CHROMA VARIATIONS AND PERCEIVED QUALITY OF COLOR IMAGES OF NATURAL SCENES

Transformations of natural images in the perceptually uniform CIELUV c olor space have been investigated with respect to perceptual image qua lity. To this end, digitized color images of four natural scenes were described on the basis of their color point distributions in the CIELU V color space. A new set of images was created by varying the chroma v alue of each pixel while the lightness and hue angle were kept constan t. The chroma was changed in two different ways. (1) through the addit ion or subtraction of the same amount of chroma to or from the chroma value of each pixel; (2) through multiplication of the chroma value of each pixel by a constant. In thr-ee experiments, subjects judged the perceptual quality, colorfulness, and naturalness of the images on a t en-point numerical category scale. The results indicate that colorfuln ess is the main perceptual attribute underlying image quality when chr oma varies. Colorfulness itself was Sound to depend on both the averag e chroma and its variability. In general, the subjects preferred sligh tly more colorful images to the original ones. The perceptual quality of the images was found to be closely related to the naturalness of th e images. (C) 1997 John Wiley & Sons, Inc.