Image salient regions encryption for generating visually meaningful ciphertext image

Image feature encryption is comprised of feature extraction and feature encryption. The existing feature encryption algorithms aim at extracting edge features as significant information for encryption purpose rather than salient regions. However, salient regions in the images usually carry more important information than edge features. Moreover, most of them protect significant information by transforming the input image into noise-like image or texture-like image. Obviously, these images are sign of encrypted image and thus can be easily attacked. In this study, we propose a salient regions encryption method by generating visually meaningful ciphertext image. First, salient regions are efficiently detected by saliency detection model in the compressed domain. Then, we encrypt these salient regions by a chaos-based encryption algorithm. With optical encryption theory, the encrypted salient regions are finally transformed into a visually meaningful ciphertext. To the best of our knowledge, it is the first time to use salient regions as important visual information for encryption to obtain ciphertext image. Results demonstrate the image salient regions have been largely hidden with the proposed method.