CSS Level 4 Gamut mapping

css_l4_gamut.py

from coloraide.gamut import Fit, clip_channels
from coloraide.util import NaN


class OklchChroma(Fit):
    """Lch chroma gamut mapping class."""

    NAME = "oklch-chroma"

    EPSILON = 0.0001
    LIMIT = 0.02
    DE = "ok"
    SPACE = "oklch"
    SPACE_COORDINATE = "{}.chroma".format(SPACE)
    MIN_LIGHTNESS = 0
    MAX_LIGHTNESS = 1

    @classmethod
    def fit(cls, color, **kwargs):
        """
        Gamut mapping via Oklch chroma.
        """

        space = color.space()
        mapcolor = color.convert(cls.SPACE)
        lightness = mapcolor.lightness

        # Return white or black if lightness is out of range
        if lightness >= cls.MAX_LIGHTNESS or lightness <= cls.MIN_LIGHTNESS:
            mapcolor.chroma = 0
            mapcolor.hue = NaN
            clip_channels(color.update(mapcolor))
            return

        # Set initial chroma boundaries
        low = 0.0
        high = mapcolor.chroma
        clip_channels(color.update(mapcolor))

        # Adjust chroma (using binary search).
        # This helps preserve the other attributes of the color.
        # Compress chroma until we are are right at the JND edge of being out of gamut.
        if not mapcolor.in_gamut(space):
            while True:
                mapcolor.chroma = (high + low) * 0.5

                if mapcolor.in_gamut(space, tolerance=0):
                    low = mapcolor.chroma
                else:
                    clip_channels(color.update(mapcolor))
                    if mapcolor.delta_e(color, method=cls.DE) < cls.LIMIT:
                        break
                    high = mapcolor.chroma

class Color2(Color): ...

Color2.register(OklchChroma, overwrite=True)

Color('green').interpolate('blue')
Color2('green').interpolate('blue')
Color('red').interpolate('blue', space="oklch")
Color2('red').interpolate('blue', space="oklch")