Of pixels. The aspect ratio of the area of a picture described by 1 pixel. The ITU-R BT.601 digital coding standard defines luminance pixels that 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-by-4/3 = 0.911 (that is, the pixels are 10 percent 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-by-4/3 = 1.094 (that is, the pixels are 9 percent wider than they are tall) The newer DTV image standards, including those for HD, define square pixels. 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 pixel aspect ratios are important is the movement of images between 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.
• Component (video). The normal interpretation of a component video signal is one in which the luminance and chrominance remain as separate components, for example, analog components in MII and Betacam VTRs, and digital components Y, Cr, Cb in ITU-R BT.601. RGB is also a component signal. Component video signals retain maximum luminance and chrominance bandwidth.
• 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 analog form of video compression, restricts the bandwidths (image detail) of components. In the composite result color is literally added to the monochrome (luminance) information using a visually acceptable technique. Since our eyes have far more luminance-resolving power than for color, the color sharpness (bandwidth) of the coded single is reduced to a value 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, limiting its use in postproduction.
• D1. A format for digital video tape recording working to the ITU-R BT.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. As a component recording system it is ideal for studio or postproduction work since its high chrominance bandwidth allows excellent chroma keying. In addition, 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, and other devices. Being component, there are no color framing requirements. Despite these advantages, D1 equipment is not extensively used in general areas of TV production, due at least partly to its high cost.
• 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 D2 cassettes nor recording formats are compatible with D1. Since it is relatively costly and does not offer the advantages of component operation, the format has fallen from favor. VTRs have not been manufactured for some years.
• D3. A VTR standard using half-inch tape cassettes for recording digitized composite (coded) PAL or NTSC signals sampled at 8 bits. Cassettes are available for 50 to 245 minutes. Since D3 uses a composite signal its characteristics are generally the same as those for D2, except that the half-inch cassette size has allowed a full family of VTR equipment to be realized 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 BT.601 recommendations at 10-bit resolution. With internal decoding, D5 VTRs can play back D3 tapes and provide component outputs. Because it is a noncompressed component digital video recorder, D5 enjoys all the performance benefits of D1, making it suitable for highend postproduction 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 (D5 HD).
• D5 HD. A D5 VTR able to handle high-definition signals. Using around 4:1 compression, the signals connect via an HD SDI link. D5 HD can be multiformat, operating at both DTV and HDTV standards. It can replay 525-line D5 as well as D5 HD cassettes. Formats include 480/60I, 1080/24P, 1080/60I, 1080/50I, 1035/60I, and 720/60P. The recorder can also slew between 24- and 25-Hz frame rates for PAL program duplication from a 1080/24P master. Cassette recording times vary according to format; the longest is 155 minutes for 1080/24P.
• D6. A digital tape format that uses a 19-mm helical-scan cassette tape to record noncompressed high-definition television material at 1.85 Gb/s. D6 is currently the only HD recording format defined by a recognized standard. The Philips VooDoo Media Recorder is based on D6 technology. 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.
• D9. This is assigned to Digital-S.
• D11. This is believed to be assigned to a half-inch tape format that records I-frame only 4:2:2
MPEG-2 SD video at 50 Mb/s.
• 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 2 seconds. Playing the recorder allows the film images to be viewed on a standard monitor; running at 16x speed shows full motion direct from the tape.
• Digital Betacam. A development of the original analog Betacam VTR, which records digitally on a Betacam-style cassette. It uses mild intrafield compression to reduce the ITU-R BT.601 sampled video data by about 2:1. Some models can replay both digital and analog Betacam cassettes.
• Drop-frame (timecode). The 525/60-line/field format used with the NTSC color coding system does not run at exactly 60 fields per second but at 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. See also: Non Drop-frame timecode
• DV. This digital VCR format is the result of co-operation between Hitachi, JVC, Sony, Matsushita, Mitsubishi, Philips, Sanyo, Sharp, Thomson, and Toshiba. It uses 6.35-mm (quarter-inch) 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 intrafield 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 on a 4-hour, 30-minute standard cassette (125-by-78-by-14.6 mm) or smaller 1-hour mini"-cassette (66-by-48-by-12.2 mm). The recording rate is 25 Mb/s.
