Symmetry watermark
AssigneeDigimarc Corporation
InventorJohn Stach
Life of this patent
Estimating the term…
Abstract
A digital watermark is generated with radial and circumferential symmetries in a particular domain of a host signal into which it is embedded. These symmetries enable a detector to compute the projective transformation and rotation angle of the embedded signal using only the symmetry properties. The embedded signal may be variable, such as being modulated with a variable message payload, yet the scale and rotation of this variable signal is detectable based on its symmetry properties.
Claims20
A method of digital watermark embedding in a two dimensional signal, the method comprising:
- generating a digital watermark signal carrying one more auxiliary data symbols to be embedded in the two dimensional signal;
- and
- embedding the digital watermark signal in the two dimensional signal such that the digital watermark has radial symmetry and circumferential symmetry;
- wherein the circumferential symmetry enables detection of rotation of the digital watermark, and the radial symmetry enables detection of scaling of the digital watermark.
A method of detecting a symmetric digital watermark embedded in an image, the method comprising:
- computing radial symmetry in an embedding domain of the image to detect a radial symmetry property of the digital watermark;
- based on the radial symmetry, determining spatial scaling of the digital watermark as a function of rotation angle;
- computing circumferential symmetry in an embedding domain to detect a circumferential symmetry property of the digital watermark;
- and
- based on use of the circumferential symmetry, determining a rotation angle of the digital watermark.
A method of detecting a symmetric digital watermark embedded in an image, the method comprising:
- transforming the image into an embedding domain;
- computing radial symmetry of the image as a function of angle to detect signal energy attributable to radial symmetry of the digital watermark;
- computing circumferential symmetry to detect signal energy attributable to circumferential symmetry of the digital watermark;
- using the radial and circumferential symmetries to extract a message payload from the digital watermark.
Dependencies are inferred from the claim text.