Watermarking is the insertion of information into images or video in such a way that the added information is not visible and yet resistant to image alterations. The fact that digital watermarks should be invisible prompts the exploitation of the characteristics of the human visual system (HVS). Unfortunately, this idea has not found a large number of followers until recently.

We have been working on HVS-based approaches for hiding a spread-spectrum watermark in an image. Both luminance and blue-channel watermarks have been investigated. We use a weighting function derived from the masking behavior of the human visual system as well as the watermark itself. Our results show that this approach facilitates the insertion of a more robust watermark in the luminance image or in the blue channel while preserving the visual quality of the original.

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