CALIBRATION METHOD AND MEASUREMENT TOOL

• US 20160353083A1
• Filed: 01/28/2015
• Published: 12/01/2016
• Est. Priority Date: 01/28/2014
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Jun Kishiwada, Kagehiro Nagao, Shin Aoki
• Inventors: KIIKUCHI, Naoki, NAGAO, Kagehiro, KISHIWADA, Jun, AOKI, Shin
• Granted Patent: US 10,277,887 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B60R 11/04 Mounting of cameras operative during drive; Arrangement of controls thereof relative to the vehicle
• CPC Class Codes: B60R 2011/0026 Windows, e.g. windscreen
• CPC Class Codes: G06T 2207/10012 Stereo images
• CPC Class Codes: G06T 2207/10021 Stereoscopic video; Stereoscopic image sequence
• CPC Class Codes: G06T 2207/10028 Range image; Depth image; 3D point clouds
• CPC Class Codes: G06T 2207/30208 Marker matrix
• CPC Class Codes: G06T 2207/30252 Vehicle exterior; Vicinity of vehicle
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light
• CPC Class Codes: G06T 7/70 Determining position or orientation of objects or cameras camera calibration G06T7/80
• CPC Class Codes: G06T 7/85 Stereo camera calibration
• 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 13/246 Calibration of cameras

Abstract

A calibration method calibrates a stereo camera. The calibration method includes: measuring a relative position between the stereo camera and an object that is placed so as to fall within an image capturing area of the stereo camera; acquiring a captured image that is captured by the stereo camera and includes the object; and determining a calibration parameter for calibrating the stereo camera based on the relative position and the captured image.

Claims

1. A calibration method for calibrating a stereo camera, the calibration method comprising:

measuring a relative position between the stereo camera and an object that is placed so as to fall within an image capturing area of the stereo camera;

acquiring a captured image that is captured by the stereo camera and includes the object; and

determining a calibration parameter for calibrating the stereo camera based on the relative position and the captured image.

2. The calibration method according to claim 1, wherein the measuring of the relative position includes

measuring a distance from the object to the stereo camera;

and

measuring a deviation of a direction of the object from a facing position of the stereo camera.

3. The calibration method according to claim 2, wherein the measuring of the distance to the stereo camera includes

measuring a distance from a point on the object to an intermediate measurement point that is located between the object and the stereo camera;

and

measuring a distance from the intermediate measurement point to the stereo camera.

4. The calibration method according to claim 2, wherein the measuring of the deviation of the direction includes

measuring coordinates that indicate a position of the stereo camera by using an object coordinate system in which a position of the object is a reference;

converting coordinates of the stereo camera using the object coordinate system and coordinates of the object using the object coordinate system into coordinates using a camera coordinate system in which a position of an optical center of the stereo camera is a reference, and

measuring a direction of the stereo camera based on coordinates that indicate a position of the stereo camera using the camera coordinate system, coordinates that indicate a position of the object using the camera coordinate system, and coordinates of an image of the object in the captured image.

5. The calibration method according to claim 4, wherein the measuring of the coordinates that indicate the position of the stereo camera by using the object coordinate system includes

measuring distances from multiple measurement points that are provided on the object to the stereo camera;

and

measuring the position of the stereo camera based on the multiple measured distances.

6. The calibration method according to claim 5, wherein the measuring of the distances includes

measuring a first distance that is a distance to an intermediate measurement point that is located between the measurement point and the optical center of the stereo camera;

measuring a second distance that is a distance from the intermediate measurement point to the optical center of the stereo camera; and

measuring a distance from the measurement point to the stereo camera by using the first distance and the second distance.

7. The calibration method according to claim 6, wherein the stereo camera is installed inside a front windshield of a vehicle and the intermediate measurement point is provided on the front windshield of the vehicle.

8. A calibration method for calibrating a stereo camera by using a measurement tool that includes a first member having a surface that includes a chart that is used to calibrate the stereo camera, a light source that is installed on the surface and that emits light with a uniform intensity regardless of a position on the surface, and a second member that covers the light source and emits the light through a plurality of holes, the calibration method comprising:

acquiring a captured image that is captured by the stereo camera and includes the measurement tool as an object;

measuring a deviation of a direction of the measurement tool from a facing position of the stereo camera based on a position of maximum brightness in the captured image; and

determining a calibration parameter for calibrating the stereo camera based on the deviation of the direction of the measurement tool and the captured image.

9. The calibration method according to claim 8, wherein

the determining includes

calculating a parallax of the chart from the captured image;

calculating an ideal parallax in consideration of the deviation of the direction of the measurement tool; and

determining a calibration parameter for calibrating the stereo camera based on the parallax and the ideal parallax.

10. A measurement tool comprising:

a first member that has a surface that includes a chart that is used to calibrate the stereo camera;

a light source that is installed on the surface and that emits light with a uniform intensity regardless of a position on the surface; and

a second member that covers the light source and emits the light through a plurality of holes.

11. The measurement tool according to claim 10, wherein the second member is a single flat plate in which the holes are formed in a direction perpendicular to the surface with a predetermined interval.

12. The measurement tool according to claim 10, wherein

the second member is two flat plates in which the holes are formed in a direction perpendicular to the surface with a predetermined interval, and

the two flat plates are arranged parallel to the surface such that, when the measurement tool is captured from a facing direction of the surface, the holes are located at identical positions on the surface.

13. The measurement tool according to claim 12, wherein the two flat plates are secured by a transparent object that is located between the two flat plates.

14. The measurement tool according to claim 10, wherein the holes are circular, and a sum of a diameter of the holes and an interval of the holes is equal to or less than a resolution limit of the stereo camera for a calibration distance between the stereo camera and the measurement tool.