Importance

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Abstract

A channel is inserted into a sequence of frames for an image, by varying one or more display characteristics of the resulting image across the display. The watermark and other data channel may be employed to watermark the video signal, and the watermark may correspond to the presence of the channel or may be data in accordance with watermark information carried within the channel. For most display devices, display variations are minimized during the design process, but human viewers may still tolerate and accept subtle variations in a displayed image. For exemplary embodiments in accordance with the present invention, slightly changing one or more display characteristics from center-to-side in accordance with watermark information allows for watermarking of the image since viewers may not be aware that display characteristics are changing. For example, a tapering function may be used in a transmitter to vary one or more color components of the video signal representing the image. A receiver includes a watermark detector that has a priori information about the watermark. The watermark detector examines specific regions of the displayed image over time, and tests the regions for the watermark during time intervals when the image remains relatively still. A histogram of each color component of the region may be generated, and the watermark detected by comparing the histograms for the watermarked and non-watermarked color components. The watermark is detected if the histogram of the watermarked color component varies in manner related to the tapering function. Watermarking of the image in this manner is robust to subsequent signal processing methods, such as scaling, cropping, rotation, and compression.

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First Claim