[Bug 371605] Re: [GM45] Bad chroma upsampling on videos

[bofphile]

** Attachment added: "lspci_vvnn.log"
   http://launchpadlibrarian.net/26307870/lspci_vvnn.log

** Description changed:

  I'm using Ubuntu 9.04 64bits with xserver-xorg-video-intel 2.7.0 from this ppa:
  https://launchpad.net/~ubuntu-x-swat/+archive/x-updates/
+ lspci -nn | grep VGA :
+ 00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller [8086:2a42] (rev 07)
  
  Description of the problem: Whenever I view videos (with totem-gstreamer or mplayer), I can see red pixelation in reds.
  Here you can see what it looks like (taken from a thread on Doom9's forum discussing this problem on Windows : http://forum.doom9.org/showthread.php?t=141066 )
  http://pwp.netcabo.pt/kado/off.png
  
  And I've made another screenshot myself:
  http://bofphile.free.fr/Images/chroma_bug.png
  
  After some research, I found out this problem may be due to bad chroma
  upsampling. Below is an explanation I read  on the Doom9's forum:
  
  "Well, since our eyes are less sensitive to chroma than to luma (i.e. we
  notice changes in brightness more than changes in color) video is
  usually compressed with the chroma (i.e. the color information) at half
  the resolution of the luma (brightness information) - that's part of
  what makes YV12 what it is.
  
  For conversion back to RGB (which is what displays, well, display) you
  of course need to scale the chroma data so it's the same size as the
  luma data, and if you get blocks it has been done by point resizing
  (i.e. by making every "chroma pixel" twice as big), whereas my shader
  turns the point resizing into bilinear resizing (i.e. I interpolate
  between the existing values to make the chroma smoother)."
  
  This problem occurs with SD (DVD) and HD (Bluray) content.
  I've already filed a bug on buzilla freedesktop: http://bugs.freedesktop.org/show_bug.cgi?id=21522

-- 
[GM45] Bad chroma upsampling on videos
https://bugs.launchpad.net/bugs/371605
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