Methods and arrangements for configuring industrial inspection systems

• US 10,593,007 B1
• Filed: 11/17/2017
• Issued: 03/17/2020
• Est. Priority Date: 06/11/2015
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Long, Scott M., Haverkate, Christopher M.
• Primary Examiner(s): Woldemariam, Aklilu K
• Application Number:
  US15/816,098
• Time in Patent Office: 851 Days
• Field of Search: 382103, 382128, 382199, 382164, 382162, 382296, 382300, 382345, 348261, 348448, 348589
• CPC Class Codes: G01N 2021/8887 based on image processing techniques
• CPC Class Codes: G06F 18/22 Matching criteria, e.g. proximity measures
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06V 10/22 by selection of a specific region containing or referencing a pattern; Locating or processing of specific regions to guide the detection or recognition
• CPC Class Codes: G06V 10/462 Salient features, e.g. scale invariant feature transforms [SIFT]
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

In computer vision systems that need to decode machine-readable indicia from captured imagery, it is critical to select imaging parameters (e.g., exposure interval, exposure aperture, camera gain, intensity and duration of supplemental illumination) that best allow detection of subtle features from imagery. In illustrative embodiments, a Shannon entropy metric or a KL divergence metric is used to guide selection of an optimal set of imaging parameters. In accordance with other aspects of the technology, different strategies identify which spatial locations within captured imagery should be successively examined for machine readable indicia, in order to have a greatest likelihood of success, within a smallest interval of time. A great variety of other features and arrangements are also detailed.

Claims

1. A camera configuration method comprising the acts:

capturing a first image of a subject with a camera, the camera employing a first combination of values for first and second imaging parameters, at least one of said first and second imaging parameters being selected from the group consisting of;

exposure interval, camera gain, illumination intensity, and flash illumination interval;

computing a probability distribution measure, said probability distribution measure comprising a difference, or similarity, between a probability distribution of pixel values in the first image, and a second probability distribution;

capturing additional images of the subject with the camera, employing other combinations of values for said first and second imaging parameters, and, for each additional image, computing said probability distribution measure comprising a difference or similarity between a probability distribution of pixel values in the further image, and the second probability distribution;

identifying which combination of values for the first and second imaging parameters yields a most extreme value of said probability distribution measure; and

setting the camera to use said combination of values for the first and second imaging parameters in capturing subsequent images;

wherein said act of identifying a combination of values for the first and second imaging parameters yielding a most extreme value of said probability distribution measure has the practical effect of establishing an optimal set of imaging parameters to best allow machine detection of subtle features from imagery.

2. The method of claim 1 in which the probability distribution measure comprises an entropy metric, and the method includes identifying which combination of values for the first and second imaging parameters yielded a maximum value of said metric.

3. The method of claim 1 in which the probability distribution measure comprises a divergence metric, and the method includes identifying which combination of values for the first and second imaging parameters yielded a minimum value of said metric.

4. The method of claim 1 in which the second probability distribution is an idealized probability distribution.

5. The method of claim 1 that includes:

generating histogram data that counts pixels of different values in the first image;

determining an entropy or divergence metric from the histogram data;

for each of said additional images, generating histogram data, and determining an entropy or divergence metric from the histogram data;

identifying the combination of values for said first and second imaging parameters that yields the captured image having histogram data with the largest entropy metric, or with the smallest divergence metric.

6. The method of claim 1 that includes determining a Shannon entropy metric having the form:

7. The method of claim 1 in which both the first and second imaging parameters are selected from the list consisting of:

exposure interval, lens aperture, camera gain, illumination intensity, and flash illumination interval.

8. The method of claim 1 in which one of said parameters comprises exposure interval, and the method includes initially determining said probability distribution measure with a first value for said exposure interval, and then decreasing the exposure interval for successive computations of said additional probability distribution measures, until a difference in said probability distribution measure between successive values of exposure interval changes sign.

9. The method of claim 1 in which said parameters comprise exposure interval and camera gain, and the method includes initially determining an entropy metric with a first value for said exposure interval and a first value for said camera gain, and thereafter alternately decreasing the exposure interval and camera gain for successive determinations of additional entropy metrics, until decreasing a first of said parameters yields a decline in entropy metric, and thereafter continuing to reduce the second of said parameters until decreasing the second parameter also yields a decline in entropy metric.

