the guide Te r m D i c t i o n a r y Media Technology Consulting

16:9 Widescreen: DVD - Video is the first domestic format natively to support anamorphic 16:9 video, producing pictures with full vertical resolution on 16:9 widescreen TV sets. Previously, widescreen pictures would have been letterboxed within a 4:3 video frame and then magnified by the 16:9 TV sets, resulting in reduced vertical resolution. For viewers with 4:3 TV sets the DVD player can create a 16:9 letterboxed image within a 4:3 frame. 2:3 pulldown: A method for converting 24-fps film to 30-fps video. 2:3 pullup: A method for converting 30-fps video to 24-fps film. 2D graphics: Computer graphics that does not use any 3D techniques and thus involves no explicit depth information. 3:2 Pull-down: Method used to map the 24 fps of film onto the 30 fps (60 fields) of 525line TV, so that one film frame occupies three TV fields, the next two, etc. It means the two fields of every other TV frame come from different film frames making operations such as rotoscoping impossible, and requiring care in editing. Quantel equipment can unravel the 3:2 sequence to allow frame-by-frame treatment and subsequently re-compose 3:2. The 3:2 sequence repeats every five TV frames and four film frames, the latter identified as A-D. Only film frame A is fully on a TV frame and so exists at one timecode only, making it the editable point of the video sequence. 3:2 pulldown: Usually synonymous with 2:3 pulldown. 3:2 pullup: Usually synonymous with 2:3 pullup. 3D graphics: Computer graphics that involves the creation of three-dimensional models within the computer

©copyright Media Technology Consulting 2005

123

1

the guide Te r m D i c t i o n a r y Media Technology Consulting

A/D or ADC: Analogue to Digital Conversion. Also referred to as digitisation or quantisation. The conversion of analogue signals into digital data - normally for subsequent use in a digital machine. For TV, samples of audio and video are taken, the accuracy of the process depending on both the sampling frequency and the resolution of the analogue amplitude information - how many bits are used to describe the analogue levels. For TV pictures 8 or 10 bits are normally used; for sound, 16 or 20 bits are common while 24 bits is also possible. The ITU-R 601 standard defines the sampling of video components based on 13.5 MHz, and AES/EBU defines sampling of 44.1 and 48 kHz for audio. For pictures the samples are called pixels, which contain data for brightness and colour. AC-3: See Dolby Digital, Table 2 Academy aperture: A specific 35mm film framing. See Appendix D for more details. Active picture: The area of a TV frame that carries picture information. Outside the active area there are line and field blanking which roughly, but not exactly, correspond to the areas defined for the original 525 and 625 line analogue systems. In digital TV the blanked/active areas are defined by ITU-R 601, SMPTE RP125 and EBU -E. For both 625 and 525 line formats active line length is 720 luminance samples at 13.5 MHz = 53.3 micro seconds. In digital video there are no half lines as there are in analogue. The field blanking is: Format625/50525/60 Field 124 lines19 lines Field 225 lines19 lines Active lines/frame576487 active region: The portion of the video signal that is used for actual image information, as opposed to blanking, closed-captioning, time code, etc. AES/EBU: The Audio Engineering Society (AES) and the EBU together have defined a standard for Digital Audio, now adopted by ANSI (American National Standards Institute). Commonly referred to as 'AES/EBU', this digital audio standard permits a variety of sampling frequencies, for example CDs at 44.1 kHz, or digital VTRs at 48 kHz. 48 kHz is widely used in broadcast TV production. Website: http://www.aes.org affine: Any linear geometric transformation including pan, rotate, scale, and shear. AIFF: Audio Interchange File Format. A standard file format for storing audio data.

©copyright Media Technology Consulting 2005

Letter A

2

the guide Te r m D i c t i o n a r y Media Technology Consulting

ALF: Auto Lock Follow. Name for Quantel's image tracking system. It can follow a number of points in a clip to sub-pixel accuracy and the data it produces can be used in numerous applications from stabilising a shot to substituting images in moving video. algorithm: A procedure or set of instructions for solving a problem or accomplishing a particular goal. aliasing: An artifact that is due to limited resolution. Aliasing: Undesirable 'beating' effects caused by sampling frequencies being too low to faithfully reproduce image detail. Examples are: 1) Temporal aliasing - eg wagon wheel spokes apparently reversing, also movement judder seen in standards converters with insufficient temporal filtering. 2) Raster scan aliasing - twinkling effects on sharp boundaries such as horizontal lines. Due to insufficient filtering this vertical aliasing, and its horizontal equivalent, are often seen in lower quality DVEs as detailed images are compressed. The steppiness of unfiltered lines presented at an angle to the TV raster is also referred to as aliasing.

alpha channel: The portion of a four-channel image that is used to store transparency information. Alpha channel: Another name for key channel - a channel to carry a key signal. analog: Information/data that is continuously variable, without discrete steps or quantization. As opposed to digital. anamorphic: Any distorted image that can be undistorted to restore it to its original format.

©copyright Media Technology Consulting 2005

Aliens: A familiar term for alias effects, such as ringing, contouring and jaggy edges caused by lack of resolution in a raster image. Some can be avoided by careful filtering or dynamic rounding.

3

the guide Te r m D i c t i o n a r y Media Technology Consulting

Anamorphic: Generally refers to the use of 16 x 9 aspect ratio pictures in a 4 x 3 system. For example, anamorphic supplementary lenses are used to change the proportions of an image to 16 x 9 on the surface of a 4 x 3 sensor by either extending the horizontal axis or compressing the vertical. Signals from 16 x 9 cameras and telecines produce an 'anamorphic' signal which is electrically the same as with 4 x 3 images but will appear horizontally squashed if displayed at 4 x 3. The alternative way of carrying 16:9 pictures within 4:3 systems is letterbox. Letterbox has the advantage of showing the correct 16:9 aspect ratio on 4:3 displays, the vertical resolution is less than 16:9 anamorphic. anamorphic format: Compositing A film format characterized by the fact that the image captured on the negative is horizontally squeezed by the use of a special lens. It is later unsqueezed at projection time by the appropriate amount. For most 35mm feature-film work, the standard anamorphic format produces a 2.35:1 aspect ratio when projected. See Cinemascope, #Panavision, and Appendix D for more details. anamorphic lens: A lens that changes the width-to-height relationship of the original image. The most common anamorphic camera lenses in film work compress the horizontal axis by 50%. See Cinemascope. animated: Having characteristics that change over time.

animation: Moving imagery that is created on a frame-by-frame basis. This may be accomplished via the use of computers or with more traditional cel animation techniques. animator: A person responsible for producing animations. Anti-aliasing: Smoothing of aliasing effects by filtering and other techniques. Most, but not all, DVEs and character generators contain anti-aliasing facilities. antialiasing: Techniques used to mitigate the artifacts caused by a lack of sufficient resolution.

©copyright Media Technology Consulting 2005

animatic: A rough animation that gives some idea about the timing of a sequence. Essentially a moving storyboard.

4

the guide Te r m D i c t i o n a r y Media Technology Consulting

aperture: (1) In a lens, the size of the opening that light passes through (usually given in terms of its f-stop or t-stop). (2) In a camera body, the mask opening that defines the area of film that will be exposed on each frame. (3) In a projector, the mask opening that defines the area of the frame that will be projected. API: Application Programming Interface - A set of interface definitions (functions, subroutines, data structures or class descriptions) which provide a convenient interface to the functions of a subsystem. They also simplify the work by insulating the application programmer from minutiae of the implementation. Arbitrated Loop:

Archive: Long-term storage of information. Pictures and sound stored in digital form can be archived and recovered without loss or distortion. The storage medium must be both reliable and stable and, as large quantities of information need to be stored, cost is of major importance. Currently the lowest cost is magnetic tape but there is increasing interest in optical disks - more expensive but with far better access. VTRs, rather than data recorders, offer the most efficient and practical means of video archive. Non-compressed component digital formats, D1 and D5 give the best quality, other formats can also be useful - there is interest in archive at 50 Mb/s, about 3:1 compression. For stills and graphics compression should be avoided. Magneto-optical (MO) disks are convenient, giving instant access to all pictures. For digital film image archive Quantel has devised the D16 format so that full film resolution images can be stored and viewed on standard ITU-R 601 recorders. Archiving an editing or compositing session, requiring data on all aspects of the session to be stored, becomes practical with integrated equipment (eg non-linear suites). Beyond an EDL this may include parameters for colour correction, DVE, keying, layering etc. This data can be transferred to a removable medium such as a floppy disk or an MO. Areal density: The density of data held on an area of the surface of a recording medium. This is one of the parameters that manufacturers of disk drives and tape recorders strive to increase.

©copyright Media Technology Consulting 2005

A technique used on computer networks to ensure that the network is clear before a fresh message is sent. When it is not carrying data frames the loop carries 'keep-alive' frames. Any node that wants to transmit places its own ID into a 'keep-alive' frame. When it receives that frame back it knows that the loop is clear and that it can send its message.

5

the guide Te r m D i c t i o n a r y Media Technology Consulting

Artefact: Particular visible effects which are a direct result of some technical limitation. Artefacts are generally not described by traditional methods of signal evaluation. For instance, the visual perception of contouring in a picture cannot be described by a signal-to-noise ratio or linearity measurement. articulate matte: A matte whose shape changes over time and which is designed to accurately follow the contours of the object to which it corresponds. artifact: A (usually undesirable) item in an image that is a side effect of the process used to generate or modify that image. ASA rating: A standard numerical rating for specifying a film's sensitivity to light. "ASA" refers to the American Standards Association, now known as the American National Standards Institute, or ANSI. Many manufacturers now use their own specific exposure index instead. See also DIN rating, ISO index.

ASCII: American Standard Code for Information Interchange. This is a standard computer character set used throughout the industry to represent keyboard characters as digital information. There is an ASCII table containing 127 characters covering all the upper and lower case characters in normal and non displayed controls such as carriage return, line feed etc. Variations and extensions of the basic code are used in special applications. ASIC: Application Specific Integrated Circuit. A custom designed integrated circuit with functions specifically tailored to a particular application. This effectively replaces the many discrete devices that could otherwise do the job but its performance will be superior. Being far more compact than the separate components, the single chip can work faster than an array of separate chips. Often a ten-fold increase in speed is achieved, while the power consumption can drop by a similar factor and reliability is greatly increased. See also: PLD

©copyright Media Technology Consulting 2005

ASCII: Abbreviation for American Standard for Computer Information Interchange. A very common alphanumeric text interchange format. The term is used colloquially to refer to data that is stored in a text format that doesn't require a special program to decode and is usually somewhat comprehensible to a human reader.

6

the guide Te r m D i c t i o n a r y Media Technology Consulting

aspect ratio: A single number that is the result of dividing the width of an image by its height. The units used to measure the width and height are irrelevant, since they will cancel when divided together to give a unitless result. See also pixel aspect ratio.

ATM: Asynchronous Transfer Mode. A high speed switched data communications system potentially capable of both local area network (LAN) and wide area network (WAN) operation. 25, 155 and 622 Mb/s ATM links are currently available. Due to the overheads of the system only a part of this bandwidth can be used for useful 'payload' data but the higher speeds could be used to carry non-compressed ITU-R 601 video as data files. It remains to be seen whether the dream of being able to transmit 'live' non-compressed video over a network will materialise. Website: http://www.atmforum.com atmosphere: A depth cue that causes objects to decrease in contrast as they move into the distance.

©copyright Media Technology Consulting 2005

Aspect ratio: 1. - of pictures. The ratio of length to height of pictures. Nearly all TV screens are currently 4:3, ie four units across to three units in height but there is a growing move towards widescreen 16:9. Pictures presented this way are believed to absorb more of our attention and have obvious advantages in certain productions, such as sport. In the change towards 16:9 some in-between ratios have been used, such as 14:9. 2. - of pixels. The aspect ratio of the area of a picture described by one pixel. The ITU-R 601 digital coding standard defines luminance pixels which are not square. In the 525/60 format there are 486 active lines each with 720 samples of which 711 may be viewable due to blanking. Therefore the pixel aspect ratio on a 4:3 screen is: 486/711 x 4/3 = 0.911 (ie the pixels are 10% taller than they are wide) For the 625/50 format there are 576 active lines each with 720 samples of which 702 are viewable so the pixel aspect ratio is: 576/702 x 4/3 = 1.094 (ie the pixels are 9% wider than they are tall) Account must be taken of pixel aspect ratios - for example in executing a DVE move - when rotating a circle, the circle must always remain circular and not become elliptical. Another area where it is important is the movement of images between (standard) computer platforms and television systems. Computers nearly always use square pixels so their aspect ratio must be adjusted to suit television. This process takes time and will not be perfect and the quality of the result will depend on the quality of the processing used.

7

the guide Te r m D i c t i o n a r y Media Technology Consulting

ATSC: The (US) Advanced Television Systems Committee. Established in 1982 to coordinate the development of voluntary national technical standards for the generation, distribution and reception of high definition television. In 1995 the ATSC published "The Digital Television Standard" which describes the US Advanced Television System. This uses MPEG-2 compression for the video and AC-3 for the audio and includes a wide range of video resolutions (as described in ATSC Table 3) and audio services (Table 2). It uses 8 and 16 VSB modulation respectively for terrestrial and cable transmission. Website: http://www.atsc.org ATV: Advanced Television. The term used in North America to describe television with capabilities beyond those of analogue NTSC. It is generally taken to include digital television (DTV) and high definition (HDTV).

