Re: [Algorithms] RGB to XYZ conversion

[Jon O. <jon...@gm...>]

Hi Sam,

I agree, the loss of 1 bit is usually nothing to worry about. Surely we
don't here. Just wanted to point it out for correctness. However, I am
interested in the variant Simon alluded to which does not require the
additional bit.

The only artifacts I've seen from using YCoCg as a production format is that
when interpolating between different colors the wrong colors can show up in
the bilinear interpolation. However, this is usually minor and barely
noticeable.

Best,
Jon Olick


On Thu, Apr 24, 2008 at 4:39 AM, Sam Martin <sam...@ge...>
wrote:

> >He missed a few signs:
> >> [y,Co,Cg]' = [1/4, 1/2, 1/4].[r,g,b]'
> >>              [1/2, 0,   -1/2]
> >>              [-1/4, 1/2, -1/4]
>
> Yeah, cheers - I was reformatting it from a copied pdf. The signs must
> have been eaten somewhere in the process.
>
> > Out of curiosity, what did you mean by "had any issues with it"? YCoCg
> > is primarily a replacement for YUV/YCbCr that allows cheaper (and
> > lossless) transforms between the two colour spaces and typically does
> a
> > good job of extracting the correlation in the RGB. If you want to use
> it
> > for image compression, then it's a good first step.
>
> As other people have commented, I'm also not bothered by the 1-bit
> 'lossy' precision aspect. That's well below the radar :)
>
> I'm actually interested in how this luminance+chroma variant stands up
> against its equivalents from an art and data 'reduction' point of view.
> Can you sensibly work as an artist in YCoCg space? How well does it
> represent the rgb correlation in comparison to its alternatives?
>
> I suspect a fair amount of effort went into defining the balance of
> luminance/chroma in other variants of this and (at least on the surface)
> YCoCg appears to just throw all that away!
>
> Cheers,
> Sam
>
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