Method of creating non-patterned security elements

摘要

Described herein is a method to encode infrared (IR) security watermarks using a named color dictionary within a PDL in a device independent manner. A set of colors is chosen that lies within the common gamut of printing devices and then defined in a device-independent color space. For each color and output device, a metameric pair of device colorant values corresponding to minimum and maximum black (K) is obtained using inversion techniques. These extremes are selected in order to obtain the maximum perceivable IR signal. The metameric pair sets are processed to extract a smaller subset that satisfies certain criteria, including bounds on the K difference, total ink area coverage, and deviation from the neutral axis. The final data is then stored in resource files that link fixed device-independent IR color names to pairs of variable device-dependent colorant values.

主权项

1. A computer-implemented method of encoding infrared security watermarks with a set of printing devices, the method comprising:
choosing a set of colors that lies within a common gamut of the set of printing devices and is defined within a device-independent color space, wherein input colors are related to output physical colorant combinations using transformation tables and interpolation between measured values; for each color in the set of colors and for each printing device in the set of printing devices, obtaining a metameric pair of device colorant values corresponding to minimum and maximum black (K) values is selected; processing the metameric pair sets to extract a smaller subset of colorant values that satisfies a given set of criteria; storing data associated with the smaller subset of colorant values that satisfies a given set of criteria in resource files in a database that link fixed device-independent infrared color names to pairs of variable device-dependent colorant values, the data having two distinctly named entries that refer to the same color bit in Lab color space to two different colorant combinations having a differential IR response; and using at least one of the printing devices and the stored data to generate an infrared readable text.