SWT - SPIHT - NVF Based Blind Medical Image Watermarking
An SWT and SPIHT based blind watermarking scheme were proposed in this section. The cover image is transformed using 3 level SWT to generate multiple subbands. By applying SPIHT over the low pass bands, the required list of significant coefficients is generated using the lower order frequency bands. For identifying the maximum allowable distortion level, the Noise Visibility Function (NVF) is employed. The watermark is preprocessed using double encryption steps, first by R-Prime shuffling and then by Cross-Chaotic mapping. The watermark is embedded by the selected positions using SPIHT, and the random positions are encrypted using Linear Congruential Generator (LCG) and used as the public key. The proposed scheme is more rigid and robust against compression, geometric and noise attacks as it employs SPIHT model for watermark embedding. The method is scalable to larger size watermark images due to the utilization of SWT transformation technique. The model ensures security by providing the public key and private key encryption for the watermarked images.