A reversible watermarking with low warping: An application to digital fundus image

Medical image security is an essential in the present world which is desired in transferring the medical images in inter or intra hospital network for diagnosis. The medical images are differed from ordinary images. Because, they are captured through different devices (for example X ray, Computed Tomography, Magnetic Resonance Imaging and Positron Emission Tomography) and different color filters (for example Red, Green and Blue). This paper describes a new reversible watermarking scheme with low alterations for digital fundus images. It is based on the special nature of fundus images in its color channels. The proposed scheme in this paper is invariant to insertion process which removes the alterations from the images once the watermark is identified. It identifies the pixel optimally for inserting the secret message in it by reviewing the capability of pixel for carrying the information and the impact of the insertion process. This process is maintained by the variable alpha - alpha which is newly introduced here to maintain the optimality. In the experiment conducted on test fundus images (The test images were taken from DRIVE and STARE public databases), the proposed scheme gives better PSNR value which is 78.7222dB for red channel and 81.0685 dB for blue channel at the capacity rate of 0.1250 bits per pixel (bpp). It is also preserving the quality of images in good condition for diagnosis since the green channel of the image is untouched.