Integer transform based reversible watermarking incorporating block selection

• We use the invariant mean value of a block to evaluate the local complexity.
• The block size can be set to a small value by the invariability of the mean value.
• The reduced size location map is created by the invariability of the mean value.
• We can modify flexibly each pixel in a block using DE or HS.

We propose a new scheme based on integer Haar wavelet transform (IHWT), which utilizes block selection and difference expansion (DE) (or histogram shifting (HS)). IHWT has the characteristic that the average of a block remains unchanged before and after watermark embedding. Hence, this invariability can be used for determining whether a block is located in a smooth region or not. Specifically, for a block, its mean value and the neighborhood surrounding it are used for estimating the correlation between it and its neighborhood. In this way, only a reduced size location map is needed, and the block size can also be set to a small value. Since small blocks have stronger intra-block correlation than large ones, the embedding distortion caused by modifying small blocks is lower. Otherwise, if the difference between any two neighboring pixels in a block is large, then the distortion produced by directly expanding it is also high. To decrease the class of distortions, DE (or HS) is introduced into the proposed method.