外文翻译及文献--基于子带离散余弦变换dct应用于图像水印的技术(编辑修改稿)

外文翻译及文献--基于子带离散余弦变换dct应用于图像水印的技术(编辑修改稿)内容摘要：

g. In these schemes, the image is being transformed via some mon frequency transform and watermarking is achieved by altering the transform coefficients of the image. The transforms that are usually used are the DCT, DFT and the DWT. A question that occurs in such approaches is the number and the position of the altered coefficients in the frequency representation of the image. Many different ideas have been presented, most of them originating from Cox’s et al system. Piva et al have extended this idea, thus providing a blind detection system. In all these cases the image is being processed as a whole but the number of coefficients altered is not more than 16000, the usual image size being 512x512. Since most of these processes have a statistical background, we would prefer to use as many coefficients as possible. This is why we suggest the use of subband DCT. In section 2, we present the subband DCT, the deposition levels and discuss the casting scheme and parameters. In section 3, we test the reading scheme and examine each band’s individual contribution in the case of no processing and also the final detection results for five mon attacks. We end with the final conclusions in section 2. SUBBAND DCT AND WATERMARK CASTING Jung and Mitra have introduced the subband DCT in 1996. It is a method that involves both wavelets and the Discrete Cosine Transform (DCT). The original image is sub sampled and filtered with the use of a high pass and a low pass filter. The bination of the two filters for each direction (horizontal and vertical) of filtering gives four subbands for each level of deposition. The band that corresponds to low pass filtering in both directions (LL band) can be further subsampled and filtered thus providing another level of deposition. Finally, each of the bands is transformed with the use of the DCT. For our experiments, we had to select the number of deposition levels and the wavelet to be used. We tried different numbers of deposition levels, namely 1, 2 and 3. Experimental results have shown that there wasn’t any significant improvement in the detection results for more levels than one, while at the same time, the image degradation was more easily observed. So we deposed the original image into one level with four bands. This was acplished using the simplest wavelet, tha。