Quad-tree Structure-Preserving Adaptive Steganography for HEVC

Modification of the optimal recursive block encoding process is commonly adopted in HEVC steganography based on block partitioning structure to embed secret messages, which inevitably disrupts the optimal rate distortion optimization process, resulting in a degradation of visual quality and an increase in bit rate. In this paper, we analyze the intra frame recursive block encoding process, categorizing modifications based on block partitioning structures into skip-level and non-skip-level modifications. Then, the rate distortion difference between these two types is compared. Additionally, the Maintenance Principle of Quad-tree Structure is introduced, which aims to preserve the stego quad-tree structure as closely as possible to the original one. Furthermore, a new cover mapping method is designed to expand the embedding capacity, and a quad-tree structure-preserving adaptive steganography is proposed. Extensive experimental results demonstrate that the proposed scheme can embed messages with fewer disruptions to the optimal rate distortion optimization process, ultimately improving the visual quality and reducing the bit rate growth.