Tone mapping techniques and color image difference in global illumination

Abstract

Tone mapping is the final step of every rendering process. Due to nonlinearities of display devices, reduced color gamuts and moderate dynamic ranges it is necessary to apply some mapping technique on the computed radiances. We described mapping methods that are considered to be state of the art today, and some newly developed techniques. The main contributions of this thesis in tone mapping techniques are interactive calibration of contrast and aperture, minimum information loss methods and incident light metering. The interactive calibration technique makes it possible to display a desired scene lighting atmosphere if the radiance values are rendered in fictitious units. Minimum information loss techniques are based on the photographers' approach. The mapping function is applied only on a certain radiance interval, which is chosen automatically. The original contrast of all pixels inside the interval is preserved. The incident light metering method was inspired by the photographers' approach, too. This method makes it possible to reproduce original colors faithfully, even if the average reflectance of a scene is very low, or very high, which is not the case with other methods. Finally, this thesis ends with a color image difference algorithm. A good image metric is often needed in computer graphics. The method described here is a perception based metric that operates in the original image space. This is the only method that stresses distance dependency explicitly.