Spectral color matching to a device-independent color value

Abstract

Methods, systems, and apparatus for mapping a nonspectral representation of a target color, such as an input color tuple, to a set of concentration values for a set of device-specific colorants. The invention includes using the input color tuple to derive a first set of colorant concentration values from a color lookup table; and refining the first set of colorant concentration values by an iterative non-linear process to generate a final set of colorant concentration values. The first set of colorant concentration values can derived by using an input color tuple as an index to obtain grid-point concentration values at two grid points of the color lookup table and calculating the first set of colorant concentration values as a linear interpolation of the grid-point concentration values. In an implementation that provides a color function table of color-additive function values, the iterative non-linear process can include iteratively (a) calculating an interim color tuple from an interim set of colorant concentration values and the color function table, the initial interim set of colorant concentration values being the first set of colorant concentration values, and (b) deriving an interim set of colorant concentration values from a difference between the input color tuple and the interim color tuple. The calculations can include calculating a partial derivative of an error function from the difference between the input color tuple and the interim color tuple; and using the partial derivative to derive a successor interim set of colorant concentration values from a current interim set of colorant concentration values.

Dependencies are inferred from the claim text.