Constructing device-state tables for inkjet printing

Abstract

An automatic system forms color LUTs (or LUT-forming data) for automated reference—typically in error diffusion (ED). A first aspect is for printers with six or more colorants. Three ramps, for different basic colorants, are photometrically measured; mainly just those results yield a transform from 3D color to system colorants. In a second aspect, some device-state candidate colors are chosen for black replacement. In a variant the choice is subject to (1) maintaining some chromatic colorant in each pixel with black; or (2) modifying use patterns to avoid alternative use of composite black vs. black; or (3) adjustments to allow for composite nonequivalence to black. A related third aspect allows replacement only if there is a given minimum amount of composite. In a fourth aspect, candidate states are dropped that have small changes in number of quanta per pixel, or no companion light colorant quantum with each dark one, best eliminating those with too many quanta of each or all colorants. In a related fifth aspect, one state is assigned to each major entry based on, at a gamut surface except at the dark end, favoring states nearer the surface over those nearer a desired major entry; and at the neutral axis, especially its dark end, favoring real black. Other assigning is best done by entry nearness. In a sixth aspect preferably 1D LUTs are formed for finding major entries based on an input-color spec, not monotonic in entry assignment to indices; precomputed ED distributions attach to indices. In a seventh aspect a state LUT formed to access states based on input specs is used to print nominal neutral colors and measured results used to adjust access. In an eighth facet related to the first, the ramps correspond to fundamental combinations of single colorants, e. g. secondaries.