Re: [Public WebGL] Premultiplied alpha blending and issues with color accuracy

[Thor Harald Johansen <thj@thj.no>]

> If all of these suggestions that you and Ben have so helpfully provided
> and explained to me should work out for me, I'll have a piece of
> software you can do high quality drawing in ready in not too long.

Oh, and on the sunny side of things, OpenGL and shaders are giving me 
new options in some other areas:

- I'm actually using the JPEG2000 RCT color space for my color channels, 
storing Y, Cb and Cr in the R, G and B channels respectively. This has 
the interesting side effect of allowing me to treat color like a complex 
number. Rotating (Cb, Cr) takes you through the color circle. Altering 
the magnitude alters the saturation. Linear interpolation gives pleasing 
results, because even complementary colors share the same brightness, so 
gamma encoded colors don't skew it as much.

- In addition to this, I have been experimenting with gamma. Linear 
gamma, x^(1/2.2), would provide perfect color mixing even with RGB, but 
this makes dark grays look like absolute s**t at 8 bits per channel. I 
then tried a gamma of 1.8, x^(1.8/2.2), the one used by old Apple 
machines. The RCT color mixing was already good, but this took it up 
another notch, while still rendering dark shades of gray without 
banding. I have yet to add the linear section specified in sRGB. 2.2 is 
an adequate approximation for the time being.

If it seems like I'm spending too much time on these details, you 
haven't heard hundreds of artists complain about the muddy color mixing 
in their painting tools yet. ;)

Thor

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