High Capacity Lossless Data Hiding for JPEG images by NLCM Relationship Constrcution

In this paper, we propose a high capacity lossless data hiding (LDH) scheme that achieves high embedding capacity and keeps the image quality unchanged. In JPEG bitstream, Huffman coding is adopted to encode image data. In fact, some Huffman codes are unused in the bitstream. The secret data can be embedded by replacing the used Huffman code with the unused Huffman code. Different from the previous schemes, the proposed scheme adopts the Non-equal length code mapping (NLCM) method to construct mapping relationship, which is not limited to the Huffman code lengths in a mapping set are equal. To further improve the embedding capacity and reduce the increased file size caused by data embedding, the proposed scheme reduces the existing coding redundancy. Experimental results show that our proposed scheme can obtain higher embedding capacity than previous high capacity schemes for JPEG images and the image quality of marked JPEG image is unchanged. In addition, the increased file size is reduced more than previous works.