Data hiding in 2-color images

In an earlier paper (Chen et al., 2000), we proposed a steganography scheme for hiding a piece of critical information in a host binary image. That scheme ensures that, in each m /spl times/ n image block of the host image, as many as [log/sub 2/ (mn + 1)] bits can be hidden in the block by changing at most 2 bits in the block. We propose a new scheme that improves (Chen et al., 2000) in its capability to maintain higher quality of the host image after data hiding by sacrificing some data hiding space. The new scheme can still offer a good data hiding ratio. It ensures that, for any bit that is modified in the host image, the bit is adjacent to another bit which has a value equal to the former's new value. Thus, the hiding effect is quite invisible.