Synthesis of authenticable color multi-halftone images
The present invention enables creating authenticable continuous tone color multi-ink multi-halftone images offering means of verifying their authenticity. The invention relies on color halftones, color separation into different ink surface coverages for different halftoning methods, mapping of an input gamut into a gamut defined by a set of inks, calculating the optimal boundary between region halftones created with different halftoning methods, and color multi-halftone image generation. The basic authentication is performed by examining the color multi-halftone image under a reference illumination and verifying that the message incorporated within the color multi-halftone is hidden and revealed under a different illumination.; Authentication can further be performed by observing the color multi-halftone image both in reflection and transmission modes and verifying that in one of these modes the message is hidden and that in the other mode the message is revealed.