Naturalness and image quality: chroma variation in colour images of natural scenes

The relationship between perceptual image quality and naturalness was studied using colour images transformed in a perceptually uniform colour space. The transformation we employed was chroma variation. To perform this transformation, digitized colour images offour natural scenes were described by their colour point distributions in the CIELUV uniform colour space. A new set of images was created by varying the chroma value of each pixel while lightness and hue-angle were kept constant. In three experiments, subjects judged the perceptual quality, colourfulness and naturalness of all images on a ten-point numerical category scale. Results indicate that both image quality and naturalness are non-monotonically related to colourfulness with an optimum near the original image. In general, a linear relation is found between perceptual image quality and naturalness.