Reversible data hiding in dual Stegano-image using an improved center folding strategy

In recent years, the dual stego-image reversible data embedding methods have been developed rapidly, e.g., exploiting modification direction, magic matrix, least significant bit matching, and center folding strategy. The kind of method can effectively embed secret data into two stego-images and maintain excellent image quality and enhance the security. In 2015, Lu et al. proposed a center folding strategy that can effectively encode messages as the smaller digits. The encoding procedure reduces the modification level of pixels, thereby maintaining good image quality. However, their strategy does not use the relationship between the adjacent digits to reduce the number of the largest digits. Inspired by joint neighboring coding, we proposed a dynamic encoding strategy to improve the center folding strategy. The encoding strategy can reduce the secret digits and decrease the occurrence frequency of the maximum digits, thereby substantially reducing the modification level of pixels. The advantage makes that the proposed method can achieve a higher PSNR value than previous methods under the same embedding rate.