Halftone watermarking and related applications
AssigneeDigimarc Corporation
InventorHugh L. Brunk
Life of this patent
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Abstract
Methods embed a digital watermark into a halftone image. One method derives halftone thresholds from a watermark image, and then uses these thresholds to convert target images into watermarked halftone images. A method for measuring digital watermark strength is used for a variety of applications, such as distinguishing original printed documents from copies. In this method, a watermarked signal is processed to extract estimates of error correction encoded bits embedded into the watermarked signal. Then, the error correction encoded bits are decoded to compute a message payload. The message payload is re-encoded to compute error correction encoded bits. A measure of watermark strength is computed from the error correction encoded bits and the estimates of error correction encoded bits.
Claims7
A method of embedding a digital watermark into a halftone image comprising:
- redundantly encoding a multi-bit message;
- transforming the encoded message to a multilevel per pixel watermark image;
- deriving halftone thresholds from the multilevel per pixel watermark image;
- converting a multilevel per pixel target image to a watermarked halftone image by:
- using the multilevel pixels in the target image to select corresponding halftone thresholds from the halftone thresholds derived from the watermark image, and applying the selected thresholds to corresponding multilevel pixels in the watermark image to create the watermarked halftone image of the target image.
Dependencies are inferred from the claim text.