Watermark detection using a fourier mellin transform

• US 6,408,082 B1
• Filed: 11/30/1999
• Issued: 06/18/2002
• Est. Priority Date: 04/25/1996
• Status: Expired due to Fees

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Sharma, Ravi K., Rhoads, Geoffrey B.
• Primary Examiner(s): Couso, Jose L.
• Application Number:
  US09/452,023
• Time in Patent Office: 931 Days
• Field of Search: 382/100, 382/112, 382/232, 382/284, 395/135, 358/124, 358/142, 358/448, 358/450, 358/454, 380/4, 380/9, 380/23, 380/25, 380/54, 283/6, 283/17, 283/72, 283/73, 283/93, 283/94, 283/113, 283/901, 348/475, 235/494, 340/825.34, 356/71, 902/1, 902/4, 902/6
• US Class Current: 382/100
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06K 19/06046 Constructional details
• CPC Class Codes: G06K 19/14 the marking being sensed by radiation
• CPC Class Codes: G06K 2019/06253 for a specific application
• CPC Class Codes: G06K 7/1417 2D bar codes
• CPC Class Codes: G06K 7/1447 extracting optical codes from image or text carrying said optical code
• CPC Class Codes: G06Q 20/341 Active cards, i.e. cards including their own processing means, e.g. including an IC or chip
• CPC Class Codes: G06Q 20/40145 Biometric identity checks
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: G06V 30/40 Document-oriented image-based pattern recognition
• CPC Class Codes: G07D 7/0034 using watermarks
• CPC Class Codes: G07D 7/004 using digital security elements, e.g. information coded on a magnetic thread or strip
• CPC Class Codes: G07F 17/16 for devices exhibiting advertisements, announcements, pictures or the like
• CPC Class Codes: G07F 7/086 by passive credit-cards adapted therefor, e.g. constructive particularities to avoid counterfeiting, e.g. by inclusion of a physical or chemical security-layer for security documents G07D7/00; for the reading of record-carriers in general G06K7/00; for the design of coded credit-cards G06K19/10
• CPC Class Codes: G07F 7/1008 Active credit-cards provided with means to personalise their use, e.g. with PIN-introduction/comparison system
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal
• CPC Class Codes: G11B 20/00891 embedded in audio data
• CPC Class Codes: H04N 1/00005 relating to image data
• CPC Class Codes: H04N 1/00037 Detecting, i.e. determining the occurrence of a predetermined state H04N1/00031 takes precedence
• CPC Class Codes: H04N 1/00079 : remotely
• CPC Class Codes: H04N 1/32122 : in a separate device, e.g. in a memory or on a display separate from image data
• CPC Class Codes: H04N 1/32154 : Transform domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/3216 : using Fourier transforms
• CPC Class Codes: H04N 1/32203 : Spatial or amplitude domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32352 : Controlling detectability or arrangements to facilitate detection or retrieval of the embedded information, e.g. using markers for decoding, detection or retrieval operations H04N1/32149 and subgroups take precedence
• CPC Class Codes: H04N 21/23892 : involving embedding information at multiplex stream level, e.g. embedding a watermark at packet level
• CPC Class Codes: H04N 21/8358 : involving watermark protecting executable software by watermarking G06F21/16; image watermarking in general G06T1/0021; watermarks inserted in still images for transmission purposes H04N1/32144; inserting watermarks during video coding H04N19/467
• CPC Class Codes: H04N 2201/3205 : of identification information, e.g. name or ID code H04N2201/3209 takes precedence
• CPC Class Codes: H04N 2201/3207 : of an address
• CPC Class Codes: H04N 2201/3225 : of data relating to an image, a page or a document
• CPC Class Codes: H04N 2201/3226 : of identification information or the like, e.g. ID code, index, title, part of an image, reduced-size image
• CPC Class Codes: H04N 2201/3233 : of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/327 : which are undetectable to the naked eye, e.g. embedded codes
• CPC Class Codes: H04N 2201/3271 : Printing or stamping
• CPC Class Codes: H04N 2201/3274 : Storage or retrieval of prestored additional information

Abstract

A watermark detector maps target media data into a log polar coordinate system and correlates the target media with a detection watermark to compute orientation parameters. The correlation process computes a measure of correlation for an array of potential orientation parameter candidates. Evaluating the correlation associated with these candidates, the detector selects one or more of the orientation parameters. It then proceeds to refine the correlation by using the computed orientation parameters, namely scale and rotation, to find additional parameters such as translation and differential scale.

Claims

1. A method for detecting a watermark comprising:

obtaining a data set representing media content;

transforming the data set in a selected transform domain;

remapping the transformed data set into a log polar coordinate system;

performing a correlation between a detection watermark and the transformed data set in the log polar coordinate system to compute one or more orientation parameters that approximate an orientation of a watermark pattern in the data set.

2. The method of claim 1 wherein the data set is a digital image.

3. The method of claim 1 wherein the selected transform domain is a spatial frequency domain.

4. The method of claim 1 wherein performing the correlation includes employing a generalized matching filter to match the detection watermark with the transformed data set and compute a measure of correlation.

5. The method of claim 1 wherein performing the correlation includes performing a matching operation between the detection watermark and the transformed data set to compute an array of correlation values, each representing a measure of correlation and having an associated orientation parameter.

6. The method of claim 5 including:

selecting one or more of the correlation values and the associated orientation parameter or parameters; and

using the orientation parameter or parameters corresponding to the selected correlation values as a starting point in an additional correlation process to find an additional correlation parameter that provides improved correlation.

7. The method of claim 6 wherein the orientation parameter includes rotation and scale parameters, and the additional correlation parameter includes a translation parameter.

8. A computer readable medium having software for performing the method of claim 1.

9. A watermark detector comprising:

means for transforming a media data set into a selected transform domain;

means for re-mapping the transformed media data set in a log polar coordinate system;

means for correlating the transformed media data set in the log polar coordinate system with a detection watermark to compute a measure of correlation; and

means for deriving one or more orientation parameters from the measure of correlation.

10. A watermark detector comprising:

a transformer for transforming a media data set to a selected transform domain;

a log polar re-mapper for mapping the transformed media data set to a log polar coordinate system;

one or more correlation filters in communication with the transformed media data set, mapped to the log polar coordinate system, the one or more correlation filters being operable to compute a measure of correlation between a detection watermark and the transformed media data set;

wherein the measure of correlation has an associated orientation parameter.