Method for calibrating common horizontal line

Abstract

The invention relates to a method for calibrating a common horizontal line of a plurality of cameras (18a, 18b, 18c) of a motor vehicle (14). The cameras (18a, 18b, 18c) are arranged at different heights (Ha, Hb, Hc). The method comprises the following steps: ascertaining (A) a common horizontal line for all the cameras (18a, 18b, 18c) by setting a common height value between the actual heights (Ha, Hb, Hc) of the cameras (18a, 18b, 18c), calculating (B) a scaling factor for each camera (18a, 18b, 18c) on the basis of the common height value and the actual height (Ha, Hb, Hc) of the respective camera (18a, 18b, 18c), and determining (B) the actual height (Ha, Hb, Hc) of each camera (18a, 18b, 18c) by means of the respective scaling factor. The camera images of the cameras (18a, 18b, 18c) are scaled (C) such that the horizontal lines of each camera (18a, 18b, 18c) map onto the common height value.

Description

Technical Field

[0001] The invention relates to a method for calibrating a common horizon of a plurality of cameras of a vehicle, and to a device for carrying out the method. Background Art

[0002] According to the prior art, a motor vehicle generally has a plurality of cameras, such as a reversing camera, a front view camera, a rearview mirror camera, etc., which are mounted on the vehicle at different heights. Due to the different heights of the cameras, the images merged by the cameras will have different horizontal lines.

[0003] US Pat. No. 8,259,174 B2 discloses a method for estimating a horizontal line in a camera image to achieve automatic calibration of the camera in a tilted direction. In this method, a camera captures two images and locates a horizontal edge in each of them. Based on the difference between the first and second images, a region in the image where no motion has occurred is located. By combining the horizontal edge with the region where no motion has occurred, a horizontal edge where no motion has occurred is obtained. The camera is calibrated based on the thus determined horizontal line.

[0004] The object of the present invention is to specify a method for calibrating a common horizon of a plurality of cameras of a vehicle, by means of which the common horizon can be determined in a simple manner.

[0005] This object is achieved by a method for calibrating a common horizon of a plurality of cameras of a vehicle, which method has the subject matter of patent claim 1. Preferred embodiments can be gathered from the dependent claims. Summary of the Invention

[0006] The present invention describes a method for calibrating a common horizon for multiple cameras of a vehicle. The cameras are arranged at different heights. The method comprises the following steps: determining a common horizon for the cameras, calculating a scaling factor for each camera based on the common height value and the actual height of the respective camera, and scaling the camera image of each camera using the corresponding scaling factor so that the horizon of each camera is mapped to the common height value.

[0007] The horizon is defined as the line separating the ground from the sky. Due to the different heights of the cameras on the vehicle, their horizons are at different heights. However, to still be able to map all camera images from all cameras to a common horizon, a common horizon is defined. This common horizon can be set to any practical height. During the zooming process to match the camera images to the common horizon, only minor changes are required to each camera image. This allows all camera images to be mapped to a common horizon.

[0008] In a preferred embodiment of the application, a value between the actual heights of the video cameras is set as the common height value. By means of the height value between the actual heights of the video cameras, only minor changes to the horizon of the video cameras are necessary, so that the correction of the individual video camera images is reduced.

[0009] In another preferred embodiment of the application, the average of all video camera heights is calculated as the common height value. This average can be calculated by means of various known methods. By means of this average, the sum of all corrections of the video camera images of all video cameras is minimized.

[0010] Preferably, the height of one video camera, which is between the maximum and minimum height, is used as the common height value. Such a height value has the advantage that, for at least one video camera, no scaling factor has to be calculated and the corresponding video camera image can be used directly. The calculation effort is thereby reduced, so that the execution of the method is simplified.

[0011] In an advantageous extension, the heights of at least two video cameras, which are arranged at the same height between the maximum and minimum height, are used as the common height value. By means of this method step, no scaling factor has to be calculated for at least two video cameras, for example rearview mirror video cameras. The video camera images of these at least two video cameras can be used directly. The calculation effort is thereby significantly reduced again, so that the execution of the method is simplified.

