Date Added: Mar 2011
In this paper, the authors propose a simple reversible data hiding method in the spatial domain for Block Truncation Coding (BTC) compressed grayscale images. The BTC method compresses a block of a grayscale image to a bitmap and a pair of quantization numbers. The proposed method first embeds secret bits into a block by changing the order of those two quantization numbers. The compression rate is not enlarged by this embedding scheme. To further improve the hiding capacity, the proposed method embeds the secret bits into the bitmap of the block by exploiting the correlation characteristic of neighboring blocks' bitmap in natural images. The experimental results show that the proposed method achieves very good hiding capacity at low compression rate.