JP2014174088A - Inspection tool, stereo camera inspection apparatus, and inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection tool for easily inspecting both vertical displacement and displacement in directions other than the vertical direction of a pair of cameras with excellent workability, and to provide a stereo camera inspection apparatus, and an inspection method.SOLUTION: An inspection tool includes: an image processing unit 4 which receives an image signal output from a pair of cameras 3a, 3b when the cameras 3a, 3b image a test chart 2, to generate a pair of test chart images where a part of a second pattern 2b is included in a first pattern 2a; a corresponding point search unit 4a which searches for each of corresponding points on the pair of test chart images from a screen of the generated pair of test chart images; a displacement calculation unit 4b which calculates a corresponding position difference between the searched corresponding points, to calculate displacement of the pair of cameras 3a, 3b from the calculated corresponding position difference; and a correction parameter calculation unit 5 which calculates a correction parameter for correcting the calculated displacement.

Description

  The present invention relates to an inspection tool used for inspecting a relative positional deviation between a pair of cameras constituting a stereo camera, and to inspect a relative positional deviation between a pair of cameras constituting a stereo camera using the inspection tool. The present invention relates to a stereo camera inspection apparatus and an inspection method.

  In recent years, a stereo camera has been installed in an automobile to monitor the front of the vehicle while traveling by measuring the distance between the obstacle and the vehicle ahead and the host vehicle by imaging the front in the direction of travel with a pair of cameras. A driving support system that automatically performs, for example, appropriate braking control of a brake based on distance information to an obstacle or a preceding vehicle measured by a camera is being put into practical use.

  As a measurement technique using a stereo camera, a specific pixel correlated with a specific pixel block (image formation position of an object) in an image captured by one camera of a pair of cameras (camera having an imaging element such as an imaging lens and a CCD) The block (image formation position of the object) is identified from the image captured by the other camera, the parallax for each image is calculated, and the object is detected by the well-known triangulation principle using the distance information between each camera. A so-called stereo method for calculating the distance data is known.

  By the way, in order to calculate the distance data to an object (for example, the above-mentioned obstacle and the preceding vehicle) with high accuracy by the stereo method which is one of such three-dimensional measurement techniques, a pair obtained by each camera is used. It is important that there is no shift other than parallax between the images.

  For this reason, after assembling the stereo camera, it is necessary to accurately inspect whether or not there is a positional deviation between the cameras that causes a decrease in the accuracy of the distance data, and to correct the deviation if there is a positional deviation. In particular, a vertical shift between cameras and a positional shift other than the vertical direction appear as horizontal line shifts in each pixel when performing stereo matching, which greatly affects the reliability of the calculated distance data.

  In order to adjust (inspect) the positional deviation between the respective cameras of the stereo camera, for example, in the technique of Patent Document 1, a test chart having a plurality of predetermined patterns arranged at different distances is captured by the stereo camera, and the imaging is performed. The calibration parameters for correcting the shift of the pair of image data caused by the positional shift of the pair of cameras are calculated from the shift amount of the coordinates corresponding to each of the images.

  By the way, in the technique of Patent Document 1, a positional deviation in the vertical direction of a pair of cameras is detected using a plurality of test charts arranged in front of the stereo camera, and the positional deviation is corrected by image processing. Therefore, in the technique of Patent Document 1, since the test chart to be used is for detecting a positional deviation in the vertical direction of the pair of cameras, it is not possible to detect a positional deviation other than the vertical direction of the camera.

  For this reason, in order to detect misalignment other than the vertical direction of the camera, it is necessary to place another test chart for detecting misalignment other than the vertical direction in front of the stereo camera instead of this test chart. Both the vertical displacement and the positional displacement other than the vertical direction could not be easily inspected with good workability.

  Therefore, the present invention provides an inspection tool and a stereo camera that can easily inspect both a vertical position shift of a pair of cameras and a position shift other than the vertical direction with a good workability. An object is to provide an inspection apparatus and an inspection method.

