外文翻譯及文獻--基于子帶離散余弦變換dct應(yīng)用于圖像水印的技術(shù)-全文預(yù)覽
【正文】 ferent constraint rules are suggested for the parametric modification of the DCT frequency coefficients. The first one embeds a linear constraint among certain selected DCT coefficients and the second defines circular detection regions according to the given parameters. The watermarks cast by the proposed algorithm are resistant to JPEG pression and filtering. 1. Introduction Digital watermarks in the general context of TV broadcasting and cryptology were discussed in. To avoid the unauthorized distribution of images or other multimedia property, various solutions have been proposed. Most of them make unobservable modifications to images, that can be detected afterwards . Such image changes are called watermarks. The watermark should not alter visibly the image and it should be robust to alterations which may be caused by various image processing techniques. Algorithms proposed for watermarking have been reported in various papers. They are either stochastic or deterministic. These algorithms are either in image intensity domain or in frequency domain. In the middle range DCT frequency coefficients from the 8*8 pixel blocks are used for embedding a constraint. In the signature is embedded in the DCT coefficients obtained after applying the DCT transform in the entire image. An watermarking algorithm has two stages: watermarking casting and detection. By means of watermark casting a specific code assigned to the owner is embedded in the image. In the detection stage the algorithm identifies the given code. Signal detection theory is a wellestablished field with many applications. A watermarked image can be processed by means of various image transformations and processing algorithms which may be able to destroy, intentionally or not, the digital watermark. Image pression is the most likely transformation that an image may undergo. The standard still image pression algorithm is JPEG. JPEG is based on the minimization of the energy in the Discrete Cosine Transform (DCT) domain. In the case of lossy pression, the image suffers information loss in the high frequency domain. In the proposed watermark casting algorithm from, the image is partitioned in 8*8 pixel blocks similar to the JPEG algorithm. The watermarking algorithm consists of two steps. The first step selects certain blocks according
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