Method and device for determining a calibration parameter of a stereo camera

• US 8,855,370 B2
• Filed: 09/26/2012
• Issued: 10/07/2014
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: CARIAD SE (Volkswagen AG)
• Original Assignee: Hella KGaA Hueck & Company
• Inventors: Hoffmann, Ingo
• Primary Examiner(s): Lu, Tom Y
• Application Number:
  US13/627,050
• Publication Number:
  US 20130021451A1
• Time in Patent Office: 741 Days
• Field of Search: None
• US Class Current: 382/103
• CPC Class Codes: G06T 2207/10012 Stereo images
• CPC Class Codes: G06T 7/85 Stereo camera calibration
• CPC Class Codes: G06V 20/584 of vehicle lights or traffic lights
• 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
• CPC Class Codes: H04N 2013/0085 Motion estimation from stereoscopic image signals

Abstract

The invention relates to a method and device for determining object property of an object with the aid of images that have been recorded with the aid of a camera. Further, the invention relates to a method for determining a calibration parameter for a stereo camera. For determining the object property of an object, the object is defined in a first image recorded with the aid of the camera. Further, the brightness of a defined object is determined. Each time after a preset time interval, a further image is recorded with the aid of the camera. The object is defined in each of the further images and each time, the brightness of the defined object of each image is determined. Dependent on the brightness curve, an object property is assigned to the object.

Claims

1. A method for determining a calibration parameter for a stereo camera, in which a relative movement of the stereo camera with respect to a further object is analysed, said method comprising the steps of:

with the aid of object images of an object recorded at least two times one after the other at an interval by the stereo camera, the distance between the stereo camera and the object is each time determined,

with the aid of the determined distances an apparent speed between the stereo camera and the object is determined,

an actual speed between the stereo camera and the object is determined, and wherein, dependent on a deviation of the apparent speed from the actual speed, at least one calibration parameter for the determination of further distances between at least one of the stereo camera and the object and the stereo camera and further objects is determined with the aid of object images recorded by the stereo camera, and

wherein the relationship between distance and speed is taken into account in the determination of at least one of the apparent and the actual speed.

2. The method according to claim 1, wherein an actual speed is determined by integration of the relative speed between the stereo camera and the object over the time interval between the recording of the object images.

3. The method according to claim 1, wherein an angle (γ

) of optical axes of the single-image cameras of the stereo camera with respect to one another is determined as a calibration parameter, the angle (γ

) preferably being determined at a pitch angle of 0° and

a roll angle of 0°

.

4. The method according to claim 3, wherein the angle (γ

) serving as a calibration parameter is determined after an adaptation of the images recorded with the aid of this single-image camera which adaptation is performed dependent on the roll and pitch angles of the single-image camera which have actually been determined, the corrected images corresponding to images that would have been recorded with the aid of single-image cameras having roll and pitch angles of respectively 0°

.

5. The method according to claim 3, wherein the determined angle (γ

) is the yaw angle or the yaw angle deviation with respect to a preset yaw angle, which yaw angle or yaw angle deviation is calculated with the aid of at least one equation derived from the projective geometry, the determined angle (γ

) being stored in an evaluation unit as an angle for evaluation and/or analysis of images recorded with the aid of single-image cameras.

6. The method according to claim 1, further comprising the step of determining a pitch angle (β

) of the stereo camera, the determined pitch angle (β

) being taken into account when determining the calibration parameter.

7. The method according to claim 1, further comprising the steps of determining a roll angle (α

) of the stereo camera, the determined roll angle (α

) being taken into account when determining the calibration parameter.

8. The method according to claim 1, wherein for determining a distance measurement, one image each is simultaneously recorded with one of each single-image camera of the stereo camera, or an image pair recorded with the aid of two single-image cameras.

9. The method according to claim 1, wherein at least one object property of an object to be assigned to the determined image correspondence is determined, and in that the actual speed or the actual change in position is determined with the aid of this object property.

10. The method according to claim 9, wherein an object property “

light source”

is operated with an alternating voltage, as a result whereof the object is considered to be stationary.

