Multi-level reversible data hiding for crypto-imagery via a block-wise substitution-transposition cipher

The research of reversible data hiding in crypto-imagery has attracted considerable attention due to privacy concerns in cloud computing applications. The schemes that vacate spare room after block-wise image encryption can avoid errors and provide more embedding capacities. However, the visual qualities of the directly decrypted images in the related schemes are unsatisfactory, and the spare room is not sufficiently utilized. Therefore, in this paper, we proposed an improved scheme to enhance conventional schemes to achieve a better performance. The block-wise substitution-transposition technique is used for image encryption to avoid carrying bit errors of the directly decrypted image. Then, prediction histogram shifting technique is applied for data embedding in the more centralized prediction error histogram generated by an efficient block predictor. Additionally, our proposed scheme supports multi-level embedding and therefore offers a high embedding rate. The receiver who holds the data hiding key can extract the embedded data, whereas the receiver who possesses the image encryption key is able to obtain a decrypted image of high visual quality. The original image can be losslessly recovered when both keys are presented. Experimental results demonstrate that the PSNRs of the decrypted images and the embedding rates of our proposed scheme are significantly improved compared to related schemes .