Enhance embedding capacity for switch map based multi-group EMD data hiding.

Exploiting Modification Direction (EMD) based data hiding achieves good stego-image quality and high security level. Recently, a section-wise EMD was proposed to enhance the embedding capacity of EMD. Later, Wang et al. introduced a switch map based multi-group EMD to further improve the embedding capacity. However, by a detail observation on the switch map in Wang et al.'s scheme, we find that more codewords with longer code-length can be put into the switch map. In this paper, we build a new switch map by Huffman code, and construct an enhanced multi-group EMD using Huffman code based switch map. Our scheme has higher embedding capacity than Wang et al.'s scheme and other EMD based data hiding methods.