AV disk drives: Most disk drives are intended for pure data applications but AV drives are designed especially for audio/video. The extremely high storage capacities achieved on modern small format drives (currently up to 18 GB on 3.5-inch diameter) result in the tracks being packed very tightly across the disks many tracks are recorded within a 'paper thin' distance. Distances are so minute that thermal re-calibration is used to ensure the read/write heads are accurately placed over the tracks. On AV disks thermal re-calibration is built-in as a part of their continuous operation whereas pure 'data' disks will regularly take time out for re-calibration - making them not well suited for video where pictures and sound must flow continuously. Axis (x, y, z): Used to describe the three dimensional axes available in DVE manipulations. At normal (clear) x lies across the screen left to right, y up the screen bottom to top and z points into the screen. Depending on the power of the equipment and the complexity of the DVE move, several sets of xyz axes may be in use at one time. For example, one set may be referred to the screen, another to the picture and a third off-set to some point in space (reference axis).

©copyright Media Technology Consulting 2005

Auditory Masking: The psycho-acoustic phenomenon of human hearing where what can be heard is affected by the components of the sound. For example, a loud sound will mask a soft sound close to it in frequency. Audio compression systems such as Dolby Digital and MPEG audio use auditory masking as their basis and only code what can be heard by the human ear.

8

the guide Te r m D i c t i o n a r y Media Technology Consulting

B-frames - MPEG Term: Bi-directional predictive frames composed by assessing the difference between the previous and the next frames in a television picture sequence. As they contain only predictive information they do not make up a complete picture and so have the advantage of taking up much less data than the I-frames. However, to see that original picture requires a whole sequence of MPEG frames to be decoded which must include an I-frame. background: In a composite, the bottom element over which all others are added. In general, the background makes up the majority of the image. Background task: Operation that is completed while the main operation continues uninterrupted. This requires an overhead in the machines' capabilities beyond that needed for their primary operation. This has particular benefits in pressured situations where time is short, or simply not available for extra operations - such as during live programming and transmission. An example of such a background task is picture exchange between a Picturebox and a Paintbox via Picturenet Plus - completed while both systems continue normal operation. backing color: The color of the uniform background that is used when shooting an element for traveling matte extraction. banding: An artifact that appears in areas of a color gradient where the lack of sufficient color resolution causes noticeable bands instead of a smooth transition. Also known as contouring. See also Mach banding. Bandwidth: The amount of information that can be passed in a given time. In television a large bandwidth is needed to show sharp picture detail and so is a factor in the quality of recorded or transmitted images. ITU-R 601 and SMPTE RP 125 allow analogue luminance bandwidth of 5.5 MHz and chrominance bandwidth of 2.75 MHz, the highest quality attainable in any standard broadcast format. Digital image systems generally require large bandwidths hence the reason why many storage and transmission systems revert to compression techniques to accommodate the signal. base: The transparent material (usually cellulose acetate) on which emulsions are applied to make photographic film. Note that it is generally not completely transparent, but rather has a slight characteristic color that may need to be compensated for when scanning. batch compositing: A method of compositing that entails the creation of a script or set of instructions that will be executed at a later time.

©copyright Media Technology Consulting 2005

Letter B

9

the guide Te r m D i c t i o n a r y Media Technology Consulting

beauty pass: When using motion control to shoot multiple passes of an object, the beauty pass is the one that features the most significant information about the object, in contrast to other passes such as the lighting pass, shadow pass, or reflection pass. Betacam: An analogue component VTR system using a 1.25-inch cassette - very similar to the domestic Betamax. This was developed by Sony and is marketed by them and several other manufacturers. Although recording the Y, R-Y and B-Y component signals onto tape many machines are operated with coded (PAL or NTSC) video in and out. The system has continued to be developed over the years to offer models for the industrial and professional markets as well as full luminance bandwidth (Betacam SP), PCM audio and SDI connections. Digital versions exist as the high-end Digital Betacam and Betacam SX for ENG and similar applications. Betacam SX: A digital tape recording format developed by Sony which uses a constrained version of MPEG-2 compression at the 4:2:2 profile, Main Level (422P@ML) using 1¼2-inch tape cassettes.

Binary: Mathematical representation of a number to base 2, ie with only two states, 1 and 0; on and off; or high and low. This is the base of the mathematics used in digital systems and computing. Binary representation requires a greater number of digits than the base 10 decimal system most of us commonly use everyday. For example the base 10 number 254 is 11111110 in binary. The result of a binary multiplication contains the sum of digits of the original numbers. So: 10101111 x 11010100 = 1001000011101100 (In decimal 175 x 212 = 37,100) Each digit is known as a bit. This example multiplies two 8-bit numbers and the result is always a 16-bit number. Multiplication is a very common process in digital television equipment. bit: The basic unit for representing data in a digital environment. A bit can have only two different values: 0 or 1. Bit (b): Binary digIT = bit One mathematical bit can define two levels or states, on or off, black or white, 0 or 1 etc; - two bits can define four levels, three bits eight, and so on: generally 2n, where n = the number of bits. In image terms eight bits can define 256 levels of brightness from black to white (with ITU-R 601, 16 = black and 235 = white).

©copyright Media Technology Consulting 2005

BG: Abbreviation for background. bicubic interpolation: Compositing A method of interpolation based on an average of the 16 nearest neighbors. See also linear interpolation, bilinear interpolation. bilinear interpolation: A method of interpolation based on an average of the four nearest neighbors. See also linear interpolation, bicubic interpolation.

10

the guide Te r m D i c t i o n a r y Media Technology Consulting

bit depth: A way of specifying the color resolution in an image by measuring the number of bits devoted to each component of the pixels in the image. Bit rate reduction (BRR): See Compression bit-mapped image: An image that consists of a rectangular, two-dimensional array of pixels. The standard method for representing an image in a digital format. Bitstream: 1. A flow of data. 2. Name of supplier of text fonts. Quantel type-capable equipment is supplied with a library of 1085 vector-based Bitstream fonts. black point: (1) On a piece of film, the measured density in the area of greatest opacity. (2) In a digital image, the numerical value that corresponds to the darkest area that will be represented when the image is eventually viewed in its final form.

Blocks: See MPEG-2 Blocks - MPEG Term: Rectangular areas of pictures, usually 8 x 8 pixels in size, which are individually subjected to DCT coding as part of a digital picture compression process. blue spill: Any contamination of the foreground subject by light reflected from the bluescreen in front of which it is placed. See also spill, green spill. bluescreen: (1) Commonly used as a generic term that refers to bluescreen photography or any similar process, which may use other colors as well as blue. (2) Literally, a screen of some sort of blue material that is suspended behind an object for which we wish to extract a matte. Ideally, the bluescreen appears to the camera as a completely uniform blue field.

©copyright Media Technology Consulting 2005

Blender: Video mixing/keying/colour correcting facility in Quantel's Henry. Blocking and 'Blockiness': See MPEG-2 Blocking and 'Blockiness' - MPEG Term: Book Artefact of compression generally showing momentarily as rectangular areas of picture with distinct boundaries. This is one of the major defects of digital compression, especially MPEG, its visibility generally depending on the amount of compression used, the quality and nature of the original pictures as well as the quality of the coder. The visible blocks may be 8 x 8 DCT blocks or 'misplaced blocks' - 16 x 16 pixel macroblocks, due to the failure of motion prediction/estimation in an MPEG coder or other motion vector system, eg standards converter.

11

the guide Te r m D i c t i o n a r y Media Technology Consulting

bluescreen photography: Compositing The process of photographing an object in front of a bluescreen with the intention of extracting a matte for that object using various keying and/or color-difference techniques. bounce light: Light that is reflected or "bounced" off other objects in a scene before it reaches the subject. Bouquet: A term - now going out of favour - for the group of compressed video channels multiplexed into a single transport stream for a digital transmission feed. The noun "Multiplex" in now used in its place. Box filter: A specific digital filter that is often used when resampling a digital image. The Box filter is fast, but fairly low quality. Browse: Method used with some still stores, graphics systems and disk-based video stores to display a selection of reduced sized images to aid choice of stored clips or stills. For moving video a timeline may be available so clips can be shuttled allowing the full sized images brought to use pre-cued.

Bug: An error in a computer program that causes the system to behave erratically, incorrectly or to stop altogether. Term dates from the original computers with tubes and relays, where real live bugs were attracted by the heat and light and used to get in the works. burn-in: Photographic double exposure of an element over a previously exposed piece of film. Bus: An internal pathway for sending digital signals from one part of a system to another. BWF: Broadcast WAV - an audio file format based on Microsoft's WAV. It can carry PCM or MPEG encoded audio and adds the metadata, such as a description, originator, date and coding history, needed for interchange between broadcasters. Website: www.ebu.ch Byte (B), Kilobyte (kB), Megabyte (MB), Gigabyte (GB), Terabyte

©copyright Media Technology Consulting 2005

Browse station: Low cost viewing station to provide browsing of stored images or video. See also: Picturenet, Picturenet Plus

12

the guide Te r m D i c t i o n a r y Media Technology Consulting

©copyright Media Technology Consulting 2005

(TB) and Petabyte (PB): 1 Byte (B) = 8 bits (b) which can describe 256 discrete values (brightness, colour, etc.). Traditionally, just as computer-folk like to start counting from zero, they also ascribe 2 raised to the power 10, 20, 30 etc (210, 220, 230 etc) to the values kilo, mega, giga, etc. which become, 1,024, 1,048,576, 1,073,741,824 etc. This can be difficult to handle for those drilled only in base-10 mathematics. Fortunately, some disk drive manufacturers, who have to deal in increasingly vast numbers, are now describing their storage capacity in powers of 10, so a 9 GB drive has 9,000,000,000 bytes capacity. Observation suggests both systems are now in use… which could lead to some confusion. Traditional New Approx duration @601 1 kB = 210 bytes = 1,024 bytes 103 bytes0.3 line 1 MB = 220 bytes = 1,048,576 bytes106 bytes1 frame 1 GB = 230 bytes = 1.074 x 109 bytes109 bytes47 sec 1 TB = 240 bytes = 1.099 x 1012 bytes1012 bytes13.25 hours 1 PB = 250 bytes = 1.126 x 1015 bytes1015 bytes550 days Currently 3.25-inch Winchester disk drives store from 4 to 18 GB. Solidstate store chips, DRAMs, increment fourfold in capacity every generation, hence the availability of 16, 64, and now 256 Mb chips. A full frame of digital television, sampled according to ITU-R 601, requires just under 1 MB of storage (830 kB for 625 lines, 701 kB for 525 lines). HDTV frames are around 5 - 6 times larger and digital film frames may be that much larger again.

13

the guide Te r m D i c t i o n a r y Media Technology Consulting

C-scope: Abbreviation for Cinemascope. camera aperture: A specific 35mm film framing, also known as full aperture. See Appendix D for more details. CCD: Abbreviation for charge-coupled device, a light-sensitive semiconductor that is often used in scanners and video cameras to capture an image. 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 proportional to the light impinging on each cell. The cells are coupled to a scanning system which, after analogue to digital conversion, presents the image as a series of binary digits. Early CCD arrays were unable to reproduce a wide range of brightness but they now offer low noise, high resolution imaging up to HDTV level. CCIR: Comité Consultatif International des Radiocommunications. This has been absorbed into the ITU under ITU-R. CCITT: International Telegraph and Telephone Consultative Committee. As the name suggests this was initially set up to establish standards for the telephone industry in Europe. It has now been superseded by ITU-T so putting both radio frequency matters (ITU-R) and telecommunications under one overall United Nations body. CDDI: Copper Data Distributed Interface. A high speed data interface - like FDDI but using copper. CDTV: Conventional Definition Television. The analogue NTSC, PAL, SECAM television system with normal 4:3 aspect ratio pictures. cel animation: Animation that is the result of sequences of images drawn on individual clear acetate cels. Many aspects of traditional cel animation are now being supplemented by digital techniques. CGI: See computer-generated imagery. channel: For a given image, the subimage that is composed only of the values from a single component of each pixel. characteristic curve: Compositing A curve that plots the relationship between light falling on a piece of film and the resulting density of the developed image.

©copyright Media Technology Consulting 2005

Letter c

14

the guide Te r m D i c t i o n a r y Media Technology Consulting

Checksum: A simple check value of a block of data, 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. Chroma keying: The process of overlaying one video signal over another, the areas of overlay being defined by a specific range of colour, or chrominance, on the foreground 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 601 digital sampling standard was to allow high quality chroma keying in post production. The 4:2:2 sampling system allowed 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 and 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. chroma-keying: A keying technique that allows one to separate an object from its background based on colors that are unique to either the foreground or background.

chrominance: The color portion of a video signal, carrying the hue and saturation values. See also luminance. Chrominance: The colour part of a signal, relating to the hue and saturation but not to the brightness or luminance of the signal. Thus black, grey and white have no chrominance, but any coloured signal has both chrominance and luminance. Although imaging equipment registers red, blue and green the television picture is handled and transmitted as U and V, I and Q, Cr and Cb, (R-Y) and (B-Y) which all represent the chrominance information of a signal. CIF: A digital video size defined by the ITU suitable for multiple video formats; it is 352 pixels wide by 288 pixels high.

©copyright Media Technology Consulting 2005

chromatic resolution: Compositing Another term for color resolution.

15

the guide Te r m D i c t i o n a r y Media Technology Consulting

Cinemascope: An anamorphic film format that produces an image with an aspect ratio of 2.35:1. Although Cinemascope (or CinemaScope) was originally a specific process developed by 20th Century Fox in the 1950s, it has become a generic term for the 2.35 anamorphic format. The most common lenses used for this purpose today are produced by Panavision. See Appendix D for more details. Cineon: A specific image file format for film. See Appendix C. circle of confusion: The size of the circle to which an idealized point will diverge when the lens is focused at different depths. Used as a way to measure the focus of a lens. clip: A small piece of film, often "clipped" from a longer shot, that can be used as a reference for color, lighting, etc. 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 video frames. In Quantel editing systems, a clip can be a single video segment or a series of video segments spliced together. A video clip can also be recorded with audio or have audio added to it.

Clip Pack: A multi-layer clip constructed in the Pack Reel of the Edit Desk in Quantel editing systems. clipping: The process (intentional or otherwise) whereby data above or below a certain threshold is removed or lost. With digital images, this usually translates to colors outside a specific range. Clone: An exact copy, indistinguishable from the original. As in copying recorded material, eg 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 process or the result will not be a clone.

