[MPlayer-dev-eng] Re: [PATCH] New video filter: deblendlogo

D Richard Felker III dalias at aerifal.cx
Sun Feb 27 05:17:55 CET 2005

On Sat, Feb 26, 2005 at 09:46:41PM -0600, Zoltan Hidvegi wrote:
> Ivo wrote:
> > Doing alpha deblending on chroma channels is utter nonsense. It only works 
> > if the logo mask is all white, which means there is no chroma, so the 
> > unblended chroma is preserved and only the luminance is corrected. With 
> > colored logo's this won't work.
> Why not?  RGB -> YUV is an affine tansformation, and affine
> transformation of convex combination of points (i.e. alpha-bending) is
> the convex combination of the affine transformed points.  This means
> that alpha-bending works just fine in YUV, as long as you use the YUV
> transformed logo image.

Exactly. Thanks, I couldn't have explained it better myself..


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