Watermarking in Halftone Images with Kernels-Alternated Error Diffusion and Haar Wavelet Transform
A halftone watermarking method of high quality, robustness, and capacity flexibility is presented in this paper. An objective halftone image quality evaluation method based on the human visual system obtained by least-mean-square is also introduced. In the encoder, the kernels-alternated error diffusion (KAEDF) is applied. This scheme is able to maintain the computational complexity at the same level as an ordinary error diffusion. Compared with Hel-Or using ordered dithering, the proposed KAEDF yields a better image quality through using error diffusion. Moreover, the Haar wavelet transform (HWT) decoding is employed instead of lookup table (LUT), so as to reduce the computational complexity. As documented in the experimental results, this technique is able to guard against degradation due to tampering, cropping, rotation, as well as print-and-scan processes in error-diffused halftone images.