In order to achieve the above-mentioned object, the inspection tool according to the present invention is an inspection tool used for inspection of a relative positional deviation of a pair of cameras constituting a stereo camera arranged with a gap by a base line length,
A first inspection tool in which a first pattern is formed on a surface disposed at a predetermined distance on the imaging direction side of the pair of cameras, and the opposite side of the pair of cameras with respect to the first inspection tool Alternatively, the images were picked up by the pair of cameras when picked up by the second inspection tool having the second pattern formed on the surface disposed at a predetermined distance on the pair of cameras and the pair of cameras. Pattern reflection means for causing a part of the second pattern of the second inspection tool to be reflected in the first pattern of the first inspection tool on the screen;
Each of the first pattern and the second pattern has a feature region that serves as an inspection point when a stereo camera inspection apparatus inspects a relative positional shift between the pair of cameras. Yes.

Further, the stereo camera inspection device according to the present invention is a stereo camera inspection device that inspects a relative positional deviation between a pair of cameras constituting a stereo camera arranged at intervals by a base line length,
A first inspection tool in which a first pattern is formed on a surface disposed at a predetermined distance on the imaging direction side of the pair of cameras, and the opposite side of the pair of cameras with respect to the first inspection tool Alternatively, the images were picked up by the pair of cameras when picked up by the second inspection tool having the second pattern formed on the surface disposed at a predetermined distance on the pair of cameras and the pair of cameras. An inspection tool provided with a pattern reflection means for causing a part of the second pattern of the second inspection tool to be reflected in the first pattern of the first inspection tool on the screen When,
A pair of cameras in which an image signal output from the pair of cameras is captured when the inspection tool is imaged by the pair of cameras, and a part of the second pattern is reflected in the first pattern. Image processing means for generating an image;
Corresponding to search each of the first and second corresponding points on the pair of images in each feature region that is an inspection point of the first and second patterns from the generated screen of the pair of images Point search means;
A corresponding position difference at each of the searched first and second corresponding points on the pair of images is calculated, and a relative position shift between the pair of cameras is calculated from the calculated corresponding position difference. Misalignment calculating means for
And correction parameter calculation means for calculating a correction parameter for correcting the calculated positional deviation.

Furthermore, the inspection method according to the present invention is an inspection method for inspecting a relative positional deviation between a pair of cameras constituting a stereo camera arranged with an interval by a base line length,
A first inspection tool in which a first pattern is formed on a surface disposed at a predetermined distance on the imaging direction side of the pair of cameras, and the opposite side of the pair of cameras with respect to the first inspection tool Alternatively, the images were picked up by the pair of cameras when picked up by the second inspection tool having the second pattern formed on the surface disposed at a predetermined distance on the pair of cameras and the pair of cameras. An inspection tool provided with a pattern reflection means for causing a part of the second pattern of the second inspection tool to be reflected in the first pattern of the first inspection tool on the screen using,
A pair of image signals output from the pair of cameras when the inspection tool is imaged by the pair of cameras, and a part of the second pattern is reflected in the first pattern. Generating an image of
Searching each of the first and second corresponding points on the pair of images in each feature region serving as an inspection point of each of the first and second patterns from the generated screen of the pair of images. When,
A corresponding position difference at each of the searched first and second corresponding points on the pair of images is calculated, and a relative position shift between the pair of cameras is calculated from the calculated corresponding position difference. And steps to
And a step of calculating a correction parameter for correcting the calculated misregistration.

  According to the present invention, when the inspection tool is imaged by the pair of cameras, the second pattern of the second inspection tool is included in the first pattern of the first inspection tool on the screen imaged by the pair of cameras. Using an inspection tool having a pattern projecting means for allowing a part of the pattern to be reflected, from the screen of a pair of images captured by a pair of cameras, an inspection point for each of the first and second patterns, In each feature region, the first and second corresponding points on the pair of images are respectively searched. Then, by calculating the corresponding position difference at each of the first and second corresponding points, and calculating the relative positional deviation between the pair of cameras from the calculated corresponding position difference, It is possible to easily inspect both misalignment and misalignment other than the vertical direction with good workability.

