Security system and method for operating it

• US 20070172143A1
• Filed: 03/04/2005
• Published: 07/26/2007
• Est. Priority Date: 04/16/2004
• Status: Abandoned Application

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Mueller-Schneiders, Stefan, Niem, Wolfgang
• Application Number:
  US10/587,796
• Publication Number:
  US 20070172143A1
• Time in Patent Office: Days
• US Class Current: 382/270
• CPC Class Codes: G08B 13/19602 Image analysis to detect motion of the intruder, e.g. by frame subtraction
• CPC Class Codes: G08B 13/1961 Movement detection not involving frame subtraction, e.g. motion detection on the basis of luminance changes in the image

Abstract

The invention relates to a security system 100, having a camera 3 for taking pictures of objects. From chronologically successive pictures taken by the camera 3, a gray variance [variant term] of the pixels is derived, which is compared with a threshold value that is dependent on the gray value. This improves the recognition accuracy of the security system 100.

Claims

1. A security system (100) having a camera (3) for taking pictures of objects, the security system (100) including at least one subsystem (101, 102), characterized in that the first subsystem (101) includes a first function module (1) with a light source whose brightness is controllable, a second function module (6) for generating a digital image sequence from pictures taken by the camera (3), and a third function module (8) for deriving the noise variance as a function of the gray value from the digital image sequence.

2. The security system as defined by claim 1, characterized in that the security system (100) includes a memory (9), in which the function values of the noise variance can be stored in memory as a function of the gray value.

3. The security system as defined by claim 1, characterized in that the second subsystem (102) includes a function module (13) for comparing a gray value variance, derived from pictures taken by the camera, with a predeterminable threshold value.

5. The method as defined by claim 1, characterized in that in the first operating state of the security system (100), the noise variance is ascertained as a function of the gray value of an image sensor (4) located in the camera (3) and is stored in a memory (9).

6. The method as defined by claim 1, characterized in that for ascertaining the noise variance as a function of the gray value, the camera (3) including the image sensor (4) is subjected to the radiation of a light source.

7. The method as defined by claim 1, characterized in that the light source is controlled such that the brightness of the light source is increased in small increments as a function of time and then after each increase is kept constant for a predeterminable length of time, so that a kind of stairstep curve for the functional dependency of the brightness of the light source on the time is created.

8. The method as defined by claim 1, characterized in that the light source, varied in steps in its brightness, is recorded by the camera (3);

that the image sensor (4) of the camera (3) converts the pictures taken into a digital image sequence; and

that from this image sequence, a functional relationship representing the noise variance as a function of the gray value is derived and is stored in the memory (9).

9. The method as defined by claim 1, characterized in that in the second operating state of the security system (100), images of a region to be secured are taken by the camera (3), and these images are examined for the presence of moving objects in the region to be secured.

10. The method as defined by claim 1, characterized in that from chronologically successive pictures of the region to be secured, the gray value variance for at least selected pixels is ascertained;

that if a deviation is found, a comparison with a threshold value is made, and this threshold value is predetermined variably as a function of the gray value.

11. The method as defined by claim 1, characterized in that the variable threshold value is read out from values stored in the memory (9).

12. The method as defined by claim 1, characterized in that the dependency of the noise variance on the gray value is ascertained for different parameters of the camera (3) and is stored as a function value in the memory device (9).

4. A method for operating a security system (100), including a camera for taking pictures of objects, characterized in that the method includes a first operating state (initializing phase) and a second operating state (operating phase).