NATURALNESS AND IMAGE QUALITY - SATURATION AND LIGHTNESS VARIATION INCOLOR IMAGES OF NATURAL SCENES

The relation between perceived image quality and naturalness was inves tigated by varying the colorfulness of natural images at various light ness levels. At each lightness level, subjects assessed perceived colo rfulness, naturalness, and quality as a function of average saturation by means of direct category scaling. Colorfulness was found to increa se monotonically with average saturation. The relation between the qua lity/naturalness judgments and average saturation could always be desc ribed by an inverted U-shaped function. A systematic difference was fo und between quality and naturalness judgments. This difference, reflec ting the subjects' preference for more colorful, but, at the same time , somewhat unnatural images, was most noticeable at the original light ness level and diminished with decreasing lightness, in particular bei ng least at the lowest lightness level investigated.