared to resolution. NTSC (525 lines) PAL (625 lines) standard-definition systems Others Horizontal Resolution This term describes the camera's capability of reproducing The camera's horizontal resolution is known by reading the the details of its subject. It is expressed by the number of maximum calibration of the vertical wedges where the black black and white vertical lines resolvable within three-fourths and white lines can be resolved. Horizontal resolution is also the width of the picture. It is important to note that horizontal measured as the maximum number of vertical black and resolution does not refer to the number of resolvable lines white lines where the camera output exceeds 5% video level. within the total picture width. This is because it must be Measurement of horizontal resolution must be performed expressed under the same conditions as vertical resolution with gamma (refer to “Gamma” ), aperture, and detail (refer to and thus only three-fourths the picture width. Horizontal res- “Detail Level” ) set to 'On', and masking set to 'Off'. olution is usually measured by framing a resolution chart. The Basics of Camera Technology 57 Others Interlace/Progressive Interlace is a scanning method, which has been adopted into next scan, only the even-numbered lines (2, 4, 6...524) are today's television broadcast system such as NTSC and PAL scanned. (refer to “NTSC/PAL” ). In brief, interlace scanning refers to Since the image rate is 60 per second, this was successful in scanning every other TV line of an image as the first field, keeping flicker to a negligible level. Also, through visual and then scanning lines in-between as the second field. experiments, it was found that despite the line scan of each Interlace scanning is a method that has been inherited from frame being reduced to one-half, the drop in vertical resolu- the black and white TV days, it is worthwhile to know why this tion was only 70% of the total 525 (625 for PAL) TV lines. continues to be used in the NTSC color broadcast system. This is due to the human eye characteristics of seeing an To display motion pictures on a video monitor with negligible after-image due to the short 1/60-second field rate. In this flicker, tests have demonstrated that at least 50 to 60 images way, researchers decided to use the above interlace scan- must be displayed within one second (here, film is an excep- ning method for the NTSC and PAL TV systems. tion). However, the bandwidth available for broadcasting the Newer broadcast transmission infrastructures are less limited TV signal (6 MHz in NTSC areas, 7 MHz in PAL areas) was in bandwidth. This gives the broadcaster the option of using not wide enough to transmit 60 full images per second. an interlace system or a non-interlaced system - the latter Apparently, it was required to consider a solution to reduce known as progressive scanning. the signal's bandwidth but with minimum quality loss. After The progressive scanning system has been adopted in com- thoroughly investigating the human eye characteristics, a puter displays, which do not require considerable transmis- solution was found. sion bandwidth. The result was to use a 1/60-second rate for each scan, but In progressive scanning, each line is scanned in order from in the first scan, from the top to bottom of the image, only the the very top to bottom. The entire 525 lines (or 625 lines for odd-numbered lines (1, 3, 5...525) are scanned, and for the PAL) are displayed in one scanning operation. Thus superior vertical resolution is achieved. 1 2 3 4 5 6 7 8 9 10 11 2nd field: Even field 1st field: Odd field 1 2 3 4 5 6 7 8 9 10 11 One frame Interlace Scanning method 58 The Basics of Camera Technology low light, Gain Up also boosts the signal noise level. Mini- required for shooting with a certain camera. It is expressed mum illumination is usually measured with the highest Gain in Lux. When comparing minimum illumination specifica- Up setting provided by the camera, and therefore does not tions, it is important to consider the conditions they were represent the camera's sensitivity in any way. Simply put, it is measured at. best to have a high minimum illumination at a relatively All cameras provide a Gain Up (refer to “Gain” ) function to smaller Gain Up setting. CCD Mechanism Minimum Illumination indicates the minimum amount of light Optical System Minimum Illumination boost signal level. Although convenient for shooting under Modulation Depth Simply put, it is the frequency response in practical frequency resolving performance of a video camera. While Horizontal ranges that governs the camera's sharpness - not the hori- Resolution (refer to “Horizontal Resolution” ) is used to indi- zontal resolution. cate only the resolving ability, it is equally important to know A camera's frequency response is usually measured by the Modulation Depth - the camera's resolving performance shooting a Multi Burst chart. A typical frequency chart has for frequency range practically used in video bandwidth. vertical black and white lines which, when converted to video, Although, horizontal resolution does indicate the ability to translate into 0- to 5-MHz signals. When measuring Modula- reproduce fine picture detail, it can somewhat be misleading tion Depth, usually the 5-MHz area is used. This is because when judging a camera's performance. This is because hori- 5 MHz is a frequency that best represents a video camera's zontal resolution only defines the finest level of detail that is performance. The closer the response is to 100% at 5 MHz, the higher the capability to reproduce clear and sharp picture on the other hand, is used to indicate how sharp or how clear