JPH0886613A - Apparatus for calibrating stereo camera - Google Patents

Abstract

PURPOSE: To simply and correctly calibrate the position in space of a camera. CONSTITUTION: The apparatus is equipped a calibration table consisting of a flat plate 1, a bored plate 3 and a plurality of calibration poles 4. The calibration poles 4 which are different in length from each other are fitted at random to optional holes 2 of the bored plate 3 and have tops of a different color from that of upper surfaces of the flat plate 1 and the bored plate 3. The calibration device calibrates cameras 5, 6 based on three-dimensional data of an image obtained on the basis of a calibration coefficient including aberrations of the two cameras 5, 6. The calibration coefficient including the aberrations of the cameras 5, 6 is obtained in accordance with a density value of the photographed image, based on which the three-dimensional data of the image are obtained to calibrate the cameras. The position in space of each camera can be simply and correctly calibrated in this manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stereo camera calibrating device for calibrating three-dimensional information obtained by stereoscopic vision by a plurality of cameras.

[0002]

2. Description of the Related Art When an object is photographed by two cameras, the depth is perceived by the displacement of the images. At this time, the distance (position of the object) to the object imaged in the camera is obtained by the following formula from the coordinate system of the camera as shown in FIG. xi = x · L / x1-x2, yi = y · L / y1-y2, zi = z
L / z1-z2 At this time, the spatial position of the camera must be accurately calibrated in order to accurately measure the distance to the target object.

[0003]

Conventionally, the following problems have been encountered in accurately calibrating the spatial position of a camera. Accurately measuring the spatial positions of two cameras and mechanically fixing the camera positions is extremely complicated and time-consuming. Even if the spatial positions of the two cameras can be fixed accurately, an error may occur in the distance to the target object due to lens aberration.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a stereo camera calibration device capable of easily and accurately calibrating the spatial position of a camera.

[0005]

A structure of the present invention for solving the above-mentioned problems is to provide a perforated plate having a plurality of holes formed on the upper surface of a flat plate and having an upper surface of a color different from the upper surface of the flat plate. , A plurality of rod members randomly fitted at arbitrary positions of a large number of holes of the perforated plate and having different lengths from each other and having tops of the flat plate and tops of different colors from the top surface of the perforated plate. A plurality of cameras each having a calibration table, whose optical axes are connected to substantially one point on the upper surface of the calibration table, and the three-dimensional information of the camera obtained by the three-dimensional information of the image obtained based on the calibration coefficient including the aberration of the cameras. It is characterized by comprising a calibration processing device for performing calibration.

[0006]

Function: The upper surface of the calibration table is photographed by a plurality of cameras. The top surface of the flat plate, the top surface of the perforated plate, and the top of the bar have different colors, so that the image captured at this time has shades. In the calibration processing device, the calibration coefficient including the aberration of the camera is obtained according to the gray value, the three-dimensional information of the image is obtained based on the calibration coefficient, and the camera is calibrated.

[0007]

FIG. 1 is a perspective view of a stereo camera calibration apparatus according to an embodiment of the present invention, FIG. 2 is a plane view of a calibration table, FIG. 3 is a side view of the calibration table, and FIG. FIG. 5 shows a block of the calibration circuit, and FIG. 6 shows a block of the three-dimensional position measuring circuit.

The calibration table will be described with reference to FIGS. A perforated plate 3 in which a large number of holes 2 are formed is provided on the upper surface of the flat plate 1, and a calibration pole 4 as a bar member is randomly fitted at an arbitrary position of the large number of holes 2 of the perforated plate 3. ing. The top surface of the flat plate 1 is painted black, the top surface of the perforated plate 3 is painted gray, and the top of the calibration pole 4 is painted white. The length of the calibration pole 4 is set randomly. Two cameras (left camera and right camera) 5 and 6 are arranged on the upper part of the calibration table in an oblique view so that the optical axes of the left camera 5 and the right camera 6 are approximately connected to one point on the calibration table. It has become. An image of the upper surface of the calibration table is taken by the left camera 5 and the right camera 6. Note that the number of cameras is not limited to two, and three or more cameras can be used.

