Multi-Ink Color-Separation Algorithm Improving Image Quality

Abstract

Current color-printing technologies often use more than the minimum three or four inks: cyan, magenta, yellow, and black (CMYK). When the number of inks exceeds three, there is the usual color-management one-to-many mapping problem. Additional constraints have to be applied to achieve greater determinacy. For CMYK ink sets, the black ink is constrained. When additional chromatic inks are added, traditional methods subdivide either colorimetric or colorant space to achieve a one-to-one mapping. However, these traditional methods cannot take advantage of all the ink combinations available for improving image quality. Alternatively, additional constraints can be defined as perceptual metrics such as color constancy, graininess, color gamut, and color look-up table smoothness. A novel color separation algorithm was developed in order to optimize color look-up tables for improved image quality. This algorithm was tested with a six-pigmented ink (CMYKGO), ink jet proofing printer. Various four and a six-ink look-up tables were created based on different metrics. The perceptual performances of these look-up tables in color reproduction accuracy, color inconstancy, graininess and gamut volume were evaluated. The results show that the additional inks not only extend color gamut but also provided the potential to improve print quality.