Color laser engraving and digital watermarking
View Patent ↗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.
1. A method of color laser exposing a document, the document comprising a multi-layer structure including a surface layer and one or more sub-layers, the one or more sub-layers including coloring, said method comprising:
receiving the document; and
selectively providing openings in the surface layer with a laser to expose one or more of the sub-layers, wherein the coloring is perceptible through the openings, and
wherein the laser is restricted so as to move only in a parallel manner relative to a surface of the document and in distance segments that correspond to sub-pixel and pixel sizes in the sub-layer, and wherein a location of the laser is used to choose an appropriate color channel, and a number of openings created for each pixel is used to represent intensity of a color channel.
2. A method of marking a document which is to receive laser engraving, said method comprising:
providing one or more sub-layers, the one or more sub-layers to include coloration;
providing variations in the coloration in terms of at least one of color intensity and color contrast, the variations conveying a machine-readable plural-bit message; and
arranging a surface layer over the one or more sub-layers, wherein the surface layer obscures the plural-bit message until laser engraving of at least a portion of the surface layer, after which the plural-bit message is machine-readable with optical scanning of the document.
3. The method of claim 2 wherein the plural-bit payload comprises a modulated pseudorandom noise sequence.
4. The method of claim 2 , further comprising laser engraving the document, wherein the plural-bit message becomes machine-readable with analysis of optical scan data representing a document area that received the laser engraving.
5. The method of claim 4 , wherein a laser used for laser engraving comprises a multi-nozzle laser.
6. The method of claim 5 , where each of the nozzles comprises an optical fiber.
7. The method of claim 4 , wherein a laser used for laser engraving comprises a diffraction grating.
8. The method of claim 2 , wherein the machine-readable plural-bit message comprises a digital watermark component.
9. A method of providing a color image or pattern on media, the document comprising a multi-layer structure including a surface layer and one or more sub-layers, the one or more sub-layers including coloring, said method comprising:
receiving the document; and
selectively providing openings in the surface layer to expose one or more of the sub-layers, wherein the coloring is perceptible through the openings to provide the color image or pattern, wherein the openings are washed open after a curing process.