10. The method of claim 1 that includes filtering the captured images before computing said probability distribution measures, said filtering comprising, for each of plural pixels in each captured image, determining whether a value of said pixel is less than, equal to, or greater than, a value of each of eight neighboring pixels, and changing the value of said pixel in accordance with said eight determinations.

11. The method of claim 1 that includes computing said probability distribution measures for each of plural blocks in plural of said captured images, and for each block, identifying which combination of values for the first and second imaging parameters yielded the most extreme value of said probability distribution measure.

12. The method of claim 1 that further includes extracting information from one of said subsequent images, by optical character recognition, barcode decoding, image fingerprint recognition, recognition by a neural network, or watermark detection.

24. The method of claim 1 in which the subject comprises a printed greyscale gradient target.

25. The method of claim 24 that further includes:

replacing the target with a printed package; and

capturing an image of the package with the camera, employing said identified combination of values for the first and second imaging parameters.

26. The method of claim 25 that includes decoding a machine-readably symbology from the captured image of said package.

27. The method of claim 1 in which the camera is a greyscale camera that produces pixels having values in the set {0, 1, 2, . . . 255}.

28. The method of claim 5 in which each of said histograms comprises 256 values, respectively corresponding to pixel values in said set {0, 1, 2, . . . 255}.

29. The method of claim 1 that includes filtering the captured images to reduce noise effects, before computing said probability distribution measures.

13. An inspection system for a production line that packages food or that applies labels to food containers, comprising:

a camera directed towards the production line to capture imagery of objects conveyed by the production line, the camera employing first and second imaging parameters, at least one of said first and second imaging parameters being selected from the group consisting of;

exposure interval, camera gain, illumination intensity, and flash illumination interval; and

means for determining optimal values of said first and second imaging parameters, to best allow decoding of payload data from 2D indicia on said objects depicted in imagery captured by said camera, wherein said means includes;

software executing on a processor that causes the system to repeatedly collect image data from one or more objects, using different combinations of values for the first and second imaging parameters;

software executing on a processor that causes the system to determine, from the collected image data, for each different combination of values for the first and second imaging parameters, an entropy or divergence value; and

software executing on a processor that causes the system identify which of said different combinations of values for the first and second imaging parameters yields a largest entropy value or a smallest divergence value;

wherein the combination of values for the first and second imaging values thereby identified is determined to comprise said optimal values for said first and second imaging parameters.

14. The system of claim 13 that further includes means for decoding a 2D machine-readable symbology captured with said camera using said values of first and second imaging parameters determined to be optimal.

15. A method comprising the acts:

capturing plural image frames depicting a subject with a camera in an environment, the camera capturing each image frame with a particular combination of values for first and second imaging parameters, at least one of said first and second imaging parameters being selected from the group consisting of;

exposure interval, camera gain, illumination intensity, and flash illumination interval, wherein different of said image frames are captured with different combinations of values for said first and second imaging parameters;

analyzing the captured image frames to identify which of said combinations of imaging parameter values is optimum for capture of imagery by said camera in said environment, by computing entropy or divergence metrics from the captured image frames, and identifying an extrema of said computed metrics; and

setting the camera to employ said identified combination of imaging parameter values in capturing an image of an object;

wherein the method has the practical effect of establishing an optimal set of imaging parameters for capturing images with said camera in said environment.

16. The method of claim 15 that further includes decoding a payload from a 2D data-carrying symbology depicted in imagery of said object captured by said camera using said identified combination of imaging parameter values.

17. The method of claim 15 in which the analyzing act comprises computing a Shannon entropy metric.

18. The method of claim 15 in which both the first and second imaging parameters are selected from the list consisting of:

exposure interval, lens aperture, camera gain, illumination intensity, and flash illumination interval.

19. The method of claim 15 that includes:

identifying, within each of the plural captured image frames, several spatially-distributed blocks; and

computing entropy metrics for each of said spatially-distributed blocks;

wherein the method determines a first optimum combination of imaging parameter values for a first block within imagery captured by said camera, and determines a second optimum combination of imaging parameter values for a second block within imagery captured by said camera.

20. The method of claim 15 in which the subject is a gradient test pattern.

21. The method of claim 15 in which the subject is not a gradient test pattern.

22. The method of claim 21 in which the subject comprises packages on a production line that packages goods or that applied labels to packaging.

23. A non-transitory computer readable medium containing software instructions for configuring a computer to control an inspection system to perform the acts of claim 15.