Improved Fourier domain patchwork and template embedding using spatial masking
Robustness against distortions caused by common image processing is one of the essential properties for image watermarking to be applicable in real-world applications. Typical distortions include lossy JPEG compression, filtering, cropping, scaling, rotation, and so on, among which geometric distortion is more challenging. Even slight geometric distortion can totally fail the watermark detection through de-synchronization. Another important property is the watermark payload. Although one-bit watermark is widely used in research work for algorithm testing and evaluation, only checking whether a specific watermark exists does not meet the requirement of many practical applications. This paper presents a practical robust image watermarking algorithm which combines template embedding and patchwork watermarking in Fourier domain. The embedded template enables the necessary robustness against geometric distortions and the patchwork approach provides a reasonable watermark pay load which can meet the requirement of most applications. A spatial perceptual mask is used to reshape the embedded energy after it is inverted to the spatial domain, which significantly improves the image quality and enhances the robustness of both template and watermark. Implementation issues and solutions, e.g. fine-tuning of embedding energy of individual pixels, are also discussed. Experimental results demonstrate the effectiveness and practicability of the proposed algorithm.