Parity-invariability-based reversible watermarking
A reversible integer transform, defined on an image pixel pair, is proposed. The transform can carry 1-bit watermark while retaining the parity of the sum of the pairs. Also, the transform makes one transformed pixel not related to the watermark bit which can be reused to construct a new pair with its next pixel. So the embedding rate can approach 1 bit per pixel for a single embedding process. Meanwhile, the decision on whether this new pair can be used for reversible embedding or not is greatly simplified. In addition, the application of the transform is able to largely increase the compression ratio of the location map, and finally increase the payload. A series of experiments has been conducted to verify the effectiveness of the proposed approach.