At 11:43 AM -0700 10/17/04, Dale Kelly wrote: >You might recall a recent posting suggesting that HDTV might be of >little value in countries using the 625 line system since that >system's quality was likely good enough. My position was, that as >good as that image might be relative to other analog based >standards, it could not compete in quality with true HDTV video >displayed on a 720 or 1080 large screen display. >I'm revisiting this subject only because I saw a very graphic >illustration supporting my argument last evening when viewing the >BBC production of "Last Night at the Proms", on the Discovery HD >channel. This is an excellent program in every way but it was >produced in the 625 (580? DTV) 16X9 format* and compared to other >HDTV programming on the same network was noticeably softer, >particularly on the medium and long shots which are such an integral >part of that program. Clearly the viewers in Britain would have >noticed and wanted the difference. > There is an obvious explanation, one that has significant relevance, as the ITU considers whether it should approve 720P for international program exchange, and the inclusion of 720@50P into the international standards. I cannot reproduce the submission to the ITU directly, however I can paraphrase the key points that the advocates of 720P have made: - Progressive formats make compression work better (one company estimates a 10%to 30% increase in the required bit rate for MPEG 2 compressed interlace video as opposed to progressive scan video), preserving bandwidth and providing the best quality to viewers. - Emerging display technologies are progressive friendly and are dominated by 1Mpixel types. - 1280x720 is friendly to modern post-production techniques, which often need to de-interlace source for processing, such as spatial scaling and rotational manipulations. - Conversion from 720p to any other format is simpler and provides better quality because there is no source de-interlacing involved. This is the key to why Dale saw a "soft" picture. In order to present the content here in the U.S. the original 1080@50i source (thanks to Alan Roberts for this very useful clarification) had to be standards converted from 50i to 60i for broadcast by Discovery Networks. This requires a de-interlacing step, then frame rate conversion, then re-interlacing. Welcome to the realities of standards conversion. It does not get better with HDTV, if we are trying to do frame rate conversions on interlaced source. We are trying to create information that was not sampled, using samples that have been compromised by interlaced acquisition. The net result is that to cover all of the artifacts of the standards conversion, we give up significant resolution. Contrast this with a 50P to 60P conversion or visa versa. We do not need to de-interlace the source, and we have excellent spatial detail available to do the frame rate conversions. The results are obvious on a progressive display. So bottom line, Dale was seeing the "kinder, gentler, softer" side of 1080i. It's time to get rid of interlace. PERIOD! There is NO GOOD reason for this archaic compression technique to be concatenated with digital compression. This is equally true for SDTV(525 or 625 line), as better results can be obtained with a high quality de-interlacing system, before the source is subjected to MPEG-2 compression. Expecting a cheap de-interlacing chip in a consumer display to do as good a job as a $75K to 100K deinterlacing system is ludicrous. On the other hand, it is dirt simple to convert progressive source for interlaced display using noting more than a convolution filter to remove the details that would cause offensive artifacts on an interlaced display. If we only put progressive source into the DTV channel, the use of interlaced acquisition would disappear quickly, in favor of progressive HD and EDTV acquisition. Regards Craig ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.