Avid has also come out with some good documents that's similar to the Quantel document. It includes a pretty good guide to different video formats--although it misses some new ones like Panasonic's AVC-Intra. It's much more digestible than Quantel's. Like the Quantel, very geeky--topics include sampling, compression, digital film, and post-production. An overview of the Avid info is at a site called Reel Seo.
Excerpts from Quantel Digital Factbook
16:9 Picture aspect ratio used for HDTV and some SDTV(usually digital). See also: Widescreen
24P Refers to 24frames-per-second,progressive scan. This has been the frame rate of motion picture film since talkies arrived. It is also one of the rates allowed for transmission in the DVB and ATSC television standards – so they can handle film without needing any frame-rate change (3:2pull-down for60 fields-per-second systems or running film at25fps for50 Hz systems). It’s now accepted as a part of television production formats – usually associated with high definition 1080 lines, progressive scan. A major attraction is a relatively easy path from this to all major television formats as well as offering direct electronic support for motion picture film and D-cinema. See also: 24PsF,25P,3:2Pull-down,1080/24P– The Global Production Format? (Opinion),ATSC,Common Image Format,D-cinema,Digital Film Supplement,DVB, Publishing
25P Refers to 25 frames-per-second,progressive scan. Despite the international appeal of 24P,25Pis widely used for HD productions in Europe and other countries using 50 Hz TV systems. This is a direct follow-on from the practice of shooting film for television at 25fps. See also: 24P,24PsF,Common Image Format,DVB
Anamorphic Generally refers to the use of16:9aspectratio pictures in a 4:3 system. For example, anamorphic supplementary lenses are used to change the proportions of an image to 16:9on the surface of a 4:3 sensor by either extending the horizontal axis or compressing the vertical. Signals from 16:9cameras and telecines produce an ‘anamorphic’ signal which is electrically the same as with 4:3 images but will appear horizontally squashed if displayed at4:3. The alternative way of carrying 16:9pictures within 4:3 systems is letterbox. Letterbox has the advantage of showing the correct16:9 aspect ratio on 4:3 displays, however the vertical resolution is less than 16:9 anamorphic. See also: Aspect ratio – of pictures
Aspect ratio 1. – of pictures. The ratio of length to height of pictures. Nearly all TV screens are currently 4:3, i.e. 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. See also: Anamorphic, Widescreen, HDTV Website: documentR95-2000 athttp://www.ebu.ch/tech_texts.html 2. – of pixels. The aspect ratio of the area of a picture described by one pixel. The ITU-R BT.601digital 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: 486/711x 4/3 = 0.911 (i.e. 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: 576/702x 4/3 = 1.094 (i.e. the pixels are 9% wider than they are tall) A The newer DTV image standards, and all 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 ratio is important is in 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 change may not be real-time and its quality will depend on the processing used. See also: ARC, Pixel
ATSC The (US) Advanced Television Systems Committee. Established in 1982 to co-ordinate 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. See also: VSB,Table 2,Table 3,Dolby Digital (DD/AC-3),MPEG-2section Website: www.atsc.org
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 analyze their picture sources to find and remove redundancy and less critical information 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,DV,MPEG-1,MPEG-2and MPEG-4. Where different techniques are used in the same stream, problems can occur and picture quality can suffer more than if the same method is used throughout. The MPEG-2family of compression schemes, which was originally designed for program transmission, has been adapted for studio use in Betacam SX and IMX recorders. C While there is much debate, and new technologies continue to be developed, it remains true that the best compressed results are produced from the highest quality source pictures. Poor inputs do not compress well. Noise, which may be interpreted as important picture detail, is the enemy of compression. See also: Compression ratio, Concatenation, Digital Betacam,ETSI,JPEG,MPEG-2,MPEG-4
Compression ratio The ratio of the size of data in the non-compressed digital video signal to the compressed version. Modern compression techniques start with component television signals beta variety of sampling systems are used,4:2:2(‘Studio’MPEG-2),4:2:0 (MPEG-2),4:1:1 (DVCPRO),etc. The compression ratio should not be used as the only method to assess the quality of a compressed signal. For a given technique, greater compression can be expected to result in 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 – where appropriate, re-assessing their quality after onward video processing. See also: Concatenation,DV,ETSI,JPEG,MPEG
Cross conversion Changing video material from one HD format to another. For example, going from 720/60Pto 1080/50I is a cross conversion. Note that this involves both changing picture size and the vertical scan from 60 Hz progressive to 50 Hz interlaced. Similar techniques are used as for standards conversion but the HD picture size means the processing has to work five or six times faster. See also: Down-res,Standards conversion,Up-res
Down conversion Down conversion is down-resing that includes changing vertical refresh rates. For instance, moving from 1080/60I to 576/50I is a down-conversion. See also: Cross conversion,Publishing,Standards conversion,Up-res
Down-res Decreasing the size of video images to fit another format. Typically this reduces an HD format to an SD format and, as the input images represent oversampled versions of output, the final quality should be excellent– better than an SD-shot original. Moving from 1080/60I to 480/60I is down-resing. Technically the process involves: spatial interpolation to reduce size while retaining quality, colour correction to compensate for the difference in HD and SD colour standards and possibly re-framing to fit16:9HD onto 4:3 SD. Note that down-res does not include any change of frame rate. See also: Down conversion,Formatconversion,Publishing,Standards conversion,Up-res
DSS Digital Satellite Service. One of the terms used to describe DTV services distributed via satellite.
