JP2012189324A - Stereo camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stereo camera which is capable of reducing influences exerted upon a distance measurement accuracy by aging by suppressing deviation in tilting of a camera optical axis of which the detection from a captured image is difficult.SOLUTION: In a stereo camera, a first single-lens camera 100 and a second single-lens camera 110 are integrally provided in parallel. The first single-lens camera 100 and the second single-lens camera 110 have reference planes 100a and 110a orthogonal to an optical axis. The stereo camera comprises a camera stay 120 which is abutted to the reference planes 100a and 110a of the first single-lens camera 100 and the second single-lens camera 110 and connects these two cameras by providing them in parallel at such a position that the optical axes of the two cameras become the same straight line, image correction means (not illustrated) which is mounted in the camera stay 120 for correcting captured images from the first single-lens camera 100 and the second single-lens camera 120, and distance calculation means (not illustrated) which determines a parallax from correction images corrected by the image correction means and calculates a distance of a subject.

Description

  The present invention relates to a stereo camera in which two monocular cameras are arranged side by side.

  In recent years, needs for environmental recognition are increasing. For example, a system that supports driving by providing a vehicle with a stereo camera and providing information such as the presence or absence of a pedestrian to the driver is being put into practical use. Such a stereo camera is an apparatus that acquires images from monocular cameras installed at a plurality of positions and measures the distance and position of an object using parallax (difference in image positions in each image). In the stereo camera, since the distance is calculated using the relative position between the monocular cameras, the positioning accuracy of the relative position between the monocular cameras or the detection accuracy of the relative position between the monocular cameras is important. In the case of a stereo camera that is mounted on a vehicle, a calibration method that does not use a special device is required for a positional shift due to a change with time.

  Patent Document 1 discloses a three-dimensional image acquisition apparatus that estimates the coordinates of feature points of an image of each camera and estimates the relative position between the monocular cameras using estimated coordinates of feature points common to the monocular cameras. It is disclosed. This patent document 1 calculates the relative position of the stereo camera from the estimation result of the three-dimensional coordinates of the feature points on the image for the purpose of calibrating the relative position shift of the camera in the stereo camera.

  However, in the apparatus disclosed in Patent Document 1 as described above, the relative position between monocular cameras is estimated while the influence of the relative position shift between monocular cameras due to the change over time on the distance measurement accuracy is reduced. Since the coordinates of the feature points used in the above are also estimated values, it is difficult to perform calibration with high accuracy, and it is necessary to perform calculation with a high load. That is, there is a problem that the calculation load is high because the inclination of the optical axis, which is difficult to estimate, is corrected only by image estimation.

  The present invention has been made in view of the above, and is a stereo camera that can reduce the influence of changes over time on distance measurement accuracy by suppressing the deviation of the tilt of the camera optical axis that is difficult to detect from a captured image. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, the present invention is a stereo camera in which a first monocular camera and a second monocular camera are integrally arranged, and includes the first monocular camera and the monocular camera. The second monocular camera has a reference plane orthogonal to the optical axis and is brought into contact with the reference planes of the first monocular camera and the second monocular camera, and the optical axes of the two cameras are the same. A connecting member that is connected in parallel at a position on a straight line, an image correcting unit that corrects a captured image from the first monocular camera and the second monocular camera attached to the connecting member, and the image Distance calculating means for obtaining parallax from the corrected image corrected by the correcting means and calculating the distance of the subject.

  According to the present invention, the connecting member is brought into contact with the reference planes of the first monocular camera and the second monocular camera, and the optical axes of the two cameras are arranged in parallel at a position where they are on the same straight line. Because the plane perpendicular to the optical axis of the two monocular cameras is used as the mounting reference plane, the tilt of the optical axis that is difficult to estimate from the captured image is suppressed, and the tilt of the optical axis that is difficult to estimate is small. As a result, the influence of the change over time on the distance measurement accuracy can be reduced.

FIG. 1 is an explanatory diagram showing the configuration of the stereo camera in this embodiment. FIG. 2 is an explanatory diagram illustrating an example of an image captured by assembling two monocular cameras by the camera stay illustrated in FIG. FIG. 3 is an explanatory view showing a state of a distance measurement effective region by two monocular cameras. FIG. 4 is an explanatory diagram illustrating an example of an L-angle camera stay and a monocular camera. FIG. 5 is a block diagram showing a system configuration of the stereo camera in this embodiment.