[0012] Advantageously, all video camera images, which are scaled to the common height value, are combined into one panoramic view. By combining the video camera images, the driver obtains a panoramic view of the surroundings of the vehicle, which improves the overview of the vehicle and the environment. By means of the common horizon, it is not noticed that the video cameras are arranged at different heights.

[0013] Furthermore, a device for executing the method is described. The device comprises at least two video cameras, which are mounted at different heights, and a graphics processing unit for processing the image information of the video cameras. By means of this device, the advantages mentioned by means of the method are essentially achieved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Embodiments of the application are shown in the drawings and are described in detail in the following description. Therein:

[0015] Figure 1 An embodiment of a device for executing the method is shown, and

[0016] Figure 2 An embodiment of a method for calibrating a common horizon of a plurality of video cameras of a vehicle is shown. DETAILED DESCRIPTION

[0017] An embodiment of a device 10 for performing the method is shown in Figure 1 The device 10 comprises here a motor vehicle 14 on which a plurality of cameras 18a, 18b, 18c are arranged at different heights H a ,H b ,H c from the ground. In addition, a graphics processing unit 22 is provided, which is connected to all cameras 18a, 18b, 18c and by means of which the method according to the application can be performed.

[0018] An embodiment of a method for calibrating a common horizon line of a plurality of cameras of a vehicle is shown in Figure 2 In a first step A, a common horizon line is set for all cameras 18a, 18b, 18c. The height value of the common horizon line is between the actual height values H a ,H b ,H c of the cameras 18a, 18b, 18c. In a second step B, based on the common height value and the actual heights H a ,H b ,H c of the cameras 18a, 18b, 18c, a scaling factor is calculated for each camera 18a, 18b, 18c. By means of the scaling factor, the camera image of each camera 18a, 18b, 18c is scaled in a next step C. Thereby, the horizon line of each camera 18a, 18b, 18c is mapped to the common height value. In a next step D, all camera images scaled to the common height value are merged into one panorama view. Thereby, a panorama view formed by all cameras 18a, 18b, 18c with a common horizon line can be displayed to the driver.

[0019] Thus, by means of the method, the camera images of cameras 18a, 18b, 18c mounted at different heights H a ,H b ,H c can be normalized to a common horizon line in a simple manner.

Claims

1. A method for calibrating a common horizon line of a plurality of video cameras (18a, 18b, 18c) of a motor vehicle (14), the video cameras being arranged at different heights (H a , H b , H c ), the method comprising the steps of: - determining (A) a common horizontal line for all cameras (18a, 18b, 18c) by setting a common height value for the cameras (18a, 18b, 18c), - based on said common height value and the actual height (H a , H b , H c ) of the respective camera (18a, 18b, 18c), a scaling factor (B) is calculated for each camera (18a, 18b, 18c), and - scaling (C) the camera images of each camera (18a, 18b, 18c) by means of a respective scaling factor, so that the horizontal line of each camera (18a, 18b, 18c) is mapped onto the common height value.

2. The method of claim 1, wherein, The following values are set as the common height value: values between the actual heights (H a , H b , H c ) of the cameras (18a, 18b, 18c).

3. The method of claim 2, wherein, - calculating the average of all heights of the cameras (18a, 18b, 18c) as the common height value.

4. The method of claim 2, wherein, - using the height of the camera (18a, 18b, 18c) whose height is between the maximum height and the minimum height as the common height value.

5. The method of claim 2, wherein, - using the height of at least two identically arranged cameras (18a, 18b, 18c) whose heights (18a, 18b, 18c) are between the maximum height and the minimum height as the common height value.

6. The method according to any of the preceding claims, characterized in that, - merging (D) all camera images scaled to the common height value into a panorama view.

7. A device for carrying out the method according to any one of the preceding claims, comprising at least two cameras (18a, 18b, 18c) mounted at different heights and a graphics processing unit (22) for processing the image information of the cameras (18a, 18b, 18c).

Images