Colourfulness judgments of natural scenes

The purpose of this study was to examine the relationship between colourfulness judgments of images of natural scenes and statistical parameters of the chroma distribution over the images in the CIE 1976 L*u*v* (CIELUV) colour space. A comparative analysis of within-scenes and between-scenes colourfulness assessments was performed. Images were created by varying chroma in the CIELUV colour space while lightness and hue-angle were kept constant. Experiment 1 shows the results of a multidimensional analysis of the differences-scaling in perceived colourfulness. Experiment 2 includes a unidimensional investigation of the direct-scaling of the magnitude of perceived colourfulness. Both experiments confirm that colourfulness judgments highly correlate with a linear combination of the mean of the distribution of chroma values and its standard deviation. That was also verified in Experiment 3 with "Mondrian"-like stimuli (spatially scrambled versions of the images of natural scenes). Colourfulness judgments of natural scenes, but not "Mondrian"-like scenes, brought out systematic differences between observers. In order to interpret and quantify these differences, a model of individual strategies in colourfulness judgments is developed and discussed.