Color laser engraving and digital watermarking

摘要

A color laser engraving method engraves a document including a surface layer and one or more sub-layers. The sub-layer includes different colors and orientations of ink. A laser provides openings in the surface layer-to expose color ink in the sub-layer-to create color images and/or text. The different orientations of the colored inks include, e.g., circular, linear and overlapped groupings of ink. A sub-layer preferably includes many repeated instances of the grouping. A digital watermark is embedded in a document via transfer of the digital watermark in an embedded image or text, or by pre-embedding the document via altering intensity of colored inks on the original document card stock. A digital watermark can be carried via modulation with a pseudo-random noise sequence.