Improvements of data embedding in DCT compressed domain

While the data embedding method [1] is able to achieve high carrier capacity, it is not reversible. In this work, we improve [1] from rewritable to reversible in which case the original content can be completely reconstructed from its manipulated counterpart. The last coefficient from each 8 × 8 block is first encoded using slightly modified Huffman coding method and it is treated as part of the external information. This concatenated information will be embedded as a whole into a DCT compressed content. Although carrier capacity is slightly compromised to accommodate the last coefficients, the carrier capacity is improved by using multiple-base notational system [2]. Quality of the output content is also improved by controlling entries in the quantization table. Experiments were carried out to verify the aforementioned improvements.