Improved Lossless Data Hiding for JPEG Images Based on Optimized VLC Mapping

Most reversible data hiding (RDH) schemes embed data into JPEG images through DCT coefficients modification, but they will cause unavoidable visual distortion in the marked images. Lossless data hiding (LDH) can not only restore the cover JPEG images in a lossless way after extraction of the embedded data but also generate marked images without any visual distortion. For LDH schemes based on variable length code (VLC) mapping, the performance depends mainly on the mapping mode. In this paper, a new LDH scheme for JPEG images based on optimized VLC mapping is proposed. First, for a given mapping mode, a mathematical model of file size change is established. Then, based on the Run/Size frequency of a cover image and the estimation of frequency change caused by simulated data embedding, an iterative method is used to find the optimal mapping mode that leads to the smallest file size increments. Lastly, data is embedded in the cover image using the optimal VLC mapping. Experimental results show that the proposed LDH scheme based on optimized VLC mapping can achieve small increase in the file size of marked images.