• DVCAM. Sony's development of native DV, which records a 15-micron 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 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. Tape speed is 33.8 mm/s and the data rate 25 Mb/s. It includes two 16-bit digital audio channels sampled at 48 kHz and an analog cue track. Both Linear (LTC) and Vertical Interval Time Code (VITC) are supported.
• DVCPRO 50. In many ways, this is a 2x variant of DVCPRO with a tape speed of 67.7 mm/s, a data rate of 50 Mb/s and 3.3:1 video compression; it is aimed at the studio/higher-quality end of the market. Sampling is 4:2:2 to give enhanced chroma resolution, useful in postproduction processes (for example, chroma keying). Four 16-bit audio tracks are provided.
• DVCPRO HD. For use with HDTV, in many ways this is a 2x variant of DVCPRO 50 with a tape speed of 135.4 mm/s and a data rate of 100 Mb/s. Sampling is 4:2:2 and video compression is 6.7:1. There are eight 16-bit, 48-kHz audio tracks. Fiber channel. An integrated set of standards 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/s on a fiberoptic or twisted-pair cable, the current top rate is 2 Gb/s. It can be used point-to-point, or switched, or in an arbitrated loop (FC-AL) connecting up to 126 devices.
• FireWire. See IEEE 1394
• HDCam. A series of VTRs based on the Betacam principles for recording HD video on a tape format that uses the same cassette shell as Digital Betacam, although with a different tape formulation. The technology supports both 1080 and 1035 active line standards. DCT-based intraframe compression is used to reduce the data rate. Four uncompressed audio channels sampled at 48 kHz, 20 bits per sample, are also supported. Latest camera/recorder systems are switchable between image standards at 1080I and 720P, as well as SD formats. One model is specifically for 1080/24P operation and aimed at some current film areas.
• HD-SDI. Standardized in SMPTE 292M, this is a high-definition version of the SDI (Serial Digital Interface) used for SD television. The serial bit-stream runs at 1.485 Gb/s to carry up to 10-bit YCrCb component video as well as audio and ancillary data. It extends the use of the coax cable and BNC connector "plug-and-play" interface familiar to television operations for decades. The interface is also specified for fiber for distances up to 2 km.
• HDTV. High Definition Television. A television format with higher definition than SDTV. While DTV at 625 or 525 lines is usually superior to PAL and NTSC, it is generally accepted that 720- line and upward is HD. HDTV also has a picture aspect ratio of 16:9. While there are many picture formats proposed and several in use, there is increasing consensus that 1080-by- 1920/24P is a practical standard for global exchange. Many organizations are planning to produce for this format.
• IEEE 1394 (aka FireWire, I-Link). This is a standard for a peer-to-peer serial digital interface that can operate at 100, 200, or 400 Mb/s. IEEE 1394A specifies working up to 400 Mb/s. 1394B extends the standard up to 1,600 Mb/s. 800 Mb/s is now available, and 1600 is expected in the near future. Its range can be over 10 meters for copper and hundreds of meters over fiber. Its high speed and low cost make it popular in multimedia and, more recently, in digital video applications. Early uses include peer-to-peer connections for digital dub editing between camcorders as well as interfacing VCRs, printers, PCs, TVs, and digital cameras. IEEE 1394 is recognized by SMPTE and EBU as a networking technology for transport of packetized video and audio. Its isochronous data channel can provide guaranteed bandwidth for frame-accurate real-time (and faster) transfers of video and audio, while its asynchronous mode can carry metadata and support I/P. Both modes may be run simultaneously.
• Interlace (scan). Method of scanning lines down a screen as used in today's television broadcasts. Each displayed picture comprises two interlaced fields: Field 2 fills in between the lines of field 1. For analog systems, this is the reason for having odd numbers of lines in a picture, like 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). The disadvantages are that it reduces the vertical definition of moving images to about 70 percent (see Interlace Factor) of the progressive scan definition and tends to cause horizontal picture detail to "dither." There is continuing debate about the use of interlaced and progressive scans for DTV formats.
