[PD] colour and brightness (Was: Re: [GEM-dev] Why is [hsv2rgb] implemented as an abstraction?)
claudiusmaximus at goto10.org
Wed Dec 12 03:15:53 CET 2007
Redirecting from GEM-dev as it's not about GEM development...
Mathieu Bouchard wrote:
> if you do a polar transform on YUV, you have something easier, faster
> and more correct all at once. I usually just skip the polar transform:
> if you apply rotations directly on YUV values, you can make very
> believable hue shifts.
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.
> HSV is dubious in part because the apparent brightness at maximum
> so-called value is very variable and seems to peak high or low at
> secondaries or primaries: compare yellow (brightness 89%) and blue
> (brightness 11%). this really makes HSV suck sometimes. YUV does not
> have this problem.
I tried a hybrid approach:
"$1 1 1"
"0.5 $2 $3"
and that seems to eliminate the bad brightness mismatches, at the cost
of some colours seeming a bit washed out (blue) or muddy (yellow).
Attached image demonstrates the difference.
Wondering if there's some set of "perceptual brightness curves" similar
to the "isophonic curves"  there are for perceived loudness of
different frequencies and levels led me to , which seems very
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