Example 7.2 Watermark distribution
A set of test results of watermark distribution and invisibility is given in Figure 7.8. The watermark used is a random sequence with Gaussian distribution N(0, 1) and length M = 1,000. Figure 7.8(a) is an original Lena image, and Figure 7.8(b) is the watermarked image (PSNR = 38.52 dB). Figure 7.8(c) is the absolute difference image (it has been enhanced to increase contrast to make the difference more visible).
Two points can be remarked from Figure 7.8:
(1)From the visual perception point of view, it is hardly to see the difference between these two images (one before embedding and one after embedding), which shows that the algorithm has a good invisibility. In fact, the normalized correlation coefficient ...
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