Method for detecting objects located on a transparent panel, and corresponding device

• US 6,323,477 B1
• Filed: 05/30/2000
• Issued: 11/27/2001
• Est. Priority Date: 01/30/1998
• Status: Expired due to Term

• Current Assignee: Leopold Kostal GmbH & Company KG
• Original Assignee: Leopold Kostal GmbH & Company KG
• Inventors: Blasing, Frank, Bendicks, Norbert
• Primary Examiner(s): Bruce, David V.
• Assistant Examiner(s): Song, Hoon K.
• Application Number:
  US09/555,532
• Time in Patent Office: 546 Days
• Field of Search: 250/208.1, 250/208.2, 250/574, 250/227.25, 250/214.AL, 250/341.8, 250/573, 340/602
• US Class Current: 250/208.1
• CPC Class Codes: B60S 1/0844 including a camera
• CPC Class Codes: G01N 21/94 Investigating contamination, e.g. dust G01N21/85 takes precedence
• CPC Class Codes: G01V 8/10 Detecting, e.g. by using light barriers by reflection from the object G01S17/00
• CPC Class Codes: G06T 2207/10012 Stereo images
• CPC Class Codes: G06T 2207/30252 Vehicle exterior; Vicinity of vehicle
• CPC Class Codes: G06T 7/0008 checking presence/absence
• CPC Class Codes: G06T 7/13 Edge detection
• CPC Class Codes: G06V 20/56 exterior to a vehicle by using sensors mounted on the vehicle

Abstract

The invention relates to a method for detecting objects which are located on a transparent panel and which produce light reflexes when illuminated, using a detector unit containing one or more optical sensor arrays. The inventive method comprises the following steps: illuminating the panel in order to produce light reflexes in or on the objects which are located on the panel, from the side of the panel behind which the detector unit is located; image detection of an illuminated section of the panel using the detector unit by preparing two panel section images which together form an image pair, the light reflexes(es) of an object located on the transparent panel produced through illumination being located at differently-positioned image points in each of said panel section images; determining the differential image of the two images of an image pair by subtracting the contents of identically positioned image points of one panel section image from those of the other panel section image and evaluating the differential image determined in terms of the contents corresponding to the individual image points.

Claims

1. A method for detecting the presence of objects on a windshield, the method comprising:

positioning an optical sensor array in optical communication with the windshield, the optical sensor array having an array of pixels for detecting light reflected from the windshield, each pixel having an individual position within the optical sensor array;

illuminating the windshield with light from a first light source positioned at a first angle of incidence with respect to the windshield and with light from a second light source positioned at a second angle of incidence with respect to the windshield;

detecting light reflected from the windshield onto pixels of the optical sensor array;

imaging the reflected light detected by the pixels of the optical sensor array to generate first and second images, wherein the first image is indicative of light from the first light source reflected by the windshield and detected by a first pixel at a first position in the optical sensor array, wherein the second image is indicative of light from the second light source reflected by the windshield and detected by a second pixel at a second position in the optical sensor array;

determining a difference image of the first and second images, the difference image being indicative of the pixels of the optical sensor array detecting light reflected by the windshield from the first and second light sources; and

analyzing the difference image to determine the presence of objects on the windshield.

2. The method of claim 1 wherein:

analyzing the difference image includes using stochastic operators.

3. The method of claim 1 wherein:

analyzing the difference image includes using time-domain low-pass filtering.

4. The method of claim 1 wherein:

analyzing the difference image includes preparing a binary image of the first and second image pairs such that each pixel of the optical sensor array is assigned either the value of 0 or 1 depending on the whether the pixels detect light reflected from the windshield.

5. The method of claim 4 wherein:

analyzing the difference image includes clustering adjacent pixels with the value 1 and then performing a statistical analysis of the clusters.

6. The method of claim 1 wherein:

analyzing the difference image includes performing a total-image energy calculation in which values of the pixels of the difference image are summed, wherein the values being indicative of the reflected light detected by the pixels, and comparing the total-image energy calculation to a threshold value.

12. The device of claim 5 wherein:

the analysis unit analyzes the difference image by clustering adjacent pixels with the value 1 and then performing a statistical analysis of the clusters.

13. The device of claim 5 wherein:

the analysis unit analyzes the difference image includes performing a total-image energy calculation in which values of the pixels of the difference image are summed up, wherein the values being indicative of the reflected light detected by the pixels, and comparing the total-image energy calculation to a threshold value.

7. A method for detecting the presence of objects on a windshield, the method comprising:

positioning a first optical sensor array adjacent to the windshield at a first angle of incidence with respect to the windshield, the first optical sensor array having an array of pixels for detecting light reflected from the windshield, each pixel having an individual position within the first optical sensor array;

positioning a second optical sensor array adjacent to the windshield at a second angle of incidence with respect to the windshield, the second optical sensor array having an array of pixels for detecting light reflected from the windshield, each pixel having an individual position within the second optical sensor array;

illuminating the windshield with light from a light source;

detecting light reflected from the windshield onto pixels of the first and second optical sensor arrays;

imaging the reflected light detected by the pixels of the first and second optical sensor arrays to generate first and second images, wherein the first image is indicative of light from the light source reflected by the windshield and detected by a pixel at a first position in the first optical sensor array, wherein the second image is indicative of light from the second light source reflected by the windshield and detected by a pixel at a second position in the second optical sensor array;

determining a difference image of the first and second images, the difference image being indicative of the pixels of the first and second optical sensor arrays detecting light reflected by the windshield from the light source; and

analyzing the difference image to determine the presence of objects on the windshield.

8. A device for detecting the presence of objects on a windshield, the device comprising:

a first light source positioned at a first angle of incidence with respect to the windshield for illuminating the windshield with light;

a second light source positioned at a second angle of incidence with respect to the windshield for illuminating the windshield with light;

an optical sensor array positioned adjacent to the windshield, the optical sensor array having an array of pixels for detecting light reflected from the windshield, each pixel having an individual position within the optical sensor array, the optical sensor array operable for imaging the reflected light detected by the pixels of the optical sensor array to generate first and second images, wherein the first image is indicative of light from the first light source reflected by the windshield and detected by a first pixel at a first position in the optical sensor array, wherein the second image is indicative of light from the second light source reflected by the windshield and detected by a second pixel at a second position in the optical sensor array;

an analysis unit for determining a difference image of the first and second images, the difference image being indicative of the pixels of the optical sensor array detecting light reflected by the windshield from the first and second light sources, wherein the analysis unit analyzes the difference image to determine the presence of objects on the windshield.

9. The device of claim 8 wherein:

the analysis unit analyzes the difference image includes using stochastic operators.

10. The device of claim 8 wherein:

the analysis unit analyzes the difference image includes using time-domain low-pass filtering.

11. The device of claim 8 wherein:

the analysis unit analyzes the difference image by preparing a binary image of the first and second image pairs such that each pixel of the optical sensor array is assigned either the value of 0 or 1 depending on the whether the pixels detect light reflected from the windshield.