Color Enhancement of Digital Images by Experts and Preference Judgments by Observers

We studied the preference judgment of pictorial images by image experts and naive observers. We first asked image experts to improve pictorial images the way they preferred. Then, we showed the different versions of each image to naive observers and asked them which version they preferred. To enhance an image, an expert divides it into large areas of interest, which mainly correspond to natural colors. To assess their preference judgments, naive observers principally focus on natural colors like sky, skin, or grass when present. A closer analysis of the digital image files showed that the segmentation process used by the experts allows to apply different corrections on the different objects. We used the previous work on memory colors by Yendrikhovskij and we showed that, to enhance an image, an expert moves the color space coordinates of identified zones towards those of memory colors corresponding to the objects being represented. The expert also follows some rules: the corrections must be plausible inside each segment and for the whole image, in relation with the illuminant of the scene. The images are accepted by observers in relation with the presence of memory colors and when the treatment of the whole image seems coherent.