Rain sensor

• US 7,646,889 B2
• Filed: 03/16/2006
• Issued: 01/12/2010
• Est. Priority Date: 04/11/2005
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Tsukamoto, Takeshi
• Primary Examiner(s): Werner; Brian P
• Assistant Examiner(s): WANG, CLAIRE X
• Application Number:
  US11/376,210
• Publication Number:
  US 20060228001A1
• Time in Patent Office: 1,398 Days
• Field of Search: 340/438, 382/104, 382/100, 382/103, 250/208.1
• US Class Current: 382/104
• CPC Class Codes: B60S 1/0822 characterized by the arrangement or type of detection means
• CPC Class Codes: B60S 1/0844 including a camera
• CPC Class Codes: G06V 20/56 exterior to a vehicle by using sensors mounted on the vehicle

Abstract

A rain sensor provided in a vehicle includes a camera and a processor. The camera takes an image of a scene outside of the vehicle through a windshield of the vehicle with an infinite focal length. The processor detects rain based on a variation degree of intensities of pixels in the image from an average intensity of the pixels.

Claims

1. A rain sensor for a vehicle, comprising:

a camera provided in the vehicle configured with a long focal length set to take an image of a scene outside of the vehicle through a windshield of the vehicle while blurring a substance on the windshield; and

a processor unit configured to detect rain based on a variation degree of intensities of pixels, which are included in the image, from an average intensity of the pixels, wherein

the processor unit is configured to

divide an image taken by the camera into sub-images according to a plurality of sub-areas defined in an area of the image;

calculate, with respect to each of the plurality of sub-areas, a moment-to-moment transition of a variation degree of intensities of pixels, which are included in the each of the plurality of sub-areas, from an average intensity of the pixels included in the each of the plurality of sub-areas, and

detect rain based on the moment-to-moment transition.

2. The rain sensor according to claim 1, further comprising:

a memory for temporarily storing, with respect to each of the plurality of sub-areas, a first variation degree of intensities of pixels included in the each of the plurality of sub-areas of an image taken by the camera at a first time previous to a second time, wherein

the processor unit calculates, with respect to the each of the plurality of sub-areas, a moment-to-moment transition by computing a difference between (i) the first variation degree stored in the memory and (ii) a second variation degree of intensities of pixels included in the each of the plurality of sub-areas of an image taken by the camera at the second time.

3. The rain sensor according to claim 2, wherein

the processor unit

applies a given process to a difference, which is computed between the first variation degree and the second variation degree with respect to the each of the plurality of sub-areas, to assign the difference a given value, and

detects rain based on a result of incorporating given values obtained from the given process with respect to all the plurality of sub-areas.

4. The rain sensor according to claim 3, wherein

in the given process,

when a difference between the first variation degree and the second variation degree is not larger than a threshold value, the difference is assigned zero as a given value, and

the result of incorporating given values is obtained as a sum of given values with respect to all the plurality of sub-areas.

5. The rain sensor according to claim 3, wherein

in the given process,

when a first difference between the first variation degree and the second variation degree is larger than a threshold value, the first difference is assigned one as a given value,

when a second difference between the first variation degree and the second variation degree is not larger than the threshold value, the second difference is assigned zero as a given value, and

the result of incorporating given values is obtained as a sum of given values with respect to all the plurality of sub-areas.

6. The rain sensor according to claim 3, wherein

in the given process,

when a difference between the first variation degree and the second variation degree is not larger than a threshold value that is unique to the each of the plurality of sub-areas, the difference is assigned zero as a given value, and

the result of incorporating given values is obtained as a sum of given values with respect to all the plurality of sub-areas.

7. The rain sensor according to claim 3, wherein

in the given process,

when a first difference between the first variation degree and the second variation degree with respect to the each of the plurality of sub-areas is larger than a threshold value that is unique to the each of the plurality of sub-areas, the first difference is assigned one as a given value,

when a second difference between the first variation degree and the second variation degree with respect to the each of the plurality of sub-areas is not larger than a threshold value that is unique to the each of the plurality of sub-areas, the second difference is assigned zero as a given value, and

the result of incorporating given values is obtained as a sum of given values with respect to all the plurality of sub-areas.

8. The rain sensor according to claim 3, wherein

in the given process,

a given value is obtained by weighting a difference between the first variation degree and the second variation degree with respect to the each of the plurality of sub-areas, using a value defined to the each of the plurality of sub-areas, and

the result of incorporating given values is obtained as a sum of given values with respect to all the plurality of sub-areas.

9. The rain sensor according to claim 3, wherein

in the given process,

when a first difference between the first variation degree and the second variation degree with respect to the each of the plurality of sub-areas is not larger than a threshold value that is unique to the each of the plurality of sub-areas, the first difference is assigned zero as a given value,

when a second difference between the first variation degree, and the second variation degree with respect to the each of the plurality of sub-areas is larger than the threshold value that is unique to the each of the plurality of sub-areas, the second difference is further weighted using a value defined to the each of the plurality of sub-areas to obtain a given value, and

the result of incorporating given values is obtained as a sum of given values with respect to all the plurality of sub-areas.

10. The rain sensor according to claim 1, wherein

the variation degree includes at least one of a variance and a standard deviation with respect to intensities of pixels included in an image taken by the camera.

11. The rain sensor according to claim 1, wherein the processor detects that rain is present when the variation degree of the moment-to-moment transition of the intensities of the pixels in the image with the long focal length exceeds a threshold, and rain is not present when the variation degree of the moment-to-moment transition of the intensities of the pixels in the image with the long focal length does not exceed the threshold.

12. The rain sensor according to claim 11, wherein the moment-to-moment transition is determined from a current variance and a previous variance from the previous most recently obtained image.