Metamer Constrained Color Correction

Abstract

At an early stage in almost all color reproduction pipelines, device RGBs are transformed to CIE XYZs. This transformation is called color correction. Because the XYZ color matching functions are not a linear combination of device spectral sensitivities there are some colors which look the same to a device but have quite different XYZ tristimuli. That such device metamerism exists is well known, yet the problem has not been adequately addressed in the color correction literature. In this article, we examine in detail the role that metamers play in developing a new color correction algorithm. Our approach works in two stages. First, for a given RGB we characterize these possible camera metamers. In the second stage this set is projected onto the XYZ color matching functions. This results in a set of XYZs any one of which might be the correct answer for color correction. Good color correction results by choosing the middle of the set. We call the process of computing the set of metamers, projecting them to XYZs and performing the selection, metamer constrained color correction. Experiments demonstrate that our new method significantly outperforms traditional linear correction methods. For the particular case of saturated colors (these are among the most difficult to deal with) the error is halved, on average, and the maximum reduced by a factor of four.