C-mode In videotape editing, operating in C-mode allows the shots on the source footage reels to be copied to the edit tape in the order they are recorded on the source tapes, rather than the order required for the finished program. So all the selected material from a source reel can be copied before loading another source reel - thus saving spooling and reel changing time. This assumes that none of the edits will need to be changed along the way! The term lives on in the disk-based editing world as the editing disk store can randomly access the footage recorded from the source tape. So C-mode editing on disks not only gives the advantages of faster and more convenient transfers but the edits can be more easily altered in a disk store's random access environment.
Camera negative (film) Camera negative film is designed to capture as much detail as possible from scenes. This not only refers to its spatial resolution but also its dynamic resolution. Modern camera negative stock has almost 10 stops' exposure range and so is able to record detail in both the low-lights and the highlights which are well beyond the range that can be shown on the final print film. This provides latitude to compensate for over or under exposure during the shoot or to change the look of a scene. The latitude
Chroma keying The process of overlaying one video signal over another, the areas of overlay being defined by a specific range of color, or chrominance, on the background signal. For this to work reliably, the chrominance must have sufficient resolution, or bandwidth. PAL or NTSC coding systems restrict chroma bandwidth and so are of very limited use for making a chroma key which, for many years, was restricted to using live, RGB camera feeds. An objective of the ITU-R BT.601 and 709 digital sampling standards was to allow high quality chroma keying in post production. The 4:2:2 sampling system allows far greater bandwidth for chroma than PAL or NTSC and helped chroma keying, and the whole business of layering, to thrive in post production. High signal quality is still important to derive good keys so some high-end operations favor using RGB (4:4:4) for keying - despite the additional storage requirements. Certainly anything but very mild compression tends to result in keying errors appearing - especially at DCT block boundaries. Chroma keying techniques have continued to advance and use many refinements, to the point where totally convincing composites can be easily created. You can no longer see the join and it may no longer be possible to distinguish between what is real and what is keyed. See also: Color space, Digital keying, Photo-real
is engineered into the film stock by giving it a very low gamma of around 0.6. Exposed and developed camera color negative film has an orange tint and is low in contrast - differing greatly from the un-tinted and high contrast print film. As not only the blue, but also the red and green layers of the film are sensitive to blue light, the orange layer is added below the blue layer to stop blue light going further. All types of film stocks use orange dye but for print films it is bleached away during processing. There are numerous stocks available. High speed stocks work well in lower lights but tend to be more grainy. The opposite is true for low speed stocks.
Cardboarding (Stereoscopic) Lack of true 3D feel to a shot making it look like it is made from cardboard cutouts. This is also referred to as Cutout Planar Effect. Caused by inadequate depth resolution due to an incorrect matching between the focal length of the recording lens (or CGI camera) and the interocular distance between the cameras. See also: Interocular
CCD Charge Coupled Device (CCD) - either assembled as a linear or two-dimensional array of light sensitive elements. Light is converted to an electrical charge in a linear fashion - proportional to the brightness impinging on each cell. The cells are coupled to a scanning system which, after analog to digital conversion, presents the image as a series of binary digits. Early CCD arrays were unable to work over a wide range of brightness but they now offer low noise, high resolution imaging up to HDTV level and for digital cinematography. See also: CMOS
CDL See: Color decision list
Checksum A simple check value of a block of data intended to recognize when data bits are wrongly presented. It is calculated by adding all the bytes in a block. It is fairly easily fooled by typical errors in data transmission systems so that, for most applications, a more sophisticated system such as CRC is preferred. See also: CRC
Chrominance The colorpart of a television signal, relating to the hue and saturation but not to the brightness or luminance of the signal. Thus pure black, gray and white have no chrominance, but any colored signal has both chrominance and luminance. Although imaging equipment registers red, blue and green television pictures are handled and transmitted as U and V, Cr and Cb, or (R-Y) and (B-Y), which all represent the chrominance information of a signal, and the pure luminance (Y). See also: YUV, Y,Cr,Cb, Composite
CIE International Commission on Illumination (Commission Internationale de l'Eclairage) is devoted to international cooperation and exchange of information among its member countries on all matters relating to the science and art of lighting. It is a technical, scientific and cultural, non-profit autonomous organization that has grown out of the interests of individuals working in illumination. It is recognized by ISO as an international standardization body. See also: X'Y'Z' Website: www.cie.co.at
CIF See Common Image Format
CIFS Common Internet File System - is a platform-independent file sharing system that supports rich, collaborative applications over the internet which could be useful for collaborative post workflows. It defines a standard remote file-system access protocol, enabling groups of users to work together and share documents via the Internet or within intranets. CIFS allows multiple clients to access and update the same file, while preventing conflicts with sophisticated file-sharing and locking semantics. These mechanisms also permit aggressive caching and read-ahead/write-behind without loss of cache coherency.
