Simplest Color Balance

Abstract

Color balance algorithms attempt to correct underexposed images, or images taken in artificial lights or special natural lights, such as sunset. They also translate the raw R,G,B values given by a CCD or CMOS matrix into more standard perceptual colors.There are many sophisticated algorithms in the literature performing color balance or other color contrast adjustments. The performance of these many color correction algorithms can be evaluated by comparing their result to the simplest possible color balance algorithm proposed here. The assumption underlying this algorithm is that the highest values of R, G, B observed in the image must correspond to white, and the lowest values to obscurity. If the photograph is taken in darkness, the highest values can be significantly smaller than 255. By stretching the color scales, the image becomes brighter. If there was a colored ambient light, for example electric light where R and G dominate, the color balance will enhance the B channel. Thus the ambient light will lose its yellowish hue. Although it does not necessarily improves the image, the simplest color balance always increases its readability.The algorithm simply stretches, as much as it can, the values of the three channels Red, Green, Blue (R, G, B), so that they occupy the maximal possible range [0, 255]. The simplest way to do so is to apply an affine transform ax+b to the each channel, computing aand b so that the maximal value in the channel becomes 255 and the minimal value 0.