Scalable image scrambling method using unified constructive permutation function on diagonal blocks

In this paper, an extension of ScaScra [1] is proposed to scal-ably scramble an image in the diagonal direction for achieving distorted scanline-like effect. The non-overlapping diagonal blocks are first defined and the unified constructive permutation function is applied to scramble pixels in each diagonal block. Scalability in scrambling is achieved by varying the block size. Experiments were carried out to objectively and subjectively verify the basic performance of the proposed extension and compare them to the results of ScaScra by using standard test images. Evaluations on pixel correlation and entropy are also carried out to verify the performance of both ScaScra and the proposed extension.