A color image database of different scenes under several fixed illuminants is constructed in this paper. It contains images
for 45 scenes captured under illumination of various color, lightness. Some analysis based on the database are described
to find the relationship between chromatic/lightness distribution of images under different illumination. Indexes as
overall mean and SD are introduced, which are reasonable to evaluate image lightness and contrast coordinating to
visually representation. In order to objectively assess the influence of illuminant color to images, investigation on
lαβand r-g chromatic map are explored. An improved hue correlation method is proposed based on , α βmean/SD
statistical analysis, which shows excellent color constancy performance on CPVO measurement. The CPVO
measurement is also established on r-g chromatic peak offset tests in this paper.
Realistic image rendition, concerning on color constancy and lightness, is usually qualified by subjective evaluation,
involving uncertainly psychophysical course. Whether common objective image quality metrics can be adopted to
evaluate the rendition results is studied in this paper. Several common objective image quality metrics such as RMES,
PSNR, and a newly universal one named Q metric are introduced. Experiments show that it's applicable to take images
under standard lighting conditions (e.g. D65) as reference images, which is necessary for objective assessment.
Experiment results confirm that introduced objective image quality metrics can help to evaluate the lightness and color
constancy ability of images, in case of taking images under standard lights as reference images.