11. The method according to claim 9, characterized in that at least one object property of the object is transmitted to the stereo camera system preferably with the aid of a data network or a communication network, in particular the position of the object in space, the distance between the object and the stereo camera or between object and an evaluation unit being transmitted.

12. The method according to claim 1, wherein the position of the object is traced over several images taken one after the other and the apparent speed and/or the apparent distance of the object is repeatedly determined, preferably with the aid of a tracking method.

13. The method according to claim 1, wherein several images recorded one after the other are analysed with the aid of an object tracking method, the apparent movement of an object in space being determined, and one of an apparent speed vector and a apparent speed or the apparent direction of motion of the object being determined.

14. The method according to claim 1, wherein with the aid of the actual speed of the object in space and the time between the recording of the first and the second images an actual change in distance of the object in space is determined, and in that the deviation of the actual change in distance from the apparent change in distance determined with the aid of the distance measurements is determined, the calibration parameter being determined with the aid of this deviation.

15. The method according to claim 1, wherein the stereo camera system comprises at least a control unit and at least two single-image cameras.

16. The method according to claim 1, wherein at least one image correspondence is determined in first object images simultaneously recorded with the aid of the at least two single-image cameras of the stereo camera,

wherein the image correspondence is assigned to an object, and

wherein the image correspondence is determined at least in second object images simultaneously recorded with the aid of the single-image cameras of the stereo camera for finding the object.

17. The method according to claim 1, wherein at least one image correspondence is determined in first object images simultaneously recorded with the aid of the at least two single-image cameras of the stereo camera,

wherein the image correspondence is assigned to an object, and

wherein the image correspondence is determined at least in second object images simultaneously recorded with the aid of the single-image cameras of the stereo camera for finding the object.

18. The method according to claim 1, wherein the actual distance or the actual speed are acquired with the aid of a measured valued determined by a radar system.

19. A device for determining a calibration parameter for a stereo camera, in which a control unit analyses a relative movement between the stereo camera and a further object,

the stereo camera records object images of the object at least two times one after the other at a time interval,

the control unit each time determines the distance between the stereo camera and the object with the aid of the recorded object images,

the control unit determines an apparent speed between the stereo camera and the object with the aid of the determined distances,

the control unit determines the actual speed between the stereo camera and the object, and

the control unit determines, dependent on the deviation of the apparent speed from the actual speed, at least one calibration parameter for the determination of further distances between the stereo camera and the object and/or between the stereo camera and further objects with the aid of object images recorded by the stereo camera,

wherein the relationship between distance and speed is taken into account in the determination of at least one of the apparent and the actual speed.

20. A device for determining a calibration parameter for a stereo camera, in which a control unit analyses a relative movement between the stereo camera and a further object,

the stereo camera records object images of the object at least two times one after the other at a time interval,

the control unit each time determines the distance between the stereo camera and the object with the aid of the recorded object images,

the control unit determines an apparent speed between the stereo camera and the object with the aid of the determined distances,

the control unit determines the actual speed between the stereo camera and the object, and

the control unit determines, dependent on the deviation of the apparent speed from the actual speed, at least one calibration parameter for the determination of further distances between the stereo camera and the object and/or between the stereo camera and further objects with the aid of object images recorded by the stereo camera, and

wherein the relationship between distance and speed is taken into account in the determination of at least one of the apparent and the actual speed.

21. The device according to claim 20, wherein the actual distance or the actual speed are acquired with the aid of a measured valued determined by a radar system.

22. A device for determining a calibration parameter for a stereo camera, in which a control unit analyses a relative movement between the stereo camera and a further object,

the stereo camera records object images of the object at least two times one after the other at a time interval,

the control unit each time determines the distance between the stereo camera and the object with the aid of the recorded object images,

the control unit determines an apparent change in distance between the stereo camera and the object with the aid of determined distances,

the control unit determines the actual change in distance between the stereo camera and the object, and

the control unit determines, dependent on the deviation of the apparent change in distance from the actual change in distance, at least one calibration parameter for the determination of further distances between the stereo camera and the object and/or between the stereo camera and at least one further object with the aid of object images recorded by the stereo camera.