CineAlta Sony brand for products designed for the digital cinematography market. See also: HDCAM
Cineon (file) An RGB bitmap file format (extension .cin) developed by Kodak and widely used for storing and transferring digitized film images. It accommodates a range of film frame sizes and includes up to full Vista Vision. The format was partly designed to hold virtually all the useful information contained in negatives and so create a useful 'digital negative' suitable as a source for post production processing and creating a digital master of a whole program. See also: 10-bit log, DPX
Clip The name is taken from the film industry and refers to a segment of sequential frames made during the filming of a scene. In television terms a clip is the same but represents a segment of sequential video frames. A video clip can also be recorded with audio or have audio added to it.
Clone An exact copy, indistinguishable from the original. As in copying recorded material, e.g. copy of a non-compressed recording to another non- compressed recording. If attempting to clone compressed material care must be taken not to decompress it as part of the processor the result will not be a clone.
Codec Originally short for a combination of a coder and decoder but now often used to describe just one or the other. Mostly codec refers to a compression coder or decoder such as JPEG, MPEG or JPEG 2000.
Coded (video) See Composite
COFDM Coded Orthogonal Frequency Division Multiplexing - a modulation scheme which is used by the DVB digital television system. It allows for the use of either 1705 carriers (usually known as '2K'), or 6817 carriers ('8K'). Concatenated error correction is used. The '2K' mode is suitable for single transmitter operation and for relatively small single-frequency networks with limited transmitter power. The '8K' mode can be used both for single transmitter operation and for large area single-frequency networks (SFN). The guard interval is selectable. The '8K' system is compatible with the '2K' system. Initially only 2K was possible but now 8K is more normal. There has been much discussion about the relative merits of COFDM vs the 8-VSB scheme used in the ATSC standard. The Japanese ISDB system uses a similar scheme, OFDM, and the Chinese have developed their own transmission scheme the DMB-T/H standard - not to be confused with the T-DMB Korean standard modulation - both radically different COFDM implementations. See also: DVB, ISDB, VSB Website: www.dvb.org www.dmb.cn
Color correction See Grading
Color cube A representation of color space by a three-dimensional diagram. For example, all definable colors of an RGB color space can be contained in an RGB color cube where R, G and B are axes at right angles to each other (like x, y and z at the corner of a cube). Different color spaces and interpretations of color are defined by different color cubes. If the exact spectral values of R, G and B are defined, that cube defines an absolute color space. Such cubes are available from a number of vendors.
Color Decision List (CDL) The American Society of Cinematographers' Color Decision List (ASC-CDL) is a proposed metadata interchange format for color correction, developed to ensure that images appear the same when displayed in different places and on different platforms. This should enable consistency of look from on- set monitoring through post production to the final grade.
Color management The control of color through a defined process. The idea is that all, or at least some, pictures, monitors or screens should portray the colors as they will appear when shown in their target medium. For example, if working on a DI project, the color management should ensure that the monitors show the colors exactly as an audience in a cinema will see them. Today that may be by use of a release print, in which case the color management has to adjust the monitoring for the film stock to be used. It could also be from a digital cinema distribution master (DCDM) and the color characteristics of that path taken into account as part of the color management.
Color space The color range between specified references. Typically three references are quoted in television: for example RGB, Y R-Y B-Y and Hue, Saturation and Luminance (HSL) are all color spaces. In print, Cyan, Magenta, Yellow and Black (CMYK) are used. Film is RGB while digital cinema uses X'Y'Z'. Moving pictures can be moved between these color spaces but it requires careful attention to the accuracy of processing involved. Operating across the media - print, film and TV, as well as between computers and TV equipment - will require conversions in color space. Modern digital techniques allow the use of both RGB and Y R-Y B-Y to best suit production requirements. See also: 2K, Keying
Color Transform Language (CTL) Color Transformation Language is a small programming language designed to serve as a building block for digital color management systems. It allows users to describe color transforms in a concise and unambiguous way by expressing them as programs that describe the transform that can be applied to pixel data. It is designed to run fast, operating on many pixels at one time. See also: OpenEXR Website: http://ampasctl.sourceforge.net
CMOS Complementary metal-oxide-semiconductor technology very widely used to manufacture electronic integrated circuits (chips). Recently the application of CMOS technology to image sensors has increased. The chips are cheaper than the alternative CCDs, they consume less power, can be more sensitive (faster), have less image lag and can include image- processing functions on the sensor chip.
