Abstract
PURPOSE: The apparent color shifts under changes in ambient illuminant, while hue and saturation of colors are defined with respect to achromatic points under a given illuminant. Without the correct estimation of achromatic point locus, it is impossible to estimate the object color under a colored illuminant. The present study introduces a simple model of shifts in achromatic point locus under a given colored illuminant.
METHODS: The achromatic point locus under a colored illuminant forms a line parallel to the lightness axis when plotted in a CIE LAB space normalized to D65. The achromatic point locus was approximated by the illuminant chromaticity at L* around 25–30. Then we applied von Kries coefficients in each lightness plane to align the achromatic points to the lightness axis. This operation transfers chromaticity of image to an apparent color of in the scene where the image was obtained. To test the efficiency of this model, color appearance of #theDress image was derived by assuming either dress body or lace part appeared achromatic. The efficiency of the color appearance estimates was evaluated by residual errors between output images and results of subjective matches.
RESULTS & DISCUSSIONS: The estimation was successful. In addition, the distribution of optimal image in the parameter space (illuminant color and intensity) showed that individual difference in apparent color seem to have a large diversity than just a bifurcation between ‘blue/black’ or ‘white/gold.’ The comparison with CIE CAM02 and RLAB showed that our method yields better color reproduction in the darker part.