| 摘要 |
An encoding system includes data in an underlying image by controlling or modifying halftone settings, which are used in the associated printing color process to produce a hard-copy document or an on-screen image. The system encodes the data into the image by selectively varying, in accordance with the data, the order of various color channels, and/or the screen angles and/or spatial frequencies, or scales, of associated halftone screens. The system encodes an N-bit payload in the image by modifying the halftone settings of certain or all of the color channels in accordance with the data. The system thus uses the color channels also as "data channels." The system prints the encoded image by incorporating the modified halftone settings into the respective halftone screens, and applying the inks in a conventional manner. To recover the data from the image, the system performs a Fourier transform of the halftone screen and determines the halftone screen angles and spatial frequencies associated with the various channels based on the angle and radius of associated energy peaks in the Fourier plane. Thereafter, the system associates data symbols with the halftone parameters. The encoding system may also authenticate the image by including therein a counterfeit check code that has a predetermined relationship with the data. The system then checks authenticity by determining if the decoded counterfeit check code has the same relationship with the decoded data. Alternatively, the system may encode halftone parameters or information that indicates the halftone parameters in a digital code that is encoded onto or proximate the image. The system then checks authenticity by determining if the settings used in the printing of the image correspond to the parameters decoded from the image and/or parameters associated with the decoded information.
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