1 is a block diagram showing a schematic configuration of a stereo camera inspection apparatus according to Embodiment 1 of the present invention. (A), (b), (c) is the figure which showed the arrangement | positioning state of a pair of 1st, 2nd camera. (A) is a figure for demonstrating an imaging surface center shift | offset | difference, (b) is a figure for demonstrating an optical center shift | offset | difference. FIG. 5A is a diagram illustrating a correction angle for an optical center shift of a pair of cameras, and FIG. 5B is a diagram illustrating a state in which the optical center shift of a pair of cameras is corrected. The figure which showed the arrangement | positioning state of the 1st test chart and 2nd test chart in Embodiment 1. FIG. (A), (b) is the figure which showed the image of the 1st test chart and the 2nd test chart imaged with the camera. The figure which showed the relationship between the distance between a camera and a test chart, and the optical center shift | offset | difference amount on an imaging surface. The flowchart which showed the calculation process of the correction parameter for correct | amending the relative position shift of a 1st, 2nd camera. The schematic block diagram which shows the shift | offset | difference correction | amendment operation | movement with respect to the stereo camera test | inspected with the stereo camera test | inspection apparatus in this embodiment. The figure which showed the arrangement | positioning state of the 1st test chart and 2nd test chart in Embodiment 2. FIG. The figure which showed the image of the 1st test chart and 2nd test chart in Embodiment 2 imaged with the camera. The figure which showed the arrangement | positioning state of the 1st test chart in 2nd Embodiment, and a 2nd test chart. The figure which showed the image of the 1st test chart and 2nd test chart in Embodiment 3 imaged with the camera.

Hereinafter, the present invention will be described based on the illustrated embodiments.
<Embodiment 1>
FIG. 1 is a block diagram showing a schematic configuration of a stereo camera inspection apparatus according to Embodiment 1 of the present invention.

(Configuration of stereo camera inspection device)
As shown in FIG. 1, a stereo camera inspection apparatus 1 includes a test chart 2 as an inspection tool to be described later, and an image processing unit (image processing means) that captures an image signal obtained by imaging the test chart 2 output from the stereo camera 3. ) 4, a correction parameter calculation unit (correction parameter calculation unit) 5, a correction parameter recording unit (correction parameter recording unit) 6, and a control unit 7.

  The stereo camera 3 has a pair of first and second cameras 3a and 3b arranged with a predetermined distance (base line length) L in the horizontal direction. The first and second cameras 3a and 3b have an image pickup lens 8 and an image pickup device (CCD image sensor or the like) 9. A subject image picked up by the image pickup lens 8 is connected to an image pickup surface (light receiving surface) of the image pickup device 9. Image.

  The image processing unit 4 takes in image signals output from the image pickup devices 9 of the pair of first and second cameras 2a and 2b of the stereo camera 3 and performs predetermined signal processing, and a pair of test chart images (image data). Is generated.

  The image processing unit 4 includes a corresponding point search unit 4a as a corresponding point search unit and a position shift calculation unit 4b as a position shift calculation unit. The corresponding point search unit 4a is configured to display the pair of characteristic regions that serve as inspection points of the checker patterns P1 and P2 (first and second patterns) of the test chart 2 described later from the screen of the generated pair of test chart images. Each corresponding point on the test chart image is searched.

  For example, a known technique such as SAD (Sum of Absolute Difference) or POC (Phase Only Correlation) can be used as the corresponding point search method.

  The positional deviation calculation unit 4b calculates the corresponding positional difference between the corresponding points on the searched pair of test chart images, and the positional deviation between the pair of first and second cameras 2a and 2b from the calculated corresponding positional difference. Is calculated.

  The correction parameter calculation unit 5 calculates a correction parameter for correcting the positional deviation calculated by the positional deviation calculation unit 4b (details will be described later).

  The correction parameter recording unit 6 is a memory unit that records the correction parameters calculated by the correction parameter calculation unit 5. Examples of the correction parameter recording unit 6 include recording media such as RAM, HDD, USB memory, and SD card. The control unit 7 controls the operation of each unit (the image processing unit 4, the correction parameter calculation unit 5, the correction parameter recording unit 6, etc.) of the stereo camera inspection apparatus 1.

  In the assembled stereo camera 3 to be inspected, the first and second cameras 3a and 3b are arranged within a predetermined tolerance with a predetermined distance (base line length) along the horizontal direction. However, if the relative displacement between the first and second cameras 3a and 3b (the positional displacement in the vertical direction and the positional displacement other than the vertical direction) occurs at the pixel unit level, the distance measurement accuracy by the stereo camera 3 is improved. Adversely affect.

  Therefore, with respect to the assembled stereo camera 3, the stereo camera inspection apparatus 1 inspects the relative positional deviation of the first and second cameras 3a, 3b, and corrects the deviation when it is determined that these deviations have occurred. Calculate and record the correction parameters for. Then, image processing is performed on the image signals output from the first and second cameras 3a and 3b based on the calculated correction parameter, and the relative positional deviation between the first and second cameras 3a and 3b is determined. Correction (calibration) is performed by image processing.

