Distribution of Watermark According to Image Complexity for Higher Stability
One of the main objectives of all watermarking algorithms is to provide a secure method for detecting all or part of the watermark pattern in case of usual attacks to a watermarked image. In this paper we introduce a method that is suitable for any spatial domain watermarking algorithms, such that, it can provide a measure for the level of robustness when a given watermark is supposed to be embedded in a known host image . In order to increase the robustness of the watermarked image, for a watermark of n bits, we embed it s times. Doing this, the entire image is divided into 16 equal size blocks. For each block the complexity of the sub-image in that block is measured. The number of repetition of watermark bits saved in each block is determined according to the complexity level of that block. The complexity of a sub-images is measured using its quad tree representation. This approach not only secures the watermarked image with respect to usual attacks, but also, enables us to save longer bit patterns of watermark, while maintaining a good level of similarity between the original image and the watermarked one.
For evaluating the performance of our method we have tested our method on 1000 images having low, medium and high level of complexity, and compared the result with the same set of images without considering the complexity of sub-images in blocks. Our new method provided %17 higher stability.
KeywordsWatermark bit distribution quad-tree image complexity
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