Color management The management of color through a process - such as DI or video grading. Television engineering folklore says that a picture never looks exactly the same on two picture monitors. By the use of probes to measure the colors on a screen, and equipment with adjustable color LUTs, the look of color can be set to the same across all monitors - within their technical limits. Such care is needed in DI where grading is a big part of the process. Today DI suites may be equipped with a digital projector and large screen. The look of colors on the screen can be set to match those expected for a chosen print stock, so the DoP and grader can see the footage exactly as it will look in the cinema, or other chosen audience. See also: WYSIWYG, X'Y'Z'
Color timing (a.k.a. Grading) The color of film exposed and processed in a laboratory is controlled by separately altering the amount of time that the red, blue and green lights are used to expose the film. This is referred to as color timing and its effect is to alter contrast of R,G and B to create a required color balance. In a lab, color timing is usually applied at the point where the edited negative is copied to the master interpositive but can be done later at other points if required. In the digital film process, color timing is applied at any required time, as required. In addition there is far more flexibility for color control with gamma, hue, luminance, saturation as well as secondary color correction. In addition, the results can be seen immediately and projected onto a large cinema screen and further adjusted if required. See also: Grading, Lights, Timing C Common Image Format (CIF) The ITU has defined common image formats. A standard definition image of 352 x 240 pixels is described for computers. For HDTV production the HD-CIF preferred format is defined in ITU-R BT.709-4 as 1920 x 1080, 16:9 aspect ratio with progressive frame rates of 24, 25 and 30 Hz (including segmented) and interlace field rates of 50 and 60 Hz. This has helped to secure the 1920 x 1080 format as the basis for international program exchange. See also: ITU-R BT.709
Component video The normal interpretation of a component video signal is one in which the luminance and chrominance remain as separate components, e.g. analog components in Betacam VTRs, digital components Y, Cr, Cb in ITU-R BT.601 and 709. RGB is also a component signal. Pure component video signals retain maximum luminance and chrominance bandwidth and the frames are independent of each other. Component video can be edited at any frame boundary. See also: Cut (edit)
Composite video Luminance and chrominance are combined along with the timing reference sync and color burst information using one of the coding standards - NTSC, PAL or SECAM - to make composite video. The process, which is an analog form of video compression, restricts the bandwidths (image detail) of the color components. In the composite result color is literally added to the monochrome (luminance or Y) information using a visually acceptable technique. As our eyes have far more luminance resolving power than for color, the color sharpness (bandwidth) of the coded signal is reduced to well below that of the luminance. This provides a good solution for transmission and viewing but it becomes difficult, if not impossible, to accurately reverse the process (decode) back into pure luminance and chrominance. This limits its use in post production as repetitive decode, recode cycles severely impair the pictures. Deriving keys from composite video gives poor results. See also: 4fsc, D2, D3
Compositing Multi-layering for moving pictures. Modern composites often use many techniques together, such as painting, retouching, rotoscoping, keying/ matting, digital effects and color correction as well as multi-layering to create complex animations and opticals for promotions, title sequences and commercials as well as in program content. Besides the creative element there are other important applications for compositing equipment such as image repair, glass painting and wire removal - especially in motion pictures. The quality of the finished work, and therefore the equipment, can be crucial especially where seamless results are demanded. See also: Digital keying, Photo-real
Compression (audio) Reduction of bandwidth or data rate for audio. Many digital schemes are in use, all of which make use of the way the ear hears (e.g. that a loud sound will tend to mask a quieter one) to reduce the information sent. Generally this is of benefit in areas where bandwidth or storage is limited, such as in delivery systems to the home, handheld players, etc. See also: Auditory masking, Dolby Digital
