Metamer constrained colour correction

At an early stage in almost all colour reproduction pipelines device RGBs are transformed to CIE XYZs. This transformation is called colour correction. Because the XYZ matching functions are not a linear combination of device spectral sensitivities there are some colours 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 colour correction literature. In this paper, we examine in detail the role that metamers play in developing a new colour correction algorithm. Our approach works in two stages. First, for a given RGB we characterise these to fall possible camera metamers. In the second stage this set is projected onto the XYZ colour matching functions. This results in a set of XYZs any one of which might be the correct answer for colour correction. Good colour 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 selection, metamer constrained colour correction. Experiments demonstrate that our new method significantly outperforms traditional linear correction methods. For the particular case of saturated colours (these are among the most difficult to deal with) the error is halved on average; the maximum error is reduced by a factor of 4.