XPost: alt.video.digital-tv 
 From: stephen.neal@nospam.as-directed.com 
  
 "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 
  
 --- SoupGate-Win32 v1.05 
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