[FEATURE]: Add "Oklch" colourspace.

[dofuuz]

Description

Oklab and Oklch has been added to CSS Color Module Level 4. But, only Oklab is available for Colour.

Adding Oklch will be great for convenience.

[KelSolaar]

Hi @dofuuz,

There is already an issue for this here: https://github.com/colour-science/colour/issues/868

Cheers,

Thomas

[dofuuz]

@KelSolaar Oklch is different from Okhsl or Okhsv. So it's not a duplicate.

[KelSolaar]

Ah yes sorry, my bad! I misread the space name... We probably won't implement this one because it is a simple polar representation that we can perform on any "Jab" like spaces: https://github.com/colour-science/colour/blob/develop/colour/models/common.py#L163

my_oklch = colour.models.Jab_to_JCh(my_oklab)

[dofuuz]

@KelSolaar Oh, I didn't know that conversion function exists. I searched for 'lab to lch'. 🤣

Anyway, providing 'Oklch' would be nice for convenience. I'll leave the decision to the contributors.

[KelSolaar]

This is a good discussion. If we do it for Oklab or JzAzBz, we might as well do it for IPT, ICtCp, ICaCb, ProLab, etc... we have so much opponent-based spaces that it becomes quite a maintenance burden as we ideally need to write tests, docs, etc.., this is why I rolled the colour.models.Jab_to_JCh and its inverse definitions.

[tjdcs]

i agree that there is value in doing this. But I wonder if it can be done by decoration with a "metaclass" or some other meta programming. (please forgive the reference to a very specific C++ concept in a much more general meaning)

[KelSolaar]

Something along those lines would work for example but it gets close to a steam factory rapidly:

import colour
import sys
from colour.models import Jab_to_JCh, JCh_to_Jab
from colour.utilities import copy_definition

__all__ = []

CALLABLES_LCH = {
    "Oklab_to_Oklch": (Jab_to_JCh, "The docstring..."),
    "Oklch_to_Oklab": (JCh_to_Jab, "The docstring..."),
}

for name, (callable_, docstring) in CALLABLES_LCH.items():
    callable_.__doc__ = docstring
    _module = sys.modules["colour.models"]
    setattr(_module, name, copy_definition(callable_, name))

print(colour.models.JCh_to_Jab)
print(colour.models.JCh_to_Jab.__name__)

print(colour.models.Oklch_to_Oklab)
print(colour.models.Oklch_to_Oklab.__name__)

<function JCh_to_Jab at 0x13c204220>
JCh_to_Jab
<function JCh_to_Jab at 0x11ce60680>
Oklch_to_Oklab

We have something magic like that here actually: https://github.com/colour-science/colour-datasets/blob/develop/colour_datasets/loaders/kuopio.py#L498

[tjdcs]

I think there is something you could do in the oklab module to automatically define the variable names too. Something like

add_polar_conversion_this_module("Oklab", "Oklch")

[Aonodensetsu]

i use oklch quite regularly, and if i was provided a full list of spaces that fall under this category i would be willing to add them to the graph manually Oklab, JzAzBz, IPT, ICtCp, ICaCb, ProLab were mentioned so far

[KelSolaar]

This was implemented! :)

[Aonodensetsu]

Great, can this be expected to appear on the README graph and on PyPi? I tried making a graph with networkx/matplotlib but the nodes overlap, so my guess is another tool was used for it prior. I updated my pyproject to pull the library from github, so no pressure on publishing.

[KelSolaar]

The graph is generated here: https://github.com/colour-science/colour/blob/develop/utilities/generate_plots.py#L166

That being said, I can see that the last build failed on RtD. I will check what is going on.

[KelSolaar]

Note that I will refine some names in a future commit, Oklch won't change though!