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blockiness on HD content?
PostPosted: Fri Jan 12, 2007 8:07 am Reply with quote
mik
 
Joined: 31 Dec 2006
Posts: 16




I see some unexpected artifacts on HD content that dont seem related to cpu loading issues: Alternating rows of the image are offset during scene motion, it looks like blocks of 16 pixels - at first I put it down to cpu overloading, but I happened to catch it during paused live tv. Any suggestions?

Example... what I see (edit) when the objects in the scene are moving to the left:
Code:

  XXYYZZ
   XXYYZZ
  XXYYZZ
   XXYYZZ


what I expect to see:
Code:

  XXYYZZ
  XXYYZZ
  XXYYZZ
  XXYYZZ

it looks like these are blocks of pixels that are something like 16 or 32 on a side - almost like interlace artifacts but in huge clusters instead of single scanlines. (edit) Actually, very much like what interlaced video looks like on a progressive monitor, except that blocks of scan lines lag a frame behind instead of single scan lines.

Update (solved) FWIW, my problem appears to be only on replay. You can see exactly the sort of artifact as the first image on the nice deinterlacing faq page at http://www.100fps.com/ . To cut to the chase, this is what you apparently get if you resize before deinterlace, say from 1080i for letterbox display on a 1024x768 monitor. Obviously a bad idea.

Thanks!


Last edited by mik on Mon Jan 22, 2007 8:09 am; edited 2 times in total
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PostPosted: Fri Jan 12, 2007 12:55 pm Reply with quote
flawlessdistortion
 
Joined: 12 Jan 2007
Posts: 6
Location: Chicago




What program are you using to watch tv? Does this happen all the time or just occasionally? This could be a result of noise in the signal. Use dtvsnr to find out your SNR (signal to noise ratio). It should generally be above 25 for a decent picture without much distortion.
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PostPosted: Fri Jan 12, 2007 2:15 pm Reply with quote
mik
 
Joined: 31 Dec 2006
Posts: 16




flawlessdistortion wrote:
What program are you using to watch tv?

mythtv (ubuntu edgy + nybbler's binaries). I'll have to see if it is a matter of the player or recorder - just recorded an hd show without livetv so we'll see.

Quote:
Does this happen all the time or just occasionally? This could be a result of noise in the signal. Use dtvsnr to find out your SNR (signal to noise ratio). It should generally be above 25 for a decent picture without much distortion.

It seems to happen all the time, regardless of content (all digital signals) - it is emphatically not random - my perception is that it is merely more visible on moving scenes rather than caused by moving scenes. In particular, there is no evidence of corruption within the shifted rows, nor do I notice dropped frames, etc. Perhaps I can capture some frames to illustrate it here.
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PostPosted: Sat Jan 13, 2007 9:23 pm Reply with quote
flawlessdistortion
 
Joined: 12 Jan 2007
Posts: 6
Location: Chicago




Hmm, yeah you might want to try and isolate the problem by viewing recorded shows and live tv. Also try watching tv in xine to see if you experience the same problems as in mythtv. Btw, when you use xine make sure you increase the buffer sizes, as high definition content is more demanding, especially as a stream.
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blockiness on HD content?
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