Psychophysical experimentation was performed on the perceived contrast of color images and its effect on observer preference. Goals of this research included the following: investigation into the roles of image lightness, chroma and sharpness manipulations on perceived image contrast; modeling the perception of image contrast with physical image parameters; the relation of perceived contrast of an image to the most preferred version of that image; and the generation of a large scale image contrast data set for later use in image difference/quality metric development. These goals were undertaken by administration of soft copy paired-comparison experiments of perceived image contrast and observer preference. These tests were performed over four months, by more than seventy observers. Perceived image contrast was determined to be scalable with respect to lightness, chroma, and sharpness manipulations. Perceived image contrast scales were image independent between five pictorial images. Significant contrast differences between images of identical white and black points were perceived, demonstrating that image white and black points do not solely determine image contrast. Significant image contrast differences were found between full color images and their achromatic versions, thus demonstrating that perceived image contrast is a function of image chroma information. It was also shown that the perceived contrast of achromatic images is higher than perceived contrast of very low chroma images. Perceived image contrast was empirically modeled using physical parameters of the images. Values based on image lightness, chroma, and sharpness information were used to model the perception of image contrast in a relative and stand-alone sense. In Reproduction Versus Preferred (RVP) contrast modeling, image parameters were taken relative to the most preferred version of the image. In Single Image Perceived (SIP) contrast modeling, parameters of single images were fit to scales of perceived contrast. RVP contrast modeling illustrated that image contrast is perceived relative to the most preferred version of that image. SIP contrast analysis indicated differences in perceived contrast were perceived image independent, and reinforced perception of image contrast relative to the most preferred version of an image. This concept of contrast perception relative to the preferred image indicates image contrast can be described without knowledge of an original scene in the image capture sense or knowledge of an original image in the image reproduction sense.
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
The Journal of Imaging Science and Technology 47N6 (2003) 494-508
RIT – Main Campus