A sensor located inside a digital camera is only able to measure the light which is reflected by an object. The reflected light varies with the spectral power distribution of the illuminant. Hence, images taken with a digital camera may show a strong color cast if an incorrect white balance setting has been chosen. Such a color cast may also be due to an automatic white balance not working correctly. In contrast, colors perceived by a human observer appear to be approximately constant. Algorithms for automatic white balance try to mimic this ability and compute a color corrected image which appears to have been taken under an illuminant with a uniform power distribution. I show how color constancy algorithms can be implemented very efficiently on modern graphics processing units. A sensor inside a digital camera measures the light which is reflected from the objects of the scene. Some of the light is absorbed, the remainder is reflected and is able to enter the lens of the camera wher...