Computing distortion of media signals embedded data with repetitive structure and log-polar mapping
A digital watermark detection method uses a matched filtering technique on a log polar re-mapping of a watermarked signal to detect peaks associated with a repetitive structure of a watermark.
1. A method of determining distortion of a signal with embedded data comprising:
transforming the signal into a transform domain to produce peaks due to a repetitive structure of the embedded data in the signal;
performing a mapping of the transformed signal to convert distortion of the embedded data into a shift; and
performing a correlation of the mapped signal with a signal representing an expected pattern of peaks associated with the repetitive structure of the embedded data signal, wherein the correlation detects the shift, and the shift provides a measure of the distortion of the signal.
2. The method of claim 1 wherein transforming comprises an autocorrelation of the signal.
3. The method of claim 1 wherein the mapping includes a log-polar mapping to convert scaling and rotation into spatial shifts.
4. The method of claim 1 wherein the correlation is computed using a matched filter.
5. The method of claim 1 wherein the embedded data is repeated in the signal as rectangular blocks.
6. A tangible medium on which is stored instructions for performing the method of claim 1 .