CALIBRATION APPARATUS, A DISTANCE MEASUREMENT SYSTEM, A CALIBRATION METHOD AND A CALIBRATION PROGRAM

• US 20120224069A1
• Filed: 08/25/2011
• Published: 09/06/2012
• Est. Priority Date: 09/13/2010
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Aoki, Shin
• Granted Patent: US 9,299,153 B2
• Time in Patent Office: Days
• US Class Current: 348/187
• CPC Class Codes: G01B 11/026 by measuring distance between sensor and object G01B11/0608 takes precedence
• CPC Class Codes: G01C 3/085 with electronic parallax measurement
• CPC Class Codes: G01C 3/14 with binocular observation at a single point, e.g. stereoscopic type G01C3/20 takes precedence
• CPC Class Codes: G06T 2207/10021 Stereoscopic video; Stereoscopic image sequence
• CPC Class Codes: G06T 2207/30252 Vehicle exterior; Vicinity of vehicle
• CPC Class Codes: G06T 7/593 from stereo images
• CPC Class Codes: G06T 7/85 Stereo camera calibration
• CPC Class Codes: G08G 1/16 Anti-collision systems road vehicle drive control systems for predicting or avoiding probable or impending collision otherwise than by control of a particular sub-unit B60W30/08
• CPC Class Codes: H04N 17/002 for television cameras

Abstract

A disclosed calibration apparatus is configured to receive inputs of two reference images and plural items of parallax data, these two reference images being captured by one of the imaging devices at two locations, and the parallax data being calculated using these two reference images and two corresponding images based on positions of plural feature points common to the reference image and the corresponding image for each pair thereof on a location basis, two corresponding images being captured by another of the imaging devices at these two locations; search for plural feature points common to these two reference images; calculate parallaxes and parallax changing amounts, based on the parallax data related to the respective feature points in these two reference images, for each of the searched feature points; and calculate a correction value for the parameter based on the calculated parallaxes and parallax changing amounts.

Claims

1. A calibration apparatus for calibrating a parameter related to positions of two imaging devices, the parameter being set in a distance measurement system which is installed in a mobile object and performs distance measurement with the imaging devices, the calibration apparatus comprising:

an image obtaining part configured to receive inputs of two reference images and plural items of parallax data, these two reference images being captured by one of the imaging devices at two locations, and the parallax data being calculated using these two reference images and two corresponding images based on positions of plural feature points common to the reference image and the corresponding image for each pair thereof on a location basis, these two corresponding images being captured by another of the imaging devices at these two locations;

a feature point searching part configured to search for the plural feature points common to these two reference images;

a parallax calculating part configured to calculate parallaxes and parallax changing amounts thereof, based on the parallax data related to the respective feature points in these two reference images, for each of the searched for feature points; and

a correction value calculating part configured to calculate a correction value for the parameter related to the positions of the imaging devices based on the calculated parallaxes and parallax changing amounts thereof.

2. The calibration apparatus claimed in claim 1, wherein the correction value calculating part is configured to create a model curve using the calculated parallaxes and parallax changing amounts thereof and calculate the correction value based on the model curve.

3. The calibration apparatus claimed in claim 2, wherein the model curve is a quadratic curve with which a displacement in parallax direction is calculated as the correction value.

4. The calibration apparatus claimed in claim 2, further comprising a reliability evaluating part configured to evaluate the presence or absence of reliability of the correction value based on a distribution of the parallaxes and dispersion of the parallax changing amounts with respect to the model curve.

5. The calibration apparatus claimed in claim 4, wherein the reliability evaluating part extracts only the data of the parallax changing amounts which are within a predetermined range from the parallax changing amounts on the model curve;

calculates an average root-mean-square of differentials between the parallax changing amounts of the extracted data and the parallax changing amounts for the corresponding parallaxes on the model curve; and

determines whether the calculated average root-mean-square is smaller than or equal to a threshold.

6. The calibration apparatus claimed in claim 4, wherein the reliability evaluating part calculates a proportion of the number of the parallaxes included in a specified parallax range and determines whether the calculated proportion is greater than or equal to a predetermined proportion.

