Method and apparatus for processing an image

• US 7,403,636 B2
• Filed: 11/12/2003
• Issued: 07/22/2008
• Est. Priority Date: 12/30/2002
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Ji, Xin, Wang, Libing, Chen, Xinwu
• Primary Examiner(s): Carter; Aaron W
• Application Number:
  US10/704,591
• Publication Number:
  US 20040131236A1
• Time in Patent Office: 1,714 Days
• Field of Search: 382/103, 382/118, 382/190, 382/199, 382/203, 382/224, 348/77
• US Class Current: 382/103
• CPC Class Codes: G06V 40/165 using facial parts and geometric relationships

Abstract

The present invention provides a method of processing an image, which includes the steps of identifying one candidate for human face region within the image, selecting a mouth neighborhood within the candidate for human face region, processing the mouth neighborhood, and classifying the candidate for human face region based on results of the processing step. According to the method of the present invention, human faces are detected just based on pixels included in the mouth neighborhood, but not all the pixels of the entire face.

Claims

1. A method of processing an image, characterized by comprising steps of:

identifying one candidate for human face region within the image;

selecting a mouth neighborhood within the candidate for human face region;

forming an edge map at least corresponding to the mouth neighborhood;

calculating edge information for the mouth neighborhood based on the edge map; and

classifying the candidate for human face region based on the edge information.

2. The method of processing an image according to claim 1, characterized in that said step of selecting selects a mouth neighborhood which is r3 times the width of the candidate for human face region, and r1 times the height of the candidate for human face region, wherein r3 is a constant greater than 0.2 and less than 1, and r1 is a constant greater than 0.1 and less than 0.7.

3. The method of processing an image according to claim 2, characterized in that r3 equals 0.7, and said r1 equals 0.3.

4. The method of processing an image according to claim 1, characterized in that said step of calculating edge information comprises steps of:

selecting a portion of the edge map which corresponds to neighborhood pixels whose characteristic values are greater than a first threshold, resulting in a series of bright areas composed of selected pixels;

calculating the size S1 of the candidate for human face region and the size S2 of the biggest bright area;

and in that said step of classifying comprises a step of;

classifying the candidate for human face region as a false human face, or one candidate with high possibility of being a false human faces if S2/S1 is less than a second threshold.

5. The method of processing an image according to claim 4, characterized in that said step of calculating edge information further comprises a step of:

calculating the size S3 of the second biggest bright area;

and in that said step of classifying further comprises a step of;

classifying the candidate for human face region as a false human face, or one candidate with high possibility of being a false human face, if S3/S2 is less than a third threshold and the center of the biggest bright area is not in a mouth area, the mouth area being a predefined portion of the mouth neighborhood.

6. The method of processing an image according to claim 5, characterized in that said step of classifying further comprises a step of:

classifying the candidate for human face region as a real human face, or one candidate with high possibility of being a real human faces if S3/S2 is less than the third threshold and the center of the biggest bright area is in the mouth area.

7. The method of processing an image according to claim 4, characterized in that said step of calculating edge information further comprises a step of:

calculating the size S3 of the second biggest bright area;

and in that said step of classifying further comprises a step of;

classifying the candidate for human face region as a false human face, or one candidate with high possibility of being a false human faces if S3/S2 is not less than a third threshold and the mid-point between the respective centers of the first and second biggest bright areas is not in a mouth area, the mouth area being a predefined portion of the mouth neighborhood.

8. The method of processing an image according to claim 7, characterized in that said step of classifying further comprises a step of:

classifying the candidate for human face region as a real human face, or one candidate with high possibility of being a real human face if S3/S2 is not less than the third threshold and the mid-point between the respective centers of the first and second biggest bright areas is in the mouth area.

9. The method of processing an image according to claim 1, characterized in that said step of calculating edge information comprises a step of:

calculating the average edge intensity within the mouth neighborhood and the average edge intensity within a mouth area, the mouth area being a predefined portion of the mouth neighborhood;

and in that said step of classifying comprises a step of;

classifying the candidate for human face region as a false human face, or one candidate with high possibility of being a false human face if the difference between the average edge intensity within the mouth area and the average edge intensity within the mouth neighborhood is not greater than a predefined threshold.

10. The method of processing an image according to claim 9, characterized in that said step of classifying further comprises a step of:

classifying the candidate for human face region as a real human face, or one candidate with high possibility of being a real human face, if the difference between the average edge intensity within the mouth area and the average edge intensity within the mouth neighborhood is greater than the predefined threshold.

