[opendtv] Re: Video compression artifacts and MPEG noise reduction

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 23 Jun 2008 08:05:54 -0400

At 1:56 AM -0700 6/20/08, Ron Economos wrote:
BTW, the 8x8 transform (and variable quantization matrix)
was put back into H.264 High Profile after it was found that
the 4x4 transform looks like shit at HD resolutions. Basically the
4x4 transform (with it's fixed quantization matrix) cannot always
generate enough coefficients to provide a sharp image. Today,
almost all broadcast HD H.264 is using High Profile.

I have no way of evaluating Ron's comment about the use of the FRE for broadcast applications. I do hear of or see too many HD feeds at the higher bit rates that FRE was designed for. Reading the stuff that Ron linked to, it would appear that the extra overhead for the 4 x 4 residuals may be the culprit. One presentation talked about the required bit rate actually increasing (presumably due to the 4 x 4 transform) at higher quality levels.

It is also unclear whether the 8 x 8 arithmetic transform is used only for coding of residuals, or if it is used for the coding of blocks during the prediction routines. If it is only used for coding the difference, I can see where it could improve coding efficiency, especially when the residuals are small, at higher bit rates ( i.e. the overhead of the small block size takes up more bits that the residuals).

One thing is clear from the presentations, h.264 with the FRE is significantly more efficient than MPEG-2 ( 8 mbps for h.264 versus 24 mbps for h.262 for essentially the same level of perceived quality.)


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