Reversible image visual transformation for privacy and content protection

In this paper, a novel image transformation scheme is proposed to protect the visual information. By mimicking an arbitrarily chosen reference image, a secret image is visually changed and can be exactly recovered from the transformed image when needed. Unlike the block-wise visual encryption methods, the proposed transformation scheme modifies the secret image by bit plane replacement and reordering so that no block effect is introduced. In particular, one or more bit planes are hidden into the other bit planes so that the most significant one(s) can be vacated. Besides replacing the vacated bit plane(s) and reordering the others according to the reference image, histogram modification may be performed to conceal the secret content if needed. To exactly recover the secret image, the required information is recorded and reversibly hidden into the transformed image by adopting a reversible data hiding algorithm. The experimental results on three image sets show that their content can be semantically changed to prevent leakage of visual information. Moreover, the applicability and efficiency of the proposed scheme have been validated by comparing the existing visual encryption schemes.