METHOD AND APPARATUS FOR COUNTING NUMBER OF PERSONS

• US 20160292890A1
• Filed: 08/24/2015
• Published: 10/06/2016
• Est. Priority Date: 04/03/2015
• Status: Active Grant

• Current Assignee: Hanwha Vision Company Limited (Hanwha Corporation)
• Original Assignee: Hanwha Techwin Co., Ltd. (Hanwha Corporation)
• Inventors: BAEK, Youngmin, BAE, Soonmin
• Granted Patent: US 9,978,155 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06T 2207/10028 Range image; Depth image; 3D point clouds
• CPC Class Codes: G06T 2207/30196 Human being; Person
• CPC Class Codes: G06T 2207/30242 Counting objects in image
• CPC Class Codes: G06T 7/215 Motion-based segmentation
• CPC Class Codes: G06T 7/64 of convexity or concavity
• CPC Class Codes: G06V 20/52 Surveillance or monitoring of activities, e.g. for recognising suspicious objects recognising microscopic objects G06V20/69

Abstract

A method and apparatus for counting a number of persons in an image are provided. The person counting apparatus includes: a detector configured to detect a movement area in a top-view distance image, of at least one image frame, providing distance information; an estimator configured to estimate a candidate head area from the movement area based on the distance information; and a determiner configured to determine whether the candidate head area is an actual head of a person based on a similarity to a circle of the candidate head area and a spherical curvature of the candidate head area estimated from the distance information about the candidate head area.

Claims

1. A method of counting a number of persons in at least one image frame, the method comprising:

detecting a movement area in a top-view distance image, of the at least one image frame, providing distance information;

estimating a candidate head area from the movement area based on the distance information; and

determining whether the candidate head area is an actual head of a person based on a similarity to a circle of the candidate head area and a spherical curvature of the candidate head area estimated from the distance information about the candidate head area.

2. The method of claim 1, wherein the estimating a candidate head area comprises:

extracting a reference pixel, which is a pixel corresponding to a greatest height from a ground surface in the at least one image frame, from the movement area;

setting an expanded area comprising the reference pixel and surrounding pixels with the same height as the reference pixel and surrounding pixels whose change in height is constant or decreases; and

setting the candidate head area comprising the reference pixel and surrounding pixels with heights that differ from the height of the reference pixel within a pre-set critical value as a candidate head area.

3. The method of claim 2, further comprising:

determining whether an area other than the expanded area exists in the movement area; and

if it is determined that the other area exists, setting the other area as another movement area, and repeating the extracting the reference pixel, the setting the expanded area and the setting, and the setting the candidate head area with respect to the other movement area.

4. The method of claim 2, wherein the estimating a candidate head area is repeatedly performed in another movement area.

5. The method of claim 1, wherein, in the determining whether the candidate head area is an actual head of a person, the similarity to a circle of the candidate head area is determined by determining whether a ratio of an area of a smallest circle surrounding the candidate head area and an area of the candidate head area exceeds a pre-set critical value.

6. The method of claim 5, wherein, in the determining whether the candidate head area is an actual head of a person, the spherical curvature of the candidate head area is determined using information about a height of a plurality of points on each of at least one reference line extending across the candidate head area.

7. The method of claim 1, wherein the determining whether the candidate head area is an actual head of a person comprises:

determining satisfaction of a circle-similarity condition by determining whether a ratio of an area of a smallest circle surrounding the candidate head area and an area of the candidate head area exceeds a first pre-set critical value is satisfied;

if at least one reference line extending across the candidate head area is approximated to a quadratic function including a location of a point on the reference line and a height of the point on the reference line from a ground surface in the at least one image frame as variables of the quadratic function, determining satisfaction of a spherical curvature condition by determining whether a pole of the quadratic function exists in the candidate head area and whether a second-order coefficient is smaller than or equal to a second pre-set critical value; and

setting the candidate head area satisfying the circle-similarity condition and the spherical curvature condition to be the actual head of a person.

8. The method of claim 7, wherein the determining satisfaction of the spherical curvature condition comprises determining whether each of a plurality of reference lines arranged at a designated interval in the candidate head area satisfies the spherical curvature condition.

