Image Watermarking Based On Wavelet Packet Transform With Best Tree

This paper proposes a watermarking embedding and extracting methods in the frequency domain based on a selection of a high frequency range containing large amount of information. The selected high-frequency range contributes to the imperceptibility of the watermark while the robustness against compression is achieved because the selected frequency range contains large amount of information. The entropy-based algorithm is adopted to find the best tree of the wavelet packet transform (WPT.) Such best tree represents the best basis of the WPT whose corresponding frequency subband contains high information energy. In addition, for security aspect of the watermarking process, the bits of the watermark image is randomly permuted before embedding them to the selected subband. The key of the pseudo-random generator provides the security for the watermark. Each bit of the permuted watermark image are embedded to the original image by adjusting the WPT coefficients of the selected subband, which also allows us to vary the level of watermarking. The proposed methods are tested with various benchmark images of various sizes and with various watermarking levels. The JPEG compression, Gaussian noise and filtering were applied as the attacks. The results showed that the average peak signal-to-noise ratio (PSNR) was varied from around 50 dB to 24 dB under various compression ratios and filtering while the average normalized correlation (NC) was closed to unity for image quality of greater than or equal to 60 %. Also, the results showed improvement over previous method when both the perceptibility and readability are considered.