XPost: alt.video.digital-tv 
 From: stephen.neal@nospam.as-directed.com 
  
 "Barry"  wrote in message 
 news:VYWHc.11135$R36.6213@newsread2.news.pas.earthlink.net... 
 > 
 > "Stephen Neal"  wrote in message 
 > news:ccp2rl$1i3$1$830fa795@news.demon.co.uk... 
 > > 
 > > "R. Mark Clayton"  wrote in message 
 > > news:ccomg4$2mb$1@hercules.btinternet.com... 
 > > > 
 > > > "Harlan Osier"  wrote in message 
 > > > news:89ec59b9.0407092222.34e3fa@posting.google.com... 
 > > > > Yes, 4 colors at 320*200 pixels. 
 > > > > 
 > > > > I cannot recommend it. 
 > > > 
 > > > Er should be 768x576, and probably 16bit colour, are you perhaps using 
 > an 
 > > > old PC as a display? 
 > > 
 > > In PAL-land DTV is nearer 720x576/704x576 non-square pixels (though some 
 > are 
 > > 540x576 to save bandwith) and the colour bit depth is effectively 24 
 bit - 
 > > with 8 bit sampling of both luma and chroma difference signals (albeit 
 > with 
 > > slightly less bit depth than 8 bits to allow for overshoot and 
 > undershoot - 
 > > black is 16 not 0 and white is 235 not 255 - or is it 240 I can never 
 > > remember (I think 16-140 is the Colour difference range?) ). 
 > > 
 > > Additionally because the luma resolution is twice that of the chroma 
 both 
 > > vertically and horizontally - as 4:2:0 sampling is used for OTA DTV - 
 only 
 > > 12 bits per luma sample are used to carry picture information i.e.. 4x8 
 > bit 
 > > luma "pixels" are accompanied by 1x8 bit Cr and 1x8bit Cb chroma sample 
 > > each - so 4x8 + 2x8 = 48 bits per 4 pixels = 12 bits per pixel? 
 > > 
 > > However the OPs observation is probably based on heavily compressed low 
 > data 
 > > rate feeds that can and do look like they are made up of lego bricks 
 > rather 
 > > than pixels.  On the other hand some DTV can look cracking - though PCs 
 > are 
 > > usually less than ideal viewing sources as they seldom cope with 
 > interlaced 
 > > source material that well. 
 > > 
 > > Steve 
 > > 
 > Yup, the SD digital channels can look very bad on an HD set and the color 
 > also needs some gamma correction.  Many HD enthusiasts are screaming at 
 the 
 > cable companies for requiring us to subscribe to channels we can't stand 
 to 
 > watch just to get HD.  The compression artifacts are almost unnoticeable 
 on 
 > an analog set. 
  
 Interesting - the same complaint is levelled at some DTV transmissions in 
 the UK viewed on 100Hz sets. (In Europe we don't have many progressive, and 
 almost no HDTV, sets, but we do have 100Hz sets which upconvert 50Hz 
 interlaced to 100Hz interlaced to reduce large area flicker) 
  
 The digital processing used to convert a 50Hz interlaced picture to 100Hz 
 also emphasises (and in some cases adds to) existing compression artefacts 
 introduced by MPEG2 coding at low-to-medium data rates. 
  
 I wonder if US HDTVs are using similar digital processing when displaying 
 480i material at 1080i or 720p? (I'm assuming US HDTV sets don't display 
 480/60i SDTV in native mode and instead upconvert - I would be surprised if 
 the TVs ran at both SDTV and HDTV scanning rates?) 
  
 Steve 
  
 > 
 > - Barry 
 > 
 > 
 > 
  
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