| 摘要 |
The present invention is a method and apparatus for watermarking text or vector graphics documents. It is based on character-wise or vector graphics element-wise grayscale or color modulation. At high resolution, halftone or dither modulation can also be used in addition or in place of grayscale/color modulation, for printed representation of electronic document. For the detection, the document is acquired through an acquisition device, document segmentation is performed, characters/elements are segmented, the watermark signal is estimated and the information is decoded. Although the proposed scheme mostly addresses the watermarking of hard-copy documents, it can easily be integrated into electronic document editing and acquisition tools, and the watermark is attached to the document electronic version. The invention is applicable either using expensive high-resolution printing and acquisition devices, either using common cheap low-resolution devices, depending on the application needs. The proposed scheme is suitable for example to the protection of security documents, contracts, technical and commercial documentation; it can use any physical support like paper, cellulose, or plastic; it can be used for copy protection, authentication, or tamper proofing; finally it can also be applied to other non security-related applications, such as document tracking, as well as document embedded annotation and watermarked-assisted automatic processing.
|
