ADAPTIVE INTEREST RATE CONTROL FOR VISUAL SEARCH

• US 20130279813A1
• Filed: 04/24/2013
• Published: 10/24/2013
• Est. Priority Date: 04/24/2012
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: Andrew LLC (CommScope Holding Company, Inc.)
• Inventors: Falchetto, Mirko, Pau, Danilo Pietro
• Granted Patent: US 9,600,744 B2
• Time in Patent Office: Days
• US Class Current: 382/201
• CPC Class Codes: G06F 18/211 Selection of the most significant subset of features
• CPC Class Codes: G06T 3/18 Image warping, e.g. rearranging pixels individually
• CPC Class Codes: G06T 7/33 using feature-based methods
• CPC Class Codes: G06T 7/337 involving reference images or patches
• CPC Class Codes: G06T 7/344 involving models
• CPC Class Codes: G06T 7/75 involving models
• CPC Class Codes: G06V 10/24 Aligning, centring, orientation detection or correction of the image
• CPC Class Codes: G06V 10/247 by affine transforms, e.g. correction due to perspective effects; Quadrilaterals, e.g. trapezoids
• CPC Class Codes: G06V 30/18143 Extracting features based on salient regional features, e.g. scale invariant feature transform [SIFT] keypoints
• CPC Class Codes: H04N 19/57 Motion estimation characterised by a search window with variable size or shape

Abstract

Image-processing apparatus and methods to adaptively vary an interest point threshold value and control a number of interest points identified in an image frame are described. Sub-regions of an image frame may be processed in a sequence, and an interest point threshold value calculated for each sub-region. The calculated value of the interest point threshold may depend upon pre-selected values and values determined from the processing of one or more prior sub-regions. By using adaptive thresholding, a number of interest points detected for each frame in a sequence of image frames may remain substantially constant, even though objects within the frames may vary appreciably.

Claims

1. An image processing system having at least one processor adapted to control a number of interest points detected in an image frame, the system comprising:

an interest point detector configured to identify one or more interest points in a first sub-region of image data associated with an image frame based upon an interest point threshold value; and

a rate controller configured to determine the interest point threshold value based at least in part upon a number of interest points identified in a previous sub-region of image data for the image frame.

2. The image processing system of claim 1, wherein at least one of the interest point detector or the rate controller comprises a field-programmable gate array.

3. The image processing system of claim 1, wherein the interest point detector is configured to receive the interest point threshold value from the rate controller and to communicate a number of identified interest points in the first sub-region to the rate controller.

4. The image processing system of claim 1, wherein the rate controller is further configured to determine the interest point threshold value based in part upon a target number of interest points preselected for the image frame.

5. The image processing system of claim 1, wherein the rate controller is further configured to determine the interest point threshold value based in part upon a target number of interest points calculated for the previous sub-region.

6. The image processing system of claim 5, wherein the target number of interest points calculated for the previous sub-region is based at least in part on a total number of interest points pre-selected for the image frame and a total number of interest points detected for all prior processed sub-regions of the image frame.

7. The image processing system of claim 1, wherein the rate controller is further configured to determine the interest point threshold value based in part upon a recognition rate.

8. The image processing system of claim 7, wherein the recognition rate is a value calculated for a previous sub-region.

9. The image processing system of claim 7, wherein the recognition rate is a cumulative rate determined based on all prior processed sub-regions of the image frame.

10. The image processing system of claim 7, further comprising:

a descriptor configured to generate descriptor data for at least one identified interest point; and

a feature matcher configured to evaluate matches between features of two or more images based at least in part on the descriptor data.

11. The image processing system of claim 10, wherein the feature matcher is further configured to determine the recognition rate and indicate the recognition rate to the rate controller.

12. The image processing system of claim 1, further comprising a selector configured to limit an amount of interest point data received from the interest point detector.

13. The image processing system of claim 12, wherein the selector is further configured to receive a target number of interest points for an image sub-region and to selectively discard interest point data received from the interest point detector based upon the target number of interest points for an image sub-region.

14. An image processing method for controlling a number of interest points by at least one processor, the method comprising:

identifying, by an interest point detector, one or more interest points in a first sub-region of image data associated with an image frame based upon an interest point threshold value; and

determining, by a rate controller, the interest point threshold value based at least in part upon a number of interest points identified in a previous sub-region of image data for the image frame.

15. The image processing method of claim 14, wherein at least one of the interest point detector or the rate controller comprises a field-programmable gate array

16. The image processing method of claim 14, further comprising:

receiving, by the interest point detector, the interest point threshold value from the rate controller; and

communicating, by the interest point detector, a number of identified interest points in the first sub-region to the rate controller.

17. The image processing method of claim 14, further comprising determining, by the rate controller, the interest point threshold value based in part upon a target number of interest points pre-selected for the image frame.

18. The image processing method of claim 14, further comprising determining, by the rate controller, the interest point threshold value based in part upon a target number of interest points calculated for the previous sub-region.

19. The image processing method of claim 18, wherein the target number of interest points calculated for the previous sub-region is based at least in part on a total number of interest points pre-selected for the image frame and a total number of interest points detected for all prior processed sub-regions of the image frame.

20. The image processing method of claim 14, wherein the rate controller is further configured to determine the interest point threshold value based in part upon a recognition rate.

21. The image processing method of claim 20, wherein the recognition rate is a value calculated for a previous sub-region.

22. The image processing method of claim 20, wherein the recognition rate is a cumulative rate determined based on all prior processed sub-regions of the image frame.

23. The image processing method of claim 20, further comprising:

generating, by a descriptor, descriptor data for at least one identified interest point; and

evaluating, by a feature matcher, a quality of matching between features of two or more images based at least in part on the descriptor data.

24. The image processing method of claim 23, further comprising determining, by the feature matcher, the recognition rate and indicating the recognition rate to the rate controller.

25. The image processing method of claim 14, further comprising a selector configured to limit an amount of interest point data received from the interest point detector.