Watermarking an image in color plane separations and detecting such watermarks

摘要

Colored images are divided into color planes and watermarks are inserted into the individual color planes (321). One or more watermarks can be inserted into one or more of the color planes (323c). In order to print a color image the image is divided into color planes corresponding to the colors of ink used for printing. A separate plate is used to print each color (324c). The different plates must be precisely aligned. Any misalignment will cause blurring in the image and may make it difficult or impossible to read a watermark in the image. Misalignment of the plates can cause the watermark data in one color plane to, in effect, cancel out the watermark data in a different color plane. With the present invention a watermark is inserted into a selected color plane only, thus there is no concellation due to misalignment of color plates. The watermark detection and reading can be done after the image is divided into color planes.