1、Rec. ITU-R BR.1292 1RECOMMENDATION ITU-R BR.1292ENGINEERING GUIDELINES FOR TELEVISION POST-PRODUCTION(Question ITU-R 239/11)(1997)Rec. ITU-R BR.1292The ITU Radiocommunication Assembly,consideringa) that television post-production operation is based on the use of television recording;b) that a number
2、 of important image manipulations required in television post-production can only be performedon component video signals, in either analogue or digital form;c) that there are now in use many formats of television recorders that operate on: analogue composite video signals, analogue component video s
3、ignals, digital composite video signals, digital component video signals without bit-rate reduction (BRR), digital component video signals with a small BRR factor, digital component video signals with a large BRR factor;d) that several such recording formats may be present in the same television pos
4、t-production installation and theymay happen to be used in tandem on the television signal chain, in a way that will be dictated by operationalconsiderations more than by a concern for maximum final picture quality;e) that every time a video signal is passed from its component to its composite form
5、or vice versa (be it in theanalogue or in the digital domain), it is subjected to a co-decoding process, and to the associated video filtering; thiscauses a small image impairment, that is hardly noticeable, but that becomes noticeable if the co-decoding process isrepeatedly applied (see Note 1).NOT
6、E 1 It should be noted that even quite “innocent”, routine post-production operations may involve acomposite-to-component co-decoding; for instance, if a video signal is taken from the PAL playback output of a videocomponent VTR, and it is then recorded on another component VTR, this process introdu
7、ces a component-to-compositeco-decoding that contributes to picture impairment. The correct practice in this case is to take the signal from thecomponent output of the playback VTR and to feed it to the component input of the recording VTR, since in this casethe signal does not have to go to its com
8、posite form at all;f) that every time a video signal is passed from its analogue to its digital form or vice versa, it is subjected to aco-decoding process, and to the associated video filtering; this causes a small image impairment, that is hardlynoticeable, but that becomes noticeable if the co-de
9、coding process is repeatedly applied (see Note 1 to e);g) that the application of a large degree of bit-rate reduction to the video signal, such as is customary inrandom-access television editing systems designed for off-line use, is likely to generate picture artefacts that may beacceptable for vie
10、wing purposes such as for off-line editing, but may well be unacceptable on the final edited master of aprogramme intended for transmission (see Note 1).NOTE 1 When evaluating the acceptability of picture artefacts generated by a high degree of BRR applied inprogramme production, account should care
11、fully be taken of the likelihood that several additional BRR processes maybe applied downstream from programme production (e.g. for primary and/or secondary distribution) before the digitalvideo signal reaches its final user, in which case the attendant artefacts may well cumulate to an intolerable
12、level,2 Rec. ITU-R BR.1292recommends1 that mixed component/composite television post-production installations where component and compositevideo recorders are placed in tandem should be avoided; video post-production installations where all the videorecorders and interfaces are in component form mus
13、t be preferred to installations where all the video recorders andinterfaces are in composite form;2 that mixed analogue/digital television post-production installations where analogue video recorders are placedin tandem with digital video recorders should be avoided; video post-production installati
14、ons where all the videorecorders and interfaces are digital must be preferred to installations where all the video recorders and interfaces areanalogue;3 that the use of random-access editing systems that apply a high degree of bit-rate reduction to the video signal,such as it is customary in random-access television editing systems designed for off-line use, may only be considered foroff-line applications, but it should be avoided for on-line application.
