FD-based detector for medical image watermarking

Abstract

In this study, the authors propose a novel technique for medical image watermark detection using the concept of the fractional differentiator (FD). The feature of FD as a non-linear high-pass filter helps in watermark detection. In the region of non-interest, the watermark image has been added in a mid-band frequency range of the discrete cosine transform coefficients of 8 × 8 different blocks by generating direct spread spectrum sequence. Their scheme produces noise-free watermarked medical images. Furthermore, they derive the test statistics of the proposed detector, which is characterised by the fractional order q. The average errors in pixels (PEs), peak-signal-to-noise ratio (PSNR), structural similarity index (SSIM) and cross-correlation coefficient (CC) have been used to quantify the capability of the proposed technique over some state-of-the-art techniques. The proposed technique shows that at a particular value of fractional order q, there is a significant reduction in average PEs. It causes an increment in PSNR, SSIM and CC. The proposed technique is tested on a large number of medical images and it is found that their proposed technique works better or comparable with other state-of-the-art techniques.