  Hereinafter, an embodiment of a stereo camera according to the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment)
In a stereo camera that includes a plurality of cameras and measures the distance of an object from a difference in image position in imaging from each camera, the tilt of the optical axis that is difficult to estimate from an image can be suppressed. The feature is that the optical axis of the monocular camera is a plane orthogonal to the reference plane for attachment to the camera stay. This will be specifically described below.

  FIG. 1 is an explanatory diagram showing the configuration of the stereo camera in this embodiment. FIG. 1A shows a single shape of each of two monocular cameras and a camera stay connecting the two cameras, and FIG. 1B shows a state of the stereo camera after assembly. In FIG. 1, reference numeral 100 denotes a first monocular camera, reference numeral 110 denotes a second monocular camera, and reference numeral 120 denotes a camera stay as a connecting member. As described above, the stereo camera includes the two monocular cameras, the first monocular camera 100 and the second monocular camera 110, and the camera stay 120 to which the two monocular cameras are attached.

  The first monocular camera 100 and the second monocular camera 110 have an optical system such as a lens, for example, an imaging device such as a CCD, capture an image of an object, acquire digital image data, and obtain the captured image data. Then, predetermined image processing is executed by an image processing unit (see FIG. 5) described later.

  Reference numerals 100a and 110a denote camera reference planes having a plane perpendicular to the optical axes of the two cameras. Reference numerals 100b and 110b denote optical axes when the two monocular cameras are attached to the camera stay 120. It is an engagement hole that can be positioned in the Y direction. Reference numeral 130 denotes a screw fixing pin capable of screw fastening while positioning the camera stay 120 and the two monocular cameras. Here, the inner diameter dimensions of the engagement holes 100b and 110b and the outer diameter of the root portion of the screw fixing pin 130 are the same dimension and designed with a predetermined fitting tolerance. In this manner, the root portion of the screw fixing pin 130 has a shape with a predetermined dimensional accuracy so that the position does not shift due to fitting with the engagement holes 100b and 110b of each camera. The front surfaces of the two monocular cameras configured as described above are used as mounting surfaces for the camera stay 120, and positioning is performed within the reference plane using the screw fixing pins 130 and the engagement holes 100b and 110b.

  The camera stay 120 is made of a material having a certain degree of rigidity that is not easily affected by changes with time or temperature. The camera stay 120 has a certain flatness so that the optical axis does not deviate even if the surface that contacts the camera reference surfaces 100a and 110a is fixed in contact with the camera reference surfaces 100a and 110a. is doing. The camera mounting surface of the camera stay 120 is processed by cutting or molding, for example. By adopting such a shape of the camera stay 120, the processing becomes easy, and since the configuration is simple, the stacking tolerance at the time of assembly can be reduced, and the accuracy at the time of assembly can be ensured.

  The camera stay 120 is formed with a plane that contacts the camera reference surfaces 100a and 110a of the two cameras, or a surface that partially contacts. The camera reference planes 100a and 110a are in contact with the surface of the camera stay 120 and are connected and fixed by a screw fixing pin 130.

  As shown in FIG. 1, the simplest and most practical stereo camera configuration includes two cameras placed in parallel, separated by a base line length B in the X-axis or Y-axis direction, that is, a camera stay 120. The first monocular camera 100 and the second monocular camera 110 are positioned and fixed.

  The initial relative positions of the first monocular camera 100 and the second monocular camera 110 are calibrated by a known method such as measuring a target whose positional relationship is known at the time of assembly. It is necessary to correct the deviation from the state.

  As described above, the first monocular camera 100 and the second monocular camera 110 are assembled with the camera front surfaces 100a and 110a as the front surfaces of the housing orthogonal to the optical axis. The first monocular camera 100 and the second monocular camera 110 are assembled by being pulled into the camera stay 120 with a screw fixing pin 130 with the front surface of the housing as an attachment surface. Therefore, the optical axis of each monocular camera can be prevented from tilting with respect to the camera stay 120. In addition, since it is applied to the same surface of the camera stay 120 also in the Z direction, translational displacement in the Z direction with respect to the camera stay 120 can be prevented.

