Thorsten Froehlich <tho### [at] trfde> wrote:
> As a mater of fact, they do! the math behind this effect that causes the 
> "better" compression is of course rather complicated. Yet, the simpler 
> explanation for this "better" compression is that there is less detail in 
> the picture because high contrast edges simply have a lot of geometry detail 
> hardly found in real-world images.

  Curiously, it seems that at least in MPEG-4 (and perhaps even MPEG-2) they
dedicated more data to the higher frequencies of the spectrum (iow to the
parts of the image with higher contrast) than to the lower frequencies.
Thus in a low-bitrate MPEG-4 you are more likely to see artifacts in areas
where there are smooth color transitions than in areas with sharp edges...

  This makes sense, though. With a proper bitrate you get a higher image
quality because sharp edges are sharp and mostly artifact-free.

-- 
                                                          - Warp

Post a reply to this message