Pixel and spatial mechanisms of color constancy

Color constancy remains an important subject of research on color standards, computer imaging, and human color vision. There are many different theories and algorithms that interpret and predict constancy. This paper analyzes three different approaches that are frequently discussed separately in the literature: pixel-based colorimetric standards of appearance; computer imaging calculations of an object's reflectance; and calculation of appearance using spatial comparisons. This paper compares and contrasts these approaches. Further, it reviews experiments that measure appearance in color constancy in a variety of situations. A pivotal tool in analyzing models of constancy is the correlation of object's reflectance with appearance. Each approach has different interpretation of this correlation. Using measurements of constancy with particular attention to reflectance, illumination, and appearance helps us to see the successes and limitations of each constancy approach.