HDCam Assigned D11,this is a series of VTRs based on the Betacam principles for recording HD video on a tape format which uses the same style of cassette shell as Digital Betacam, although with a different tape formulation. The technology supports both 1080 and 1035 line standards. Various methods are believed to be used to reduce the video data including pre-filtering,DCT-based intra-frame compression and sampling at around 3:1:1. Together these are said to provide data reduction of between 7and 10:1. Four non-compressed audio channels sampled at48 kHz,20 bits per sample, are also supported. HDCam camcorders provide HD acquisition and recording in a compact ergonomic package. One model is specifically for1080/24Poperation and aimed at addressing some current film areas. See also: 24PsF,CineAlta,D11 Website www.sonybiz.net/cinealta
HD D5 A D5 VTR that is able to handle component high definition signals. Using around 5:1 compression the signals connect via an HD-SDI link. HD D5 can be multi-format, operating at both SD and HD TV standards. It can replay 525-line D5 as well as HD D5 cassettes. Formats include 480/60I,1080/24P,1080/60I,1080/50I,1035/59.94I and 720/60P. The recorder can also slew between 24and 25 Hz frame rates for PAL programme duplication from a 1080/24Pmaster. Cassette recording times vary according to format, the longest is 155 minutes for1080/24P. Website: www.panasonic-broadcast.com
HD-SDI Standardized in SMPTE292M,this is a high definition version of the SDI (Serial Digital Interface) used forSD television. The serial bit-stream runs at1.485 Gb/s to carry up to 10-bitY,Cr,Cb 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 fibre for distances up to 2km. See also: Dual link,HSDL,SDI
HDTV High Definition Television. A television format with higher definition than SDTV. While DTV at625 or525 lines is usually superior to PAL and NTSC, it is generally accepted that720- line and upward is HD. This also has a picture aspect ratio of16:9. While there are many picture formats proposed and several in use, there is increasing consensus that1080 x 1920/24Pis a practical standard for global exchange. Many are planning to produce on this format. See also: 24P,ATSC,Common Image Format,DVB,Table 3
I 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-2uses two types of inter-frame processed pictures – the ‘P’(predictive) and ‘B’ (bi-directional) frames. As ‘P’ and ‘B’ frames are not complete in themselves but relate to other adjacent frames, they cannot be edited independently. See also: Cutedit,MPEG-2
Interlace (scan) Method of scanning lines down a screen – as used in most of today’s television broadcasts. Each displayed picture comprises two interlaced fields: field two fills in between the lines of field one. One field displays odd lines, then the other shows even lines. For analogue systems, this is the reason for having odd numbers of lines in a TV frame e.g. 525 and 625,so that each of the two fields contain 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 or data rate. Disadvantages are that it reduces vertical definition of moving images to about70% (see Interlace Factor) of the progressive scan definition and tends to cause some horizontal picture detail to ‘dither’. Forprocessing, such as in DVE picture size changes, movement between fields has to be detected if the higher-quality frame-based processing is used. There is continuing debate about the use of interlaced and progressive scans for DTV formats. See also: Interlace Factor, Interlace or Progressive (Opinion),Progressive
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 ofMPEG-2are coded in this way and use DCT. In the MPEG-2 sequence only I-frames can be edited as they are the only independent frames. See also: DCT,I-frame only,JPEG,MPEG-2