  In the present embodiment, as shown in FIGS. 2A, 2B, and 2C, a pair of first and second cameras arranged with a predetermined distance (base line length) L in the horizontal direction. With respect to 3a and 3b, the arranged horizontal direction is defined as the X-axis direction, the vertical direction is defined as the Y-axis direction, and the optical axis M direction is defined as the Z-axis direction.

  Here, with reference to FIGS. 3A and 3B, the shift of the center position of the image pickup surface (the light receiving surface of the image pickup device 9), which is the “position shift in the vertical direction” defined in the present embodiment (hereinafter referred to as “position shift in the vertical direction”) 3 (a)) and the optical center position shift (hereinafter referred to as “optical center shift”); FIG. 3 (b)) will be described.

  In FIG. 3A, for example, when the actual center position A2 is shifted by Ys in the Y-axis direction with respect to the ideal center position A1 of the imaging surface (light receiving surface) of the imaging device 9 on the second camera 3b side. The image position formed on the image sensor 9 via the imaging lens 8 (focal length: f) changes by ys (= Ys). In this case, the displacement ys on the imaging surface of the imaging element 9 with respect to the measurement objects B1 and B2 having different distances (Z1, Z2) is the same.

  Therefore, the imaging plane center shift relative to the pair of cameras is corrected by moving the imaging planes C1 and C2 captured by the pair of cameras (first and second cameras 3a and 3b) by ys with respect to the other. can do.

  On the other hand, in FIG. 3B, for example, the actual optical center position A4 is only Yo in the Y-axis direction with respect to the ideal optical center position A3 of the imaging lens 8 (focal length: f) on the second camera 3b side. If they are shifted, the image positions formed on the image sensor 9 are shifted by yo1, yo2 (yo1> yo2) corresponding to the measurement objects B1, B2 having different distances (Z1, Z2). The shift yo1 corresponds to the measurement object B1, and the shift yo2 corresponds to the measurement object B2.

  Then, as shown in FIG. 4A, the imaging lens of the second camera 3b (right camera) as described above when the imaging surface C1 imaged by the first camera 3a (left camera) is used as a reference. When the optical center of 8 is shifted by Yo in the Y-axis direction, the center of the imaging surface C2 imaged by the second camera 3b is also shifted by Yo in the Y-axis direction.

In FIG. 4A, when the correction angle around the Z axis for correcting the optical center shift Yo of the imaging lens 8 of the second camera 3b (right camera) is θ, When the base line length between the two cameras 3a and 3b is L, the correction angle θ is
θ = arcsin (Yo / L)
Can be obtained.

  Therefore, as shown in FIG. 4B, the image pickup surfaces C1 and C2 picked up by the pair of cameras (first and second cameras 3a and 3b) are rotated around the Z axis by the correction angle θ, thereby It is possible to correct the optical center shift with respect to the camera. Accordingly, as shown in FIG. 4B, the base line direction L1 at the center of the imaging surfaces C1 and C2 of the pair of cameras can be made to coincide with the horizontal direction.

(Configuration of test chart 2)
As shown in FIG. 5, the test chart 2 according to the present embodiment is a first inspection tool arranged at a distance Z1 on the imaging direction side (front side) of the first and second cameras 3a and 3b. A first test chart 2a and a second test chart 2b as a second inspection tool arranged further apart from the first test chart 2a by a distance Z2 are provided. The first test chart 2a and the second test chart 2b may be integrally formed or may be separated.

  As shown in FIGS. 6A and 6B, the rectangular first test chart 2a has a black and white checker pattern P1 formed on the surface on the camera side, and a rectangular shape as a pattern display means at the center. An opening 2c is formed. The first test chart 2a should have a sufficiently large size so that it appears in the entire imaging range of the imaging lens 8 of the first and second cameras 3a and 3b. As a result, information on corresponding points, which will be described later, of the entire imaging range can be used, so that information on positional deviations of the first and second cameras 3a and 3b can be acquired more accurately. However, if the size is too large, installation space is restricted.

  Therefore, the first test chart 2a is most desirably a size that substantially corresponds to the imaging range of the imaging lens 8 of the first and second cameras 3a and 3b at the distance Z1 from the first and second cameras 3a and 3b. .

