[Ffmpeg-devel] upsampling of subsampled video data
Mon Sep 11 07:54:51 CEST 2006
> IIRC there are 3 different coefficients for YUV<->RGB conversion by
> different standards groups. Is it important to have a programmable
> converter to select one of these, or would be one constant enough
> without too much quality los for the others?
I would expect a converter to handle Rec. 601 (NTSC/PAL) coefficients
as well as Rec. 709 (HDTV) coefficients. In both cases it would be
nice to have two conversions, one that preserves the 16-235 range of
Y'CbCr luma in RGB, and another that expands to 0-255 RGB.
Charles Poynton's book and website are good resources for this.
> The quantization levels for YUV are different from RGB and
> requantizing the Y as RGB will introduce ugly banding.
One way to reduce banding is to use error-diffusion dithering. I get
pretty good results on 8-bit to 8-bit conversions, at the cost of
introducing some noise in the least significant bits. (I'd rather see
a little noise than a lot of banding :)
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