Reversible Data Hiding in Encrypted Images Based on Bit-Plane Classification and Adaptive Group Coding

Abstract

Reversible data hiding in encrypted images (RDH-EI) is a key technique for secure communication, secure cloud storage and privacy protection. Most existing RDH-EI algorithms rely on a single and static bit-plane encoding strategy, failing to fully exploit the structural differences of bit-planes from the block level to the sequence level, thereby limiting further improvements on embedding capacity. To address this issue, this paper proposes a novel RDH-EI algorithm based on Bit-plane Classification and Adaptive Group Coding (hereafter BCAGC algorithm). The core contributions are as follows: (1) A bit-plane classification mechanism is proposed. It categorises bit-planes into simple or complex types according to the number of non-all-zero 4-bit sequence (NAZ-4BS) patterns. (2) An adaptive group coding scheme is proposed. It dynamically selects between fixed-length coding and Huffman coding based on bit-plane types and the frequency distribution of NAZ-4BS patterns, thereby achieving compact coding tables and efficient bit-plane compression. Experimental results demonstrate that the proposed BCAGC algorithm achieves average embedding rates of 4.1472, 4.0565 and 3.4465 bpp on the BOSSbase, BOWS-2 and UCID datasets, respectively, outperforming several state-of-the-art RDH-EI methods.