Exploring More Capacity for Grayscale-Invariance Reversible Data Hiding

Grayscale-invariant reversible data hiding (RDH) in color images was developed recently in which the grayscales of the marked color image are required to be the same as that of the host color image. Recently, some grayscale-invariant RDH schemes were proposed but their performance on embedding capacity and distortion is not satisfactory due to the large number of correction bits generated for losslessly recovering the host green scales. In this work, we propose a grayscale-invariant RDH method which reduces the need for correction bits. We design a self-correcting mechanism which modifies the green scales for keeping grayscales unchanged while remembering the information of the host green scales. To obtain this task, we observe that all previous methods generated correction bits in a functional approach which results in many correction bits. Instead of the functional approach, we use a relational approach to preserve the grayscales. By this approach, the proposed algorithm only has to generate a small number of correction bits for recovering green scales. Moreover, this relational approach allows the algorithm to embed more message bits into some green scales. The experimental results show that the proposed method significantly improves the embedding capacity and the rate-distortion performance compared to previous works.