A new approach is proposed for estimating illuminant colors from color images under an unknown scene illuminant.
The approach is based on a combination of a gray-world-assumption-based illuminant color estimation method and a
method using color gamuts. The former method, which is one we had previously proposed, improved on the original
method that hypothesizes that the average of all the object colors in a scene is achromatic. Since the original method
estimates scene illuminant colors by calculating the average of all the image pixel values, its estimations are incorrect
when certain image colors are dominant. Our previous method improves on it by choosing several colors on the basis
of an opponent-color property, which is that the average color of opponent colors is achromatic, instead of using all
colors. However, it cannot estimate illuminant colors when there are only a few image colors or when the image colors
are unevenly distributed in local areas in the color space. The approach we propose in this paper combines our previous
method and one using high chroma and low chroma gamuts, which makes it possible to find colors that satisfy the gray
world assumption. High chroma gamuts are used for adding appropriate colors to the original image and low chroma
gamuts are used for narrowing down illuminant color possibilities. Experimental results obtained using actual images
show that even if the image colors are localized in a certain area in the color space, the illuminant colors are accurately
estimated, with smaller estimation error average than that generated in the conventional method.