The Influence of Luminance on Local Tone Mapping

We study the influence of the choice of color space for local tone mapping methods. Many local tone mapping methods do not perform well when applied independently to the three color channels of an RGB image. A common solution is to only treat the luminance channel. However, the question of which color space provides the most suitable luminance definition has not been addressed. The correlation between luminance and chrominance is known to have an influence on the rendered image but the relation between a measure of correlation and the appearance of the image has not yet been found. We consider four color transforms and introduce a measure to evaluate how well they decorrelate luminance and chrominance information. We apply two local tone mapping algorithms to the luminance channel given by the four transforms and visually compare the results. As each transform leads to another luminance definition, the resulting color images will be different as well. Our results confirm that less correlation between luminance and chrominance results in better performance of the local tone mapping algorithms. Namely, they provide a better increase in local contrast in the luminance channel and less hue shifts. However, we show that a perfect decorrelation is not always necessary.