Method of registration in a contraband detection system

• US 7,738,687 B2
• Filed: 12/11/2006
• Issued: 06/15/2010
• Est. Priority Date: 04/07/2005
• Status: Active Grant

• Current Assignee: Leidos Security Detection & Automation Incorporated (Leidos Holdings, Inc.)
• Original Assignee: L-3 Communications Security & Detection Systems, Inc. (Leidos Holdings, Inc.)
• Inventors: Tortora, John O., Stillson, Jeffrey H., Krug, Kristoph D.
• Primary Examiner(s): Lu; Tom Y
• Application Number:
  US11/637,226
• Publication Number:
  US 20070172129A1
• Time in Patent Office: 1,282 Days
• Field of Search: 382/131, 382/132, 382/141, 382/151, 382/285, 382/294
• US Class Current: 382/132
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
• CPC Class Codes: G06V 10/757 Matching configurations of points or features

Abstract

A multi-level contraband detection system. At a first level, the system obtains volumetric information about an item under inspection. The volumetric information provides a basis for identifying suspect objects in the item under inspection and their locations. The location information is expressed in a first coordinate system relative to the device used for first level scanning. When first level scanning identifies a suspicious object, the item under inspection is passed to a second level scanner that can take further measurements on the suspicious objects. The second level machine is controlled in a second coordinate system. A translation between the two coordinate systems is obtained by registering a multi-dimensional image obtained at the first level with positioning information obtained at the second level. Registration is performed using a coarse and then a fine registration process for quick and accurate registration.

Claims

1. A method of registering a first image with a second image, the method comprising;

a) identifying a plurality of points in the first image;

b) identifying a plurality of points in the second image;

c) for each of a plurality of pairs of subsets, each pair of subsets comprising a subset of the plurality points in the first image and a subset of the plurality of points in the second image, computing a transformation that maps the subset of points in the first image to the subset of points in the second image;

d) identifying a likely transformation from the transformations for each of the plurality of subsets; and

e) using the likely transformation in registering the first image and the second image.

2. The method of claim 1, wherein identifying a likely transformation comprises selecting a transformation based on the frequency of occurrence of the likely transformation in the transformations computed for the plurality of pairs of subsets.

3. The method of claim 1, wherein identifying a likely transformation comprises deemphasizing transformations for pairs of the plurality of pairs of subsets having a high error.

4. The method of claim 3, wherein deemphasizing transformations comprises:

i) computing errors in transformation for each of the plurality of pairs;

ii) selecting those transformations having an error below a threshold; and

iii) identifying a likely transformation from the selected transformations.

5. The method of claim 4, wherein identifying a likely transformation comprises selecting a transformation from a cluster.

6. The method of claim 1, wherein identifying a plurality of points in the first image comprises extracting features from the first image and selecting the plurality of points on the features.

7. The method of claim 6, wherein identifying a plurality of points in the second image comprises extracting features from the second image and selecting the plurality of points on the features.

8. The method of claim 6, wherein computing a transformation that maps the subset of the plurality of points in the first image to the subset of the plurality of points in the second image, comprises mapping a subset consisting essentially of two points in the first image to a subset consisting essentially of two points in the second image.

9. The method of claim 1, wherein the first image is a three-dimensional image end the second image is a two-dimensional image and identifying a plurality of points in the first image comprises selecting a plurality of locations in the three-dimensional image and projecting those locations into points in a two-dimensional projection.

10. The method of claim 1, additionally comprising scaling at least one of the first or second images to match the scale of the first image to the second image.

11. A method of operating a contraband detection system to inspect an item, the method comprising:

a) forming a volumetric image of the item in a first coordinate system;

b) identifying a region of interest in the item using the volumetric image;

c) forming a projection image of the item in a second coordinate system;

d) registering the volumetric image to the projection image to identify the region of interest in the second coordinate system; and

e) selecting a region of the item for further inspection based on the region of interest in the second coordinate system.

12. The method of operating a contraband detection system of claim 11, further comprising probing the selected region of interest in the item using coherent x-ray scattering.

13. The method of operating a contraband detection system of claim 12, wherein forming a volumetric image comprises processing data obtained from a helical CT scan of the item.

14. The method of operating a contraband detection system of claim 13, wherein the volumetric image is formed in a first location and the projection image is formed in a second location, and the method further comprises moving the item from the first location to the second location.

15. The method of operating a contraband detection system of claim 14, wherein moving the item from the first location to the second location comprises moving the item on a plurality of conveyors.

16. A method of operating a contraband detection system to inspect an item, the method comprising:

a) forming a first image of the item in a first coordinate system, the first image including a region of interest;

b) extracting features from the first image to form a first symbolic image;

c) forming a second image of the item in a second coordinate system;

d) extracting features from the second image to form a second symbolic image; and

e) registering the first symbolic image to the second symbolic image to identify the region of interest in the second coordinate system.

17. The method of claim 16, wherein forming the second image of the item comprises forming a projection image of the item.

18. The method of claim 17, wherein forming a projection image of the item comprises forming an x-ray projection image of the item.

19. The method of claim 17, wherein forming the first image of the item comprises forming a volumetric image.

20. The method of claim 16, further comprising inspecting the region of interest with a coherent x-ray scattering probe.