• Interlace factor. The reduction in vertical definition during vertical image movement due to interlaced (rather than progressive) scans. Typically this is assumed to be 30 percent, and is in addition to the Kell Factor (another 30 percent reduction), making an overall reduction of 50 percent. Note that, when scanning film frame-per-frame (that is, 24 or 25fps—not 3:2 pull-down to 60fps), or a succession of electronic frames each representing a single snapshot in time, there is no vertical movement between fields and the interlace factor has no effect.
• ITU-R BT.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 digitizing component television video in both 525- and 625-line systems and is derived from the SMPTE RP125. ITU-R BT.601 deals with both color 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 BT. 656. ITU-R BT.601 is normally taken to refer to color 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 digitizing. Some headroom is allowed with black at level 16 (not 0) and white at level 235 (not 255)—to minimize clipping of noise and overshoots. Using 8-bit digitizing approximately 16 million unique colors are possible: 28 each for Y (luminance), Cr and Cb (the digitized color 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.
• ITU-R BT.656. The international standard for interconnecting digital television equipment operating to the 4:2:2 standard defined in ITU-R BT.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.
• ITU-R BT.709. Recommendation for 1125/60 and 1250/50 HD defining values and a "4:2:2" sampling structure that is 5.5 times that of ITU-R BT.601. Actual rates are 74.25 MHz for luminance Y, or R, G, B, and 37.125 MHz for color difference Cb and Cr, all at 8 bits or 10 bits. The standard refers to 1035 and 1152 active lines. SMPTE 274M refers to 1080 active lines.
• JPEG. Joint Photographic Experts Group (ISO/ITU-T). JPEG is a standard for the data compression of still pictures (intraframe). In particular, JPEG's work has focused on pictures coded to the ITU-R BT.601 standard. It offers data compression of between 2 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-by-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 "quantising" factor (reducing many to zero), and the more visible low frequencies by a lower factor. The "quantising" 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 that they use slightly different Huffman tables.
• 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. A set of parameters defining a point in a transition—for example, of a DVE effect. 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," meaning that they can be programmed to transition between two, or more, states. Examples are color correction to make a steady change in color, and keyer settings, perhaps to made an object slowly appear or disappear.
• Luminance. A component of video, the black and white or brightness element, of an image. It is written as Y, so the Y in Y (B-Y) (R-Y),YUV, YIQ, Y, Cr, Cb is the luminance information of the signal. In a color TV system the luminance signal is usually derived from the RGB signals, originating from a camera or telecine, by a matrix or summation of approximately Y = 0.3R + 0.6G + 0.1B.
• MPEG. Moving Picture Experts Group. This a working group of ISO/IEC for the development of international standards for compression, decompression, processing, and coded representation of moving pictures, audio, and their combination. Four MPEG standards were originally planned, but the accommodation of HDTV within MPEG-2 has meant that MPEG-3 is now redundant. MPEG-4 is for multimedia applications. More work is in progress: MPEG-7 is about metadata.
• Non-drop-frame timecode. Timecode that does not use drop-frame and always identifies 30 frames per second. The timecode running time will not exactly match normal time. The mismatch amounts to 1:1000, an 18-frame overrun every 10 minutes. This applies where 59.94, 29.97, or 23.976 picture rates are used in 525/60 systems as well as DTV.
• Nonlinear (editing). Nonlinear means "not linear"—that is, the recording medium is not tape and editing can be performed in a nonlinear sequence, not necessarily the sequence of the program. It describes editing with quick access to source clips and record space, usually using computer disks to store footage. This removes the spooling and pre-rolls of VTR operations and so greatly speeding work. Yet greater speed and flexibility are possible with real-time random access to any frame (true random access). The term is widely used in association with offline editing systems storing highly compressed pictures but online nonlinear systems are increasingly available. There is a wide range of systems claiming online quality, many using video compression. Prospective users must gauge the suitability of the results for their application, bearing in mind that, for transmission/distribution, the signals will be decompressed and recompressed again. Noncompressed systems, which require no compromise in picture quality, are becoming more widely used.