MPEG-4 ISO/IEC 14496. Whereas MPEG-1and MPEG-2are only about efficient storage and transmission of video and audio,MPEG-4 adds interactive graphics applications (synthetic content) and Interactive multimedia (World Wide Web, distribution often adds access to content). First published in early 1999,ithas already grown to embrace a wide range of service types. It specifies low bitrates (5-64kb/s) for mobile and internet applications with frame rates up to 15 Hz,and images up to 352x 288 pixels. At the higher end it works up SD, HD resolutions and beyond and uses bitrates up to 10 Mb/s. The video coding is said to be three times more complex than MPEG-2butis already 15 percent more efficient and may rise to 50 percent. There is also more complexity for the decoders but it is hoped that Moore’s Law will take care of that. It also includes multimedia storage, access and communication as well as viewer interaction and 3D broadcasting. Aural and visual objects (AVOs) represent the content which may be natural – from cameras ormicrophones,orsynthetic – generated by computers. Their composition is described by the Binary Format for Scene description (BIFS) – scene construction information to form composite audiovisual scenes from the AVOs. Hence, a weather forecast could require relatively little data – a fixed background image with a numberofcloud,sun,etc.,symbols appearing and moving, audio objects to describe the action and a video ‘talking head’ all composed and choreographed as defined by the BIFS. Viewer interactivity is provided by the selection and movement of objects or the overall point of view – both visually and aurally. QuickTime 6 and RealPlayer8 already make use ofMPEG-4. DVB is showing interest in including it in future specifications but there is no sign of a large-scale decamp from the very well established MPEG-2. Website: www.cselt.it/mpeg
MPEG-4 ISO/IEC 14496. Whereas MPEG-1and MPEG-2are only about efficient storage and transmission of video and audio,MPEG-4adds interactive graphics applications (synthetic content) and Interactive multimedia (World Wide Web, distribution of and access to content). First published in early 1999,ithas already grown to embrace a wide range of service types. It specifies low bitrates (5-64kb/s) for mobile and internet applications with frame rates up to 15 Hz, and images up to 352x 288 pixels. At the higher end it works up SD, HD resolutions and beyond and uses bitrates up to 10 Mb/s. The video coding is said to be three times more complex than MPEG-2butis already 15 percent more efficient and may rise to 50 percent. There is also more complexity for the decoders but it is hoped that Moore’s Law will take care of that. It also includes multimedia storage, access and communication as well as viewer interaction and 3D broadcasting. Aural and visual objects (AVOs) represent the content which may be natural – from cameras ormicrophones,orsynthetic – generated by computers. Their composition is described by the Binary Format for Scene description (BIFS) – scene construction information to form composite audiovisual scenes from the AVOs. Hence, a weather forecast could require relatively little data – a fixed background image with a numberofcloud,sun,etc.,symbols appearing and moving, audio objects to describe the action and a video ‘talking head’ all composed and choreographed as defined by the BIFS. Viewer interactivity is provided by the selection and movement of objects or the overall point of view – both visually and aurally. QuickTime 6 and RealPlayer8 already make use ofMPEG-4. DVB is showing interest in including it in future specifications but there is no sign of a large-scale decamp from the very well established MPEG-2. Website: www.cselt.it/mpeg
NTSC (television standard) The colour television system used in the USA,Canada,Mexico,Japan and more, where NTSC M is the broadcast standard (M defining the 525/60 line and field format). It was defined by the NTSC in 1953. The bandwidth of the NTSC system is 4.2MHzforthe luminance signal and 1.3 and 0.4 MHz for the I and Q colour channels. Note that the NTSC term is often incorrectly used to describe the 525-line format even when it is in component or digital form. In both these cases, NTSC, which includes the colour coding system, is not used. See also: YIQ
PAL Phase Alternating Line. The colour coding system for television widely used in Europe and throughout the world, almost always with the 625 line/50 field system. It was derived from the NTSC system but by reversing the phase of the reference colour 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 colour difference signals, U and V. Note that the PAL term is frequently used to describe any 625/50I analogue format– even if it is component, or in the 576/50I digital television system where PAL coding is not used.