9. The method of claim 1, further comprising, if a tracked path of the candidate head area in the at least one image frame passes a counting line and a ratio of a total number of image frames in which the candidate head area is detected to a number of valid frames in which the candidate head area is determined as being the actual head of a person is equal to or greater than a pre-set critical value, counting the candidate head area as a person.

10. The method of claim 1, wherein the determining whether the candidate head area is an actual head of a person comprises, if a tracked path of the estimated candidate head area in the at least one image frame passes a counting line, determining whether the estimated candidate head area is the actual head of a person.

11. A person counting apparatus comprising:

a detector configured to detect a movement area in a top-view distance image, of at least one image frame, providing distance information;

an estimator configured to estimate a candidate head area from the movement area based on the distance information; and

a determiner configured to determine whether the candidate head area is an actual head of a person based on a similarity to a circle of the candidate head area and a spherical curvature of the candidate head area estimated from the distance information about the candidate head area.

12. The apparatus of claim 11, wherein the estimator comprises:

a reference pixel extractor configured to extract a reference pixel, which is a pixel corresponding to a greatest height from a ground surface in the at least one image frame, from the movement area;

an area expander configured to set an expanded area comprising the reference pixel and surrounding pixels with the same height as the reference pixel and surrounding pixels whose change in height is constant or decreases; and

a candidate head area setter configured to set the candidate head area comprising the reference pixel and surrounding pixels with heights that differ from the height of the reference pixel within a pre-set critical value as a candidate head area.

13. The apparatus of claim 12, wherein the estimator is further configured to determine whether an area other than the expanded area exists in the movement area;

and

wherein, in response to the determining that the other area exists, the estimator is configured to set the other area as another movement area, and repeat the extracting the reference pixel, the setting the expanded area and the setting, and the setting the candidate head area with respect to the other movement area.

14. The apparatus of claim 12, wherein the estimator is further configured to repeatedly perform the estimating a candidate head area in another movement area.

15. The apparatus of claim 11, wherein, in order to determine whether the candidate head area is an actual head of a person, the determiner is configured to determine the similarity to a circle of the candidate head area by determining whether a ratio of an area of a smallest circle surrounding the candidate head area and an area of the candidate head area exceeds a pre-set critical value.

16. The apparatus of claim 15, wherein, in order to determine whether the candidate head area is an actual head of a person, the determiner is configured to determine the spherical curvature of the candidate head area using information about a height of a plurality of points on each of at least one reference line extending across the candidate head area.

17. The apparatus of claim 11, wherein the determiner comprises:

a first determiner configured to determine satisfaction of a circle-similarity condition by determining whether a ratio of an area of a smallest circle surrounding the candidate head area and an area of the candidate head area exceeds a first pre-set critical value is satisfied;

a second determiner configured to, if at least one reference line extending across the candidate head area is approximated to a quadratic function including a location of the point on the reference line and a height of the point on the reference line from a ground surface in the at least one image frame as variables of the quadratic function, determine satisfaction of a spherical curvature condition by determining whether a pole of the quadratic function exists in the candidate head area and whether a second-order coefficient is smaller than or equal to a second pre-set critical value; and

a third determiner configured to determine the candidate head area satisfying the circle-similarity condition and the spherical curvature condition to be the actual head of a person.

18. The apparatus of claim 17, wherein the determiner is configured to determines whether each of a plurality of reference lines arranged at a designated interval in the candidate head area satisfies the spherical curvature condition.

19. The apparatus of claim 11, further comprising a counter, which, if a tracked path of the candidate head area in the at least one image frame passes a counting line and a ratio of a total number of image frames in which the candidate head area is detected to a number of valid frames in which the candidate head area is determined as being the actual head of a person is equal to or greater than a pre-set critical value, counts the candidate head area as a person.

20. The apparatus of claim 11, wherein, if a tracked path of the estimated candidate head area in the at least one image frame passes a counting line, the determiner is configured to determine whether the estimated candidate head area is the actual head of a person.