Improving the capability of reduced difference expansion based digital image data hiding

Difference Expansion along with its variants such as Reduced Difference Expansion (RDE) is a popular approach in the field of data hiding. Nevertheless, current works have not yet achieved the optimal performance, in terms of the capacity of the secret data and the quality of the stego media. In this paper, we propose a two layer-based algorithm in order to specifically improve the capability of RDE method regarding to the capacity and the quality of the stego image. This is done in the following manners. The first is enhancing the difference transformation scheme by taking the difference between the two closest pixels; and correspondingly, a new pixel construction scheme is also adjusted. The second is optimizing the size of the pixel blocks. The third stage is expanding the algorithm for both grayscale and RGB color images. Fourth, the proposed method improves the use of non-changeable blocks to hide the secret data. Finally, every block is processed once again to embed more secret bits. It occurs by replacing the Least Significant Bit (LSB) of each pixel. The experimental results show that this method has made a significant improvement in terms of the capacity since around 1.85 bits are carried by each pixel where the quality is slightly higher than that of the presented by previous research. Overall, by using the same block size, this proposed method delivers higher performance for both capacity and quality; furthermore, by using a bigger block size, this method is able to obtain a significant increase of the capacity with only slightly decrease of the quality.