• NTSC (television standard). The color television system used in the USA, Canada, Mexico, Japan, and other countries, where NTSC M is the broadcast standard (M defining the 525/60 line and field format; often the standard is just referred to as NTSC). It was defined by the NTSC. The bandwidth of the NTSC system is 4.2 MHz for the luminance signal and 1.3 and 0.4 MHz for the I and Q color channels.
• Offline (editing). A decision-making process using low-cost equipment usually to produce an EDL or a rough cut that can then be conformed or referred to in a high-quality online suite, and so reducing decision-making time in the more expensive online environment. While most offline suites enable shot selection and the defining of basic transitions such as cuts and dissolves, very few allow settings for the DVEs, color correctors, keyers, and layering that are increasingly a part of the online editing process. AAF may well help produce a solution to this.
• OfflineRT. An offline editing solution encompassing a low-resolution, compressed, yet high-quality video format offering several effects in real-time—with no additional hardware required—such as multiple video/graphics layers, transitions, text, and color correction, allowing for the first time creation of real-time effects on a PowerBook. Online (editing). Production of the complete, final edit performed at full program quality—the buck stops here! Because it produces higher quality results than offline editing, online editing time costs more but the difference is declining. Preparation in an offline suite will help save time and money in the online editing phase. To produce the finished edit, online has to include a wide range of tools, offer flexibility to try ideas and accommodate late changes, and the ability to work fast to maintain the creative flow and to handle pressured situations.
• OMFI. Open Media Framework Interchange is an open standard for postproduction interchange of digital media among applications and across platforms. It describes a file format and supports video, audio, graphics, animation, and effects as well as comprehensive edit decision information. Transfer may be by removable disk or over a high-speed network or telephone line to another location.
• PAL. Phase Alternating Line. The color coding system for television widely used in Europe and throughout the world, almost always with the 625/50 line/field system. It was derived from the NTSC system but by reversing the phase of the reference color burst on alternate lines (Phase Alternating Line) is able to correct for hue shifts caused by phase errors in the transmission path. Bandwidth for the PAL-I system is typically 5.5 MHz luminance, and 1.3 MHz for each of the color difference signals, U and V.
• PAL-M. A version of the PAL standard, but using a 525 line, 60-field structure. Used only in parts of South America (for example, Brazil).
• Progressive (scan). Method of scanning lines down a screen where all the lines of a picture are displayed in one vertical scan. There are no fields or half-pictures as with interlace scans. It is commonly used with computer displays and is now starting to be used for some DTV formats, for example, 1080/24P. (The "P" denotes progressive.) A high picture rate is required to give good movement portrayal, such as for fast action and camera pans, and to avoid display flickering. For television applications this implies a high bandwidth or data rate, and for CRT displays, high scanning rates. The vertical definition is equal to around 70 percent of the number of lines (Kell Factor) and does not show the dither of detail associated with interlaced scans.
• RAID. Redundant array of independent disks. A grouping of standard disk drives together with a RAID controller to create storage that acts as one disk to provide performance beyond that available from individual drives. Primarily designed for operation with computers, RAIDs can offer very high capacities, fast data transfer rates, and much increased security of data. Data security is achieved through disk redundancy, so that disk errors or failures can be detected and corrected. A series of RAID configurations is defined by levels, and, being designed by computer people, they start counting from zero. Different levels are suited to different applications.
Level 0. No redundancy; the benefits are only of speed and capacity generated by combining a number of disks.
Level 1. A complete mirror system—two sets of disks both reading and writing the same data. This has the benefits of level 0 plus the security of full redundancy—but at twice the cost. Some performance advantage can be gained in reads because only one copy need be read, so two reads can be occurring simultaneously.
