Adaptive reversible data hiding based on a local smoothness estimator

A novel reversible watermarking (RW) scheme based on a local smoothness estimator and multi-step embedding strategy is proposed in this paper. All the pixels are divided into four equal parts. Correspondingly, the watermark embedding process is separated into four independent steps. Thus each step is performed to embed watermark information into its corresponding image part. In each step, for each to-be-embedded pixel, a local smoothness estimator defined as the variance of its total neighbors is presented to estimate its local smoothness. An obvious advantage of introducing this estimator is that it can determine those pixels in smooth regions accurately. In fact, accurate determination means the decrease in embedding distortion. At the low embedding rate (ER), modifications induced by difference expansion (DE) are done only to those pixels located in smooth regions. Hence, the proposed method can obtain high embedding capacity while maintaining good visual quality. With ER gradually increased, adaptive embedding is employed. In adaptive embedding, for one to-be-embedded pixel, 1 or 2 bits are adaptively embedded according to the strength of relationship among all the pixels surrounding it. The experimental results demonstrate that the proposed method is effective.