Multi-layer multi-image encoding method for hiding graylevel images

Abstract

This paper proposes an encoding method to hide multiple covert images in multiple layers into a host image to form an overt image. The codes encoded in the overt image are classified into five groups, identification codes, image number codes, graylevel codes, dimension codes, and information codes. Identification codes are used to determine whether the overt image contains codes proposed in this paper or not; image number codes are used to indicate the number of covert images encoded in the overt image; graylevel codes are used to indicate the graylevel numbers of covert images; dimension codes are used to determine the sizes of covert images; information codes are used to decode covert images. Moreover, a covert image in an upper layer can hide several other covert images in a lower layer. The codes encoded in an upper-layer covert image are classified into four groups, image number codes, graylevel codes, dimension codes, and information codes. The host image and keys are not needed for decoding and all the reconstructed covert images do not contain any distortion when the proposed encoding method is used. The designer can quickly decode covert images, but people without authorization cannot successfully decode covert images. Moreover, the overt image looks almost the same as the host image.