©copyright Media Technology Consulting 2005

Clip Audio: Quantel term for audio that has been recorded with, or added to, a video clip in an on-line, non-linear editor. An audio-only clip is stored with only one frame of video (for ident) repeated for the audio duration.

16

the guide Te r m D i c t i o n a r y Media Technology Consulting

Cloud tank: A large water-filled glass enclosure that is used to create clouds and other atmospheric effects. The clouds are usually produced by injecting some opaque liquid (such as white paint) into the water. CMY: Cyan, magenta, and yellow. The three complementary colors, or a method of specifying the colors in an image based on a mix of these three components. Co-sited sampling: This is a sampling technique applied to colour difference component video signals (Y, Cr, Cb) where the colour 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 colour difference signals are sampled at the same instant, and simultaneously with one of the luminance samples. Co-sited sampling is the 'norm' for component video as it ensures the luminance and the chrominance digital information is coincident, minimising chroma/luma delay. Coded (video): See Composite

color correction: Any process that alters the perceived color balance of an image. color difference method: Compositing A compositing technique that utilizes the difference in color between the different channels of an image in order to extract a matte. The technique relies on the subject being photographed in front of a uniformly colored background, such as a bluescreen. color resolution: The amount of data allocated for specifying the value of an individual color in an image. See also bit depth. color space: Any method for representing the color in an image. Usually based on certain components such as RGB, HSV, etc.

©copyright Media Technology Consulting 2005

COFDM: A transmission scheme proposed for DVB in Europe based on Coded Orthogonal Frequency Division Multiplexing. It allows for the use of either 1705 carriers (usually known as '2k'), or 6817 carriers ('8k'). Concatenated error correcting 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. The guard interval is selectable. The '8k' system is compatible with the '2k' system.

17

the guide Te r m D i c t i o n a r y Media Technology Consulting

color temperature: A method of specifying color based on an absolute temperature scale, degrees Kelvin (K). The color is equivalent to the color of light that would be emitted if a pure black object were heated to that temperature. Higher color temperatures are more blue, lower temperatures are more red. color timer: A person who adjusts the scene-to-scene color continuity when preparing the final print of a film. color timing: The color balance of a particular image or scene, or the process of color correcting and balancing that image or scene. color wedge: A series of images that feature incremental alterations in the color of a certain element (or sometimes the entire frame) for the purpose of choosing a final value for the color of that element. Colour framing: See Field sequence

complementary color: Compositing The color that results when the primary color is subtracted from white. complementary matte: Compositing The matte that results when the primary matte is inverted. component: One of the elements that is used to define the color of a pixel. In most digital images, the pixel color is specified in terms of its red, green, and blue components. Component (video): The normal interpretation of a component video signal is one in which the luminance and chrominance remain as separate components, eg analogue components in MII and Betacam VTRs, digital components Y, Cr, Cb in ITU-R 601. RGB is also a component signal. Component video signals retain maximum luminance and chrominance bandwidth.

©copyright Media Technology Consulting 2005

Colour space: The colour range between specified references. Typically three references are quoted in television: RGB, Y, R-Y, B-Y and Hue Saturation and Luminance (HSL). In print, Cyan, Magenta, Yellow and Black (CMYK) are used. Moving pictures between these is possible but 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 colour space.

18

the guide Te r m D i c t i o n a r y Media Technology Consulting

component video: Video signal in which the luminance and chrominance elements are maintained separately. Composite (video): Luminance and chrominance are combined along with the timing reference 'sync' information using one of the coding standards - NTSC, PAL or SECAM - to make composite video. The process, which is an analogue form of video compression, restricts the bandwidths (image detail) of components. In the composite result colour is literally added to the monochrome (luminance) information using a visually acceptable technique. As our eyes have far more luminance resolving power than for colour, the colour sharpness (bandwidth) of the coded single is reduced to far below that of the luminance. This provides a good solution for transmission but it becomes difficult, if not impossible, to accurately reverse the process (decode) into pure luminance and chrominance which limits its use in post production. composite video: Video signal in which the luminance and chrominance elements are combined (encoded) into a single signal.

Compositing: Simultaneous multi-layering and design for moving pictures. Modern designs often use many techniques together, such as painting, retouching, rotoscoping, keying/matting, digital effects and colour correction as well as multi-layering to create complex animations and opticals for promotions, title sequences and commercials as well as in programme 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. For example, adding a foreground convincingly over a background - placing an actor into a scene - without any tell-tale blue edges or other signs that the scene is composed. compositing engine: Compositing Within a package used for compositing, the code that is responsible for the actual image processing operations, in contrast to other code that may deal with the user interface, file input/output, etc. compositor: A person who creates composites. 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 (eg that a loud sound will tend to mask a quieter one) to reduce the information sent. Generally this is to benefit in areas where bandwidth and storage are limited, such as in delivery systems to the home.

©copyright Media Technology Consulting 2005

compositing: The manipulated combination of at least two source images to produce an integrated result.

19

the guide Te r m D i c t i o n a r y Media Technology Consulting

Compression (video): The process of reducing the bandwidth or data rate of a video stream. The analogue broadcast standards used today, PAL, NTSC and SECAM are, in fact, compression systems which reduce the data content of their original RGB sources. Digital compression systems analyse their picture sources to find and remove redundancy both within and between picture frames. The techniques were primarily developed for digital data transmission but have been adopted as a means of reducing transmission bandwidths and storage requirements on disks and VTRs. A number of compression techniques are in regular use, these include ETSI, JPEG, Motion JPEG, MPEG-1 and MPEG-2. Where different techniques are used in the same stream, problems can occur and picture quality can suffer. Considerable interest is currently being created by the MPEG-2 family of compression schemes which was designed for programme transmission although specific variants are also used for programme acquisition and editing. 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 is the enemy of compression.

Compression ratio: The ratio of the data in the non-compressed digital video signal to the compressed version. Modern compression techniques start with the component television signal but a variety of sampling ratios are used, 4:2:2, 4:2:0 (MPEG-2), 4:1:1 (DVCPRO), etc. The 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 worse quality but different techniques give widely differing quality of results for the same compression ratio. The only sure method of judgement is to make a very close inspection of the resulting pictures. Compressionist: One who controls the compression process to produce results better than would normally be expected from an automated system. computer graphics: An image or images created or manipulated with the aid of a computer. computer-generated imagery: Compositing An image or images created or manipulated with the aid of a computer. Often used to refer specifically to 3D computer animation, although it is really a much broader term.

©copyright Media Technology Consulting 2005

compression ratio: The ratio of the data sizes between the uncompressed element and the compressed equivalent.

20

the guide Te r m D i c t i o n a r y Media Technology Consulting

Concatenation: The linking together of systems. In digital television this refers to the concatenation of compression systems which is currently 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 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. Conditional access: Digital Television signals can be scrambled in such a way that they cannot be understood by a conventional decoder. Only when unscrambled by a special system can the original pictures be seen by the viewer. By controlling the operation of the de-scrambling system through the use of a prepaid access card, or by a transmitted code, the broadcaster can control access to a particular channel or service. Conditional access can be used to control many things from pay per view subscription through to target viewing areas.

Consolidation: Clearing continuous space on a disk store to allow consistent recording. This generally involves the moving of fragmented data on the disks to one area, leaving the remainder free so that recording can proceed track-totrack - 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. A true random access store has no need of consolidation. continuity: The smooth flow of action or events from one shot or scene to the next, without any indication that the different shots/scenes may have been photographed at different times or processed differently.

©copyright Media Technology Consulting 2005

Conform: Making the final edit according to a prepared scheme such as a rough cut or EDL. EDLs can be used to directly control conforming in an on-line edit suite (auto-conforming). The time to conform varies widely, from a tape suite which takes much longer than the finished programme running time, to a disk-based true random access suite that reduces time by loading material in C-mode, conforming itself takes only a moment and still allows any adjustments to be easily made. Note that with server-based editing, material may be loaded on the server - if required, by many ports - further reducing the total time to produce the finished programme.

21

the guide Te r m D i c t i o n a r y Media Technology Consulting

contouring: An artifact that results from not having enough color resolution to properly represent a color gradient. See also Mach banding. Contouring: An unwanted artefact similar to posterisation. Digital systems exhibit contouring when insufficient quantising levels are used or inaccurate processing, or truncation occurs. contrast: The ratio of the brightest tones in an image to the darkest. control points: The specific points that are interpreted to define the shape of a curve. Control track: A linear track recorded onto video tape 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 in film. 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 editing. convolution filter: A matrix of numbers used to control the weighted averaging performed in a convolve operation. Sometimes also referred to as the convolution mask.

convolution mask: See convolution filter. convolve: An image processing operation that involves the specialized averaging of a neighborhood of pixels using a convolution filter. Also known as a spatial convolution. cool: A nonexact term that is used to describe an image that is biased toward the blue portion of the spectrum. Corner pinning: A technique for defining 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 an alternative to precisely setting the many parameters needed

©copyright Media Technology Consulting 2005

convolution kernel: The group of pixels that will be considered when performing a convolve operation. Generally we are only worried about the size of the kernel, which is usually a square matrix with an odd number of elements in each dimension. The most common kernel size is 3 $X 3. Occasionally the term is used as a synonym for the convolution filter.

22

the guide Te r m D i c t i o n a r y Media Technology Consulting

to accurately position a picture in 3D space. This works well with graphical user interfaces, eg 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 licence plate on a moving vehicle. CPU: Abbreviation for central processing unit, the computational heart of a computer. crawling: An undesirable artifact characterized by edges that do not remain stable over time. CRC: Cyclic Redundancy Check - an advanced checksum technique. It uses a check value calculated for a data stream by feeding it through a shifter with feedback terms 'EXORed' back in. 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. ITU-R 601 data is subjected to CRCs, if an error is found the data is concealed by repeating appropriate adjacent data, also Ethernet packets use CRCs etc. CRF: Cutting Room Floor. Moving material to CRF in Quantel editing systems removes it from the work area - but not from the disk store.

CSDI: Compressed Serial Data Interface - in the process of being ratified by the SMPTE. It uses the same signal format as DVCPRO and, as this is a compressed format, enables video data to be transferred at four times real time rate over SDI links. cukaloris: Panel with irregular holes cut in it to project patterned shadows onto a subject. Also known as a kukaloris, cuke, or cookie. cursor: A graphical marker, usually controlled by a device such as a mouse or a tablet, that is used to point to a position or object on a computer's display. Cut (edit): A transition at a frame boundary from one clip to another. On tape a cut edit is performed by recording (dubbing) the new clip at the out-point of the last, whereas with true random access editing no re-recording is required - there is simply an instruction to read frames in a new order. Simple non-linear disk systems may need to shuffle their recorded data in order

©copyright Media Technology Consulting 2005

cropping: The removal (intentionally or otherwise) of part of an image that is outside a specific boundary.

23

the guide Te r m D i c t i o n a r y Media Technology Consulting

to achieve the required frame-to-frame access for continuous replay. The editable frame boundaries may be restricted by video coding systems, PAL, NTSC, SECAM and MPEG. Non-compressed component video and that compressed using only intra-frame compression (eg motion JPEG) can be edited on any frame boundary without additional processing.

©copyright Media Technology Consulting 2005

CVBS: Composite Video Blank and Sync. Unmodulated analog single channel Video (without Audio). Usually transmitted over a 75 ohm BNC (professional) or RCA connector (consumer). This signal contains the color burst frequence on every line and must be terminated into 75 ohms to prevent reflections.

24

the guide Te r m D i c t i o n a r y Media Technology Consulting

D-max: See maximum density. D-min: See minimum density. D1: A format for digital video tape recording working to the ITU-R 601, 4:2:2 standard using 8-bit sampling. The tape is 19 mm wide and allows up to 94 minutes to be recorded on a cassette. Being a component recording system it is ideal for studio or post production work with its high chrominance bandwidth allowing excellent chroma keying. Also multiple generations are possible with very little degradation and D1 equipment can integrate without transcoding to most digital effects systems, telecines, graphics devices, disk recorders, etc. Being component there are no colour framing requirements. Despite the advantages, D1 equipment is not extensively used in general areas of TV production, at least partly due to its high cost. See also: D2, 8-bit, DVTR For further reading - see Appendix D1 format: A digital component video format. D1 is considered to be a nearly lossless format. D16: A recording format for digital film images making use of standard D1 recorders. The scheme was developed specifically to handle Quantel's Domino (Digital Opticals for Movies) pictures and record them over the space that sixteen 625 line digital pictures would occupy. This way three film frames can be recorded or played every two seconds. Playing the recorder allows the film images to be viewed on a standard monitor; running at x16 speed shows full motion direct from the tape. D2: The VTR standard for digital composite (coded) PAL or NTSC signals. It uses 19 mm tape and records up to 208 minutes on a single cassette. Neither cassettes nor recording formats are compatible with D1. D2 has often been used as a direct replacement for 1-inch analogue VTRs. Although offering good stunt modes and multiple generations with low losses, being a coded system means coded characteristics are present. The user must be aware of cross-colour, transcoding footprints, low chrominance bandwidths and colour framing sequences. Employing an 8-bit format to sample the whole coded signal results in reduced amplitude resolution making D2 more susceptible to contouring artefacts. See also: Component, D1, D3, D5, DVTR For further reading - see Appendix D2 format: A digital composite video format. D2 is a lower quality than D1, but is also significantly less expensive.