Level 2. An array of nine disks. Each byte is recorded with one bit on each of eight disks and a parity bit recorded to the ninth. This level is rarely, if ever, used.
Level 3. An array of n+1 disks recording 512 byte sectors on each of the n disks to create n-by-512 "super sectors" + 1-by-512 parity sector on the additional disk, which is used to check the data. The minimum unit of transfer is a whole superblock. This level is most suitable for systems in which large amounts of sequential data are transferred, such as for audio and video. For these it is the most efficient RAID level, since it is never necessary to read/modify/write the parity block. It is less suitable for database types of access in which small amounts of data need to be transferred at random.
Level 4. The same as level 3, but allows individual blocks can be transferred. When data is written it is necessary to read the old data and parity blocks before writing the new data as well as the updated parity block, which reduces performance.
Level 5. The same as level 4, but the role of the parity disk is rotated for each block. In Level 4 the parity disk receives excessive load for writes and no load for reads. In Level 5 the load is balanced across the disks.
Soft RAID. A RAID system implemented by low-level software in the host system instead of a dedicated RAID controller. While saving on hardware costs, operation consumes some of the host's power.
• RGB. The abbreviation for the red, green, and blue signals, the primary colors of television. Cameras and telecines have red, green, and blue receptors, and TV screens have red, green, and blue phosphors illuminated by red, green, and blue guns. Much of the picture monitoring in a production center is in RGB. RGB is digitized with 4:4:4 sampling, which occupies 50 percent more data than 4:2:2.
• Rotoscoping.The practice of using frames of live footage as reference for painting animated sequences. While the painting will always depend on the skill of the artist, modern graphics equipment integrated with a video disk store makes rotoscoping, or any graphical treatment of video frames, quick and easy. This has led to many new designs and looks appearing on television as well as more mundane practices such as image repair.
• RS232. A standard for serial data communications defined by EIA standard RS-232. It is designed for short distances only—up to 10 meters. It uses single-ended signaling with a conductor per channel plus a common ground, which is relatively cheap and easy to arrange but susceptible to interference, hence the distance limitation.
• RS422. Not to be confused with 4:2:2 sampling or 422P MPEG, this is a standard for serial data communications defined by EIA standard RS-422. It uses current-loop, balanced signaling with a twisted pair of conductors per channel, with two pairs for bi-directional operation. It is more costly than RS232 but has a high level of immunity to interference and can operate over reasonably long distances—up to 300m/1000 ft. RS 422 is widely used for control links around production and post areas for a range of equipment—VTRs, mixers, and other devices.
• Safe area. The area of picture into which it is safe to place material, graphics, text, or action, so that it will be viewable when received at home. Initially this was necessary with 4:3 aspect ratio screens since they were always overscanned to avoid showing the black that surrounds that active picture. Typically, 5 percent in from the edges was considered safe. More recently, the whole Safe Area issue has become far more complicated because there are both 4:3 and 16:9 displays, as well as 4:3, 16:9 and sometimes 14:9 (a compromised version of 16:9 that is more acceptable to those viewing on 4:3 screens) aspect ratios for program output. In the U.K. action has been taken to produce all commercials in such a way that their message is conveyed whichever display aspect is used.
• SAN. Storage area network. A network that allows applications direct access to shared storage by cutting out the usual client/server "middle men." This may be used to provide improved workflow and better work-sharing on a common store. For this the application has to be storage aware," since the design effectively connects shared storage to the workstations—in a similar way to local disk drives. A SAN is not networking in the conventional sense. Whereas networking usually transfers data between applications, with indirect access to data, a SAN primarily connects applications to data with indirect access to other applications. The type of network should be chosen according to needs. SANs are scalable, but additions may be complex to implement. Currently, expansion is ultimately limited by architecture and management
considerations.
• SECAM (Sequential Couleur avec Mémoire) The television broadcast standard in France, the Middle East, and most of Eastern Europe, SECAM provides for sequential color transmission and storage in the receiver. SECAM processes 625 lines, a maximum of 833 pixels per line and 50 Hz picture frequency.