details. Modulation Depth of video cameras for standard def- an image is reproduced. For this reason, modulation depth inition broadcasting is typically in the range between 50% to focuses on the response of the frequency ranges most used 80% (at 5 MHz). in video. It must be noted that Modulation Depth can be influenced by VTRs viewable - not clearly or sharply viewable. Modulation Depth, Camera Functions Modulation Depth is an important factor that governs the the performance of the camera lens and thus measurements should be conducted with an appropriate lens. Response cf2: Pbo (1-1/4 ) (XQ3430) cf1: Pbo (2/3 ) (XQ3457) 1.2 Power HAD (520,000 pixels) 1.0 0.8 0.8 Pbo (1-1/4 ) (XQ3430) Pbo (2/3 ) (XQ3457) 0.6 0.4 0.2 0 –0.2 0 2 4 6 8 10 12 14 16 18 20 Horizontal frequency (MHz) –0.4 –0.6 Depth of modulation characteristic The Basics of Camera Technology 59 Others Overall Y Response (with Optical LPF, without Lens) Others NTSC/PAL NTSC is an acronym that stands for National Television Sys- adopted in Europe, China, Malaysia, Australia, New Zealand, tems Committee. This is an organization that stipulated the the Middle East, and parts of Africa. It has an improved color standards for the NTSC television systems. When used in coding system that reduces the color shift problem that video terminology, NTSC refers to color television systems sometimes happens with NTSC color coding. Most countries used in North America, Japan, and parts of South America. that use PAL It employs an interlace scanning system with It employs an interlace scanning system (refer to “Interlace/ 625 lines per frame/25 frames per second. Some systems, Progressive” ) of 525 lines per frame/30 frames per second. for example, PAL-M as used in Brazil, use PAL color coding PAL is the acronym, which stands for Phase Alternate by with 525 line 60 Hz scanning. Line. This term refers to the color television system mainly 525 TV line 625 TV line NTSC PAL 30 frames/sec 25 frames/sec 30 25 5 3 4 3 2 2 1 1 PsF (Progressive, Segmented Frames) PsF stands for Progressive, Segmented Frames. This abbre- devices (telecine, camcorder, studio camera, etc.) are divided viation is used to transcribe types of high-definition progres- into two segments and travel through the HD SDI (refer to sive video formats (refer to “Interlace/Progressive” ), which “SDI” ), base-band interface (or through the SDTI infrastruc- are distinguished from the pure high-definition progressive ture in a compressed form) in the same manner as an inter- video formats. The PsF method has been originated to retain laced signal. These are then reconstructed into full the compatibility of progressive frames with interlaced signals progressive frames at the receiving device. represented by the major SDTV formats employed. In the 24 Although the segmented signal structurally resembles an PsF format for example, each progressive frame is handled interlaced signal, it should NOT be confused with interlace as two segments and time shifted (each separated segment images. The segmented frame format is approved by the ITU is treated as an odd and even field) by 1/48th of a second. Rec. 709-3 and is supported by most major manufacturers. Complete progressive picture frames from acquisition 60 The Basics of Camera Technology RS-170A is a color-synchronization signal standard enacted Otherwise, sync shock may be caused during switching. by EIA (Electronic Industries Association). This standard includes additional regulations that did not exist in the original color-synchronization signal standard enacted by FCC (Fed- Optical System RS-170A 2. For color-framing servo control In composite VTRs, the CTL signal is used for color-frame adding these regulations was to prevent hue differences on servo lock. Pulses that indicate the first field of the color- TV receivers depending on the broadcast station or program. framing sequence are written on the CTL track of the tape by However, the rapid technical advances seen in TV receivers detecting the SC-H of the first field when the video signal is have reduced the above hue differences, and these addi- input to the VTR. If the SC-H is not maintained as regulated, tional regulations have become of less importance, except in the pulses on the CTL track, which should indicate the first the following cases: field, will not be written in the appropriate area. Thus color- CCD Mechanism eral Communication Commission). The main objective of frame capstan lock cannot be accomplished. 3. In digital devices In switchers with automatic delay lines, the phases of the The A/D converters in digital VTRs and TBCs use the sub- input video signals are adjusted by detecting the burst sig- carrier as the reference for A/D conversion timing. If SC-H is nals. Thus, when switching from one signal to another, the not maintained, A/D conversion will take place at the wrong SC-H phase (phase between the sub-carrier and horizontal areas, and will result in picture shift when the signal is repro- sync chip) of the input signals must be maintained within a duced on picture monitors. Camera Functions 1. When using video switchers with automatic video-delay lines. defined range. VTRs S/N (signal-to-noise) Ratio Although many techniques have been developed for the the logarithm of signal amplitude divided by the root mean reduction of noise, it is still unavoidable in any class of square value (rms) of the noise level. The following equation device. In cameras and other video equipment, noise level is gives the S/N ratio of cameras and other video equipment. expressed in terms of S/N ratio (signal-to-noise ratio). S/N ratio is defined in decibels (dB) and is calculated by taking S/N ratio = 20 log (Sp-p/N rms) (dB) Others SDI SDI is an acronym that stands for Serial Digital Interface. SDI is an industry-standard interface designed for transmitting non-compressed (known as baseband) digital video and audio. SDI has become extremely popular for two reasons its compatibility with analog coax cables and for its long transmission distance. The SDI interface is offered in three versions: composite digital SDI (standard definition), compo- 1. Virtually degradation-free picture and audio quality by noise-resistant digital transmission. 