©copyright Media Technology Consulting 2005

Letter D

25

the guide Te r m D i c t i o n a r y Media Technology Consulting

D3: A VTR standard using 1¼2-inch tape cassettes for recording digitised composite (coded) PAL or NTSC signals sampled at 8 bits. Cassettes are available for 50 to 245 minutes. Since this uses a composite signal the characteristics are generally as for D2 except that the 1¼2-inch cassette size has allowed a full family of VTR equipment to be realised in one format, including a camcorder. D4: There is no D4. Most DVTR formats hail from Japan where 4 is regarded as an unlucky number. D5: A VTR format using the same cassette as D3 but recording component signals sampled to ITU-R 601 recommendations at 10-bit resolution. With internal decoding D5 VTRs can play back D3 tapes and provide component outputs. Being a non-compressed component digital video recorder means D5 enjoys all the performance benefits of D1, making it suitable for highend post production as well as more general studio use. Besides servicing the current 625 and 525 line TV standards the format also has provision for HDTV recording by use of about 4:1 compression (HD D5).

D6: A digital tape format which uses a 19mm helical-scan cassette tape to record uncompressed High Definition Television material at 1.88 GB/s. D6 is currently the only High Definition recording format defined by a recognised standard. D6 accepts both the European 1250/50 interlaced format and the Japanese 260M version of the 1125/60 interlaced format which uses 1035 active lines. It does not accept the ITU format of 1080 active lines. ANSI/SMPTE 277M and 278M are D6 standards. D7: This has been assigned to DVCRPO. dailies: Imagery produced during the previous day's work, or a meeting to view this work. Data recorders: Machines designed to record and replay data. They usually include a high degree of error correction to ensure that the output data is absolutely correct and, due to their recording format, the data is not easily editable. This compares with video recorders which will conceal missing or incorrect data by repeating adjacent areas of picture and which are designed to allow

©copyright Media Technology Consulting 2005

D5 format: A digital component video format. D5 is considered to be of the same quality as D1, and also has provisions for storing HDTV-format imagery.

26

the guide Te r m D i c t i o n a r y Media Technology Consulting

direct access to every frame for editing. Where data recorders are used for recording video there has to be an attendant 'work station' to see the pictures or hear the sound, whereas VTRs produce the signals directly. Although many data recorders are based on VTRs' original designs, and vice versa, VTRs are more efficient for pictures and sound while data recorders are most appropriate for data. dB: See Decibel DCT (compression): Discrete Cosine Transform - widely-used as the first stage of compression of digital video pictures. DCT operates on blocks of the picture (usually 8 x 8 pixels) resolving them into frequencies, amplitudes and colours. In itself DCT may not reduce the amount of data but it prepares it for following processes that will. JPEG and MPEG depend on DCT. See also: ETSI, JPEG, MPEG-2 DD2: Using D2 tape, data recorders have been developed offering (by computer standards) vast storage of data (which may be images). A choice of data transfer rates is available to suit computer interfaces. Like other computer storage media, images are not directly viewable, and editing is difficult.

Decibel (dB): Units of measurement expressing ratios using logarithmic scales to give results related to human aural or visual perception. Many different attributes are given to a reference point termed 0 dB - for example a standard level of sound or power - subsequent measurements then being relative to that reference. Many performance levels are quoted in dB - for example signal to noise ratio (S/N). Decibel ratios are given by the expression: 20 log10 Level 1 / Level 2 where levels 1 and 2 could be audio, video or any other appropriate voltage levels. decimation: The process of throwing away unnecessary information when reducing the size of an image. decoder: A device that separates a composite video signal into a component video signal. Dedicated hardware: Hardware and software built for a specific task (eg a DVE), not general purpose (computer). Dedicated hardware gives much improved processing

©copyright Media Technology Consulting 2005

decibel (dB): Unit of loudness measured on a logarithmic scale. The human ear can perceive a 1 dB change in loudness.

27

the guide Te r m D i c t i o n a r y Media Technology Consulting

speeds, between 10 and 100 fold, over systems using the same technology applied to general purpose architecture and operating system software. This becomes important in image processing where tasks require a great deal of power, especially as the demands increase in proportion to the picture size - an important point for working with HDTV. deinterlace: The process of separating the two fields that make up a video image into two distinct images. densitometer: Instrument used to measure the optical density of a piece of processed film. density space: A nonlinear color space that is based on the density of a piece of developed negative relative to the amount of light that reached it. depth channel: Another term for the Z-channel. depth cue: Information that helps to determine the distance of an object from the camera.

depth of focus: A term that is often improperly used when one wishes to refer to the depth of field. Depth of focus is a specific term for the point behind the lens (inside the camera body) where a piece of film should be placed so that the image will be properly focused. desaturation: A term to describe the removal or loss of color in an image. A completely desaturated image would consist only of shades of gray. detail generator: An adjustment available on some video cameras that introduces additional sharpening into the captured image.

©copyright Media Technology Consulting 2005

depth of field: The depth of field of a specific lens is the range of acceptable focus in front of and behind the primary focus setting. It is a function not only of the specific lens used but also of the distance from the lens to the primary focal plane, and of the chosen aperture. Larger apertures will narrow the depth of field; smaller apertures will increase it.

28

the guide Te r m D i c t i o n a r y Media Technology Consulting

Diagnostics: Tests to check the correct operation of hardware and software. As digital systems continue to become more complex, built-in automated testing becomes an essential part of the equipment. Some extra hardware and software has to be added to make the tests operate. Digital systems with such provisions can often be quickly assessed by a trained service engineer, so speeding repair. difference matte: A matte created by subtracting an image in which the subject is present from an otherwise identical image in which it is not present. diffusion: An effect, caused by atmosphere or special filters placed on the lens, that is characterized by a scattering of light, elevated dark areas, and an overall softer look. digital: A method of representing data via discrete, well-defined samples. As opposed to analog. Digital Betacam: A development of the original analogue Betacam VTR which records digitally on a Betacam-style cassette. It uses mild intra-field compression to reduce the ITU-R 601 sampled video data by about 2:1. Some models can replay both digital and analogue Betacam cassettes.

Digital disk recorder (DDR): Disk systems that record digital video. Their application is often as a replacement for a VTR or as video caches to provide extra digital video sources for far less cost than a DVTR. They have the advantage of not requiring pre-rolls or spooling but their operation is not true random access. Digital keying and chroma keying: Digital chroma keying differs from analogue in that it can key uniquely from any one of the 16 million colours of component digital video. It is then possible to key from relatively subdued colours, rather than relying on highly saturated colours which can cause colour-spill problems on the foreground. A high quality digital chroma keyer examines each of the three components (Y, B-Y, R-Y) of the picture and generates a linear key for each. These are then combined into a composite linear key for the final keying operation. The use of three keys allows much greater subtlety of selection than with a chrominance-only key.

©copyright Media Technology Consulting 2005

digital compositing: The digitally manipulated combination of at least two source images to produce an integrated result.

29

the guide Te r m D i c t i o n a r y Media Technology Consulting

Digital mixing: Digital mixing requires 'scaling' each of two digital signals and then adding them. Mathematically this can be shown as: A x K = (Mix)1 B x (1-K) = (Mix)2 Result = (Mix)1 + (Mix)2 where A and B represent the two TV signals, and K the positional coefficient or value at any point of the mix. In a digital system, K will also be a number, normally an 8-bit value, to provide a smooth mix or dissolve. When two 8-bit numbers are multiplied together, the result is a 16-bit number (see Binary). When mixing, it is important to add the two 16-bit numbers to obtain an accurate result. This result must then be truncated or rounded to 8 bits for transmission to other parts of the digital system. Truncation by simply dropping the lower bits of the partial result (Mix)1 or (Mix)2, to 10 bits, or even 12 or 14 bits, will introduce inaccuracies. Hence it is important that all partial results, eg (Mix)1 and (Mix)2, maintain 16-bit resolution. The final rounding of the result to 8 bits can reveal visible 1-bit artefacts - but these can be avoided with Dynamic Rounding.

Digitiser: A system which converts an analogue input to a digital representation. Examples include analogue to digital converters (ADCs), touch tablets and mice. Some of these, mouse and touch tablet for example, are systems which take a spatial measurement and present it to a computer in a digital format. Digitising time: Time taken to record footage into a disk-based editing system. The name suggests the material is being played from an analogue source which, with the rapidly increasing use of DVTRs, is not always the case. A better term is 'loading'. Digitising time is often regarded as dead time but it need not be. It can be reduced if some initial selection of footage has been made for example by logging. Also, using Quantel systems fitted with Scene Select, the footage can be marked while being loaded and so instantly available as a rough cut on completion, so speeding the final edit.

©copyright Media Technology Consulting 2005

Digital S: A 1.25-inch digital tape format which uses a high-density metal particle tape running at 57.8mm/s to record a video data rate of 50 Mb/s. The tape can be shuttled and search up to x 32 speed. Video sampled at 4:2:2 is compressed at 3.3:1 using DCT-based intra-frame compression. Two audio channels are recorded at 16-bit, 48 kHz sampling; each is individually editable. The format also includes two cue tracks and four further audio channels in a cassette housing with the same dimensions as VHS.

30

the guide Te r m D i c t i o n a r y Media Technology Consulting

digitization: The process of sampling any analog subject to produce a digital representation. Within the field of digital compositing, usually refers to the process of converting a video or film source to digital information. dilation: An image processing technique that results in brighter areas of the image increasing in size and darker areas decreasing. See also erosion. DIN rating: A standard numerical rating for specifying a film's sensitivity to light. "DIN" is an abbreviation for Deutsche Industrie Norm (German Industry Standard). Many manufacturers now use their own specific exposure index instead. See also ASA rating, ISO index. Dirac filter: Another name for the impulse filter.

director: The person with the primary responsibility for overseeing the creative aspects of a project or production. Discrete 5.1 Audio: This reproduces six separate (discrete) channels - Left, Centre, Right, Left Rear, Right Rear and sub-woofer. All the five main channels have full frequency response which, together with a separate low-frequency sub-woofer, create a three-dimensional effect. Discretionary Compression™: Quantel term for switching between compression and no compression freely at any video frame boundary - typically used on an on-line non-linear edit suite. This allows compression to be used where the editing requires only cuts, and no compression where video processing is required (dissolves, wipes, DVEs, layering etc). This method offers the advantage of the storage economy of compression for most material while maintaining picture quality where otherwise decompression and recompression would have to be used, or the pictures may compress poorly, eg with graphics.

©copyright Media Technology Consulting 2005

Direct Editing: Editing at a workstation which directly edits material stored in a server. For this the workstation does not need large-scale video and audio storage but depends totally on the server store. The arrangement allows background loading of new material, via several ports if required, and playout of finished results, while removing the need to duplicate storage or transfer material to/from the workstation and allowing any number of connected workstations to share work. The efficiency of direct editing allows fast throughput and is attractive to news as well as post production. This depends on a server that can act as an edit store as well as a powerful interface to the edit workstation. Quantel's edit systems and Clipbox video server can operate this way.

31

the guide Te r m D i c t i o n a r y Media Technology Consulting

Disks: See Hard disks, Optical disks, AV disks dissolve: A specific transition effect in which one scene gradually fades out at the same time that a second scene fades in. Halfway through a linear dissolve the image will be a 50% mix of both scenes. dither: A method for representing more colors than would normally be available with a given palette. Dithering uses combinations of colored pixels and relies on the fact that the human eye will average them together and interpret the result as a new intermediate color. Dither: In digital television, analogue original pictures are converted to digits: a continuous range of luminance and chrominance values are translated into a set range of numbers. While some analogue values will correspond exactly to numbers, others will, inevitably, fall in between. Given that there will always be some degree of noise in the analogue original signal the numbers may dither by one Least Significant Bit (LSB) between the two nearest values. This has the advantage of allowing the digital system to describe analogue values between LSBs to give a very accurate digital rendition of the analogue world. If the image is produced by a computer, or as the result of digital processing, the dither may not exist - leading to contouring effects. With the use of Dynamic Rounding dither can be added to pictures to give a more accurate result.

DOF: Abbreviation for depth of field. Dolby Digital: A digital audio compression system that uses auditory masking for compression. It works with from 1 to 5.1 channels of audio and can carry Dolby Surround coded two-channel material. It applies audio masking over all channels and dynamically allocates bandwidth from a 'common pool'. Dolby Digital is a constant bit rate system supporting from 64 kb/s to 640 kb/s rates; typically 64 kb/s mono, 192 kb/s two-channel, 320 kb/s 35mm Cinema 5.1, 384 kb/s Laserdisc/DVD 5.1 and DVD 448 kb/s 5.1. DVD players and ATSC receivers with Dolby Digital capability can provide a backward-compatible mix-down by extracting the five main channels and coding them into analogue Dolby Surround for Pro Logic playback. See also: Auditory masking, ATSC, Table 2 Website: http://www.dolby.com

©copyright Media Technology Consulting 2005

DOD: Abbreviation for domain of definition.

32

the guide Te r m D i c t i o n a r y Media Technology Consulting

Dolby Digital (DD/AC-3): A digital audio compression system that uses auditory masking for compression. It works with from 1 to 5.1 channels of audio and can carry Dolby Surround coded two-channel material. It applies audio masking over all channels and dynamically allocates bandwidth from a 'common pool'. Dolby Digital is a constant bit rate system supporting from 64 kb/s to 640 kb/s rates; typically 64 kb/s mono, 192 kb/s two-channel, 320 kb/s 35mm Cinema 5.1, 384 kb/s Laserdisc/DVD 5.1 and DVD 448 kb/s 5.1. DVD players and ATSC receivers with Dolby Digital capability can provide a backward-compatible mix-down by extracting the five main channels and coding them into analogue Dolby Surround for Pro Logic playback. Website: http://www.dolby.com Dolby Surround, Dolby Stereo, Dolby 4:2:4 Matrix: Analogue coding of four audio channels - Left, Centre, Right, Surround (LCRS), into two channels referred to as Right-total and Left-total (Rt, Lt). On playback, a Dolby Surround Pro Logic decoder converts the two channels to LCRS and, optionally, a sub-woofer channel. The Pro Logic circuits are used to steer the audio and increase channel separation. The Dolby Surround system, originally developed for the cinema, is a method of getting more audio channels but suffers from poor channel separation, a mono limited bandwidth surround channel and other limitations. A Dolby Surround track can be carried by analogue audio or linear PCM, Dolby Digital and MPEG compression systems.