Compression (video) The process of reducing the bandwidth or data rate of a video stream. The analog broadcast standards used today, PAL, NTSC and SECAM are, in fact, compression systems which reduce the information contained in the original RGB sources. Digital compression systems analyze their picture sources to find and remove redundancy both within and acrosspicture frames. The techniques were primarily developed for digital data transmission but have been adopted as a means of reducing broadcast transmission bandwidths and storage requirements on disks and VTRs. A number of compression techniques are in regular use for moving images. These include ETSI, JPEG, Motion JPEG, JPEG 2000, DV, MPEG-1, MPEG-2, MPEG-4, AVC Intra, Windows Media and Real. Where different techniques are used in the same stream, problems can occur and picture quality can suffer more than if the same method is used throughout. The MPEG-2 family of compression schemes, which was originally designed for program transmission, has been adapted for studio use in Betacam SX and IMX recorders. While there is much debate, and new technologies continue to be developed, it remains true that the best compressed results are produced from the highest quality source pictures. Poor inputs do not compress well. Noise, which may be interpreted as important picture detail, is the enemy of compression. See also: Compression ratio, Concatenation, Digital Betacam, ETSI, JPEG, JPEG 2000, MPEG-2, MPEG-4, Windows Media
Compression ratio The ratio of the amount of data in the non-compressed digital video signal to the compressed version. Modern compression techniques start with component television signals but a variety of sampling systems are used, 4:2:2 ('Studio' MPEG-2), 4:2:0 (MPEG-2), 4:1:1 (NTSC, DVCPRO), etc. The compression ratio should not be used as the only method to assess the quality of a compressed signal. For a given technique, greater compression can be expected to result in lower picture quality but different techniques give widely differing quality of results for the same compression ratio. See also: Concatenation, DV, ETSI, JPEG, JPEG 2000, MPEG
Concatenation The linking together of systems in a linear manner. In digital television this often refers to the concatenation of compression systems which is a subject of concern because any compression beyond about 2:1 results in the removal of information that cannot be recovered. As the use of compression increases, so too does the likelihood that material will undergo a number of compressions between acquisition and transmission. Although the effects of one compression cycle might not be very noticeable, the impact of multiple decompressions and recompressions - with the material returned to baseband in between - can cause considerable damage. The damage is likely to be greatest where different compression schemes are concatenated in a particular signal path.
Conform Cutting together recorded material according to a prepared scheme such as a rough cut or EDL (Edit Decision List). EDLs can be used to directly control conforming in an online edit suite (auto-conforming). The time to conform varies widely, from a tape-based suite which takes much longer than the finished program's running time, to a nonlinear online suite with true random access to all material. This reduces time by loading material in C-mode and the conforming itself takes only a moment and still allows any subsequent adjustments to be easily made. Note that with in-server editing, material may be loaded onto the server as an independent task, rather than involving the edit equipment itself. This circumvents the loading time so further reducing the total time to produce the finished program. The same is also true of nonlinear edit systems with the bandwidth to support loading as a background task. There are a number of established ways, or modes, of approaching video editing. A-mode is a simple sequential method, starting from the beginning of the program and going through to the end. B-mode uses all shots from one particular source before the next source is used (i.e. checkerboarding). C-mode is similar to B-mode but works sequentially through the playback source rather than the record tape. D-mode is similar to A-mode except that dissolves and other transitions are performed last, at the end of the conform. E-mode is similar to C-mode but with transitions at the end, as in D-mode. Note that the logic of the above modes is based on the characteristics of videotape. As tape is increasingly replaced by other recording media, network conform is becoming increasingly used. Part of the work of the Advanced Media Workflow Association (AMWA) is to provide new industry standards for this important area. See also: Background loading, Delta editing, In-server editing, Uncommitted editing Website: www.aafassociation.org
Consolidation Clearing continuous space on a disk store to allow consistent recording. This generally involves the moving of data on the disks to one area, leaving the remainder free so that recording can proceed track-to-track - without having to make random accesses. The larger the amount of data stored, the longer consolidation may take. Careful consideration must be given to large-capacity multi-user systems, such as video servers, especially when used for transmission or on-air. The need for consolidation arises because of the store's inability to continuously record television frames randomly at video rate. See also: Defragmentation, True random access
