IR or thermal image enhancement method based on background information for video analysis

• US 10,452,922 B2
• Filed: 06/13/2016
• Issued: 10/22/2019
• Est. Priority Date: 06/15/2015
• Status: Active Grant

• Current Assignee: Davantis Technologies SL
• Original Assignee: Davantis Technologies SL
• Inventors: Herrero Molina, Nicolas, Balcells Capellades, Marti, Lluis Barba, Jordi
• Primary Examiner(s): Liu, Li
• Application Number:
  US15/580,257
• Publication Number:
  US 20180225522A1
• Time in Patent Office: 1,226 Days
• CPC Class Codes: G06T 2207/10028 Range image; Depth image; 3D point clouds
• CPC Class Codes: G06T 2207/10048 Infrared image
• CPC Class Codes: G06T 5/90 Dynamic range modification of images or parts thereof
• CPC Class Codes: G06V 10/25 Determination of region of interest [ROI] or a volume of interest [VOI]
• CPC Class Codes: G06V 20/52 Surveillance or monitoring of activities, e.g. for recognising suspicious objects recognising microscopic objects G06V20/69
• CPC Class Codes: G08B 13/19613 Recognition of a predetermined image pattern or behaviour pattern indicating theft or intrusion
• CPC Class Codes: G08B 29/24 Self-calibration, e.g. compensating for environmental drift or ageing of components

Abstract

An image enhancement method for video analysis or automatic video surveillance systems has at least one image acquisition device, through which an IR thermal spectrum image is captured from an area of space, a scene calibration system and a detection system, through which at least one object type is detected. The method includes at least one processing stage in which the contrast of the captured image is enhanced by the image acquisition device through the image'"'"'s depth or scene information obtained directly or indirectly by the scene calibration system or entered manually by the user.

Claims

1. An image enhancement method for video analysis or automatic surveillance system, comprising;

at least one image acquisition device through which an IR or thermal spectrum input image of an area of space is captured, the input image being digitized by the image acquisition device or an image digitizing system,

a scene calibration system, and

a detection system through which at least one type of object is detected;

the method comprising;

at least one processing stage in which a contrast of the input image is improved through the input image'"'"'s depth or scene information obtained directly or indirectly by the scene calibration system or entered manually by a user, the at least one processing stage comprising at least one scene equalization stage defined from the input image'"'"'s depth or scene information;

the at least one scene equalization stage comprises at least the following steps;

define a region of interest (r);

calculate a histogram of the input image pixels contained in the region of interest p_Ir(i) and use this information to obtain a corresponding transformation function T_r;

wherein

2. The image enhancement method for video analysis or automatic surveillance system according to claim 1, wherein the region of interest (r) comprises smaller target object types that are difficult for the detection system to detect.

3. The image enhancement method for video analysis or automatic surveillance system according to claim 2, wherein the region of interest (r) comprises at least all of the pixels for which an expected size of a target object is in the range (T_min,T_min+ε

(T_max−

T_min));

with

T_min being a minimum size of the target object that the detection system can detect;

T_max being a maximum possible size of the target object; and

ε

is a number between 0 and 1.

4. The image enhancement method for video analysis or automatic surveillance system according to claim 1, wherein the equalization stage comprises at least one step that estimates a range of the histogram of the region of interest through calculation of an entropy in the region of interest in the following way:

5. The image enhancement method for video analysis or automatic surveillance system according to claim 4, wherein the entropy is calculated using the following moving average

(t)=(t−

1)·

(1−

ρ

)+H_r(t)·

ρ

with ρ

being a number between 0 and 1.

6. The image enhancement method for video analysis or automatic surveillance system according to claim 1, further comprising an equalization smoothing stage in which a new image is obtained from a weighted sum of the equalized image and the input image in the following way:

I_F(x,y)=g(x,y)·

O(x,y)+(1−

g(x,y))·

I(x,y)

wherein g(x,y) is any function whose value is maximum and equal to 1 in the center of the region of interest (r);

I(x,y) is the input image, and

O(x,y) is the equalized image.

7. The image enhancement method for video analysis or automatic surveillance system according to claim 6, wherein

8. The image enhancement method for video analysis or automatic surveillance system according to claim 1, wherein the depth or scene information is obtained from a scene calibration system applying a calibration procedure consisting of at least the following phases:

a sample acquisition phase divided into the following sub-phases;

an image acquisition sub-phase;

an image processing sub-phase, which determines whether there is a moving object in the input image; and

a person pre-classification sub-phase, which determines whether or not the moving object is a person and stores its size and position information in case it is; and

a calibration phase which obtains the size of a person for each position of the image based on the size and position data obtained for each object identified as a person in the sample acquisition phase.

9. The image enhancement method for video analysis or automatic surveillance system according to claim 8, wherein the region of interest (r) is defined as the transit area during the calibration procedure, this transit area being where samples are obtained during the sample acquisition phase.

10. The image enhancement method for video analysis or automatic surveillance system according to claim 8, wherein the region of interest (r) is obtained according to the procedure:

Divide the image into N resizable cells;

Mark the cells in which the scene calibration system has obtained at least one sample in the sample acquisition phase;

Define the region of interest (r) as a convex area that surrounds the marked cells.

11. The image enhancement system for video analysis or automatic surveillance system of claim 1, comprising functional elements suitable for carrying out a plurality of image enhancement procedures.

12. The image enhancement system for video analysis or automatic surveillance system according to claim 1, wherein the detection system, through which the at least one object type is detected, comprises at least:

a static scene segmentation system that classifies pixels into at least two types;

moving objects and objects belonging to a background of the input image;

a candidate generation system which groups associated moving pixels into objects;

a classification system which classifies the objects according to whether or not they are target object types; and

a tracking system that maintains temporal coherence of the objects so that, depending on detection rules entered by the user, respective intrusion alarms can be generated.

13. The image enhancement system for video analysis or automatic surveillance system according to claim 12, wherein the image acquisition device is analog and the system consists of a digitizing stage for the image captured by the image acquisition device prior to the processing stage.