Creating an imperceptible watermark which can be read by a broad range of cell phone cameras is a difficult problem. The problems are caused by the inherently low resolution and noise levels of typical cell phone cameras. The quality limitations of these devices compared to a typical digital camera are caused by the small size of the cell phone and cost trade-offs made by the manufacturer.In order to achieve this, a low resolution watermark is required which can be resolved by a typical cell phone camera. The visibility of a traditional luminance watermark was too great at this lower resolution, so a chrominance watermark was developed. The chrominance watermark takes advantage of the relatively low sensitivity of the human visual system to chrominance changes. This enables a chrominance watermark to be inserted into an image which is imperceptible to the human eye but can be read using a typical cell phone camera.Sample images will be presented showing images with a very low visibility which can be easily read by a typical cell phone camera.
In digital watermarking, a major aim is to insert the maximum possible watermark signal while minimizing visibility. Many watermarking systems embed data in the luminance channel to ensure watermark survival through operations such as grayscale conversion. For these systems, one method of reducing visibility is for the luminance changes due to the watermark signal to be inserted into the colors least visible to the human visual system, while minimizing the changes in the image hue. In this paper, we develop a system that takes advantage of the low sensitivity of the human visual system to high frequency changes along the yellow-blue axis, to place most of the watermark in the yellow component of the image. We also describe how watermark detection can potentially be enhanced, by using a priori knowledge of this embedding system to intelligently examine possible watermarked images.
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