US Patent 7415128 Method and apparatus for providing an asymmetric watermark carrier

A low-frequency, temporally asymmetric watermark carrier decreases in luminance at a slower rate than it increases in luminance. This allows the carrier to be embedded, e.g., in a video work, in a manner that renders the resultant watermark virtually invisible to the human eye. Moreover, the resultant watermark is substantially resistant to common pirating techniques in which high-frequency visual content (e.g., including watermark data) tends to be filtered out by piracy processing.