High capacity reversible image watermarking using error expansion and context‐dependent embedding

A novel prediction error expansion‐based reversible image watermarking technique is proposed. The proposed approach exploits the variance of neighbouring pixels in a way that the embedding of information bits in each pixel of an image depends on the scale of variation present in its eight neighbouring pixel values. A rhombus predictor is employed in the proposed scheme for its efficacy. In contrast to existing prediction‐error expansion based reversible watermarking techniques, the embedding phase of the proposed approach depends only on the context of the pixel to be watermarked. Exploiting the neighbourhood information of each pixel in this way, avoids the need of a location map (LM) or histogram shifting (HS) to distinguish marked pixels from unmarked pixels. Consequently, the proposed approach does not require a large amount of auxiliary information in the form of a LM or HS of unmarked pixels, and thus introduces less distortion, yielding good embedding performance, especially at high capacity.