On Friday 21 September 2012 21:46:36 Steinar H. Gunderson wrote:
> No, actually that's fine, because Y'CrCb are defined by a conversion from
> the nonlinear RGB, not from linear tristimulus values. They are not
> supposed to be perceptually correct quantities; the only thing they really
> are good for are doing the inverse transformation to RGB.
>
It does some harm, because of the subsequent subsampling:

http://www.cis.rit.edu/fairchild/PDFs/PRO29.pdf

> FWIW, I'm not saying that calculation on nonlinear R'G'B' is horrible and
> that you should throw out all and rewrite all Frei0r code; I think there
> are much more important sins in there right now, like the linear tool that
> was brought up earlier in this thread. Also, performance matters for a lot
> of things, and the correct processing will inherently be slower, at least
> on the CPU.

Agree on that, will see what I can do on the "levels" plugin.
Actually I do use it quite often, but never noticed the problem, as I usually
don't touch the "output" parameters. Seems that my videos only need their
histograms "stretched", never "squeezed"...

Marko Cebokli