2. Conventional coax cable can be used. 3. Only one BNC cable required for connecting video, audio, and time code. 4. Longer transmission distance (as compared to analog) allows flexible cabling (up to 200 m for SD and 100 m for HD) nent digital SDI (standard definition ) and HD-SDI (high definition). SDI offers the following advantages over analog I/Os: Technically, the transmission rates are 270 Mbps and 1.5 Gbps for standard-definition SDI and high-definition SDI, respectively. The Basics of Camera Technology 61 Others Sensitivity The sensitivity of a camera is described by the iris (refer to important to know that the true sensitivity may differ from the “Iris” ) opening required to provide a video signal with suffi- total sensitivity of the camera. This is because the total sen- cient level under a specified lighting condition. In general, sitivity of a camera correlates with the camera's S/N ratio. sensitivity is measured using a 89.9% reflectance grayscale That is, the camera's sensitivity can be improved by increas- chart illuminated with a 2000 lux, 3200K illuminant. The ing the gain of the video amp, but with a drop in the camera's camera's F-stop (refer to “F-number” ) provides a white video S/N ratio. An example of sensitivity specification is shown level of 100% when the chart is shot is the sensitivity of the below. camera. In CCD cameras, sensitivity is mainly determined by the aperture ratio of the photo-sensing sites. The more F5.6 at 2000 lux (3200K, 89.9 reflectance) light gathered onto each photo sensor, the larger the CCD output, and the higher the sensitivity. However, it is also *Note: the gain selector must be set at 0 dB. Synchronization Signal (Sync Signal) Synchronization signals play important roles for a picture to is scanned, the scan then returns to the top center of the dis- be correctly displayed on a video monitor. These are mixed play to scan the next field (in case of interlace scanning - in the video signals to lock the timing of the camera images to refer to “Interlace/Progressive” ). The horizontal sync syn- the picture monitor's scan. There are two kinds of the syn- chronizes the timing that the electron beam returns from bot- chronization signals: the Horizontal synchronization signal tom to top to the first video line in each field. In this way, the (HSYNC) and the vertical synchronization signal (VSYNC). video signal is scanned so the picture is correctly positioned To better understand these sync signals, let's review the in the video monitor. operation will be repeated until the very scanning operation of a picture monitor. bottom line is scanned, then go back to the upper-left to scan On the picture monitor, the electron(ic) guns that project the the next field (in case of interlace scanning - refer to “Inter- electron beams start scanning the screen phosphor from the lace/Progressive” ). HSYNC is the signal that synchronizes upper-left corner, and then move towards the upper right cor- the timing when electron beam return from right-end to left- ner. After reaching the upper right corner, the scan is shifted end of the monitor screen in this operation. VSYNC synchro- down vertically to scan the subsequent line from the left to nizes the timing of vertical direction when electron beams right again. This operation repeats until the very bottom line return from bottom to top. Scanning operation 1 field (1/60 sec.) Video signal of 1 scanning line Vertical sync signal Horizontal sync signal Sync signals in NTSC format 62 The Basics of Camera Technology The VBS (Video Burst Sync) signal is a composite video sig- Sync) signal does not contain picture content and the active nal in which the active video area contains picture content or video area is kept at setup level. Optical System VBS/BS Signal color bars. As opposed to the VBS signal, the BS (Burst CCD Mechanism Video Burst Camera Functions H-sync VBS Signal BS Signal VTRs Vertical Resolution Vertical resolution describes the fineness of images in the of all existing NTSC video equipment is 525 TV lines (to be vertical direction. While horizontal resolution (refer to “Hori- precise, the effective vertical resolution is 486 TV lines due to zontal Resolution” ) varies from camera to camera and is interlace scanning) regardless of the different horizontal resolutions each equipment provides. Therefore, unlike horizon- lution is determined only by the number of scanning lines in tal resolution, vertical resolution is usually of less concern the particular TV format. For example, the vertical resolution when evaluating a camera's performance. The Basics of Camera Technology 63 Others used as a reference to describe picture quality, vertical reso- INDEX A G Adaptive Highlight Control ....................................................24 Gain .......................................................................................... 31 Additive Mixing ........................................................................ 54 Gamma .................................................................................... 32 Angle of View ............................................................................2 Genlock ................................................................................... 