The calibration circuit will be described with reference to FIG. The images photographed by the left camera 5 and the right camera 6 are input to the associating circuit 7, and the associating circuit 7 performs the associating based on the gray level of the images. The information of the associating circuit 7 is input to the calibration coefficient processing circuit 8, and the calibration coefficient processing circuit 8
Then, the calibration coefficient is obtained. The three-dimensional position measuring circuit will be described with reference to FIG. Similar to the calibration circuit, the images taken by the left camera 5 and the right camera 6 are input to the associating circuit 7, and the associating circuit 7 performs the associating based on the gray level of the image. Information of the associating circuit 7 is input to the three-dimensional position processing circuit 9, and the calibration coefficient obtained by the calibration coefficient processing circuit 8 is input to the three-dimensional position processing circuit 9.
The three-dimensional position processing circuit 9 obtains the three-dimensional position of the photographing point based on the information of the associating circuit 7 and the calibration coefficient. A calibration processing device is configured by the calibration circuit and the three-dimensional position measurement circuit shown in FIGS.

The procedure of calibration by the above-mentioned stereo camera calibration device will be specifically described. First, as shown in FIG. 1, the calibration pole 4 is set at a random position on the calibration table, and the left camera 5 and the right camera 6 are arranged in an inward perspective to capture an image of the calibration table. Since the upper surface of the flat plate 1 is painted black, the upper surface of the perforated plate 3 is painted gray, and the top of the calibration pole 4 is painted white, the images on the calibration table are color-coded. .

As shown in FIG. 5, the images of the left camera 5 and the right camera 6 are input to the association circuit 7. Since this image is color-coded into three colors, the associating circuit 7 performs the associating by using the density of the image. For the association, the minimum value of the correlation value Corr is obtained by the cross-correlation equation of the following equation (1) (association: association circuit 7).

[Equation 1]

The top of the calibration pole 4 (xw, yw, zw)
In, the coordinates of the associated left and right images are (x1,
y1) and (xr, yr). A plurality of corresponding points, which are the coordinates of the associated left and right images, are obtained. Using these corresponding points, the calibration coefficients a0 to a of the following equation (2) are calculated by the method of least squares.
20 is calculated (calibration coefficient processing circuit 8).

[Equation 2]

As shown in FIG. 6, the images of the left camera 5 and the right camera 6 are input to the association circuit 7. Similarly to the above, the corresponding points (x1, y1) and (xr, yr), which are the coordinates of the left and right images associated by the cross-correlation formula, are obtained (associating circuit 7). (Xw, yw, zw) is calculated by the following equation using the calibration coefficients a0 to a20 obtained by the calibration coefficient processing circuit 8 to obtain the three-dimensional position of the top of the calibration pole 4 (third order Original position processing circuit 9). Although the following arithmetic expression shows an example in which xw is obtained and the equation is solved to obtain the calibration coefficients a0 to a6, yw and zw are obtained and the equation is similarly solved to obtain the calibration coefficients a7 to a13 and The calibration coefficients a14 to a20 can be obtained.

(Equation 3)

In this way, the three-dimensional position of the top of the calibration pole 4 is obtained, the calibration is performed by the calibration table and the image, and the positions of the left camera 5 and the right camera 6 are not accurately measured. Further, since the calibration is performed using the calibration table and the image, the aberrations of the lenses of the left camera 5 and the right camera 6 are removed.

[0015]

According to the stereo camera calibration apparatus of the present invention, the spatial position of the camera can be calibrated by the calibration table and the image, so that it is not necessary to accurately measure the position of the camera. Therefore, the three-dimensional information can be calibrated accurately and easily. Further, since the lens aberration of the camera can be removed, the three-dimensional information can be accurately obtained even at the four corners of the image.

[Brief description of drawings]

FIG. 1 is an overall perspective view of a stereo camera calibration device according to an embodiment of the present invention.

FIG. 2 is a plan view of a calibration table.

FIG. 3 is a side view of a calibration table.

FIG. 4 is an external view of a calibration pole.

FIG. 5 is a block diagram of a calibration circuit.

FIG. 6 is a block diagram of a three-dimensional position measuring circuit.

FIG. 7 is a conceptual diagram of stereo vision.

[Explanation of symbols]

 1 Flat plate 2 Hole 3 Perforated plate 4 Calibration pole 5 Left camera 6 Right camera 7 Corresponding circuit 8 Calibration coefficient processing circuit 9 Three-dimensional position processing circuit

Claims (1)

[Claims] 1. A perforated plate having a large number of holes formed in the upper surface of a flat plate and having an upper surface of a color different from the upper surface of the flat plate, and randomly fitted at arbitrary positions of the large number of holes of the perforated plate. A calibration table composed of a plurality of rods having different lengths and different tops of the flat plate and the top face of the perforated plate, and a plurality of rods having different color tops, and the light beams of the mutual lights are provided at substantially one point on the top face of the calibration table. Stereo camera calibration, comprising: a plurality of cameras whose axes are connected to each other; and a calibration processing device that calibrates the cameras based on three-dimensional information of an image obtained based on a calibration coefficient including aberrations of the cameras. apparatus.