[Gegl-developer] babl HCY color space extension

[SBP <vorstar mac com>]

Hi there!

I'm interested in using babl as a color space converter for a software
of mine. I find the HCY (hue, chroma, luma) color space useful, so I
decided to include it in babl in order to migrate my color conversion
codebase to babl.

The extension is based on the work and code of Kuzma Shapran
(https://code.google.com/archive/p/colour-space-viewer), and mimics the
HSV/HSL extensions. I have made a test program as well, using values
from the original implementation passed through babl's gamma-to-linear
conversion routines.

I'd like to submit this extension, but don't know how. Should I send it
as an attachment, or perhaps make a pull request from git?

A couple of points though.

The original implementation uses the Rec. 601 luma coefficients, and as
I'm aware babl prefers the sRGB Y values for the D50 illuminant
(rgb-constants.h). Should I use these instead of the original ones?

While reading the code for the HSV extension I noticed a little
possible improvement. Instead of computing x with fabs and fmod, given
that we have cases for each hue sector, it's possible to predict the
result of these operations and avoid using those functions, which I
suppose would be faster. Already tested with the included test.
Sounds ok? How do I post the patch?

Cheers!

Sirius.

PS. It would be cool to have support in babl for all kinds of color
spaces, thus becoming the standard for color conversions in C (as I
find this niche quite barren...). Is this consistent with the project
goals? So as to make more extensions ;) The list at
https://github.com/scijs/color-space looks rather tasty!