32 ATW (Auto Tracing White Balance) ....................................24 AWB (Auto White Balance) ................................................... 24 H H/V Ratio ................................................................................. 33 B HAD SensorTM ........................................................................ 16 Black Balance ......................................................................... 25 HD/SD (High Definition/Standard Definition) ..................... 57 Black Clip .................................................................................25 Horizontal Resolution ............................................................ 57 Black Gamma ......................................................................... 25 Black Shading ......................................................................... 26 I C Interlace/Progressive ............................................................ 58 Camera Control System ........................................................ 54 Iris ............................................................................................... 6 Center Marker ......................................................................... 26 IT/FIT CCD .............................................................................. 16 Intercom (Intercommunication) System ............................. 33 Chromatic Aberration ...............................................................3 Clear Scan/Extended Clear Scan (ECS) ............................ 26 ClipLinkTM/Index Picture/Automatic Logging Function ...... 50 Color Bars ................................................................................27 Color Conversion Filters .......................................................... 3 Color Signal Forms ................................................................ 56 Color Temperature ...................................................................4 K Knee Aperture ........................................................................ 33 Knee Correction ..................................................................... 34 L Lens File .................................................................................. 34 Level Dependence ................................................................. 34 Crispening ............................................................................... 28 Light and Color ......................................................................... 7 Cross Color Suppression ...................................................... 28 Limiter ...................................................................................... 35 D Decibels (dB) ........................................................................... 56 Depth of Field ............................................................................4 Detail Level ..............................................................................29 DynaLatitudeTM ........................................................................ 30 Linear Matrix Circuit .............................................................. 36 Low Key Saturation ............................................................... 36 M Minimum Illumination ............................................................ 59 Mix Ratio ................................................................................. 37 Dynamic Contrast Control (Automatic Knee Control) ....... 30 Modulation Depth ................................................................... 59 Dynamic Range ...................................................................... 57 MTF (Modulation Transfer Function) .................................... 8 E Electric Soft Focus .................................................................31 EVS/Super EVS ...................................................................... 14 EZ Focus .................................................................................50 Multi Matrix .............................................................................. 38 N Neutral Density (ND) Filters ................................................... 8 NTSC/PAL .............................................................................. 60 EZ Mode .................................................................................. 51 F Field Integration and Frame Integration Mode ..................15 O On Chip Lens .......................................................................... 17 Optical Low Pass Filter ........................................................... 9 File System ..............................................................................31 Flange-Back/Back Focal Length ............................................4 P Flare ........................................................................................... 5 Pedestal/Master Black .......................................................... 38 F-number ...................................................................................5 Picture Element ...................................................................... 18 Focal Length ............................................................................. 6 Preset White ........................................................................... 39 Prism .......................................................................................... 9 PsF (Progressive, Segmented Frames) ............................. 60 64 The Basics of Camera Technology R Readout Mechanism ............................................................. 