• Serial Digital Interface (SDI) The standard based on a 270 Mbps transfer rate. This is a 10-bit, scrambled, polarity independent interface, with common scrambling for both component ITU-R 601 and composite digital video and four channels of (embedded) digital audio.
• Scrub (audio). Replay of audio tracks at a speed and pitch corresponding to jog speed—as heard with analog audio tape "scrubbing" backward and forward past an audio replay head. This feature, which is natural for analog, fixed-head recorders may be provided on a digital system recording on disks to help set up cues.
• SD. Short form for SDTV.
• SDI. See Serial Digital Interface
• SDTI. Serial Digital Transport Interface (SMPTE 305M). Based on SDI, this provides realtime streaming transfers. It does not define the format of the signals carried but brings the possibility to create a number of packetized data formats for broadcast use. There are direct mappings for SDTI to carry Sony SX, HD-CAM, DV-DIFF (DVCAM, DVCPRO 25/50, Digital-S) and MPEG TS.
• SDTI-CP. Serial Digital Transport Interface—Contents Package. A uniform "container" designed for streaming pictures (still and moving), audio, data, and metadata over networks. Developed for use on SDTI, the Contents Package can also be stored. Packets are handled identically, no matter what they contain, enabling one network to carry any type of content. Network efficiencies are achieved through SMPTE KLV compliance, which places a header of Key—the type of content, and Length—number of bytes ahead of Value, the content. This enables network nodes, switches, and bridges to quickly identify the content of the packet without having to read the entire message.
• SDTV. Standard definition television. A digital television system in which the quality is approximately equivalent to that of analog 525/60 and 625/50 NTSC and PAL systems. Serial digital interface (SDI). The standard based on a 270 Mb/s transfer rate. This is a 10-bit, scrambled, polarity-independent interface, with common scrambling for both component ITU-R BT.601 and composite digital video and four groups each of four channels of embedded digital audio. Most new broadcast digital equipment includes SDI, which greatly simplifies its installation and signal distribution. It uses the standard 75-ohm BNC connector and coax cable that is commonly used for analog video, and can transmit the signal over 200 meters (depending on cable type).
• SMPTE. Society of Motion Picture and Television Engineers. A U.S. organization, with international branches, that includes representatives of the broadcasters, the equipment manufacturers, and individuals working in the film and television industry. It has within its structure a number of committees that make recommendations (RP 125, for example) to the ITU-R and to ANSI in the USA.
• Square pixels. See Aspect ratio—of pixels
• Storage capacity (for video). Using the ITU-R BT.601 4:2:2 digital coding standard for SD, each picture occupies a large amount of storage space, especially when related to computer storage devices such as DRAM and disks—so much so that the numbers can become confusing unless a few benchmark statistics are remembered. Fortunately, the units of mega, giga, and tera make it easy to express the vast numbers involved; "One gig" trips off the tongue far more easily than "One thousand million" and sounds less intimidating. Storage capacities for SD video can all be worked out directly from the 601 standard. because sync words and blanking can be regenerated and added at the output, only the active picture area need be stored. In line with the modern trend of many disk drive manufacturers, kilobyte, megabyte, and gigabyte are taken here to represent 10,3 10,6 and 10,9. respectively.
Every line of a 625/50 or 525/60 TV picture has 720 luminance (Y) samples and 360 each of two chrominance samples (Cr and Cb), making a total of 1440 samples per line.
In the 625-line standard there are 576 active lines per picture, giving 1440-by-576 = 829,440 pixels per picture.
Sampled at 8 bits per pixel, a picture is made up of 6,635,520 bits or 829,440 8-bit bytes— generally written as 830K.
With 25 pictures a second there are 830-by-25 = 20,750 kbytes or 21MB per second.
The 525/60 picture has 487 active lines, so there are 1440-by-487 = 701,280 pixels per picture.
With each pixel sampled at 8-bit resolution, there are 5,610,240 bits, or 701.3K At 30 frames per second, there are a total of 21,039 kbytes, or 21MB per second.
