Color Correction by Calculating a Metamer Boundary Descriptor

Color correction describes the transformation process between device RGB values and CIEXYZ resp. CIELab values. In every metamer color reproduction system this is the first color transformation after image acquisition. In general, this mapping is not unique since the spectral sensitivities of most of the devices do not satisfy the Luther condition and because the acquisition and viewing light sources have a different power spectrum. Therefore, there exists a set of colors with different reflectance spectra which result in the same device RGB response (device metamerism), but have different color appearances for an observer under the viewing light source. We present a novel method to determine this metamere subspace (which depends on the device response) in the viewing CIELab space by calculating a Metamer Boundary Descriptor (MBD) matrix. This MBD describes the metamer subspace approximately by storing boundary points of the set in every entry. By calculating the center of gravity of this MBD we get a good color choice in the sense of a small mean error. To calculate the entries of the MBD we use a priori knowledge about the physics of natural reflectance spectra and a linear programming technique. This method improves the performance of targetand regression-based methods especially in the area of saturated colors. Simulation experiments including a comparison with existing methods are given in the text.