  FIG. 2 is an explanatory view showing an example of an image captured by assembling two monocular cameras by the camera stay 120 shown in FIG. As shown in the X, Y, and Z axes of FIG. 2, the X direction is a direction in which two cameras are arranged in parallel, and the Y direction is a vertical direction orthogonal to the X direction (a vertical direction orthogonal to the optical axis The Z direction is the optical axis direction of the shooting screen (the subject direction orthogonal to the paper surface of FIG. 2). In FIG. 2, the first monocular camera 100 is illustrated as a camera 1 and the captured image is illustrated as a solid line, and the second monocular camera 110 is illustrated as a camera 2 using a broken line. FIG. 3 is an explanatory view showing a state of a distance measurement effective region by two monocular cameras. In FIG. 3, (A) is a distance measurement effective area 150a obtained by assembling and photographing two monocular cameras by the above-described camera stay 120, and (B) is obtained by assembling and photographing two monocular cameras tilted. The distance measurement effective area 150b is shown.

  As described above, when the first monocular camera 100 and the second monocular camera 110 attached to the camera stay 120 are so small that the optical axis tilt is negligible, the first monocular camera 100 and the second monocular camera. An image when the relative positions between the cameras 110 are shifted is as shown in FIG.

  In FIG. 2, the deviation in the Z direction can be corrected from the area of the imaging region. Furthermore, translational displacement in the Y direction and rotational deviation about the Z axis can be corrected from the coordinates of corresponding points in the captured image. These correction processes are performed by an image processing unit (see FIG. 5) described later.

  In addition, when measuring the distance of an object at a long distance in FIG. 2, the image position changes greatly due to the inclination of the optical axis, so that corresponding point search can be performed in a small area by suppressing the inclination of the optical axis. . In addition, it is possible to prevent the distance measurement effective area (the overlapping area of the angles of view of the two cameras) from being reduced and the distance measurement effective area from moving to the left or right (see FIG. 3). .

  By the way, although the camera stay 120 described above has a flat plate configuration, in addition to this configuration, for example, the camera stay 120 may be pressed into the abutting portion as an L-shaped angle shape to perform positioning in the reference plane. . The stereo camera uses the front surface of the monocular camera housing as a mounting surface for the camera stay (camera reference surface 100a), and is orthogonal to the front surface of the housing and parallel to the base line length direction (parallel to the xz plane in FIG. 1). The second reference plane may be used as the second reference plane. An example of this is shown in FIG.

  FIG. 4 is an explanatory diagram illustrating an example of an L-angle camera stay and a monocular camera. FIG. 4A shows the single shapes of two monocular cameras and camera stays connecting the two cameras, and FIG. 4B shows the state of the stereo camera after assembly. The camera stay 120 shown in FIG. 4 has an L-angle shape having a first reference surface 120a and a second reference surface 120b. The first reference surface 120a and the second reference surface 120b are formed at a right angle with a predetermined accuracy. The camera reference planes 100c and 110c are also formed at right angles to the reference planes 100a and 110a in the first monocular camera 100 and the second monocular camera 110 so as to match the shape of the camera stay 120 so as to be able to abut. . Note that the camera reference surfaces 100c and 110c are formed only on the portion of the camera stay 120 that contacts the second reference surface 120b.

  With the configuration shown in FIG. 4, the first monocular camera 100 and the second monocular camera 110 are fixed to the camera stay 120, so that the camera does not need to be adjusted between the cameras by the positioning pin or the abutting portion. It depends on the processing accuracy of the reference planes (100a, 110a, 100c, 110c) of the stay 120 and the two monocular cameras. That is, with the configuration shown in FIG. 4, the rotational shift around the optical axis between the first monocular camera 100 and the second monocular camera 110 due to the second reference plane 120b can be performed without adjustment during assembly. It is determined by the processing accuracy of each camera reference plane of the first monocular camera 100 and the second monocular camera 110.

