Printing a true-ink reference, and refining gray accuracy, for optimum color calibration in incremental printing

Abstract

Ramps are printed with ink of a particular color, and also nominally in that color but by inks of other colors. A measured actual-ink ramp is a standard to fix the other-colors ramp, and correct other printing in those colors. In one aspect a particular color is gray, actual ink black (K), and other-color inks magenta (M), yellow (Y) and cyan (C). In another aspect, actual ink is red (R), green (G) or blue (B); other colors M, Y and C in respective pairs. For gray/black, the K ramp is a zero-chroma standard to lower composite-black (cK) chroma below ˜2.5 ΔE. A sampling aspect prints for each gray tone plural cK-ink combinations preferably bracketing nominal gray values; and searches these for one nearest the particular gray—or most closely bracketing it, for interpolation—for best match. Bracketing is best optimized, by a color-space pattern centered on nominal. Other aspects are taught.