[PD] colour and brightness (Was: Re: [GEM-dev] Why is [hsv2rgb] implemented as an abstraction?)
matju at artengine.ca
Fri Dec 21 19:44:49 CET 2007
On Wed, 12 Dec 2007, Claude Heiland-Allen wrote:
> Interesting, I'm in the process of experimenting a bit with different
> colour spaces, got in a real headache with XYZ and CIE L*a*b and so on,
> but YUV's simplicity may win.
Yes, XYZ and Lab and Luv are quite harder to wrap one's head around (in my
opinion). I'd rather just stick with YUV. If I wanted things to look
better I'd spend some time with gamma correction of both inputs and
outputs, which probably accounts for most of the incorrectness of my
colour models, and then I wouldn't go much further than that.
> and that seems to eliminate the bad brightness mismatches, at the cost of
> some colours seeming a bit washed out (blue) or muddy (yellow).
This can be because you start with a colour that is not vibrant, even
though it's the most vibrant version of the hue that you can do with the
screen, and then you rotate it to another hue which still has plenty of
headspace for being more vibrant.
But I'm thinking that this can also be because YUV is weighted so that it
makes better use of the precision available in the signal, for typical
colours, so that it is more resistant to noise. Therefore, U and V are not
adjusted to cause equivalent saturation. This is something that you can
fix with a diagonal matrix before and after each translation... if working
with separate floats, this probably ends up being a pair of [*] boxes on
either just the U or just the V, but I don't know what's the scale factor
that you should use.
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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada
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