CAT stands for Cromatic Adaptation Transform.
Chromatic adaptation means that the human eye performs an automated white balance. Colour is thus perceived by the human observer quite independently of the colour temperature; a white shirt looks the same white to us under fluorescent light as it does under incandescent lighting, a red rose is similarly red to humans under both lights.
The Cromatic Adaptation Transform (CAT) is a mathematical process in colour processing that simulates the adaptation of colour perception to different light sources. It is based on the natural phenomenon of colour adaptation, in which the human eye adapts to changing light conditions as described above in order to perceive colours consistently. In digital image processing, CAT is used to transform the colours of an image so that they appear constant under different lighting situations such as natural or artificial light.
CAT is used in colour science and image processing to harmonise the colour representation on different devices such as cameras, monitors or printers and to ensure uniform colour perception. For this purpose, the colour values are adapted to the conditions of a reference light source, usually the standard illuminant D65.
The most common CAT models, such as Bradford and von Kries, use different mathematical approaches to calculate the light adjustment. This process is particularly important in digital photography, for the colour calibration of devices and in image processing in order to ensure precise and consistent colour reproduction.
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