Note that both 625- and 525-line systems require approximately the same amount of storage for a given time—21MB for every second. To store one hour takes 76GB. Looked at another way, each gigabyte (GB) of storage will hold 47 seconds of noncompressed video.
If compression is used, simply divide or multiply the numbers by the compression ratio. For example, with 5:1 compression, 1GB will hold 47-by-5 = 235 seconds, and 1 hour takes 76/5 = 18GB (approximately).
There are many video formats for HD, but the 1080-by-1920 system is popular. Using 4:2:2 sampling, each line has 1920 Y samples and 960 each of Cr and Cb = 3840 samples per line. So each picture of 3840-by-1080 = 4.147 M samples. For 10-bit accuracy each picture has the equivalent data of 5.18 M (8-bit) bytes. Thirty frames per second produce 155MBps—7.4 times that of SD. The hour of video now needs 560GB of storage.
• Subpixel. A spatial resolution smaller than that of pixels. Although digital images are
composed of pixels, it can be useful to resolve image detail to a size smaller than a pixel—that is, a subpixel. For example, the data for generating a smooth curve on the screen needs to be created to a finer accuracy than the pixel grid itself—otherwise the curve will look jagged. Again, when tracking an object in a scene or executing a DVE move, the size and position of the manipulated picture must be calculated, and the picture resolved, to a far finer accuracy than the pixels—otherwise the move will appear jerky. Moving an image with subpixel accuracy requires picture interpolation since its detail, which was originally placed on lines and pixels, now has to appear to be where none may have existed—for example, between lines. The original picture has to be effectively rendered onto an intermediate pixel/line position. The example of moving a picture down a whole line is achieved relatively easily by readdressing the lines of the output. But to move it by half a line requires both an address change and interpolation to take information from the adjacent lines and calculate new pixel values. Good DVEs work to a grid many times finer than the line/pixel structure.
• Widescreen. A TV picture that has an aspect ratio wider than the "normal" 4:3—usually 16:9— while still using the normal 525/60 or 625/50 or SD video; 16:9 is also the aspect ratio used for HDTV. There is an intermediate scheme using 14:9, which is found to be more acceptable for those still using 4:3 displays. Widescreen is used on some analog transmissions as well as many digital transmissions. The mixture of 4:3 and 16:9 programming and screens has greatly complicated the issue of safe areas.
• Y, Cr, Cb. The digital luminance and color difference signals in ITU-R BT.601 coding. The Y luminance signal is sampled at l3.5 MHz, and the two color difference signals are sampled at 6.75 MHz cosited with one of the luminance samples. Cr is the digitized version of the analog component (R-Y), and Cb is likewise the digitized version of (B-Y). For the HD SMPTE 274M standard, sampling rates are 5.5 times greater—74.25 MHz for Y and 37.125 MHz for Cr and Cb.
• Y, (R-Y), (B-Y). These are the analog luminance, Y, and color difference signals (R-Y) and (BY) of component video. Y is pure luminance information, while the two color difference signals together provide the color information. The latter are the difference between a color and luminance: red-luminance and blue-luminance. The signals are derived from the original RGB source (for example, a camera or telecine). The Y, (R-Y), (B-Y) signals are fundamental to much of television. For example, in ITU-R BT.601 it is these signals that are digitized to make 4:2:2 component digital video; in the PAL and NTSC TV systems they are used to generate the final composite coded signal; and in DTV they are sampled to create the MPEG-2 video bitstream.
• YUV. Convenient shorthand commonly—but incorrectly—used to describe the analog luminance and color difference signals in component video systems. Y is correct for luminance, but U and V are, in fact, the two subcarrier modulation axes used in the PAL color coding system. Scaled and filtered versions of the B-Y and R-Y color difference signals are used to modulate the PAL subcarrier in the U and V axes, respectively. The confusion arises because U and V are associated with the color difference signals, but clearly they are not the same thing. Or could it just be because YUV trips off the tongue much more easily than Y, B-Y, R-Y?
back to top
