White Point - White Point Conversion

White Point Conversion

Further information: Chromatic adaptation

If the color of an object is recorded under one illuminant, then it is possible to estimate the color of that object under another illuminant, given only the white points of the two illuminants. If the image is "uncalibrated" (the illuminant's white point unknown), the white point has to be estimated. However, if one merely wants to white balance (make neutral objects appear neutral in the recording), this may not be necessary.

Expressing color as tristimulus coordinates in the LMS color space, one can "translate" the object's color according to the Von Kries transform simply by scaling the LMS coordinates by the ratio of the maximum of the tristimulus values at both white points. This provides a simple, but rough estimate. Another method that is sometimes preferred uses a Bradford transform or another chromatic adaptation transform; in general, these work by transforming into an intermediate space, scaling the amounts of the primaries in that space, and converting back by the inverse transform.

To truly calculate the color of an object under another illuminant, not merely how it will be perceived, it is necessary to record multi-spectral or hyper-spectral color information.

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