Signal processors and methods for estimating geometric transformations of images for digital data extraction

Patent metadata

Field	Value
Publication number	US-12014441-B2
Application number	US-202117479910-A
Country	US
Kind code	B2
Filing date	Sep 20, 2021
Priority date	Jul 16, 2015
Publication date	Jun 18, 2024
Grant date	Jun 18, 2024

Abstract

Signal processing devices and methods estimate a geometric transform of an image. One method measures correlation between a transformed reference signal component and an image, updates, based on the measured correlation that is below a threshold, coordinates of the reference signal component to a location within a neighborhood around the coordinates of the transformed reference signal component; determines a new geometric transform that transforms the reference signal components to updated coordinates; and applies the new geometric transform to extract encoded digital data from the image.

First claim

What is claimed:

1. A method of determining a geometric transform of a reference signal in an image for extracting digital data, the method comprising:
with a programmed processor or digital logic circuit:
for plural reference signal components of a reference signal, transforming coordinates of a reference signal component according to a candidate geometric transform;
measuring correlation between the transformed reference signal component and the image, the measured correlation comprising a combination of complex components of a frequency domain transform of the image at neighboring integer coordinates around the coordinates of the transformed reference signal component, wherein the complex combination combines complex components according to a phase relationship at the neighboring integer coordinates, wherein the phase relationship comprises weighting neighboring integer coordinates according to a point spread function;
updating, based on the measured correlation that is below a threshold, the coordinates of the reference signal component to a location within a neighborhood around the coordinates of the transformed reference signal component;
determining a new geometric transform that transforms the reference signal components to the updated coordinates; and
applying the new geometric transform to extract encoded digital data from the image.

2. The method of claim 1 wherein the phase relationship comprises matching phase at upper right and lower left integer neighbors, and matching phase at upper left and lower right integer neighbors, and phase at the upper right and upper left integer neighbors differ by 180 degrees.

3. The method of claim 1 wherein the reference signal components comprise sinusoids.

4. The method of claim 1 including:
determining a signal confidence metric for a reference signal in an image block based on applying the new geometric transform to approximate geometric distortion of the image block; and
weighting digital message elements extracted from the image block by the signal confidence metric.

5. The method of claim 1 comprising:
for geometric transform candidates, performing the transforming and the measuring of correlation with a lower frequency subset of the plural reference signal components to determine a subset of the geometric transform candidates to refine; and
in plural refinement stages, performing the transforming, the measuring of correlation, the updating of coordinates and the determining of a new geometric transform on the subset of the geometric transform candidates.

6. The method of claim 1 comprising:
performing the acts of transforming, measuring, updating, determining the new geometric transform, and
applying the new geometric transform in special purpose digital logic circuitry.

7. A non-transitory computer readable medium, on which is stored instructions, which when executed by a processor, perform a method of determining a geometric transform of a reference signal in an image for extracting digital data, the method comprising: the following acts:
for plural reference signal components of a reference signal, transforming coordinates of a reference signal component according to a candidate geometric transform;
measuring correlation between the transformed reference signal component and the image, the measured correlation comprising a combination of complex components of a frequency domain transform of the image at neighboring integer coordinates around the coordinates of the transformed reference signal component, wherein the complex combination combines complex components according to a phase relationship at the neighboring integer coordinates, wherein the phase relationship comprises weighting neighboring integer coordinates according to a point spread function;
updating, based on the measured correlation that is below a threshold, the coordinates of the reference signal component to a location within a neighborhood around the coordinates of the transformed reference signal component;
determining a new geometric transform that transforms the reference signal components to the updated coordinates; and
applying the new geometric transform to extract encoded digital data from the image.

8. The non-transitory computer readable medium of claim 7 , wherein the phase relationship comprises matching phase at upper right and lower left integer neighbors, and matching phase at upper left and lower right integer neighbors, and phase at the upper right and upper left integer neighbors differ by 180 degrees.

9. The non-transitory computer readable medium of claim 7 , wherein the reference signal components comprise sinusoids.

10. The non-transitory computer readable medium of claim 7 in which said instructions include instructions, which when executed by a processor, perform the following acts:
determining a signal confidence metric for a reference signal in an image block based on applying the new geometric transform to approximate geometric distortion of the image block; and
weighting digital message elements extracted from the image block by the signal confidence metric.

11. The non-transitory computer readable medium of claim 7 in which said instructions include instructions, which when executed by a processor, perform the following acts:
for geometric transform candidates, performing the transforming and the measuring of correlation with a lower frequency subset of the plural reference signal components to determine a subset of the geometric transform candidates to refine; and
in plural refinement stages, performing the transforming, the measuring of correlation, the updating of coordinates and the determining of a new geometric transform on the subset of the geometric transform candidates.

12. The non-transitory computer readable medium of claim 7 in which said instructions include instructions, which when executed by a processor, perform the following acts:
executing instructions on one or more processors to execute the acts of transforming, measuring, updating, determining the new geometric transform, and applying the new geometric transform.

13. The non-transitory computer readable medium of claim 7 in which said instructions include instructions, which when executed by a processor, perform the following acts:
performing the acts of transforming, measuring, updating, determining the new geometric transform, and
applying the new geometric transform in special purpose digital logic circuitry.

14. An apparatus for determining a geometric transform of a reference signal in an image for extracting digital data, the apparatus comprising:
means for transforming coordinates of a reference signal component according to a candidate geometric transform, for plural reference signal components of a reference signal;
means for measuring correlation between the transformed reference signal component and the image, the measured correlation comprising a combination of complex components of the frequency domain transform of the image at neighboring integer coordinates around the coordinates of the transformed reference signal component, wherein the complex combination combines complex components according to a phase relationship at the neighboring integer coordinates, wherein the phase relationship comprises weighting neighboring integer coordinates according to a point spread function;
means for updating, based on the measured correlation that is below a threshold, the coordinates of the reference signal component to a location within a neighborhood around the coordinates of the transformed reference signal component;
determining a new geometric transform that transfor

Assignees

• Digimarc Corp

Inventors

• Sharma Ravi K
• Lord John D
• Lyons Robert G
• Alattar Osama M
• Boles Jacob L

Classifications

• G06T2201/0052

  Embedding of the watermark in the frequency domain · CPC title

• G06T3/10

  Selection of transformation methods according to the characteristics of the input images · CPC title

• G06T3/02

  Affine transformations (for image registration G06T3/147; for image mosaicing G06T3/4038) · CPC title

• G06T2201/0081

  whereby both original and watermarked images are required at decoder, e.g. destination-based, non-blind, non-oblivious · CPC title

• G06T2201/0065

  Extraction of an embedded watermark; Reliable detection · CPC title