Dominance: Field dominance defines whether a field type 1 or type 2 represents the start of a new TV frame. Usually it is field 1 but there is no fixed rule. Dominance may go unnoticed until flash fields occur at edits made on existing cuts. Replay dominance set to the opposite way to the recording can cause a juddery image display. Much equipment, including Quantel's, allows the selection of field dominance and can handle either. dots per inch: A common method for measuring spatial resolution in the print industry. The horizontal and vertical scales are assumed to be equal, unless specified otherwise. double exposure: In the optical world, a double exposure is accomplished by exposing two different images onto a single negative. The result is a mixture of the two images. In the digital world, this effect is accomplished by mathematically averaging the two images.

©copyright Media Technology Consulting 2005

domain of definition: A (usually rectangular) region that defines the maximum boundaries of useful information in an image. Generally, everything outside of the DOD will have a value of 0 in all channels of the image. The DOD is usually determined automatically, as opposed to a region of interest.

33

the guide Te r m D i c t i o n a r y Media Technology Consulting

double framing: The process of duplicating and repeating every frame in an image sequence. The result is a new image sequence that appears to be moving at half the original speed. Also known as double printing. DPI: Abbreviation for dots per inch. DRAM: Dynamic RAM (Random Access Memory). High density, cost-effective memory chips (integrated circuits). Their importance is such that the Japanese call them the 'rice of electronics'. DRAMs are used extensively in computers and generally in digital circuit design. In digital video equipment they make up stores to hold pictures. Being solid state there are no moving parts and they offer the fastest access for data. Each bit is stored on a single transistor, and the chip must be powered and clocked to retain data. Current sizes available are 16 and 64 Mb (per chip), with 256 Mb now becoming commercially available. Development continues with plans to produce 1 GB chips early in the next century. Such projects require the use of x-ray lithography with chip features smaller than a micrometer - some 1000 times narrower than a human hair.

Drop-frame (timecode): The 525/60 line/field format used with the NTSC colour coding system does not run at exactly 60 fields per second but 59.94, or 29.97 frames per second - a difference of 1:1000. Timecode identifies 30 frames per second. Drop-frame timecode compensates by dropping two frames at every minute except the tenth. Note that the 625/50 PAL system is exact and does not require drop-frame. DSS: Digital Satellite Service. The term used to describe DTV services distributed via satellite. DTT: Digital Terrestrial Television. The term used in Europe to describe the broadcast of digital television services using terrestrial frequencies. DTV: Digital Television - everything that can be broadcast to the home digitally whether by cable, satellite or terrestrially. Although the signals produced by converting analogue pictures into their digital equivalent - digitising -

©copyright Media Technology Consulting 2005

drop frame: Video footage in which two frames are dropped every minute except the tenth. It is used to compensate for the fact that time code works at exactly 30 frames per second but NTSC video runs at only 29.97 fps.

34

the guide Te r m D i c t i o n a r y Media Technology Consulting

actually increases their bandwidth, they are then available for digital compression which can easily reduce four signals into the space of one analogue channel, while still maintaining acceptable levels of quality. Services such as video on demand (VOD) may resort to heavy compression to pack many feeds into one channel so that any selected movie can be on the cable within a tightly specified time-frame. There is a price to pay: the heavier the compression, the poorer the pictures. As well as current line rates, field rates and aspect ratios, DTV is taken to include 16:9 and the higher resolution standards of HDTV. For the US these are all described in the ATSC's table 3. Data can also be delivered. dubbing: The process of making a copy of a video tape.

DVB: Digital Video Broadcasting, the group, with over 200 members in 25 countries, which developed the preferred scheme for digital broadcasting in Europe. The DVB Group has put together a satellite system - DVB-S - that can be used with any transponder, current or planned, a matching cable system - DVB-C - and a digital terrestrial system - DVB-T. Website: htt://www.dvb.org DVB-T: The DVB-T is a transmission scheme for terrestrial digital television. Its specification was approved by ETSI in February 1997 and DVB-T services are planned for 1998, both within and outside Europe. As with the other DVB standards, MPEG-2 sound and vision coding form the basis of DVB-T. It uses a transmission scheme based on Coded Orthogonal Frequency Division Multiplexing (COFDM), which spreads the signals over a large number of carriers to enable it to operate effectively in very strong multipath environments. The multipath immunity of this approach means that DVB-T can operate an overlapping network of transmitting stations with a single frequency. In the areas of overlap, the weaker of the two received signals is rejected.

©copyright Media Technology Consulting 2005

DV: This digital VCR format is a co-operation between Hitachi, JVC, Sony, Matsushita, Mitsubishi, Philips, Sanyo, Sharp, Thomson and Toshiba. It uses 6.35 mm (0.25-inch) wide tape in a range of products to record 525/60 or 625/50 video for the consumer (DV) and professional markets (Panasonic's DVCPRO and Sony's DVCAM). All models use digital intra-field DCT-based 'DV' compression (about 5:1) to record 8-bit component digital video based on 13.5 MHz luminance sampling. The consumer versions and DVCAM sample video at 4:1:1 (525/60) or 4:2:0 (625/50) video and provide two 16-bit/48 or 44.1 kHz, or four 12-bit/32 kHz audio channels onto a 4 hour 30 minutes standard cassette (125 x 78 x 14.6 mm) or smaller 1 hour 'mini' cassette (66 x 48 x 12.2 mm). The video recording rate is 25 Mb/s.

35

the guide Te r m D i c t i o n a r y Media Technology Consulting

DVCAM: Sony's development of native DV which records a 15micron (15x10-6m, fifteen thousandths of a millimetre) track on a metal evaporated (ME) tape. DVCAM uses DV compression of a 4:2:0 signal for 625/50 (PAL) sources and 4:1:1 for 525/60 (NTSC). Audio is recorded in one of two forms four 12-bit channels sampled at 32 kHz, or two 16-bit channels sampled at 48 kHz. DVCPRO: Panasonic's development of native DV which records a 18 micron (18x106m, eighteen thousandths of a millimetre) track on metal particle tape. DVCPRO uses native DV compression at 5:1 from a 4:1:1 8-bit sampled source. It uses 12 tracks per frame for 625/50 sources and 10 tracks per frame for 525/60 sources, both use 4:1:1 sampling. Tape speed is 33.813mm/s. It includes two 16-bit digital audio channels sampled at 48 kHz and an analogue cue track. Both Linear (LTC) and Vertical Interval Time Code (VITC) are supported.

DVD: Digital Versatile Disk - a high density development of the Compact Disk. It is the same size as a CD but stores from 4.38 GB (seven times CD capacity) on a single sided, single layer disk. DVDs can also be double sided or dual layer - storing even more data. The capacities commonly available at present: DVD-5 Single-side, single layer 4.38 GB DVD-9 Single-side, dual layer 7.95 GB DVD-10 Double-sided, single layer 8.75 GB Future versions will have capacities rising from the current 4.38 GB to 15 GB with blue laser technology in the medium term, in the longer term 50 GB is a target achievable with advanced modulation schemes. DVD-Video: DVD-Video combines the DVD optical disk with MPEG-2 video compression, has multiple multi-channel audio tracks, subtitles and copy protection capability for recording video on a CD-sized disk. To maximise quality and playing time DVD-Video movies use Variable Bit Rate (VBR) MPEG-2 coding where the bit rate varies with the demands of the material. A typical 525/60 TV format, 24fps movie would have an average bit rate of 3.5 Mb/s, but for sections with a great deal of movement it could peak at 8 or 9 Mb/s. For a 30 fps telecined result of 24fps movie material only 24 fps are coded onto the disk, the 3:2 pulldown conversion back to 30 fps being performed in the player. This allows a 120 minute 24 fps movie to fit on a DVD-5.

©copyright Media Technology Consulting 2005

DVCPRO 50: This variant of DV uses a video data rate of 50 Mb/s - double that of other DV systems - and is aimed at the higher quality end of the market. Sampling is 4:2:2 to give enhanced chroma resolution, useful in post production processes (eg chroma keying). Four 16-bit audio tracks are provided.

36

the guide Te r m D i c t i o n a r y Media Technology Consulting

DVE: An abbreviation for digital video effect, this usually refers to any of a number of geometric transformations that are typically performed by specialized real-time video equipment. Examples of a DVE move include animated pans, rotations, or flips, as well as various hardware-specific effects such as page turns or customized wipes. DVE: Digital Video Effects (systems). These have been supplied as separate machines but increasingly are being included as an integral part of systems. The list of effects varies but will always include picture manipulations such as zoom and position and may go on to rotations, 3D perspective, page turns, picture bending, blurs etc. Picture quality and control also vary widely. See also: Axis, Global

DVTR: DVTR - Digital Video Tape Recorder. The first DVTR for commercial use was shown in 1986, working to the ITU-R 601 component digital standard and the associated D1 standard for DVTRs. It used 19 mm cassettes recording 34, 78 or (using thinner tape) 94 minutes. Today many DVTR formats are available. D2 and D3, both recording composite signals, are designed mainly to replace C-format (1-inch) analogue machines; Digital Betacam makes use of mild data compression (around 2:1) to record the ITU-R 601 video. D5, like D1, records the full, non-compressed ITU-R 601 signal but on 1¼2-inch tape cassettes. In the professional and news areas video compression is used. Multiple generations on DVTRs do not suffer from degradation due to tape noise, moiré, etc. However the tape is subject to wear and tear. The possibility of this producing errors and drop-outs necessitates complex error concealment circuitry. In extreme cases multiple passes can introduce cumulative texturing or other artefacts. The safest haven for work that requires heavy multi-generation work is a disk-based system. DX: Abbreviation for double exposure. Dylan: The product name of a storage system developed by Quantel for the economic and secure storage of non-compressed, or compressed ITU-R 601 4:2:2 video with true random access. It makes an excellent store for editing systems (Henry and Editbox), for compositing (Hal) and for servers (Clipbox). Each Dylan uses 20 standard 3.25-inch SCSI disk drives interfaced with Chatter™ Disk Management. Built-in redundancy, error checking and correction mean that should a disk drive fail, operation continues and no data is lost. The missing data is rebuilt when the disk is replaced.

©copyright Media Technology Consulting 2005

DVI: An audio compression format derived from and very similar to one defined by the IMA, giving 4:1 compression.

37

the guide Te r m D i c t i o n a r y Media Technology Consulting

dynamic range: (1) The range of brightness values in a scene or an image, from brightest to darkest, often expressed as a ratio. (2) In a digital image, the total number of different colors in the image. dynamic resolution: Another term for color resolution.

©copyright Media Technology Consulting 2005

Dynamic Rounding®: An intelligent truncation method for digital signals devised by Quantel. There are many instances in digital systems where a number uses more bits than the system normally accommodates. This has to be rectified in a way that will keep as much information as possible and not cause noticeable defects - even after many processes. A common example is image processing which requires that two signals are multiplied, as in digital mixing, producing a 16-bit result from two original 8-bit numbers. This has to be truncated, or rounded, back to 8-bits. Simply dropping the lower bits can result in visible contouring artefacts especially when handling pure, noisefree, computer generated pictures. Dynamic Rounding is a mathematical technique for truncating the word length of pixels - usually to their normal 8 bits. Rather than simply losing the lower bits, it uses the information in those bits to be dropped to control, via a randomiser, the dither of the LSB of the truncated result. This effectively removes the visible artefacts and is non-cumulative on any number of passes. Other attempts at a solution have involved increasing the number of bits, usually to 10, making the LSBs smaller but only masking the problem for a few generations. Dynamic Rounding is licensable from Quantel and is used in a growing number of digital products both from Quantel and other manufacturers.

38

the guide Te r m D i c t i o n a r y Media Technology Consulting

E-split: See exposure split. EBU: European Broadcasting Union. An organisation comprising European broadcasters which co-ordinates production and technical interests of European broadcasting. It has within its structure a number of committees which make recommendations to ITU-R. Website: http://www.ebu.ch ECC: Error Check and Correct. This system appends check data to a data packet in a communications channel or to a data block on a disk, which allows the receiving or reading system both to detect small errors in the data stream (caused by line noise or disk defects) and, provided they are not too long, to correct them. edge detection: An algorithm used to enhance or isolate transition areas, or "edges," in an image. edge matte: A specialized matte that includes only the outlines or borders of an object. edge numbers: Sequential numbers printed along the edge of a piece of film by the manufacturer to help identify particular frames. editing: The process of assembling shots and scenes into a final product, making decisions about their length and ordering. EDL: Edit Decision List. A list of the decisions which describe a series of edits often recorded on a floppy disk. EDLs can be produced during an off-line session and passed to the on-line suite to control the conforming of the final edit. In order to work across a range of equipment there are some widely adopted standards such as CMX 3400 and 3600. effects animation: A term that is usually used to refer to elements that were created via cel animation or digital rotoscoping techniques but are not character related. Common examples include sparks, lightning, or smoke. effects filter: Any of a number of different optical filters that can introduce diffusion, flares, glows, etc. Dangerous when shooting bluescreen elements.

©copyright Media Technology Consulting 2005

Letter E

39

the guide Te r m D i c t i o n a r y Media Technology Consulting

EI: Abbreviation for exposure index. eight-perf: A nickname for the VistaVision film format that comes from the fact that each VistaVision frame has eight perforations along each edge. Electronic programme guides: DTV allows broadcasters to transmit electronic programme guides. For many, this service is considered essential to keep viewers up to date with the increased number of channels DTV brings. The programme guide database allows a receiver to build an on-screen grid of programme information and contains control information to facilitate navigation.