  As shown in FIGS. 6A and 6B, the rectangular second test chart 2b has an opening 2c through the opening 2c of the first test chart 2a from the first and second cameras 3a and 3b. Only the chart area corresponding to the frame is picked up. On the surface of the second test chart 2b, a checker pattern P2 having a smaller size than the checker pattern of the first test chart 2a is formed.

  In the present embodiment, the checker pattern P1 that is the first pattern is different from the checker pattern P2 that is the second pattern, but if the corresponding points described later are formed so as to be obtainable, the same pattern is used. There may be. Further, as in the third embodiment described later, the opening 2c in the first test chart 2a is not only the space surrounded by the opening edge of the first test chart 2a but also the first test chart 2a is divided. The space formed by is also meant.

  By the way, when the above-described optical center shift (see FIG. 3B) occurs in the camera (for example, the second camera 3b), as shown in the measurement result shown in FIG. The amount of deviation on the surface (light receiving surface) varies depending on the distance between the first and second cameras 3a and 3b and the first test chart 2a. The measurement results in FIG. 7 are obtained when the baseline length between the first and second cameras 3a and 3b is 100 mm, the pixel pitch of the imaging surface of the imaging device 9 is 0.00375 mm, and the optical center deviation is 1 mm.

  As is apparent from the measurement results of FIG. 7, the closer the distance between the first and second cameras 3a, 3b and the test chart 2a is, the larger the shift amount on the imaging surface is and the higher the measurement sensitivity.

  Therefore, in order to accurately calculate the optical center deviation of the camera, the distance Z1 between the first and second cameras 3a and 3b and the first test chart 2a should be as close as possible. In addition, in order to accurately calculate the center of the imaging surface of the camera (positional displacement in the Y-axis direction), it is better that the first and second cameras 3a and 3b and the second test chart 2b are separated from each other. That is, the distance Z2 between the first test chart 2a and the second test chart 2b is preferably long.

  However, the distance Z1 between the first and second cameras 3a, 3b and the first test chart 2a is the distance Z1 because the image captured by the imaging lens 8 needs to be focused on the imaging surface of the image sensor 9. Is longer than the minimum distance at which the imaging lens 8 is in focus. Therefore, in FIG. 5, for example, the distance Z1 between the first and second cameras 3a, 3b and the first test chart 2a is set to 2 m, which is near the minimum distance at which the imaging lens 8 is in focus in this embodiment. Then, by setting the distance Z2 between the first test chart 2a and the second test chart 2b to 2 m, it is possible to accurately calculate the optical center shift and the Y-axis position shift of the first and second cameras 3a and 3b.

(Correction parameter calculation process)
Next, the vertical displacement of the first and second cameras 3a and 3b by the stereo camera inspection apparatus 1 using the test chart 2 (first and second test charts 2a and 2b) A correction parameter calculation process for correcting (center deviation) will be described.

  In the present embodiment, first, as shown in FIG. 6A, in the test chart image (first test chart 2a) of the entire imaged screen, the feature region (change in light and shade) of the first test chart 2a that becomes an inspection point. A plurality of checker pattern corners (the portions indicated by ◯) are set.

  Then, the position of the corresponding first corresponding point D1 on the screen imaged by each of the first and second cameras 3a and 3b is searched in this feature region, and the searched corresponding first corresponding point D1 is displayed on the screen. From the corresponding positional difference, the entire positional deviation including the vertical deviation (imaging surface center deviation and optical center deviation) and the positional deviation other than the vertical direction in the camera on the second camera 3b side with reference to the first camera 3a side. Obtaining and calculating a correction parameter for correcting this deviation.

  Next, as shown in FIG. 6B, in the test chart image (first and second test charts 2a and 2b) in the captured screen, the characteristic area (light / dark) of the first test chart 2a serving as the inspection point is displayed. A plurality of checker pattern corner portions with a large change (circled portion) and a characteristic region of the second test chart 2b (a checker pattern corner portion with a large shading change: a portion represented by x) are set.

  Then, the positions of the corresponding first and second corresponding points D1 and D2 on the screen imaged by the first and second cameras 3a and 3b in these feature regions are searched, and the searched first and second points are searched. From the corresponding position difference on the screen with respect to the corresponding points D1 and D2, the image plane center deviation and the optical center deviation in the camera on the second camera 3b side are obtained with reference to the first camera 3a side, and this deviation is obtained. A final correction parameter for correction is calculated.

