The calculation of color difference is one of the most basic techniques in image processing fields. For example, color clustering and edge detection are the first steps of most image processes and we compute them by using a color difference formula. Although the CIELAB color difference formula is a commonly used one, the results obtained with it are not in accordance with human feelings when the color difference becomes large. In this paper, we have performed psychophysical experiments on color similarity between colors that have large color differences. We have then analyzed the results and found that the similarity is strongly restricted by the basic color categories. In accordance with this result, we propose a new color similarity metric based on the CIEDE2000 color difference formula and categorical color perception.
