Watermarking image encryption using deterministic phase mask and singular value decomposition in fractional Mellin transform domain

The aim of this study is watermarking image encryption based on the fractional Mellin transform (FrMT) and singular value decomposition (SVD) using deterministic phase masks (DPMs). DPMs are used in the input as well as in the frequency planes of double random phase encoding. The use of DPM structured phase mask provides an advantage of extra encryption parameters, besides overcoming the problem of axis alignment associated with an optical setup. The encrypted image resulting from the application of FrMT is attenuated by a factor and then combined with a host image to provide a watermarked image. Afterwards, SVD is performed to get three decomposed matrices, i.e. one diagonal matrix and two unitary matrices. The decryption process is the reverse of encryption. Digital implementation of the proposed scheme has been performed using MATLAB R2014a (8.3.0.532). The watermark image is retrieved by using the corresponding FrMT orders and conjugate of DPMs. Use of the FrMT provides enhanced security due to the non‐linear nature of the transform. The effect of noise on the watermarked image has also been investigated. Mean square error between the output and input watermarks shows the accuracy of the proposed scheme.