Implement OKLAB color space conversions

[Neraste]

This PR aims to implement the conversions to/from OKLAB and OKLCH color spaces, from the post of Ottosson¹. Inverse of the $M_1$ and $M_2$ matrices of the XYZ - OKLAB conversion were computed with Python's numpy.linalg.inv.

I’m not sure about the scale of OKLAB and OKLCH. Components are usually in the $[0, 1]$ range, and I multiplied most of them by 100, because the final functions convert.xxx.yyy are supposed to output integers. This value is usually not reached however (for OKLAB’s $a$, and $b$, and OKLCH’s $c$, see the updated readme for bounds).

Progress:

• XYZ - OKLAB;
• RGB - OKLAB;
• OKLAB - OKLCH;
• Factorization of sRGB non-linear transformation and its inverse;
• Add/complete bounds in documentation.

Fixes #111.

Footnotes

1. Ottosson, Björn (23 Dec 2020), "A perceptual color space for image processing", visited on 2025-05-07. ↩

[Qix-]

Thanks, this is incredible work! Released as 3.1.0. Really appreciate the PR!

[Neraste]

You're welcome!