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Reversible Data Hiding Using Prior Pixel Pairs in Two-Dimensional Histogram with Tri-Directional Modification of Difference Histogram

Histogram shifting and modification brought a new trend in contemporary world especially in the field of reversible data hiding (RDH) because of its rich applications. A new approach of RDH with histogram modification is introduced in the proposed work: tri-directional modification of difference histogram (TDMDH). Compared with previous proposed methods in RDH, the TDMDH method gives better embedding capacity (EC) and PSNR experimentally. Li's method proposed a difference pixel pair mapping, which embeds the data in four different directions (i.e. up, down, left, right). The proposed method enhance the work of Li's method with one more different direction embed data (i.e. diagonally up and down). This modification gives a better PSNR because of diverting more number of prior pixel pairs (PPPs) participating in embedding and fewer for shifting. This modification will gradually increase the EC with the persistence of signal-to-noise ratio. TDMDH alters two pixels to embed a bit. This modification leads to low PSNR value especially in low texture images, to improve it difference expansion is used for double-bit embedding on diagonally expanded or shifted pixel pairs. The information about embed data will be embedded to watermarked image for blind decoding. Gradient adjusted prediction and noiselevel were used to assess the PPPs, which are suitable for embedding or shifting. The proposed method secures better PSNR value (more than 50dB) from USC-SIPI image database when compared with existing methods of RDH.