18 Reference File ........................................................................ 39 Return Video ........................................................................... 40 RPN (Residual Point Noise) ................................................. 19 RS-170A .................................................................................. 61 S S/N (signal-to-noise) Ratio ................................................... 61 Scene File ............................................................................... 40 SDI ........................................................................................... 61 Sensitivity ................................................................................ 62 SetupLogTM ............................................................................. 51 SetupNaviTM ............................................................................ 51 Skin Tone Detail Correction ................................................. 41 Spatial Offset Technology .................................................... 20 Sub-carrier Phase Control/Horizontal Phase Control ...... 41 Synchronization Signal (Sync Signal) ................................ 62 T Tally .......................................................................................... 42 Tele-Prompter ........................................................................ 42 TLCS (Total Level Control System) .................................... 43 Triax ......................................................................................... 44 TruEyeTM (Knee Saturation Function) Processing ............ 44 Turbo Gain .............................................................................. 45 V V Modulation ........................................................................... 45 Variable Speed Electronic Shutter ...................................... 21 VBS/BS Signal ....................................................................... 63 Vertical Resolution ................................................................. 63 Vertical Smear ........................................................................ 22 W White Balance ........................................................................ 46 White Clip ................................................................................ 47 White Shading ........................................................................ 10 Z Zebra ........................................................................................ 47 Zoom ........................................................................................ 11 The Basics of Camera Technology 65 Acknowledgement With the advent of sophisticated information networks made possible by the development of the Internet, we now have the capability to search and access the information we need much more easily and quickly than ever before. However, in my searches for information, I could not locate any documentation or literature that comprehensively explains professional video camera terminology in a manner that is easily understood by the layman. All of my searches turned up documents that were highly technical and very difficult to comprehend for people who are new to this industry or are unfamiliar with technical language and jargon. I felt that, "There should be some solution to this lack of good information." And, this is how the production of this document began. My goal in creating this document was to cover most of the basic terminologies that I feel to be significant in understanding professional video cameras. I also paid special attention to write in a style so that explanations are comprehensible to even those who have a limited technical background. I hope that this document invites its reader to become a part of the world of professional video cameras and that it provide a helpful solution in making a induction process a smooth one. Creating this document is the result of more than my individual effort. Without the support and cooperation of my colleagues in a number of different departments within Sony Corporation, this document could not have been completed. I would like to thank all of those who have been involved in this project. I am especially thankful to: Mr. Satoshi Amemiya, a Senior Technical Writer in the Marketing Communication Section, Product Information Department, Business Planning Division, B&P Company, Sony Corporation for his comprehensive suggestions and advice on the content of this document. Mr. Atsushi Furuzono and Hitoshi Nakamura of the Contents Creation Business Group, B&P Company, Sony Corporation for their detailed advice, explanations, and verification of the entire content from a technical point of view. Mr. Isao Matsufune of the Contents Creation Business Division, B&P Company, Sony Corporation for his help in checking the chapter on VTRs. Mr. Kinichi Ohtsu of the Contents Creation Division, B&P Company, Sony Corporation for his help in checking the chapter on Camera Functions. Mr. James Webb, a Technical Writer in the Marketing Communication Group, Product Information Department, B&P Company, Sony Corporation for his suggestions on the appropriate use of English expressions. Finally, I would like to express my gratitude to Ms. Michi Ichikawa, General Manager, and Ms. Kazuko Yagura, Senior Manager of the Product Information Department, B&P Company, Sony Corporation, for their support in providing me with the opportunity to create this document. September 22, 2003 Toshitaka Ikumo Marketing Communication Group Product Information Department Business Planning Division B&P Company Sony Corporation The Basics of Camera Technology MK10088V1KYP03NOV Printed in Japan