Chromatic Adaptation

Description

CAT plugins chromatically adapt a given XYZ coordinate from its current reference white point to a new desired white point. This is useful during conversion when one color space is converted to another color space that uses a difference reference white.

Plugin Class

Plugins are created by subclassing coloraide.cat.CAT.

class CAT(Plugin, metaclass=ABCMeta):
    """Chromatic adaptation."""

    NAME = ""

    @abstractmethod
    def adapt(self, w1: tuple[float, float], w2: tuple[float, float], xyz: VectorLike) -> Vector:
        """Adapt a given XYZ color using the provided white points."""

Once registered, the plugin can then be used via chromatic_adaptation by passing its NAME via the method along two white points (as XYZ values): w1 as the current white point and w2 as the target white point.

It should be noted that chromatic_adaptation is not usually directly used by the user, so a more likely approach is to override the DELTA_E parameter of a subclassed Color object to specify the plugin as the default for chromatic adaptation.

Von Kries CAT

Currently, ColorAide only ships with Von Kries based adaptation methods. If it is desired to create a Von Kries based plugin, it is recommended to subclass the VonKries class which is based on CAT. When subclassing a VonKries based CAT, the NAME and a MATRIX must be provided. The general calculations related to the source and target white point, will automatically be calculated and an appropriate matrix and inverted matrix will be returned to perform the adaptation without any additional logic.

class Bradford(VonKries):
    """
    Bradford CAT.

    http://brucelindbloom.com/Eqn_ChromAdapt.html
    https://hrcak.srce.hr/file/95370
    """

    NAME = "bradford"

    MATRIX = [
        [0.8951000, 0.2664000, -0.1614000],
        [-0.7502000, 1.7135000, 0.0367000],
        [0.0389000, -0.0685000, 1.0296000]
    ]