11. The method of processing an image according to claim 5, characterized in that the mouth area is r2 times the width of the candidate for human face region, and at most r1 times the height of the candidate for human face region, wherein r2 is a constant greater than 0.1 and less than 0.7, and r1 is a constant greater than 0.1 and less than 0.7.

12. The method of processing an image according to claim 11, characterized in that r2 equals 0.5, and said r1 equals 0.3.

13. An apparatus for processing an image, characterized by comprising:

a candidate identifier, for identifying one candidate for human face region within the image;

a mouth neighborhood selector, for selecting a mouth neighborhood within the candidate for human face region that has been identified by said candidate identifier;

a converter, for converting a portion of the image including at least the mouth neighborhood into an edge map;

an edge information calculator, for calculating edge information for the mouth neighborhood based on the edge map; and

a classifier, for classifying the candidate for human face region that has been identified by said candidate identifier based on the edge information.

14. The apparatus for processing an image according to claim 13, characterized in that said mouth neighborhood selector selects a mouth neighborhood which is r3 times the width of the candidate for human face region, and r1 times the height of the candidate for human face region, wherein r3 is a constant greater than 0.2 and less than 1, and r1 is a constant greater than 0.1 and less than 0.7.

15. The apparatus for processing an image according to claim 14, characterized in that r3 equals 0.7, and said r1 equals 0.3.

16. The apparatus for processing an image according to claim 13, characterized in that said edge information calculator comprises:

a bright area identifier, for identifying within the edge map a series of bright areas each of which is composed of pixels whose characteristic values are greater than a first threshold;

a size calculator, for calculating the size S1 of the candidate for human face region and the size S2 of the biggest bright area;

and in that said classifier classifies the candidate for human face region as a false human face, or one candidate with high possibility of being a false human face, if S2/S1 is less than a second threshold.

17. The apparatus for processing an image according to claim 16, characterized in that said size calculator also calculates the size S3 of the second biggest bright area;

and in that said classifier further classifies the candidate for human face region as a false human face, or one candidate with high possibility of being a false human face, if S3/S2 is less than a third threshold and the center of the biggest bright area is not in a mouth area the mouth area being a predefined portion of the mouth neighborhood.

18. The apparatus for processing an image according to claim 17, characterized in that said classifier further classifies the candidate for human face region as a real human face, or one candidate with high possibility of being a real human faces if S3/S2 is less than the third threshold and the center of the biggest bright area is in the mouth area.

19. The apparatus for processing an image according to claim 16, characterized in that said size calculator also calculates the size S3 of the second biggest bright area;

and in that said classifier further classifies the candidate for human face region as a false human face, or one candidate with high possibility of being a false human face, if S3/S2 is not less than a third threshold and the mid-point between the respective centers of the first and second biggest bright areas is not in a mouth area, the mouth area being a predefined portion of the mouth neighborhood.

20. The apparatus for processing an image according to claim 19, characterized in that said classifier further classifies the candidate for human face region as a real human face, or one candidate with high possibility of being a real human face, if S3/S2 is not less than the third threshold and the mid-point between the respective centers of the first and second biggest bright areas is in the mouth area.

21. The apparatus for processing an image according to claim 13, characterized in that said edge information calculator comprises:

an edge intensity calculator, for calculating the average edge intensity within the mouth neighborhood and the average edge intensity within a mouth area, the mouth area being a predefined portion of the mouth neighborhood;

and in that said classifier classifies the candidate for human face region as a false human face, or one candidate with high possibility of being a false human face, if the difference between the average edge intensity within the mouth area and the average edge intensity within the mouth neighborhood is not greater than a predefined threshold.

22. The apparatus for processing an image according to claim 21, characterized in that said classifier further classifies the candidate for human face region as a real human face, or one candidate with high possibility of being a real human face, if the difference between the average edge intensity within the mouth area and the average edge intensity within the mouth neighborhood is greater than the predefined threshold.

23. The apparatus for processing an image according to claim 17, characterized in that the mouth area is r2 times the width of the candidate for human face region, and at most r1 times the height of the candidate for human face region, wherein r2 is a constant greater than 0.1 and less than 0.7, and r1 is a constant greater than 0.1 and less than 0.7.

24. The apparatus for processing an image according to claim 23, characterized in that said r2 equals 0.5, and said r1 equals 0.3.