Machine vision methods for identifying extrema of objects in rotated reference frames

• US 5,872,870 A
• Filed: 02/16/1996
• Issued: 02/16/1999
• Est. Priority Date: 02/16/1996
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Michael, David
• Primary Examiner(s): Tran, Phuoc
• Application Number:
  US08/603,286
• Time in Patent Office: 1,096 Days
• Field of Search: 382/171, 382/174, 382/183, 382/288, 382/289, 382/292, 382/199, 382/291, 382/204, 382/203
• US Class Current: 382/291
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/66 of image moments or centre of gravity
• CPC Class Codes: G06T 7/70 Determining position or orientation of objects or cameras camera calibration G06T7/80

Abstract

A method for determining extrema of an object with respect to a reference frame that is rotated in comparison to that of the image and the equipment that acquired it is characterized by the steps of taking a first projection of the object with respect to an axis of a coordinaate system that is rotated with respect to the reference frame of the acquisition equipment, identifying in that projection locations representing extrema of the object, and outputting those locations as indicative of the extrema with respect to the axis.

Claims

1. A method for determining extrema of an object in an image acquired by an image acquiring apparatus, where the image is aligned with a coordinate system of the image acquiring apparatus, the method comprising

taking a first projection of the object with respect to a first axis of a specified coordinate system that is rotated with respect to the coordinate system of the image acquiring apparatus;

identifying in the first projection locations representing one or more extrema of the object; and

outputting those one or more locations as indicative of extrema of the object with respect to the first axis of the specified coordinate system.

2. A method according to claim 1, comprising the steps of

taking a second projection of the object with respect to a second axis of the specified coordinate system;

identifying in the second projection locations representing one or more extrema of the object; and

outputting those one or more locations as indicative of extrema of the object with respect to a second axis of the specified coordinate system.

3. A method according to claim 1, comprising the steps of

determining one or more moments of the object;

and

selecting the specified coordinate system as a function of an orientation of those moments.

4. A method according to claim 1, including a step for identifying the object by segmenting the image.

5. A method according to claim 4, wherein the segmenting step includes the step of a finding threshold intensity that distinguishes the object in the image.

6. A method according to claim 5, wherein the segmenting step includes the step of an additional threshold intensity that distinguish the object'"'"'s edges in the image.

7. A method according to claim 6, wherein the segmenting step includes the step of proportionally counting the object'"'"'s edges in determining an extrema of the object.

8. A method according to claim 6, comprising the steps of

determining one or more moments of the object;

and

proportionally counting the object'"'"'s edges in determining a moment of the object.

9. A method according to claim 4, wherein the segmenting step includes the step of finding edges of the object in the image.

10. A method according to claim 8, wherein the segmenting step includes the step of tracking the boundary of the object in order to find its edges.

11. A method according to claim 1, comprising a step for identifying the object by performing connectivity analysis on the image.

12. A method according to claim 1, comprising the steps of

segmenting the image;

and

identifying the object by performing connectivity analysis on the segmented image.

13. A method according to any of claims 11 and 12, comprising the steps of

generating a run length coding of the image;

and

performing the connectivity analysis using that the run length coding.

14. A method according to claim 1, comprising the steps of

generating a mask;

and

applying the mask to the image to identify the object.

15. A method according to claim 14, wherein the step of generating the mask comprises the step of segmenting the image.

16. A method according to claim 15, wherein the segmenting step includes the step of a finding threshold intensity that distinguishes the object in the image.

17. A method according to claim 15, wherein the segmenting step includes the step of an additional threshold intensity that distinguish the object'"'"'s edges in the image.

18. A method according to claim 17, wherein the segmenting step includes the step of proportionally counting the object'"'"'s edges in determining an extrema of the object.

19. A method according to claim 17, comprising the steps of

determining one or more moments of the object;

and

proportionally counting the object'"'"'s edges in determining a moment of the object.

20. A method according to claim 15, wherein the segmenting step includes the step of finding edges of the object in the image.

21. A method according to claim 20, wherein the segmenting step includes the step of tracking the boundary of the object in order to find its edges.

22. A method according to claim 14, wherein the step of generating the mask comprises the step of performing connectivity analysis on the image.

23. A method according to claim 14, wherein the step of generating the mask comprises the steps of

segmenting the image;

and

identifying the object by performing connectivity analysis on the segmented image.

24. A method according to any of claims 22 and 23, comprising the steps of

generating a run length coding of the image;

and

performing the connectivity analysis using that the run length coding.

25. A method for determining extrema of an object in an image acquired by an image acquiring apparatus, where the image is aligned with a coordinate system of the image acquiring apparatus, the method comprising

analyzing the image to generate a mask for the object;

applying the mask to the image to isolate the object from the image;

taking a first projection of the object with respect to a first axis of a specified coordinate system that is rotated with respect to the coordinate system of the image acquiring apparatus;

identifying in the first projection locations representing one or more extrema of the object; and

outputting those one or more locations as indicative of a extrema of the object with respect to the first axis of the specified coordinate system.

26. A method for determining extrema of an object in an image acquired by an image acquiring apparatus, the method comprising

analyzing the image to generate a mask for the object;

applying the mask to the image to isolate the object from the image;

determining one or more moments of the object;

taking a first projection of the object with respect to a first axis of a specified coordinate based on an orientation of those moments;

identifying in the first projection locations representing one or more extrema of the object; and

outputting those one or more locations as indicative of a extrema of the object with respect to the first axis of the specified coordinate system.

27. A method according to claim 26, further comprising

determining a location a center of mass of the object;

and

outputting the locations representing one or more extrema relative to the location of the center of mass of the object.