Re: Correct implementation of RGB channel decorrelation


"Thomas Richter" <thor@xxxxxxxxxxxxxxxxx> wrote in message news:fptrvi$ne4$1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
LiloLilo schrieb:
Probably. What are your objectives? Lossy? Lossless?

Lossless

What's the problem with YCbCr? Or probably with the RCT in
JPEG2000, if you need a reversible transform?

I need channel decorrelation as first step of an image compression algorithm
to help improve compression.
I need a color decorrelation step wich is fast, lossless and easy to
implement. Also patent free.

I don't remember whether the RCT was patent free or not, but it's at least trivial
enough. But, yes, it will also expand the range of the chrominance components. It's
something your code must be able to handle. You can also try a lifting based implementation
of the YCbCr transformation with fix-point precision. Will of course also expand the
bitrange.


dunno much about RCT.

I am not sure if YCbCr can be made lossless...

also, what YCbCr primarily offers (preservation of perceptual color accuracy in the fast of loss), is not of much use for lossless compression anyways.

additionally, YCbCr is not always the "best fit" anyways (for example, for those of us who are partly colorblind, and live with the constant experience that computer-based images always look "off" compared with anything that exists IRL anyways...).


the original idea, (G, R-G, B-G), though not theoretically ideal, is very easy to make lossless, and IME works fairly well in practice...


So long,
Thomas

.

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