The Alternating Least Squares Technique for Nonuniform Intensity Color Correction

Color correction involves mapping device RGBs to display counterparts or to corresponding XYZs. A popular methodology is to take an image of a color chart and then solve for the best 33 3 matrix that maps the RGBs to the corresponding known XYZs. However, this approach fails at times when the intensity of the light varies across the chart. This variation needs to be removed before estimating the correction matrix. This is typically achieved by acquiring an image of a uniform gray chart in the same location, and then dividing the color checker image by the gray-chart image. Of course, taking images of two charts doubles the complexity of color correction. In this article, we present an alternative color correction algorithm that simultaneously estimates the intensity variation and the 33 3 transformation matrix from a single image of a color chart. We show that the color correction problem, that is, finding the 33 3 correction matrix, can be solved using a simple alternating least-squares procedure. Experiments validate our approach. VC 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 232–242, 2015; Published Online 24 May 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/col.21889