Embedded audio: Audio that is carried within an SDI connection - so simplifying cabling and routing. The standard (ANSI/SMPTE 272M-1994) allows up to four groups each of four mono audio channels. Generally VTRs only support Group 1 but other equipment may use more, for example Quantel's Clipbox server connection to an edit seat uses groups 1-3 (12 channels). 48 kHz synchronous audio sampling is pretty well universal in TV but the standard also includes 44.1 and 32 kHz synchronous and asynchronous sampling. Synchronous means that the audio sampling clock is genlocked to the associated video (1920 samples per frame in 625/50, 8008 samples per five frames in 525/60). Up to 24-bit samples are allowed but mostly only up to 20 are currently used. 48 kHz sampling means an average of just over three samples per line, so three samples per channel are sent on most lines and four occasionally the pattern is not specified in the standard. Four channels are packed into an Ancillary Data Packet and sent once per line (hence a total of 4 x 3 = 12 or 4 x 4 = 16 audio samples per packet per line). emulsion: The light-sensitive material that is applied to a transparent base to create photographic film. encoder: (1) A piece of video equipment that combines a component video signal into a composite video signal. (2) A generalized term used to refer to a number of different data capture devices, usually ones that convert measurements into digital data. Encryption: The process of coding data so that a specific code or key is required to restore the original data. In conditional access broadcasts this is used to make transmissions secure from unauthorised reception - as is often found on satellite or cable systems.

©copyright Media Technology Consulting 2005

element: A discrete image or sequence of images that will be added to a composite.

40

the guide Te r m D i c t i o n a r y Media Technology Consulting

ENG: Electronic News Gathering. Term applied to a small portable outfit, with a broadcast quality TV camera, VTR and/or microwave link, usually used for news. The term was originated to distinguish between news gathering on film and video tape (electronic). Also refers to compatible studio or portable editing equipment. Entry point: A point in a coded bit stream from which a complete picture can be decoded without first having to store data from earlier pictures. In the MPEG-2 frame sequence this can only be at an I-frame - the only frames encoded with no reference to others.

Error detection, concealment and correction: No means of digital recording is perfect. Both magnetic tape and disks suffer from a few marginal areas where recording and replay is difficult or even impossible. However the errors can be detected and some action taken for a remedy by concealment or correction. The former attempts to hide the problem by making it not so noticeable whereas the latter actually corrects the error so that perfect data is output. When the recorded data is an image, an error can simply be concealed by using data from previous or following TV lines or fields. The result is not guaranteed to be identical to the original but the process is relatively simple and, as important, quick. If the stored information is from a database, a computer program or for more special image processing, then 100% accuracy of data is essential. This can be ensured by recording data in a manner where any errors can be detected and then the exact correct data calculated from other recorded information. This is error correction. A difference between computer systems and TV is that the latter is continuous and cannot wait for a late correction. Either the correct result must be ready in time or some other action taken - the show must go on - placing a very tight time constraint on any TV-rate error correction. In contrast, a computer can usually run slowly for a moment or wait a few milliseconds. Digital VTRs monitor the error rate and provide warnings of excessive errors which, although not immediately visible, may build up during multiple passes. Although error rates from disks are generally many times lower than those expected from digital video tape, they can still occur. To protect against this there is disk redundancy and the replay of all data is checked. If an error is detected there is sufficient additional information stored to calculate and substitute the correct data. The total failure of a disk drive can be covered and the missing data re-generated and recorded onto a new replacement - making the system highly accurate and very secure.See also: ECC, Dylan, EXOR

©copyright Media Technology Consulting 2005

erosion: An image processing technique that results in darker areas of the image increasing in size and brighter areas decreasing. See also dilation.

41

the guide Te r m D i c t i o n a r y Media Technology Consulting

Ethernet: Ethernet is a form of Local Area Network (LAN) widely used for interconnecting computers and standardised in IEEE 802.3, allowing a wide variety of manufacturers to produce compatible interfaces and extend capabilities - repeaters, bridges, etc. The data transmission rate is 10, 100 or 1,000 Mb/s, but overheads in packaging data and packet separation mean actual throughput is often 5-10 times less than the bit rate. Using Carrier Sense Multiple Access/Collision Detect (CSMA/CD) a would-be talker on the net, rather than waiting their turn (as on a Token Passing Ring LAN) simply waits until the cable is free. There are many connection methods for Ethernet varying from copper to fibre optic. Currently the three most common are: 10 Base-2 Thinwire Ethernet using relatively low cost 50 ohm coaxial cable and BNC connectors. A maximum length, without repeaters, of 180m and connecting up to 30 devices. 10 Base-T The standard for 4-wire twisted pair cable using RJ connectors. This gives extremely low cost per node network capabilities. 100 Base-T A.K.A. Fast Ethernet 100 Mb/s 4-wire twisted pair cable using RJ connectors is now becoming very popular. Similar technology to 10 Base-T but uses Cat. 5 cable. Gigabit Ethernet Development of existing ethernet technology to support even higher transfer rates, ie 1000 Mb/s.

ETSI compression: A compression technique, based on DCT. Unlike MPEG, which has complex coders and simpler decoders and is designed for broadcast, it is symmetric with the same processing power at the coder and decoder and is designed for applications where there are only a few recipients, such as contribution links and feeds to cable head ends. ETSI compression is intraframe, simpler than MPEG and imposes less delay in the signal path, typically 120 msec against around a second, enabling interviews to be conducted over satellite links without unwarranted delays. Data rate is 34 Mb/s. Website: http://www.etsi.fr EUREKA: A European parliamentary body formed to encourage and co-ordinate international collaborative European research projects.

©copyright Media Technology Consulting 2005

ETSI: The European Telecommunications Standardisation Institute. Responsible, amongst other things, for the definition of a compression scheme which, unlike MPEG-2, makes equal demands of the encoder and the decoder. ETSI compression is currently used in a large percentage of satellite contribution links as it only imposes a short processing delay on the signals.

42

the guide Te r m D i c t i o n a r y Media Technology Consulting

EXOR: The mathematical operation of EXclusively ORring a number of data bits. For example the EXOR of two bits is 1, only if exactly one of them is 1. The EXOR is widely used in data recovery (see RAID). If the EXOR of a number of blocks of data is stored, when one of those blocks is lost, its contents can be deduced by EXORing the undamaged blocks with the stored EXOR. exposure index: A standardized, but manufacturer-specific, numerical rating system for specifying a film's sensitivity to light. There are also several industry-standard systems in use, including the ASA rating, the ISO index, and the DIN rating. To make it even more interesting, many manufacturers will specify a rating for both daylight lighting and tungsten lighting. exposure latitude: Amount of over- or underexposure a given type of film can tolerate and still produce acceptable results. exposure split: A simple split-screen shot in which multiple exposures of a given scene are combined in order to bring areas of widely divergent brightness into the same shot. Also known as an E-split.

©copyright Media Technology Consulting 2005

exposure wedge: A series of images that feature incremental alterations in the exposure (brightness) of a certain element (or sometimes the entire frame) for the purpose of choosing a final value for the exposure of that element.

43

the guide Te r m D i c t i o n a r y Media Technology Consulting

f-stop: A measurement of the aperture of a lens. fade: Decreasing the brightness of an image over time, eventually resulting in a black image. fast Fourier transform: An algorithm for converting an image so that it is represented in terms of the magnitude and phase of the various frequencies that make up the image. Yes, there is a regular Fourier transform, but nobody uses it because it's not . . . fast. FDDI: Fibre Data Distribution Interface. A high speed fibre optic data interface operating up to 100 Mb/s. FDDI is most commonly used as backbone data distribution for lower bandwidth networks such as Ethernet or Token Ring. Fettle (colour): A suite of colour manipulation controls provided on some Quantel systems. Operating in Y, Cr, Cb colour space the mathematics and control of luminance and colour is relatively straightforward. FFT: Abbreviation for fast Fourier transform. FG: Abbreviation for foreground. Fibre Channel: An integrated set of standards being developed by ANSI designed to improve data speeds between workstations, supercomputers, storage devices and displays while providing one standard for networking storage and data transfer. Planned to run up to 4 Gb/second on a fibre-optic or twisted-pair cable, the current top rate is 1 Gbps. It can be used point-to point, switched or in an arbitrated loop (FC-AL) connecting up to 126 devices. Website: Fibre Channel field: (1) An image composed of either the even or odd scan lines of a video image. Two fields played sequentially will make up a video frame. (2) A unit of measure on a field chart. field chart: A method of dividing an image into a grid so that certain areas of the frame can be specified by grid coordinates.

©copyright Media Technology Consulting 2005

Letter F

44

the guide Te r m D i c t i o n a r y Media Technology Consulting

field dominance: The order in which the fields in an interlaced image are displayed. Essentially, whether the even or the odd field is displayed first for any given frame. field of view: The range of a scene that will be captured by a specific camera. FOV is usually measured as the number of horizontal degrees (out of 360), although a vertical field of view is also a valid measurement. Field sequence: A television frame, or picture, comprises two fields. Each successive frame of component 525 and 625 line television repeats a pattern and so can be edited to frame boundaries - like film editing. Composite video, coded as PAL, NTSC or SECAM, carries colour information on a subcarrier whose cyclic pattern repeats over a longer period - 4 frames in PAL and 2 frames in NTSC or SECAM - known respectively as the 8 and the 4-field sequence. An edit should not break the sequence, so dictating a less precise operation than with component video (where there is no subcarrier). The same restrictions apply whether the signals are analogue or digital. ITU-R 601 component digital signals can edit on any frame boundaries while composite digital systems, (eg with D2 or D3 VTRs) are restricted to 4 or 8-field boundaries, otherwise picture hopping or quality changes (through additional processing) will occur.

film gauge: The width of a particular film stock, i.e., 16mm, 35mm, etc. film recorder: A device that is capable of transferring digital images to a piece of film negative. film recording: The process of transferring digital images to a piece of film negative via the use of a film recorder. film speed: A very context-dependent term that may refer to (1) the rate that film is moving through a camera or a projector (24 frames per second in normal feature-film work) or to (2) the light sensitivity of the film itself. Slowspeed film is less light sensitive; high-speed film is more sensitive.

©copyright Media Technology Consulting 2005

file format: A standardized description of how a piece of data (such as an image) is to be stored.

45

the guide Te r m D i c t i o n a r y Media Technology Consulting

film weave: Irregular horizontal movement (generally undesirable) of a piece of film as it moves through a camera or projector. filter: (1) A translucent material that is placed in front of a light or camera to modify the color that is transmitted. Certain of these optical filters may also be designed to introduce specific artifacts, such as diffusion, flares, etc. (2) Any of a number of algorithms used within the computer for sampling an image. Different filters can be used when transforming an image, and can result in differing amounts of sharpness or artifacts. (3) The process of using either of the aforementioned types of filters. final: The term given to a composite shot once it is considered complete and has been approved by the appropriate decision makers. FireWire (IEEE 1394): A serial interface, introduced by Apple Inc. in 1987, offering transfer rates of 100, 200 and 400 Mb/s. Initially used to transfer data between mainframes without reformatting, but limited to 4.5 m, it can now be extended to over 70 m and 16 nodes. There is increasing interest from broadcasters to use FireWire to transport A/V data, such as MPEG-2. Fixed disks: See Hard disks

flare: Any of a number of effects that will show up on an image as the result of a light source shining directly into the lens of a camera. flashing: Flashing is an optical process whereby unprocessed negative is exposed to a small amount of light for the purpose of reducing the contrast or saturation of the scene that will eventually be photographed with that film. In the digital realm, flashing is the application of any number of nonspecific techniques to produce similar results. An image that appears to suffer from some of these characteristics is often referred to as appearing "flashed." flat: Another term for low contrast. flat lens: Another term for a spherical lens. Sometimes also used as a relative term for measuring the distortion and exposure variance of any lens.

©copyright Media Technology Consulting 2005

fixed matte: As opposed to a traveling matte, a fixed matte will not change position or shape during the shot.

46

the guide Te r m D i c t i o n a r y Media Technology Consulting

flip: A simple geometric transform in which an image is mirrored about the Xaxis so that it is now upside-down. This process is different from merely rotating the image 180 degrees. flop: A simple geometric transform in which an image is mirrored about the Yaxis. focal length: A measure of the magnification power of a given lens, based on the distance from the center of the lens to the film. Also known as simply the "length" of a lens. A longer focal length will produce greater magnification than a shorter length. focus: (1) To adjust a lens so that the image it produces is as sharp as possible. (2) The point in space behind a lens where this sharpness occurs. folding: The process of consolidating discrete mathematical operations into a single function.

format: (1) The size, resolution, aspect ratio, etc. for a given image. (2) The file format for a given image. (3) The physical medium (such as film, video, etc.) used to capture or display an image sequence. (4) A multitude of additional variations and subcategories of the first three definitions. four-perf: A nickname for the standard 35mm film format that refers to the fact that each frame spans four pairs of perforations. FOV: Abbreviation for field of view. fps: Abbreviation for frames per second. See frame rate. fractal compression: A lossy image-compression algorithm that is based on repeated use of scaled and rotated pixel patterns.

©copyright Media Technology Consulting 2005

foreground: Usually the primary element to be added to a composite and placed over the background. Often, there may be several foreground elements in a composite.

