In this paper, we describe our dot-pattern code, which can embed information onto the paper. Its main features are 1) no need to reserve a special room for the code, 2) obscure and unnoticeable, 3) comparatively large information capacity, 4) the absolute coordinates in the paper is measurable. We describe how to embed and detect the information onto / from the paper, and we estimate it by examination. From the examination, we found that our dot-pattern code is applicable to various kinds of papers, printers including ink-jet and scanners. We also found that even when the density of the black dot is greater than 6%, over 8,000 bits could be safely embedded with error rate less than 10-6. We also found that the embedded information could be detected correctly after the paper had been damaged.
Digital watermarking of comic images effectively protects the copyright of the content in electronic book applications. The characteristics of comic images were analyzed to determine the effect of digital watermarking on the line shapes. Modification of the shape edges by conventional watermarking methods can degrade image quality because the human eye is sensitive to the edges. The analysis revealed that slight changes in the black pixels in a comic image are barely perceived by the human eye when the image is displayed on a tablet PC. A method was then developed for embedding watermarks that minimizes modification of the white pixels compared to modification of the black ones. Experimental evaluation showed that this method improves the quality of watermarked grayscale comic images. Watermark robustness was almost the same as that with the conventional method in an assumed use case.
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