Patent ID: 8610958

Claim:
A computer-based method for producing a printed authenticable color multi-ink multi-halftone image, comprising the steps of (a) selecting two halftoning methods h 1 and h 2 having different halftoning parameters; (b) selecting a color input image and an input color gamut; (c) positioning a message and determining its foreground and background regions within said input image; (d) gamut mapping by computation said input color gamut onto a printable destination gamut yielding gamut mapped input colors; (e) under a selected reference illuminant, establishing with an accurate ink spreading enhanced color prediction model colorimetric to ink surface coverages mappings m 1 and m 2 between desired input colorimetric values and ink surface coverages for each of said respective halftoning methods h 1 and h 2 ensuring that the gamut mapped input colors yield substantially similar colorimetric values when halftoned with said halftoning method h 1 and halftoned with said halftoning method h 2 ; (f) by relying on said colorimetric to ink surface coverage mappings m 1 and m 2 , separating by computation the gamut mapped input color image into multi-valued ink separations s 1 to be halftoned by said halftoning method h 1 and into multi-valued ink separations s 2 to be halftoned by said halftoning method h 2 ; (g) halftoning said multi-valued ink separations s 1 with said halftoning method h 1 and s 2 with said halftoning method h 2 yielding respectively halftoned p 1 and p 2 ink separation layers; (h) merging said message foreground and background regions of the halftoned ink separation layers p 1 and p 2 into merged ink color separation layers q by computing optimal boundaries between said message background regions rendered with said halftoned ink separation layers p 1 and said message foreground regions rendered with said halftoned ink separation layers p 2 ; (i) printing said merged ink color separation layers q, thereby obtaining said color multi-ink multi-halftone image; where under the selected reference illuminant the message incorporated into the color multi-halftone image is hidden since its foreground and background regions are indistinguishable.