47

the guide Te r m D i c t i o n a r y Media Technology Consulting

Fragmentation: The scattering of data over a (disk) store caused by successive recording and deletion operations. Generally this will eventually result in the store becoming slow - a situation that is not acceptable for video recording or replay. The slowing is caused by the increased time needed to access randomly distributed data. With such stores de-fragmentation routines arrange the data (by copying from one part of the disk to another) so that it is accessible in the required order for replay. Clearly any change in replay, be it a transmission running order or the revision of an edit, could require further de-fragmentation. True random access stores, able to play frames in any order at video rate, never need de-fragmentation. frame: A single image that is usually part of a group designed to be viewed as a moving sequence. frame rate: The rate at which sequences of images are captured or displayed. The frame rate is usually measured in frames per second, or fps. Framestore: The name, coined by Quantel, given to solid state video storage, usually built with DRAMs. Technically it implies storage of one complete frame or picture, but the term is also used more generically to encompass the storage of a few lines to many frames. With large DRAM capacities available, framestores are increasingly used to enhance equipment design.

freeze frame: A single frame that is held for a duration of time. Frequency: The number of oscillations of a signal over a given period of time (usually one second). For example it defines subcarrier frequencies in analogue television colour coding systems, or clock rate frequencies in digital systems. Here are some commonly found frequencies in TV: PAL subcarrier: 4.43 MHz NTSC subcarrier: 3.58 MHz ITU-R 601 clock rate: 27 MHz ITU-R 601 luminance sampling rate: 13.5 MHz ITU-R 601 chrominance sampling rate: 6.75 MHz (for 4:2:2 sampling)

©copyright Media Technology Consulting 2005

freeze: The process of stopping the action. In digital compositing, this is usually accomplished by repeating the same frame for a duration of time.

48

the guide Te r m D i c t i o n a r y Media Technology Consulting

fringing: An artifact of the matting process in which a foreground element has a noticeable (usually bright) outline. FTP: File Transfer Protocol. The high level Internet standard protocol for transferring files from one machine to another. FTP is usually implemented at application level. full aperture: A specific 35mm film framing, also known as camera aperture. See Appendix D for more details.

©copyright Media Technology Consulting 2005

Full motion video: A general term for moving images displayed from a desktop platform. Its quality varies and is undefined. MPEG-2 section DTV Index Introduction Quantel and Digital Technology Tutorial - Into Digits Appendix Directory OPINION ATM: The ideal interface? 8 bits or 10 bits? Compression, the way of the future Keying, which colour space? Step-by-step to HD Resolution independence - a universal panacea? Why simultaneous true random access? Why true random access? Copyright ©1998 Quantel. All rights reserved. Comments or e-mail to [email protected]

49

the guide Te r m D i c t i o n a r y Media Technology Consulting

G-matte: Abbreviation for garbage matte. gamma: (1) In film, a measure of the contrast of an image or emulsion, based on the slope of the straight-line portion of the characteristic curve. (2) An adjustment applied to a video monitor to compensate for its nonlinear response to a signal. (3) A digital effect used to modify the apparent brightness of an image. gamut: The range of colors that any given device or format is able to display or represent. garbage matte: A rough, simple matte that isolates unwanted elements from the primary element in an image. Gateway: A device connecting between two computer networks. Today many images for use in film or TV are produced on computer systems so an effective connection between these and the dedicated hardware of television is required. Quantel has embedded a gateway as part of its picture networking interface. gauge: See film gauge. Gaussian blur: A specific method for blurring an image based on a Gaussian filter. Gaussian filter: A specific digital filter that is often used when resampling an image. gel: Abbreviation for gelatin filter, a flexible colored optical filter. Generation (loss): The signal degradation caused by successive recordings. Freshly recorded material is first generation, one re-recording, or copy, makes the second, etc. This is of major concern in analogue linear editing but much less so using a digital suite. Non-compressed component DVTRs should provide at least twenty generations before any artefacts become noticeable but the very best multi-generation results are possible with disk-based systems. These can re-recorded millions of times without causing dropouts or errors. Generations are effectively limitless. Besides the limitations of recording, the action of processors such as decoders and coders will make a significant contribution to generation loss. The decode/recode cycle of NTSC and PAL is well known for its limitations but equal caution is needed for digital video compression systems, especially those using MPEG, and

©copyright Media Technology Consulting 2005

Letter G

50

the guide Te r m D i c t i o n a r y Media Technology Consulting

the colour space conversions that typically occur between computers handling RGB and video equipment using Y, Cr, Cb. See also: Error detection, concatenation, concealment and correction generation loss: The loss of quality of an image due to repeated duplication. Generation loss is significantly reduced and in some cases completely eliminated when dealing with digital images. geometric transformation: An effect that causes some or all of the pixels in a given image to change their current location. Such effects include translation, rotation, scaling, warping, and various specialized distortion effects. GIF: Graphics Interchange Format, a specific image file format. See Appendix C. Gigabit Ethernet: See Ethernet Global (control): The top level of control in a multi-channel DVE system. A number of objects (channels) can be controlled at one time, for example to alter their opacity or to move them all together relative to a global axis - one which may be quite separate from the objects themselves. This way the viewing point of all the assembled objects can be changed. For example a cube assembled from six channels could be moved in 3D space as a single action from a global control.

GOP - MPEG Term: Group Of Pictures. In an MPEG signal the GOP is a group of pictures or frames between successive I-frames, the others being P and/or B-frames. In the widest application, television transmission, the GOP is typically from 12 frames in a 25 fps signal and 15 frames in a 30 fps signal (ie about half a second) but this can vary - a new sequence starting with an I-frame may be forced if there is a big change at the input, such as a cut. The length of a GOP represents the editability of that MPEG signal. Additional processing, possibly requiring an MPEG decode/recode, will be needed to successfully cut within a GOP. This is one of the reasons that MPEG is not generally regarded as editable (see Cut edit) - some work is being done on this subject. GPI: General Purpose Interface. This is used for cueing equipment - usually by a contact closure. It is simple, frame accurate and therefore can be easily applied over a wide range of equipment. Being electro-mechanical it cannot be expected to be as reliable as pure electronic controls. grading: Another term for color timing, used primarily in Great Britain.

©copyright Media Technology Consulting 2005

GOP: See MPEG-2

51

the guide Te r m D i c t i o n a r y Media Technology Consulting

grain: The individual particles of silver halide in a piece of film that capture an image when exposed to light. Because the distribution and sensitivity of these particles are not uniform, they are perceived (particularly when projected) as causing a noticeable graininess. Different film stocks will have different visual grain characteristics. Grand Alliance (Digital HDTV): The United States grouping, formed in May 1993, to propose 'the best of the best' HDTV systems. The participants were: AT&T, General Instrument Corporation, Massachusetts Institute of Technology, Philips Consumer Electronics, David Sarnoff Research Centre, Thomson Consumer Electronics and Zenith Electronics Corporation. The Grand Alliance has played a big part in arriving at the ATSC digital television standard which uses MPEG-2 video compression and the audio surround-sound compressed with Dolby AC-3. So that a wide variety of source material, including that from computers, can be best accommodated, two line standards are included each operating at 24, 30 and 60 Hz. graphical user interface: A user interface that utilizes images and other graphical elements to simplify the process of interacting with the software. Also known as the "look and feel" of the software. gray card: A card (gray) usually designed to reflect about 18% of the light that strikes it; used as a reference for measuring exposure.

greeble: To add random detail to a surface. Usually created by adding geometric detail like small randomly sized cubes or other geomtric instances. green spill: Any contamination of the foreground subject by light reflected from the greenscreen in front of which it is placed. See also spill, blue spill. greenscreen: Identical in use and concept to a bluescreen (only it's green). Grid Compression™: A proprietary video compression system developed and used by Quantel. For editability it is intra-frame and used in the Newsbox editing system and Clipbox video server where it can provide compression ratios of 5:1, 10:1 and 20:1.

©copyright Media Technology Consulting 2005

grayscale image: A completely desaturated image, with no color, only shades of gray.

52

the guide Te r m D i c t i o n a r y Media Technology Consulting

GSM: The digital cellular telephony system defined by the European Union; in this context, the audio compression algorithm used by GSM phones, giving 10:1 compression GUI: Abbreviation for graphical user interface.

©copyright Media Technology Consulting 2005

GUI: Graphical User Interface. A means of operating a system through the use of interactive graphics displayed on a screen. Examples in the computer world are the Apple Macintosh and Microsoft Windows, both designed for general purpose use and usually operated with a mouse. In 1981 Quantel introduced Paintbox with its on-screen menu system operated from a pressure sensitive pen and touch tablet. The control has been further developed to cover a wide range of operations including DVEs, editing, VTR control and audio and today is applied to the whole range of Quantel products. Besides its success in offering effective control, it also enables easy updates to accommodate new facilities.

53

the guide Te r m D i c t i o n a r y Media Technology Consulting

H.261: A video compression scheme defined by the ITU, originally for use in video telephony and related systems; particularly suited to operation at moderately low rates (e.g. ISDN). H.263: A video compression scheme defined by the ITU, originally for use in video telephony and related systems; particularly suited to operation at very low rates (e.g. over a modem). handles: Extra frames at the beginning and end of a shot that are not intended for use in the final shot but are included in the composite in case the shot's length changes slightly. Hard disks (fixed disks): Hard or fixed disk drives comprise an assembly of up to 10 rigid platters coated with magnetic oxide, each capable of storing data on both sides. Each recording surface has a write/read head, any one of which may be activated at a given instant. Hard disks give rapid access to vast amounts of data, are highly reliable as they have only two moving parts - the swinging head assembly and the spinning disk. They can be written and read millions of times. The use of disks to store video is rapidly changing editing, and transmission. For high capacity, disks pack data very tightly indeed. Areal density, the amount of data stored per unit area of the disk surface, is a measure of technology. Currently delivered drives achieve up to 1.5 Gb per square inch but this figure is set to grow. For this the heads fly only a few molecules off the disk surface, so that even imperfections in the surface can cause heating of the head assembly, and track widths are minute - 10,000 TPI (tracks per inch). As a result high capacity disk drives have to be handled with great care, especially when running. Vibration could easily send heads off-track or crashing into the disk surface - with possible terminal consequences. Hard disk technology is moving very fast with ever higher capacities becoming available in smaller packages at lower costs per megabyte. Those currently available range in capacity from about 4 to 18 GB on 31¼2-inch drives to as much as 47 GB available on 51¼4-inch drives. Ever since 1980 capacities have consistently doubled every two years and that trend looks set to continue. Peak data transfer rates range from 10-20 M transfers/sec - which may be 8 or 16 bits wide. Average rates do not equal the 21 MB/s continuous rate needed for ITU-R 601 video. While capacities grow and data transfers become faster, access time changes relatively little, still remaining well outside that needed to provide real-time random access for television. HD D5: A compressed recording system developed by Panasonic which uses compression at about 4:1 to record HD material on standard D5 cassettes. HD D5 supports both the 1080 and the 1035 interlaced line standards at both 60 Hz and 59.94 Hz field rates. Four uncompressed audio channels sampled at 40 kHz, 20 bits per sample, are also supported.

©copyright Media Technology Consulting 2005

Letter H

54

the guide Te r m D i c t i o n a r y Media Technology Consulting

HDTV: High-definition television. A proposed new television standard with significantly greater spatial resolution than standard NTSC, PAL, or SECAM. Hermite curve: A specific type of spline curve that allows for explicit control over the curve's tangent at every control point. Hexadecimal: A numbering system, often referred to as 'Hex', that works to base 16 and is particularly useful as a shorthand method for describing binary numbers. Decimal 0-9 are the same as Hex, then 10 is A, 11 is B, up to 15 which is F. Decimal Binary Hex 0-9 0-1001 0-9 10 1010 A 11 1011 B 12 1100 C 13 1101 D 14 1110 E 15 1111 F 16 10000 10 27 11011 1B 100 1100100 64 255 11111111 FF High Definition Television: A television format with a screen aspect ratio of 16:9 (the current is 4:3) and approximately twice the resolution in both horizontal and vertical dimensions of existing standard definition television (SDTV). There is no agreement for the hoped-for world HDTV studio standard. The only consensus so far is that transmission, for home viewing and contribution, will be digital and compressed using MPEG-2. In Europe 1250/50, with its simple relationship to 625/50 is favoured, while in the USA the ATSC describes different picture sizes and frame rates, not all of which are HD, in Table 3 of its standard. The most talked about of these is 1080i (1080 active lines, interlaced) with some interest in the 720p also. ITU-R have two production standards based on 1125/60 and 1250/50 formats.

©copyright Media Technology Consulting 2005

HDCam: Sometimes called HD Betacam - is a means of recording compressed highdefinition video on a tape format which uses the same cassette shell as Digital Betacam, although with a different tape formulation. The technology is aimed specifically at the USA and Japanese 1125/60 markets and supports both 1080 and 1035 active line standards. Quantisation from 10 bits to 8 bits and DCT intra-frame compression are used to reduce the data rate. Four uncompressed audio channels sampled at 48 kHz, 20 bits per sample, are also supported.

55

the guide Te r m D i c t i o n a r y Media Technology Consulting

high-pass filter: A spatial filter that enhances high-frequency detail. It is used as a method for sharpening an image. HiPPI: High performance parallel interface (ANSI X3.283-1996). Capable of transfers up to 100 MB/s (800 with the Super HiPPI under development) it is targeted at high performance computing and optimised for applications involving streaming large volumes of data rather than bursty network activity. The parallel connection is limited to short distance and so Serial HiPPI is now available. histogram: A graphical representation of the distribution (usually frequency of occurrence) of a particular characteristic of the pixels in an image. histogram equalization: An image processing technique that adjusts the contrast in an image so that it fits into a certain range. histogram sliding: Equivalent to adding a certain number to the values of every pixel in an image.

HLS: Hue, luminance, and saturation. A method of specifying the colors in an image based on a mix of these three components. hold: To stop the action by using the same frame repeatedly. hold-out matte: A matte used to prevent a foreground element from completely obscuring an object in the background plate. hot: A nonexact term for describing an image that is too bright. Completely unrelated to the terms warm and cool. HSB: Hue, saturation, and brightness. A method of specifying the colors in an image based on a mix of these three components.

©copyright Media Technology Consulting 2005

histogram stretching: Equivalent to multiplying the values of every pixel in an image by a certain amount.

56

the guide Te r m D i c t i o n a r y Media Technology Consulting

HSL: Hue, saturation, and lightness. A method of specifying the colors in an image based on a mix of these three components. HSV: hue, saturation, and value. A method of specifying the colors in an image based on a mix of these three components. hue: A specific color from the color spectrum, disregarding its saturation or value. Huffman coding: A lossless image-compression scheme. See also run-length encoding, JPEG, MPEG.