  Hereinafter, further details will be described with reference to the flowchart shown in FIG.

  As shown in FIGS. 5 and 6, when the test chart 2 is imaged by the first and second cameras 3a and 3b of the stereo camera 3, substantially the entire first test chart 2a and the opening of the first test chart 2a. A corresponding chart area is imaged in the opening 2c of the second test chart 2b through 2c (step S1).

  The image processing unit 4 of the stereo camera inspection apparatus 1 takes in image signals output from the image pickup devices 9 of the first and second cameras 3a and 3b, performs predetermined image processing, and FIG. A pair of test chart images as shown in b) are generated.

  Then, the corresponding point search unit 4a searches for the first corresponding point D1 in the entire screen of the first test chart 2a from the screen of the pair of test chart images generated by the image processing unit 4. At this time, the second corresponding point D2 of the second test chart 2b is simultaneously searched for the reliability determination described later. Then, the positional deviation calculation unit 4b calculates a corresponding position difference (dx, dy) between the searched first corresponding point D1 and second corresponding point D2 (step S2).

  Then, it is determined whether or not the value of the corresponding position difference (dx, dy), which is calculated data, is highly reliable as data (step S3). As this determination method, for example, when the calculated tendency of the corresponding position difference (dx, dy) at the first corresponding point D1 and the second corresponding point D2 is different without matching, the first test chart It is determined that 2a and the second test chart 2b are installed in an inclined manner rather than in parallel. Thereby, it is determined that the calculated data is not reliable.

  If it is determined in step S3 that the calculated data is not reliable (step S3: NO), readjustment is performed so that the first test chart 2a and the second test chart 2b are accurately arranged in parallel. (Step S4), the process returns to Step S1.

  On the other hand, if it is determined in step S3 that the calculated data is reliable (step S3: YES), a correction parameter that minimizes the corresponding positional difference (dy) across the entire screen acquired from the first test chart 2a. Is calculated (step S5). This corresponding position difference (dy) is based on the first corresponding point D1. It is sufficient to calculate the corresponding position difference (dy) using the first corresponding point D1, but the second corresponding point D2 may be used.

  Then, the image processing unit 4 performs an image correction process on the test chart screen image obtained in step S1 based on the correction parameter calculated in step S5 so as to minimize the displacement (step). S6).

  The following perspective transformation can be used for the image correction process in step S6. Here, assuming that the original coordinate position before conversion is (x1, y1) and the coordinate position after conversion is (x0, y0), the perspective transformation is generally 3 as shown in the following equations (1) and (2). It can be expressed using a × 3 matrix M.

However, A shows the coordinate showing a magnification. For details of the perspective transformation matrix M, see, for example, “Koichirou Deguchi,“ Geometry of Image and Space Computer Vision ”, Shosodo, 1991”.

  A correction parameter is calculated so that the positional deviation of the first and second cameras 3a and 3b is the coordinate after the perspective transformation and the sum of squares is minimized over the entire screen of the imaging surface.

  Then, the corresponding point search unit 4a, from the screen subjected to the image correction process in step S6, the x and y coordinates of the first corresponding point D1 of the first test chart 2a and the second corresponding point D2 of the second test chart 2b. Explore. Then, the positional deviation calculation unit 4b calculates the corresponding positional difference (dx, dy) between the first corresponding point D1 and the second corresponding point D2 on the screen of the pair of test chart images (step S7). .

  Then, from the corresponding position difference (dy) calculated in step S7, a final correction parameter for correcting the imaging surface center shift and the optical center shift, which are causes of the position difference, is calculated (step S8). Then, the correction parameter calculated in step S8 is recorded in the correction parameter recording unit 6 (step S9). The recorded correction parameters are used for the correction operation of the relative positional deviation (imaging surface center deviation and optical center deviation) of the first and second cameras 3a and 3b of the stereo camera 3 to be described later.

  By the way, only the correction of the image correction process in step S6 (the perspective transformation by the above formulas (1) and (2)) is not effective for the vertical displacement of the first and second cameras 3a and 3b. It is enough. That is, the reason why the first and second cameras 3a and 3b are displaced in the vertical direction is that there are two components, the above-described image plane center shift (Ys) and optical center shift (Yo).

