We have studied the preference judgement of pictorial images with two types of population: image experts and naive observers. We used eight images of indoor and outdoor scenes. The images were first presented to image experts working in pre-press companies. We asked them to improve the images the way they preferred and to comment on their manipulations. They saved the intermediate enhanced versions they judged important. In the second part of this study, we showed those different versions of the same image produced by experts to naive observers. We used a pair comparison protocol in which all possible pairs were presented. The question was "which image do you prefer?" Observers told us their criteria for choosing an image. Several results emerged from this study. To enhance an image, an expert divides it into large zones of interest, which mainly correspond to natural colors. Likewise, when judging an image for preference, naive observers principally focus on natural colors like sky, skin or grass when present. Both experts and naives do not focus on parts if no memory colors are associated. The segmentation process into zones permits to first adjust the illuminant and then to correct the other parts with respect to the plausibility and coherence of the whole image. Further studies are necessary to correlate the chromatic signal in the retina to those data.
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