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.

基于像素值排序（PVO）的可逆数据隐藏方案可提供具有中等嵌入能力的高保真隐身图像。本文提出了一种基于增强的成对像素值排序的可逆数据隐藏方案，以提高嵌入能力。所提出的方案将主机图像按之字形顺序划分为三个像素的非重叠块，并基于该块的每个像素的菱形均值将这些块分为两类，即绝对平滑块和可能复杂块。在绝对平滑的情况下，成对嵌入使用两个不同的预测变量进行两次遍历。在pass-1中，使用增强的成对改进的PVO方法将秘密数据嵌入到块中。所提出的方法减少了最小值像素，并增加了最大值像素以嵌入秘密数据。在第二遍中，秘密数据使用一种新颖的基于成对的嵌入策略隐藏，其中根据排序的均值序列，第一个像素的值将增加或保持不变，而最后一个像素的值将减少或保持不变。另外，通过使用预测误差扩展，通过在任何方向上修改其值，还可以使用中等像素来嵌入秘密数据。因此，pass-2嵌入的方式使其成为pass-1嵌入的补充，从而可以利用其他嵌入数据来保持隐蔽图像质量。在可能的复杂块的情况下，秘密数据以逐像素方式嵌入每个像素的局部复杂度。在块分类中使用菱形均值可以嵌入到宿主图像的每个像素中，同时确保其可逆性。因此，提出的方案显着增加了嵌入能力。实验结果表明，与基于PVO的可逆数据隐藏方案相比，该方案的嵌入能力几乎提高了一倍。此外，它在高嵌入容量下具有较高的PSNR。