  As a feature of these two components, the y deviation amount of the first and second cameras 3a and 3b on the imaging surface is the distance of the imaging surface center deviation (the first and second cameras 3a and 3b and the first and second test charts). Whereas the installation distance between 2a and 2b is constant, the optical center deviation changes with respect to the distance. Therefore, in the calculation of the correction parameter in step S8, the first and second corresponding points D1 and D2 of the first and second test charts 2a and 2b having two distance information are used, so that the two distances are used. Get the positional deviation (Y1, Y2). This positional deviation (Y1, Y2) can be expressed by a positional deviation (ys) due to an imaging surface center deviation and a positional deviation (yo) due to an optical center deviation as follows.

Y1 = yo1 + ys
Y2 = yo2 + ys

And in order to convert each of the above yo1 and yo2 into optical center shift Yo,
yo1 = Yo ・ f / Z1
yo2 = Yo ・ f / Z2
In other words, the optical center shift Yo can be obtained from the following equation (3).
Y1-Y2 = (1 / Z1-1 / Z2) Yo · f Equation (3)

  Z1 is the distance between the first and second cameras 3a and 3b and the first test chart 2a, Z2 is the distance between the first and second cameras 3a and 3b and the second test chart 2b, and f is the first and second 2 is the focal length of the imaging lens 8 of the cameras 3a and 3b.

  In this way, by obtaining the imaging surface center misalignment (Ys) and optical center misalignment (Yo), which are the causes of the vertical misalignment of the first and second cameras 3a and 3b, these are obtained as in step S8. It is possible to calculate a correction parameter for correcting the deviation.

  The correction parameter for the imaging surface center deviation (Ys) is a value of the distance translated in the Y-axis direction corresponding to the correction amount of the imaging surface center deviation (Ys), and the correction parameter for the optical center deviation (Yo) is The value of the correction angle θ around the Z-axis according to the correction amount of the optical center deviation (Yo).

The correction angle θ can be obtained by the following equation (4).
θ = arcsin (Yo / L) ... Formula (4)
Here, L is the baseline length between the first and second cameras 3a and 3b.

  Thus, according to the stereo camera inspection apparatus 1 of the present embodiment, the first test chart 2a having the opening 2c in the center on the front side of the first and second cameras 3a and 3b and the second on the rear side thereof. A test chart 2b is arranged. Then, on the screen of the captured pair of test chart images, the corresponding position difference (dx, dy) between the first corresponding point D1 and the second corresponding point D2 is calculated, respectively, and from the calculated corresponding position difference, It is possible to easily detect both the vertical and horizontal misalignments of the first and second cameras 3a and 3b with good workability.

  Further, as shown in FIG. 7, the position shift due to the optical center shift decreases in proportion to the reciprocal as the measurement distance increases. Therefore, as in the present embodiment, the distance (measurement distance) between the first and second cameras 3a, 3b and the first test chart 2a is set near the minimum focus position of the imaging lens 8, and the first and first By making the distance (measurement distance) between the two cameras 3a and 3b and the second test chart 2b as far as possible in consideration of the installation space, the optical center deviation can be measured with higher accuracy.

(Deviation correction operation for stereo camera 3)
FIG. 9 is a schematic block diagram showing a shift correction operation of the stereo camera 3 inspected by the stereo camera inspection apparatus 1 with respect to the first and second cameras 3a and 3b.

  As described above, when a relative positional shift occurs with respect to the first and second cameras 3a and 3b of the stereo camera 3, the correction parameters for correcting these shifts in the stereo camera inspection apparatus 1 are as follows. The correction parameter is calculated and recorded in the correction parameter recording unit 6.

  As shown in FIG. 9, when a relative displacement occurs in the first and second cameras 3 a and 3 b of the stereo camera 3, the correction parameter recording unit 6 corrects the relative displacement. The correction parameters are input to the first and second image correction units 10a and 10b.

  Then, the parallax calculation unit 11 includes an image obtained by the first camera 3a that has been corrected for deviation by the first image correction unit 10a and an image obtained by the second camera 3b that has been corrected for deviation by the second image correction unit 10b. To calculate the parallax and output the parallax image to the outside.

  In the present embodiment, assuming that both the imaging surface center shift and the optical center shift have occurred, the shift correction is performed in both the first camera 3a and the second camera 3b. However, for example, in the case where only the imaging surface center shift has occurred and the first camera 3a side is used as a reference, the first camera 3a side can be changed so that shift correction is not performed. Needless to say.

