Method for examining distance data and device thereof

• US 6,404,484 B1
• Filed: 09/21/2000
• Issued: 06/11/2002
• Est. Priority Date: 09/22/1999
• Status: Active Grant

• Current Assignee: Subaru Corp.
• Original Assignee: Fuji Heavy Industries Limited (Subaru Corp.)
• Inventors: Sogawa, Yoshiyuki
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US09/667,425
• Time in Patent Office: 628 Days
• Field of Search: 396/121, 356/3-3-, 180/167
• US Class Current: 356/3.14
• CPC Class Codes: G01C 11/06 by comparison of two or more pictures of the same area
• CPC Class Codes: G01C 3/085 with electronic parallax measurement
• CPC Class Codes: G06T 2207/30208 Marker matrix
• CPC Class Codes: G06T 2207/30252 Vehicle exterior; Vicinity of vehicle
• CPC Class Codes: G06T 7/593 from stereo images
• CPC Class Codes: H04N 13/239 using two 2D image sensors having a relative position equal to or related to the interocular distance H04N13/243 takes precedence
• CPC Class Codes: H04N 2013/0081 Depth or disparity estimation from stereoscopic image signals

Abstract

In a method of examining the reliability of distance data calculated based on stereoscopic images, a pair of photographed images is obtained by taking pictures of a test chart 21 carrying a brightness pattern with a stereo camera, the test chart 21 being placed in a shooting direction of the stereo camera. The distance data is calculated from these photographed images by stereo matching. Using the distance data concerning the test chart shown in the photographed images as the evaluation samples, a histogram showing a relationship between distance values of evaluation samples and their frequency of occurrence is produced. The reliability of the calculated distance data is judged by evaluating properties of the histogram thus produced based on the distance between the stereo camera and the test chart.

Claims

1. A method for examining reliability of distance data calculated based on stereoscopic images, comprising:

obtaining a pair of photographed images by taking pictures of at least a test chart carrying a brightness pattern with a stereo camera, said test chart being placed in a shooting direction of said stereo camera with a predetermined distance from said stereo camera;

calculating said distance data from the pair of photographed images;

producing a histogram showing a relationship between distance values of evaluation samples and their frequency of occurrence by adopting said distance data concerning said test chart shown in said photographed images as said evaluation samples; and

judging said reliability of said calculated distance data by evaluating properties of said produced histogram based on said predetermined distance between said stereo camera and said test chart.

2. The method for examining the distance data according to claim 1, wherein

said reliability of said calculated distance data is judged based on the ratio of the number of said evaluation samples included in an appropriate range set in said histogram to the total number of said evaluation samples in said judging step; and

said appropriate range is a specific distance range including said predetermined distance between said stereo camera and said test chart.

3. The method for examining the distance data according to claim 1, wherein

said reliability of said calculated distance data is judged based on whether a peak distance value in a peak portion of the frequency of occurrence in said histogram exists within an appropriate range in said judging step;

and

said appropriate range is a specific distance range including said predetermined distance between said stereo camera and said test chart.

4. The method for examining the distance data according to claim 3, wherein

said peak distance value is a distance value having maximum frequency of occurrence.

5. The method for examining the distance data according to claim 3, wherein

said peak distance value is a value calculated based on a distance value having maximum frequency of occurrence and a distance value adjacent to said distance value having maximum frequency of occurrence in said histogram.

6. The method for examining the distance data according to claim 3, wherein said peak distance value is a distance value calculated in sub-pixel units.

7. The method for examining the distance data according to claim 1, wherein said brightness pattern has a configuration with blocks of the same shape while varying brightness gradations are arranged at random.

8. The method for examining the distance data according to claim 3, wherein

said producing step includes:

adopting said distance data corresponding to each of multiple evaluation sub-areas set in the photographed images as said evaluation samples; and

producing histograms showing a relationship between the distance values of said evaluation samples and their frequency of occurrence, and wherein said judging step includes;

determining whether peak distance values in peak portions of the frequency of occurrence exit within the appropriate range of each of said histograms; and

deciding that calculation results of the distance data are good when all of said peak distance values have been judged to exist within the appropriate range.

9. The method according to claim 1, wherein obtaining a pair of photographed images by taking pictures of a test chart carrying a brightness pattern with a stereo camera includes taking pictures of a test chart having a pattern of brightness blocks with gradations of brightness arranged to avoid any regularity in brightness variations.

10. The method according to claim 9 wherein there are 16 gray scale shades of gradations on the test chart.

11. A distance data examination device for examining reliability of distance data calculated based on stereoscopic images comprising:

a stereo camera fitted to a vehicle body and outputting a pair of photographed images by taking pictures of conditions ahead of said vehicle;

a stereo processing unit for calculating distance data from the pair of photographed images; and

an examination unit for judging said reliability of said calculated distance data based on said photographed images obtained by taking pictures of a test chart carrying a brightness pattern with said stereo camera, said test chart being placed at ahead of said vehicle during examination with a predetermined direction and distance from said stereo camera,

wherein said examination unit adopts said distance data corresponding to an evaluation area provided at a central part of each of said photographed images as evaluation samples, produces a histogram showing a relationship between distance values of said evaluation samples and their frequency of occurrence, and judges said reliability of said calculated distance data by evaluating properties of said produced histogram based on said predetermined distance between said stereo camera and said test chart.

12. The examination device according to claim 11, wherein

said examination unit judges said reliability of said calculated distance data based on the ratio of the number of said evaluation samples included in an appropriate range set in said histogram to the total number of said evaluation samples; and

said appropriate range is a specific distance range including said predetermined distance between said stereo camera and said test chart.

13. The examination device according to claim 11, wherein

said examination unit judges said reliability of said calculated distance data based on whether a distance value in a peak portion of the frequency of occurrence exists within an appropriate range;

and

said appropriate range is a specific distance range including said predetermined distance between said stereo camera and said test chart.

14. The examination device according to claim 11, wherein said brightness pattern has a configuration with blocks of the same shape while varying brightness gradations are arranged at random.

15. The examination device according to claim 11, wherein

said examination unit adopts distance data corresponding to each of multiple evaluation sub-areas set in said photographed images in said calculated distance data as said evaluation samples, produces histograms showing a relationship between the distance values of said evaluation samples and their frequency of occurrence, judges whether peak distance values in peak portions of the frequency of occurrence exist within appropriate range for each of said histograms, and further judges that calculation results of the distance data are good when all of said peak distance values have been judged to exist within said appropriate range.

16. The examination device according to claim 11 wherein said histogram is based on a test chart brightness pattern comprised of brightness blocks with gradations of brightness arranged to avoid any regularity in brightness variations.

17. The examination device according to claim 16 wherein there are 16 gray scale shades of gradations on the test chart.