7. The calibration apparatus claimed in claim 1, further comprising a normalization processing part configured to normalize the parallax changing amounts;

and a data storing part configured to store the normalized parallax changing amounts such that they are associated with the corresponding parallaxes, wherein

the correction value calculating part calculates the correction value for the parameter related to the positions of the imaging devices based on the stored parallaxes and the normalized parallax changing amounts.

8. The calibration apparatus claimed in claim 7, wherein the normalization processing part calculates the normalized parallax changing amount by dividing the parallax changing amount by a proportional factor of a quadratic function representing the model curve.

9. The calibration apparatus claimed in claim 4, wherein the reliability evaluating part evaluates the reliability of the correction value based on the number of data items stored in a data storing part, the data storing part being configured to store the parallax changing amounts such that they are associated with the corresponding parallaxes.

10. A distance measurement system comprising:

a calibration apparatus claimed in claim 1;

two imaging devices with the same focal length, the imaging devices being spaced apart and disposed such that the respective imaging planes are on the same straight line;

a parallax data generating apparatus configured to calculate and output plural items of parallax data, the parallax data being calculated using these two reference images and two corresponding images based on positions of plural feature points common to the reference image and the corresponding image for each pair thereof on a location basis, these two corresponding images being captured by another of the imaging devices at these two locations.

11. The distance measurement system claimed in claim 10, wherein the parallax data generating apparatus obtains the correction value from the calibration apparatus, performs the correction for the plural items of parallax data using the correction value, and outputs the corrected parallax data to the calibration apparatus.

12. A calibration method for calibrating a parameter related to positions of two imaging devices, the parameter being set in a distance measurement system which is installed in a mobile object and performs distance measurement with the imaging devices, the calibration method comprising:

a step of receiving inputs of two reference images and plural items of parallax data, these two reference images being captured by one of the imaging devices at two locations, and the parallax data being calculated using these two reference images and two corresponding images based on positions of plural feature points common to the reference image and the corresponding image for each pair thereof on a location basis, these two corresponding images being captured by another of the imaging devices at these two locations;

a step of searching for the plural feature points common to these two reference images;

a step of calculating parallaxes and parallax changing amounts thereof, based on the parallax data related to the respective feature points in these two reference images, for each of the searched for feature points; and

a step of calculating a correction value for the parameter related to the positions of the imaging devices based on the calculated parallaxes and parallax changing amounts thereof.

13. The calibration method claimed in claim 12, wherein the step of calculating the correction value includes creating a model curve using the calculated parallaxes and parallax changing amounts thereof and calculating the correction value based on the model curve.

14. The calibration method claimed in claim 13, wherein the model curve is a quadratic curve with which a displacement in a parallax direction is calculated as the correction value.

15. The calibration method claimed in claim 13, further comprising a step of evaluating the presence or absence of reliability of the correction value based on a distribution of the parallaxes and dispersion of the parallax changing amounts with respect to the model curve.

16. The calibration method claimed in claim 15, wherein the step of evaluating includes extracting only the data of the parallax changing amounts which are within a predetermined range from the parallax changing amounts on the model curve;

calculating an average root-mean-square of differentials between the parallax changing amounts of the extracted data and the parallax changing amounts for the corresponding parallaxes on the model curve; and

determining whether the calculated average root-mean-square is smaller than or equal to a threshold.

17. The calibration method claimed in claim 15, wherein the reliability evaluating includes calculating a proportion of the number of the parallaxes included in a specified parallax range and determining whether the calculated proportion is greater than or equal to a predetermined proportion.

18. The calibration method claimed in claim 12, further comprising a step of normalizing the parallax changing amounts;

and

a step of storing the normalized parallax changing amounts such that they are associated with the corresponding parallaxes, wherein

the step of calculating the correction value includes calculating the correction value for the parameter related to the positions of the imaging devices based on the stored parallaxes and the normalized parallax changing amounts.

19. The calibration method claimed in claim 18, wherein the step of normalizing includes calculating the normalized parallax changing amount by dividing the parallax changing amount by a proportional factor of a quadratic function representing the model curve.

20. The calibration method claimed in claim 15, wherein the step of evaluating includes evaluating the reliability of the correction value based on the number of data items stored in a data storing part, the data storing part being configured to store the parallax changing amounts such that they are associated with the corresponding parallaxes.

21-22. -22. (canceled)