Watermarking of ordered dither halftone images by bit interleaving

In this paper, we present a blind watermarking method to embed watermarks into dithered halftone images by pairing the sub-images derived from a new bit-interleaving method. The new bit-interleaving method is based on a secret key. The embedded watermark is thus undeletable. The search space of encoding is dispersed into the whole image through this new bit interleaving to great decrease the chance of disturbances in the local grey value. Combining the bit interleaving method with a variety of sub-image pairing methods, we can increase the distance of encoding and thus increase the robustness or embedding capacity. Totally speaking, the proposed method increases the embedding capacity with good visual quality, security and robustness against the cropping and tampering attacks.