Homomorphic Filter Based Image Watermarking

This paper proposes a spatial domain image watermarking method based on homomorphic filter. In the proposed method, after applying the homomorphic filter to the host color image, a watermark image is embedded into the natural logarithm reflectance component of the image. Based on the concept that the reflectance component contains most of the image details with low energy, the watermark energy added to this component will be imperceptually noticed by the human eye. The embedding watermark is also protected by a key-based stream cipher, so that without the correct secret key, one cannot reconstruct the watermark. To identify the existence of the embedded watermark, the semi-blind detection approach is applied. The performance of the proposed method in terms of correlation coefficient between the original and extracted watermarks is measured and presented. Its robustness against image blurring and image sharpening at various strengths is also evaluated. The results show the potential of the proposed method for a practical system.