Constant bit rate (CBR) compression Compression systems that are used to create a fixed rate of output data. This is usually to fit within a given bandwidth such as that available on a video tape recorder or a constant bit rate transmission channel. With video, the amount of useful information contained in the material varies widely both spatially and temporally - with movement. For example, a football match with crowds and grass texture as well as fast panning cameras typically contains far more information than a largely static head-and-shoulders shot of a newsreader. Using constant bit rate means that the quality is altered to reduce the information to fit the fixed bit rate. In the football case, the grass may go flat during a camera pan, with the texture suddenly reappearing when the camera is still. As overflowing the available bit rate could have disastrous results with bits being lost, the aim is always to use just under the available bit rate. The degree of success in almost filling the available space (not easily done live) is a measure of the quality and efficiency of the compression system. See also: Variable bit rate
Content Pictures, sound, text, graphics, etc., that are edited and ready for delivery to customers - typically as programs for television. See also: Essence
Contouring An unwanted artifact similar to posterization. Digital video systems exhibit contouring when insufficient quantizing levels or inaccurate processing are used, or poor truncation occurs. The result is that the picture's brightness changes in steps that are too large and become visible over relatively even-brightness areas - like the sky. See also: Dynamic Rounding
Control track A linear track recorded onto videotape at frame frequency as a reference for the running speed of a VTR, for the positioning or reading of the video tracks and to drive a tape counter. It is a magnetic equivalent of sprocket holes infilm. One of the main purposes of 'striping' tapes is to record a continuous control track for the pictures and audio to be added later - as in insert editing. Control tracks are not used in disk recording and nonlinear editing.
Convergence (Stereoscopic) In human eyesight, convergence is the ability of our eyes to divert eye optical axes horizontally in an inward direction. The convergence 'near point' is the closest point which is still possible to perceive one image. In practice, the eyes can easily converge inward but have much less ability to diverge outward, as it is something we don't do in life and only when looking at 3D images that have positive parallax beyond the individual human interocular. In cameras - 'toeing' of the cameras (to simulate the eyes converging) to focus on a depth point in the scene, either in front of, behind or at the point of interest. The 'convergence point' is where the axes of toed in cameras align on the Z-axis. Convergence can be adjusted in post production by horizontal movement. Note that sometimes the term 'vergence' is used to describe both convergence and divergence. Convergence pullers are camera-crew members on a Stereoscopic shoot who are responsible for setting up and shifting the convergence during a shot. See also: Parallax
Corner pinning A technique for controlling the position and rotation of pictures in a DVE by dragging their corners to fit a background scene: for example, to fit a (DVE) picture into a frame hanging on a wall. Corner pinning was developed by Quantel as a practical alternative to precisely setting the many parameters needed to accurately position a picture in 3D space. This works well with graphical user interfaces, e.g. pen and tablet. It can also be combined with the data derived from four-point image tracking to substitute objects in moving images, for example replacing the license plate on a moving vehicle. See also: Tracking
Co-sited sampling This is a sampling technique applied to color difference component video signals (Y, Cr, Cb) where the color difference signals, Cr and Cb, are sampled at a sub-multiple of the luminance, Y, frequency - for example as in 4:2:2. If co-sited sampling is applied, the two color difference signals are sampled at the same instant, and simultaneously with a luminance sample. Co-sited sampling is the 'norm' for component video as it ensures the luminance and the chrominance digital information is coincident, minimizing chroma/luma delay.
CRC Cyclic Redundancy Check - an advanced checksum technique used to recognize errors in digital data. It performs the same function as a checksum but is considerably harder to fool. A CRC can detect errors but not repair them, unlike an ECC. A CRC is attached to almost any burst of data which might possibly be corrupted. On disks, any error detected by a CRC is corrected by an ECC. See also: Asynchronous, Checksum, ECC.
Cross conversion Changing video material from one HD format to another. For example, going from 720/60P to 1080/50I is a cross conversion. Note that this example involves both changing picture size and the vertical scan rate from 60 Hz progressive to 50 Hz interlaced. Similar techniques are used as for standards conversion but the HD picture size means the processing has to work five or six times faster. See also: Down-res, Frame-rate conversion, Standards conversion, Up-res
CSMA/CD See: Ethernet
Cut (edit) A transition at a frame boundary from one clip or shot to another. On tape a cut edit is performed by recording (dubbing) the new clip at the out-point of the last, whereas with with true random access storage no re-recording is required - there is simply an instruction to read frames in a new order. Simple nonlinear disk systems may need to shuffle, or de-fragment their recorded data in order to achieve the required frame-to-frame access for continuous replay.