  The L-angle camera stay 120 shown in FIG. 4 is more advantageous in rigidity than the flat camera stay 120 shown in FIG. Further, the L-angle-shaped camera stay 120 shown in FIG. 4 has the first reference surface 120a and the second reference surface 120b formed in an L shape with a right angle, so that the camera reference surfaces 100a, Assembling is also improved by bringing 110a, 100c, 110c into contact with the L-shaped surface.

  FIG. 5 is a block diagram showing a system configuration according to this embodiment. Here, as shown in FIG. 1 or FIG. 4 described above, the first monocular camera 100, the second monocular camera 110 (simply abbreviated as “camera” in the drawing) fixed to a predetermined position of the camera stay 120, and the image processing unit 160. A distance calculation unit 165 and a distance output unit 170.

  The image processing unit 160 is configured by a microcomputer system, and includes an input / output interface, a CPU, a ROM, a RAM, an external storage device, and the like. The ROM stores an image processing program for performing processing such as correcting a captured image according to data obtained by capturing an object. The RAM is used as a working memory. In FIG. 5, the image processing unit 160 and the distance calculation unit 165 are divided into separate blocks, but a configuration in which these functions are combined into one may be used.

  The image processing unit 160 is obtained from the first monocular camera 100 and the second monocular camera 110 according to the internal parameters and external parameters of the first monocular camera 100 and the second monocular camera 110 connected to the camera stay 120. Correct the shot image. The distance calculation unit 165 obtains the parallax from the corrected image output from the image processing unit, calculates the distance of the object, and sends it to the distance output unit 170. The distance output unit 170 includes a display device such as a liquid crystal monitor, and displays a 3D (three-dimensional) map according to the measurement distance output from the distance calculation unit 165.

  As described above, according to this embodiment, the camera stay 120 is brought into contact with the reference planes of the first monocular camera 100 and the second monocular camera 110, and the optical axes of the two cameras are identical. By connecting in parallel to the position on the line, the plane perpendicular to the optical axis of the two monocular cameras is used as the reference plane for mounting, so it is possible to suppress the tilting of the optical axis that is difficult to estimate from the captured image. However, since the inclination of the optical axis, which is difficult to estimate, is small, the influence of the change over time on the distance measurement accuracy can be reduced.

DESCRIPTION OF SYMBOLS 100 1st monocular camera 100a, 110a Camera reference surface 100b, 110b Engagement hole 100c, 110c Camera reference surface 110 2nd monocular camera 120 Camera stay 130 Screw fixing pin 120a 1st reference surface 120b 2nd reference surface 160 Image processing Section 165 Distance calculation section 170 Distance output section

JP 2007-263669 A

Claims (4)

A stereo camera in which a first monocular camera and a second monocular camera are integrally arranged,
The first monocular camera and the second monocular camera have a reference plane orthogonal to the optical axis,
A connecting member that is brought into contact with the reference plane of the first monocular camera and the second monocular camera and is connected in parallel at a position where the optical axes of the two cameras are on the same straight line;
Image correcting means for correcting captured images from the first monocular camera and the second monocular camera attached to the connecting member;
Distance calculating means for obtaining parallax from the corrected image corrected by the image correcting means and calculating the distance of the subject;
Stereo camera characterized by comprising. A stereo camera in which a first monocular camera and a second monocular camera are integrally arranged,
The first monocular camera and the second monocular camera have a first reference plane orthogonal to an optical axis and a second reference plane orthogonal to the first reference plane,
A connecting member that is brought into contact with the first reference surface and the second reference surface and connected in parallel at a position where the optical axes of the two cameras are on the same straight line;
Image correcting means for correcting captured images from the first monocular camera and the second monocular camera attached to the connecting member;
Distance calculating means for obtaining parallax from the corrected image corrected by the image correcting means and calculating the distance of the subject;
Stereo camera characterized by comprising.   The image correction means corrects a shift in a Z direction, which is a subject direction of captured images from the first monocular camera and the second monocular camera, from an area of the captured image. 2. The stereo camera according to 2.   The image correction unit is configured to perform a vertical direction with respect to a direction in which the first monocular camera and the second monocular camera are arranged side by side with respect to a captured image from the first monocular camera and the second monocular camera. The stereo camera according to claim 1, wherein the translational deviation in the Y direction or the rotational deviation of the photographed image with the subject direction as an axis is corrected from the corresponding point coordinates of the photographed image.

Images