Discrete Wavelet Transform Analysis

Chapter – 4 Proposed Solution In previous chapter is about existing watermarking methods DCT and DWT, from that two technique taking the advantages of both technique i.e. as DCT is having smaller processing time and DWT have good robustness. So proposed solution to developed hybrid which is combination of DWT and DCT technique which have better performance then alone DCT and DWT as described below.
4.1 The Combined Discrete Wavelet Transform – Discrete Cosine Transform
By this method taking the advantages of both DWT and DCT method for the watermarking purpose. In this technique first of all taking the DWT of the original image from which will get 4 coefficients of image named

Even very simple attacks such as median filtering or a lossy compression, can destroy the embedded watermark when spatial based methods are involved. Therefore, in this study only frequency based watermarking methods have been considered. The major consideration in frequency based methods is the robustness of the method to different attacks. To achieve a better performance with respect to robustness, watermark should be embedded in the lower or middle frequency contents of the image as far as possible. The reason is that the main watermark attacks change or eliminate high frequency content of the image. From this viewpoint, the main difference between the frequencies based watermarking algorithms, is their choice of frequency coefficients to use for embedding watermark data. In fact the robustness of the algorithms is also dependent on the frequency at which the watermark data is added. Two commonly measurements that are used to quantify the error between images are described as

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