©copyright Media Technology Consulting 2005

Huffman coding: This compresses data by assigning short codes to frequently-occurring sequences and longer ones to those less frequent. Assignments are held in a Huffman Table. The more likely a sequence is to occur the shorter will be the code that replaces it. It is widely used in video compression systems where it often contributes a 2:1 reduction in data.

57

the guide Te r m D i c t i o n a r y Media Technology Consulting

I-frames: See MPEG-2 I-frames - MPEG Term: Contain data to construct a whole picture as their compression is intraframe, very similar to JPEG. ICMP: Internet Control Message Protocol. The part of the Internet Protocol that handles the error and control messages data link layer. The second layer of the Open Systems Interconnect (OSI) communications model. It puts messages together and co-ordinates their flow. IDTV: Integrated Digital TV Receiver. For viewers to receive DTV services they will require a new type of receiver either in the form of a new television set (IDTV) or a set top box. Although no standards have been set at the time of writing the ATSC in the USA has produced a number of recommendations for manufacturers. Among these it states that the receiver should be capable of appropriately decoding and displaying the video scanning formats defined in ATSC's Table 3 and the audio services defined in Table 2. A receiver's ability to receive and display the services in Table 3 does not necessarily mean that it can display a true HD image. To display such an image requires a density of at least 1,000,000 pixels. IETF: The IETF is the main standards organization for the Internet. The IETF is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual. Illegal colours: Colours that force a colour system to go outside its normal bounds. Usually these are the result of electronically painted images rather than direct camera outputs. For example, removing the luminance from a high intensity blue or adding luminance to a strong yellow in a paint system may well send a subsequent PAL or NTSC coded signal too high or low - producing at least inferior results and maybe causing technical problems. Out of gamut detectors can be used to warn of possible problems. ILM: See Industrial Light and Magic. IMA: Often used as a name for the 4:1 audio compression scheme defined by this body.

©copyright Media Technology Consulting 2005

Letter I

58

the guide Te r m D i c t i o n a r y Media Technology Consulting

image processing: The use of various tools and algorithms to modify digital images within a computer. IMAX: A proprietary film capture/projection process that uses an extremely largeformat negative. impulse filter: A specific digital filter that is often used when resampling a digital image. It is considered to be the lowest-quality, highest-speed filter in common use. Also known as the Dirac filter or the nearest-neighbor filter. in-betweening: The process of interpolating between the keyframes of an animation sequence. in-camera effects: Visual effects that are accomplished solely during principle photography, involving no additional postproduction.

Industrial Light and Magic: A pioneering visual effects company that was the first to widely use digital compositing in feature-film work. Integrated system: Single system which contains more or less enough tools to complete a whole area of operation. In many cases this has only become possible through digital technology and, in turn, it can make it very cost effective. One of an increasing number of examples is Quantel's Editbox which includes most tools required for editing with all operations co-ordinated in one control system. Inter-frame (compression): Compression which involves more than one frame. Inter-frame compression compares consecutive frames to remove common elements and arrive at "difference" information. MPEG-2 uses two types of inter-frame processed pictures - the 'P' (predictive) and 'B' (bi-directional) frames. As 'B' and 'P' frames are not complete in themselves, but relate to other adjacent frames, they cannot be edited independently. Inter-frame (compression) - MPEG Term: Compression that involves more than one frame. Inter-frame compression compares consecutive frames to remove common elements and arrive at "difference" information. MPEG-2 uses two types of inter-frame processed pictures - the 'P' (predictive) and 'B' (bi-directional) frames. As 'B' and 'P' frames are not complete in themselves, but relate to other adjacent frames, they cannot be edited independently.

©copyright Media Technology Consulting 2005

indexed color: A method of storing image data, in which the value of the pixel refers to an entry in a table of available colors instead of a numerical specification of the color itself.

59

the guide Te r m D i c t i o n a r y Media Technology Consulting

Interactive TV: A new service, enabled by DTV, which will give the viewer the opportunity to participate in the programme via a control panel connected to a phone line. interframe coding: The process used in MPEG encoding whereby intermediate images in a sequence are defined by their deviation from specific keyframes. Interlace (scan): Method of scanning lines down a screen - as used in today's television broadcasts. Each displayed picture comprises two interlaced fields: field two fills in between the lines of field one. For analogue systems, this is the reason for having odd numbers of lines in a picture eg 525 and 625, so that each field contains a half-line, causing the constant vertical scan to place the lines of one field between those of the other. The technique improves the portrayal of motion and reduces picture flicker without having to increase the picture rate (and therefore the bandwidth/data rate). Disadvantages are that it reduces vertical definition to about 80 or 70% (known as the Kell Factor) of the progressive, or non-interlaced, definition and tends to cause horizontal picture detail to dither. Interlaced also reduces dynamic revolution in the vertical direction. There is continuing debate about the use of interlaced or non-interlaced (progressive, as used for computer screens) scans for the new DTV formats and displays.

interocular distance: The spacing b etween the eyes, usually referring to the human average of about 2 1/2inches; an important factor for the production of stereoscopic imagery. interpolation: The process of using certain rules or formulas to derive new data based on a set of existing data. See also bicubic interpolation, bilinear interpolation, linear interpolation. Interpolation (spatial): When re-positioning or re-sizing a digital image inevitably more, less or different pixels are required from those in the original image. Simply replicating or removing pixels causes unwanted artefacts. For far better results the new pixels have to be interpolated - calculated by making suitably weighted averages of adjacent pixels - to produce a more transparent result. The quality of the results will depend on the techniques used and the number of pixels (points - hence 16-point interpolation), or area of original picture, used to calculate the result. See also: Anti-aliasing, Interpolation (temporal), Sub-pixel

©copyright Media Technology Consulting 2005

interlacing: The technique used to produce video images whereby two alternating field images are displayed in rapid sequence so that they appear to produce a complete frame.

60

the guide Te r m D i c t i o n a r y Media Technology Consulting

Interpolation (temporal): Interpolation between the same point in space on successive frames. It can be used to provide motion smoothing and is extensively used in standards converters to reduce the judder caused by the 50/60 Hz field rate difference. The technique can also be adapted to create frame averaging for special effects. Intra-frame (compression): Compression that occurs within one frame. The compression process only removes redundant information from within the frame itself. No account is taken of other frames. JPEG and the 'I' frames of MPEG-2 are coded in this way. In the MPEG-2 sequence only I-frames can be edited as they are the only independent frames.

ISDN: Integrated Services Digital Network - allows data to be transmitted at high speed over the public telephone network. ISDN operates from the Basic Rate of 64 kb/sec to the Primary Rate of 2 Mb/s (usually called ISDN-30 as it comprises 30 Basic Rate channels). Most of the Western world currently has the capability to install ISDN-2 with 128 kb/sec and very rapid growth is predicted for ISDN generally. In the television and film industries audio facilities are already using it. The cost of a call is usually similar to using a normal telephone. Quantel has developed systems to allow the exchange of images between its machines on a global basis using ISDN and other technologies such as Frame Relay, SMDS, ATM, etc. A TV frame takes between 2-3 minutes to transfer at the ISDN Basic Rate. Nominally ISDN operates internationally but there are variations in standards, service and ISDN adapter technologies. Some operators in the USA use a similar system, Switch 56 (56 kb/sec and upwards), although the availability of ISDN is becoming wider. ISO: International Standards Organisation. An international organisation that specifies international standards, including those for networking protocols, compression systems, disks, etc. Website: http://www.iso.ch ISO index: A standard numerical rating for specifying a film's sensitivity to light. "ISO" refers to the International Standards Organization. The ISO Index actually incorporates both the American ASA rating and the European DIN rating. Many manufacturers now use their own specific exposure index instead. See also ASA rating, DIN rating.

©copyright Media Technology Consulting 2005

IP: Multicasting is a term used for sending packets of data to multiple destinations at the same time. Multicast provides one-to-many and many-tomany network delivery services for applications such as video conferencing and audio where servers hosts need to communicate simultaneously.

61

the guide Te r m D i c t i o n a r y Media Technology Consulting

ISO layer: A model containing seven conceptual layers, each providing a set of services that are used in network operations. ITC: Independent Television Commission. It is responsible as a regulator, both legally and technically, for all independent programming in the United Kingdom, be it cable, satellite or terrestrial. Website: http://www.itc.co.uk ITS: International Teleproduction Society. A United States association of members from the industry dedicated to promoting and furthering the use of video as a medium of communication. Also has a UK chapter. Website: http://www.itsnet.org ITU: International Telecommunications Union. The United Nations regulatory body covering all forms of communication. The ITU sets mandatory standards and regulates the radio frequency spectrum. ITU-R (previously CCIR) deals with radio spectrum management issues and regulation while ITU-T (previously CCITT) deals with telecommunications standardisation. Website:http://www.itu.ch

ITU-R 601: Full title: ITU-R Rec. BT. 601-5. This standard defines the encoding parameters of digital television for studios. It is the international standard for digitising component television video in both 525 and 625 line systems and is derived from the SMPTE RP125. ITU-R 601 deals with both colour difference (Y, R-Y, B-Y) and RGB video, and defines sampling systems, RGB/Y, R-Y, B-Y matrix values and filter characteristics. It does not actually define the electro-mechanical interface - see ITU-R 656. ITU-R 601 is normally taken to refer to colour difference component digital video (rather than RGB), for which it defines 4:2:2 sampling at 13.5 MHz with 720 luminance samples per active line and 8 or 10-bit digitising. Some headroom is allowed with black at level 16 (not 0) and white at level 235 (not 255) to minimise clipping of noise and overshoots. Using 8-bit digitising approximately 16 million unique colours are possible: 28 each for Y (luminance), Cr and Cb (the digitised colour difference signals) = 224 = 16,777,216 possible combinations. The sampling frequency of 13.5 MHz was chosen to provide a politically acceptable common sampling standard between 525/60 and 625/50 systems, being a multiple of 2.25 MHz, the lowest common frequency to provide a static sampling pattern for both.

©copyright Media Technology Consulting 2005

ITU: The main international standards body for telephony and communications.

62

the guide Te r m D i c t i o n a r y Media Technology Consulting

ITU-R 656: Interfaces for digital component video signals in 525-line and 625-line television systems. The international standard for interconnecting digital television equipment operating to the 4:2:2 standard defined in ITU-R 601. It defines blanking, embedded sync words, the video multiplexing formats used by both the parallel (now rarely used) and serial interfaces, the electrical characteristics of the interface and the mechanical details of the connectors

Java: A general purpose programming language developed by Sun Microsystems and best known for its widespread use on the World Wide Web. Unlike other software, programs written in Java can run on any platform type, so long as they contain a Java Virtual Machine. Website: http://java.sun.com Java on Quantel: Embedding the Java Virtual Machine into Quantel dedicated platforms has provided a programming window into Quantel equipment to add third party software applications. JPEG: A (typically lossy) compression technique, or a specific image format that utilizes this technique. "JPEG" is an abbreviation for the Joint Photographic Experts Group. JPEG: Joint Photographic Experts Group, ISO/ITU-T. JPEG is a standard for the data compression of still pictures (intra-frame). In particular its work has been involved with pictures coded to the ITU-R 601 standard. It offers data compression of between two and 100 times and three levels of processing are defined: the baseline, extended and lossless encoding. JPEG baseline compression coding, which is overwhelmingly the most common in both the broadcast and computer environments, starts with applying DCT to 8 x 8 pixel blocks of the picture, transforming them into frequency and amplitude data. This itself may not reduce data but then the generally less visible high frequencies can be divided by a high factor (reducing many to zero), and the more visible low frequencies by a lower factor. The factor can be set according to data size or picture quality requirements - effectively adjusting the compression ratio. The final stage is Huffman coding which is lossless but can further reduce data by about 2:1. Baseline JPEG coding is very similar to the I-frames of MPEG, the main difference being they use slightly different Huffman tables

©copyright Media Technology Consulting 2005

Letter J

63

the guide Te r m D i c t i o n a r y Media Technology Consulting

kernel: The group of pixels that will be considered when performing some kind of spatial filtering. See also convolution kernel. key: Another term for a matte. Keycode: A machine-readable bar-code printed along the edge of camera negative stock outside the perforations. It gives key numbers, film type, film stock manufacturer code, and offset from zero-frame reference mark (in perforations). It has applications in telecine for accurate film-to-tape transfer and in editing for conforming neg. cuts to EDLs. keyframe: Any frame in which a particular aspect of an item (its size, location, color, etc.) is specifically defined. The non-keyframe frames will then contain interpolated values. Keyframe: A set of parameters defining a point in a transition, eg of a DVE effect. For example a keyframe may define a picture size, position and rotation. Any digital effect must have a minimum of two keyframes, start and finish, although more complex moves will use more - maybe as many as 100. Increasingly, more parameters are becoming 'keyframeable', ie they can be programmed to transition between two, or more, states. Examples are colour correction to made a steady change of colour, and keyer settings, perhaps to made an object slowly appear or disappear. keyframe animation: The process of creating animation using keyframes. keyframing: Another term for keyframe animation. keying: The process of algorithmically extracting an object from its background and combining it with a different background. Keying: The process of selectively overlaying an area of one picture (or clip) onto another. If the switch between the overlaid and background pictures is simply a hard switch this can lead to jagged edges of the overlaid, or keyed, pictures. They are usually subjected to further processing to give a cleaner, more convincing, result. The whole technology of deriving a key signal has greatly expanded through the use of digital technology, so that many operations may be used together, eg softening the key, colour correcting key spill areas, and more. keystoning, keystone distortion: A geometric distortion resulting when a rectangular plane is projected or photographed at an angle not perpendicular to the axis of the lens. The result is that the rectangle becomes trapezoidal. kukaloris: See cukaloris.

©copyright Media Technology Consulting 2005

Letter K

64