Enhanced pairwise IPVO-based reversible data hiding scheme using rhombus context

Abstract

Pixel-Value-Ordering (PVO) based reversible data hiding schemes provide high-fidelity stego-images with moderate embedding capacity. In this paper, a novel reversible data hiding scheme based on enhanced pairwise pixel value ordering is proposed to increase embedding capacity. The proposed scheme divides a host image into non-overlapping blocks of three pixels in zig-zag order and categorizes the blocks into two categories namely absolute smooth and probably complex based on the rhombus mean for each pixel of the block. In the case of absolute smooth, the pairwise embedding is done in two-pass using two different predictors. In the pass-1, enhanced pairwise improved PVO method is used to embed the secret data in the block. The proposed method decreases the minimum valued pixels and increases the maximum valued pixels for embedding the secret data. In the pass-2, secret data is hidden using a novel recovery based pairwise embedding strategy, where the value of the first pixel according to the sorted mean sequence will be either increased or remains unchanged while the value of the last pixel will be either decreased or remains unchanged. Additionally, the medium pixel is also used to embed the secret data by modifying its value in any direction using prediction error expansion. Therefore, the pass-2 embedding is done in such a way that it becomes the complement of pass-1 embedding so that stego-image quality can be maintained with additional embedded data. In case of probable complex blocks, the secret data is embedded in pixel wise manner to local complexity of each pixel. The use of rhombus mean in block categorization allows embedding in each and every pixel of the host image while ensuring its reversibility. Thus, the proposed scheme significantly increases the embedding capacity. The experimental results show that the proposed scheme has almost doubled on the embedding capacity than the previous PVO-based reversible data hiding schemes. Further, it has higher PSNR at high embedding capacity.