Ewald Snel ([EMAIL PROTECTED]): > > > I wrote a vertical chrominance filter (*) for the XVideo module > > > using inline MMX assembly. This allows me to improve output > > > quality without any speed penalty. > > > > Do you mean for upsampling to 4:2:2 ? How do you filter? Do you > > average to create the new chroma line? > > Something like that, the filter uses 0.75x nearest chrominance sample > and 0.25x second nearest chrominance sample. This is more accurate as > it doesn't shift the chrominance signal by 1 pixel.
Please, please correct me if I'm wrong here. In MPEG sampling, the chrominance sample is halfway between the two luminance samples on the same vertical scanline (by is138182): o o where o == luma sample x x == chroma sample o o So, if we look vertically down a 2-pixel wide line, we see: o1 o x1 o2 o o == luma sample x2 x == chroma sample o3 o x3 o4 o So, are not the chroma samples above and below the same distance away? I thought this was the purpose of MPEG sampling, that is, it's reasonable to convert to 4:2:2 sampling by doubling the scanlines. Are you sure that maybe the images where you see that nasty chroma artifact aren't from when the DVD is using interlaced encoding? In this case, each second chroma sample is from a different field, and you can get blocky errors because you don't correllate samples correctly. What do you mean by shifting the chroma by one pixel? -- Billy Biggs [EMAIL PROTECTED] _______________________________________________ Xpert mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xpert
