Multi-round dynamic swap optimisation for table-based steganography

The reference-table-based (RTB) steganography employs two pixels to conceal a secret digit, according to a predetermined reference table. Most of the RTB steganographic schemes discussed in the literature do not consider the non-uniformity of the secret digits and the locating numbers indicated by the pixel pairs. In contrast, the non-uniformity of the locating numbers exists for most of host images. When a non-uniform secret sequence is embedded, the quality control of the stego image is quite challengeable when compared with a uniform secret sequence. To the best of the authors knowledge, most of the existing algorithms focus on the uniform sequences. In this study, they propose a multi-round dynamic swap optimisation (MRDSO) algorithm for RTB steganography, which is more suitable for non-uniform secret sequences. By optimising the permutation of the reference table, the proposed algorithm increases the scenarios that the locating number indicated by the pixel pair is equal to the secret digit, which means that these host pixels can carry the secret digit without any distortion. The experimental results show that the proposed MRDSO algorithm increases the quality of the stego image by 0.1-1.7 dB.