METHODS AND SYSTEMS FOR EFFICIENT IMAGE CROPPING AND ANALYSIS

• US 20150294175A1
• Filed: 04/10/2014
• Published: 10/15/2015
• Est. Priority Date: 04/10/2014
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Bala, Raja, Burry, Aaron M.
• Granted Patent: US 9,569,681 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06T 2207/20021 Dividing image into blocks, subimages or windows
• CPC Class Codes: G06T 2207/20132 Image cropping
• CPC Class Codes: G06T 3/00 Geometric image transformations in the plane of the image
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: G06V 20/62 Text, e.g. of license plates, overlay texts or captions on TV images

Abstract

A system and method for cropping a license plate image to facilitate license plate recognition by obtaining an image that includes the license plate image, dividing the image into multiple sub-blocks, computing an activity measure for each sub-block; determining an activity threshold, determining that a sub-block is an active sub-block by comparing the activity measure for the sub-block with the activity threshold, generating a second image of the license plate information, where the second image includes the active sub-block, and obtaining the license plate information based on the second image.

Claims

1. A method comprising:

obtaining an image comprising license plate information;

dividing the image into a plurality of sub-blocks;

computing a spatial activity measure for each sub-block of the plurality of sub-blocks;

determining an activity threshold;

determining that a sub-block of the plurality of sub-blocks is an active sub-block by comparing the spatial activity measure for the sub-block with the activity threshold;

generating, using one or more processors, a second image of the license plate information, wherein the second image comprises the active sub-block; and

obtaining the license plate information based on the second image.

2. The method of claim 1, wherein, prior to obtaining the image, the image is generated by vertically cropping a third image comprising the license plate information.

3. The method of claim 1, wherein, prior to obtaining the image, the image is generated by removing tilt from a third image comprising the license plate information.

4. The method of claim 1, further comprising performing a frequency analysis on each sub-block of the plurality of sub-blocks, wherein the spatial activity measure for each sub-block is based on the frequency analysis of that sub-block.

5. The method of claim 1, further comprising generating an activity profile for the image based on the spatial activity measure for each sub-block, wherein the activity threshold is based on the activity profile.

6. The method of claim 1, further comprising determining that a second sub-block of the plurality of sub-blocks is an inactive sub-block by comparing the spatial activity measure for the second sub-block with the activity threshold, wherein the second image does not comprise the inactive sub-block.

7. The method of claim 6, further comprising determining that a third sub-block of the plurality of sub-blocks is an inactive sub-block by determining that the third sub-block is between the inactive sub-block and an edge of the image.

8. The method of claim 1, further comprising determining that a second sub-block of the plurality of sub-blocks is a second active sub-block by determining that the second sub-block is between the active sub-block and a third active sub-block in the image.

9. The method of claim 1, further comprising:

determining a third image of the license plate comprising only active sub-blocks;

determining that the third image is overcropped with respect the license plate information based on comparing a ratio of the third image with an expected license plate ratio; and

wherein, the second image additionally comprises one or more inactive sub-blocks.

10. The method of claim 1, wherein the spatial activity measure is computed using the formula:

11. A system comprising:

a processing system comprising one or more processors; and

a memory system comprising one or more computer-readable media, wherein the one or more computer-readable media contain instructions that, when executed by the processing system, cause the processing system to perform operations comprising;

obtaining an image comprising license plate information;

dividing the image into a plurality of sub-blocks;

computing a spatial activity measure for each sub-block of the plurality of sub-blocks;

determining an activity threshold;

determining that a sub-block of the plurality of sub-blocks is an active sub-block by comparing the spatial activity measure for the sub-block with the activity threshold;

generating, using one or more processors, a second image of the license plate information, wherein the second image comprises the active sub-block; and

obtaining the license plate information based on the second image.

12. The system of claim 11, wherein, prior to obtaining the image, the image is generated by vertically cropping a third image comprising the license plate information.

13. The system of claim 11, wherein, prior to obtaining the image, the image is generated by removing tilt from a third image comprising the license plate information.

14. The system of claim 11, the operations further comprising performing a frequency analysis on each sub-block of the plurality of sub-blocks, wherein the spatial activity measure for each sub-block is based on the frequency analysis of that sub-block.

15. The system of claim 11, the operations further comprising generating an activity profile for the image based on the spatial activity measure for each sub-block, wherein the activity threshold is based on the activity profile.

16. The system of claim 11, the operations further comprising determining that a second sub-block of the plurality of sub-blocks is an inactive sub-block by comparing the spatial activity measure for the second sub-block with the activity threshold, wherein the second image does not comprise the inactive sub-block.

17. The system of claim 16, the operations further comprising determining that a third sub-block of the plurality of sub-blocks is an inactive sub-block by determining that the third sub-block is between the inactive sub-block and an edge of the image.

18. The system of claim 11, the operations further comprising determining that a second sub-block of the plurality of sub-blocks is a second active sub-block by determining that the second sub-block is between the active sub-block and a third active sub-block in the image.

19. The system of claim 11, the operations further comprising:

determining a third image of the license plate comprising only active sub-blocks;

determining that the third image is overcropped with respect the license plate information based on comparing a ratio of the third image with an expected license plate ratio; and

wherein, the second image additionally comprises one or more inactive sub-blocks.

20. The system of claim 11, wherein the spatial activity measure is computed using the formula: