Perceived image contrast and observer preference

A large-scale investigation into the perception of contrast in color images was performed. Experiments were performed to determine the influence of image lightness, chroma, and sharpness transforms on perceived image contrast and observer preference. The influence of lightness, chroma, and sharpness manipulations was investigated separately by independent soft-copy, paired-comparison tests of contrast perception and image preference. The perception of contrast between images of different transforms and different subject matter was also investigated as was the perception of image contrast relative to the most preferred image manipulation. In all, five experiments of contrast perception and four experiments of image preference were performed by at least thirtytwo observers each. Results of the lightness, chroma, and sharpness-contrast experiments indicate perceived image contrast is a function of multiple image characteristics as opposed to simply being a function of the dynamic range of image intensity. In the Lightness-Contrast Experiments, images of identical white and black points were scaled to have significant differences in contrast based on their manipulations from the original image. In the Chroma-Contrast Experiments, images of identical lightness channels were scaled to have significant differences in perceived contrast due to relative chroma amount. In the Sharpness-Contrast Experiments, images of identical white and black points were scaled to have significantly different levels of perceived contrast due to sharpness. In the Scale- Linking Experiment, it was found that images of the above manipulations could be scaled similarly for perceived contrast. All scales of perceived contrast and image preference were found to be image independent among pictorial images. Empirical modeling of perceived contrast indicates differences in perceived contrast can be quantified as a function of image colorimetry, independent of original scene information