Pixel (orPel) A shortened version of’ Picture cell’ or ‘Picture element’. The name given to one sample of picture information. Pixel can refer to an individual sample of R,G,B luminance or chrominance, or sometimes to a collection of such samples if they are co-sited and together produce one picture element. See also: Aspect ratio – ofpixels,Sub-pixel
Progressive (scan) Method of scanning lines down a screen where all the lines of a picture are displayed in one continuous vertical scan. There are no fields or half pictures as with interlace scans. It’s commonly used with computer displays and is now starting to be used for some DTV formats,e.g. – 1080/24P,720/60P. The ‘P’denotes progressive. A high picture refresh rate is required to give good movement portrayal, such as for fast action and camera pans, and to avoid a flickery display. For television applications using progressive scanning, this implies a high bandwidth or data rate and high scanning rates on CRT displays. The vertical definition is equal to around 70% of the number of lines (Kell Factor) and does not show the dither of detail associated with interlaced scans. See also: 24P,Interlace,Interlace Factor, Interlaced or Progressive (Opinion)
Resolution A measure of the finest detail that can be seen,or resolved,in a reproduced image. Whilst it is influenced by the number of pixels in the display (e.g. high definition 1920 x 1080,broadcastSDTV720 x 576 or720 x 487) note that the pixel numbers do not define the resolution but merely the resolution of that part of the equipment chain. The quality of lenses,display tubes, film processes, editsystems and film scanners, etc. in fact any element in the programme stream (from scene to screen),must be taken into accounting assessing overall system resolution. See also: ATSC,Concatenation,HDTV,Table 3
SD Shortform for SDTV.
SDTV Standard Definition Television. A digital television system in which the quality is approximately equivalent to that of analogue 525/60 or625/50 systems.
Serial Digital Interface (SDI) The standard digital television studio connection based on a 270 Mb/s transfer rate. This is a 10-bit,scrambled,polarity-independentinterface,with common scrambling for both componentITU-RBT.601and 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 as is commonly used for analogue video, and can transmit the signal over200 meters (depending on cable type). See also: 4:2:2,Dual link, Embedded audio,HD-SDI
Standards conversion Changing the standard of existing television material that may involve two processes (four if going from and to analogue coded systems such as PAL and NTSC). The two main processes are format conversion to change the spatial (horizontal and vertical) sizes of the pictures and changing the vertical scan rate. For broadcast applications this needs to be completed retaining the maximum possible fidelity of the input content. The former process involves the relatively straightforward task of spatial interpolation – spreading the information from the original pictures over a different pixel structure. Note that the crude method of dropping or repeating lines/pixels will give very poor results and the detail of the interpolation process is important for best results. The second process is more complex as, changing the number of frames or fields per second means creating new ones or removing some – preferably without upsetting the movement in the pictures, so simply repeating or dropping fields or frames will not do. For this the movement within the pictures has to be analyzed so that in-between pictures can be synthesized. This is a very specialized area and there are highly developed techniques used on the best modern standards converters that do this very well. See also: Format(conversion)
Table 3 (ATSC) Table 3 of the ATSC DTV Standard, Annexe A, summarises the picture formats allowable for DTV transmission in the USA. Any one of these may be compressed and transmitted. An ATSC receiver must be able to display pictures from any of these formats.
ATSC Annexe A,Table 3 Picture formats Legend
Aspect Ratio: 1= square samples, 2= 4:3 display aspect ratio, 3 = 16:9 display aspect ratio
Frame Rate: 1= 23.976 Hz, 2= 24Hz, 4= 29.97Hz, 5 = 30 Hz, 7= 59.94,8 = 60Hz
Vertical Scan: 0 = interlaced scan 1= progressive scan
*Note that1088lines are actually coded in order to satisfy the MPEG-2requirementthat the coded vertical size be a multiple of16(progressive scan) or32(interlaced scan).
The wide range of formats in Table 3 caters for schemes familiar to television and computers and takes account of different resolutions, scanning techniques and refresh rates. Although each has its own application and purpose, some of the combinations are more familiar than others, for example: 480 x 704at29.97and 30 Hz frame rates, interlaced scan is very close to ITU-RBT.601 – although the 704pixels per line is not directly compatible with 601’s 720. Other familiar standards can be seen in the table. Forexample,480 x 640,square pixels,4:3 aspect ratio and progressive scan is the VGA computer standard. It’s included in the DTV specification to allow direct digital transmission of a signal to VGA displays. For each frame size, a range of alternative frame rates is available to provide compatibility with existing transmission systems and receivers. 29.97Hzis needed to keep step with NTSC simulcasts. This frame rate is not required once NTSC is no longer transmitted! 30 Hz is easier to use, and does not involve considerations such as drop- frame timecode. 24Hzprogressive (24P) offers compatibility with film material.
Up-res The process which increases the number of pixels used to represent an image by interpolating between existing pixels to create the same image on a larger format. There is no implied change of vertical scan rate. Despite its name, the process does not increase the resolution of the image. See also: Down-res, Format conversion
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 or625/50 orSD video. 16:9is also the aspect ratio used for HDTV. There is an intermediate scheme using 14:9which is found to be more acceptable for those still using 4:3 displays. Widescreen is used on some analogue transmissions as well as many digital transmissions. The mixture of4:3 and 16:9programming and screens has greatly complicated the issue of safe areas.
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