[cairo] alpha blending

James Cloos cloos at jhcloos.com
Wed Mar 25 12:33:38 PDT 2015

>>>>> "BS" == Bill Spitzak <spitzak at gmail.com> writes:

BS> There are a couple problems:

BS> First there is "coverage" values which are calculated by the filling
BS> algorithm. These in fact are not gamma corrected, .5 should mean
BS> .5. All masks and alpha channels are coverage values

In case I wasn't clear, the bug I referenced (and therefor my query
here) were only about changing the way A is combined, and leaving the
R, G & B as they are.

Would that still lead to the issues you noted were the existing OPs

That being asked, the bug's proposal, then, is little different than
converting everything to linear on input and back to gamma values on
output, yes?

Except that cairo explicitly does not treat alpha as gamma-corrected
because unlike PDF it uses the one value for a combination of coverage
and transparancy?

Therefore gamma-correcting alpha is contrary to cairo's design? 

James Cloos <cloos at jhcloos.com>         OpenPGP: 0x997A9F17ED7DAEA6

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