  As described above, for example, even when both a vertical position shift and a position shift other than the vertical direction are generated on the second camera 3b side with respect to the reference position of the first camera 3a, the stereo camera inspection apparatus 1 described above. The correction parameters can be corrected based on the correction parameters recorded in the correction parameter recording unit 6. Thereby, it is possible to output an accurate parallax image from images captured by the first and second cameras 3a and 3b of the stereo camera 3.

<Embodiment 2>
FIG. 10 is a diagram showing a configuration of a test chart according to the second embodiment of the present invention.

(Configuration of Test Chart in Embodiment 2)
As shown in FIG. 10, the test chart 2 according to the present embodiment includes a first test chart 2a and a first test chart that are arranged at a distance Z1 in front of the first and second cameras 3a and 3b. 2a includes a second test chart 2b disposed below the first and second cameras 3a and 3b, and a reflector 12 disposed on a part of the surface of the first test chart 2a.

  In the present embodiment, the pair of cameras 3a and 3b, the reflector 12 and the second test chart 2b are in positions where the second test chart 2b is reflected on the reflector 12 and the pair of cameras 3a and 3b are not reflected. Has been placed. The distance Z1 is about 2 m, for example, as in the first embodiment.

  FIG. 11 is a diagram showing a state in which the second test chart 2a is reflected in the surface region of the reflector 12 in the screen of the first test chart 2a.

  The chart patterns of the first and second test charts 2a and 2b are the same checker patterns as those of the first embodiment shown in FIG.

  Similarly, in the present embodiment, in the test chart images (first and second test charts 2a and 2b) in the captured screen, the feature region (checker pattern having a large density change) of the first test chart 2a serving as an inspection point. And a plurality of characteristic regions (corner portions of the checker pattern having large shading change) of the second test chart 2b. Then, the positions of the corresponding first and second corresponding points D1 and D2 on the screen imaged by the first and second cameras 3a and 3b in these feature regions are searched, and the searched first and second points are searched. From the corresponding position difference on the screen with respect to the corresponding points D1 and D2, the image plane center deviation and the optical center deviation in the camera on the second camera 3b side are obtained with reference to the first camera 3a side, and this deviation is obtained. A correction parameter for correction is calculated.

  Thus, in this embodiment, the reflecting plate 12 is disposed on a part of the surface of the first test chart 2a, and the front side of the first test chart 2a (the first and second cameras 3a, 3a, The second test chart 2b arranged on the lower side of 3b is reflected. With such a configuration, it is not necessary to arrange the second test chart 2b on the rear side of the first test chart 2a. Therefore, the arrangement space for the first and second test charts 2a and 2b can be reduced, and inspection can be performed even in a small room. be able to.

<Embodiment 3>
FIG. 12 is a diagram illustrating a configuration of a test chart according to the third embodiment of the present invention.

(Configuration of Test Chart in Embodiment 3)
As shown in FIG. 12, the test chart 2 according to the present embodiment includes a first test chart 2a and a first test chart that are arranged at a distance Z1 in front of the first and second cameras 3a and 3b. The second test chart 2b is further arranged away from 2a by a distance Z2.

  In the first test chart 2a, as shown in FIG. 13, a black and white checker pattern is formed on the surface on the camera side, and three rectangular openings 2c are formed by dividing the entire central area into three. Yes. As a result, as shown in FIG. 13, areas corresponding to the second test chart 2 b appear in the three openings 2 c of the first test chart 2 a in the screens captured by the first and second cameras 3 a and 3. Include. Therefore, the feature regions of the first and second test charts 2a and 2b having different distances (corner portions of the checker pattern having a large shade change) in the entire center region of the screen imaged by the first and second cameras 3a and 3 Can be set alternately.

  Similarly, in the present embodiment, in the test chart images (first and second test charts 2a and 2b) in the captured screen, the characteristic region (the change in shading is large) of the first test chart 2a serving as the inspection point. A plurality of feature regions (corner portions of the checker pattern having a large density change) of the second test chart 2b are set. Then, the positions of the corresponding first and second corresponding points D1 and D2 on the screen imaged by the first and second cameras 3a and 3b in these feature regions are searched, and the searched first and second points are searched. From the corresponding position difference on the screen with respect to the corresponding points D1 and D2, the image plane center deviation and the optical center deviation in the camera on the second camera 3b side are obtained with reference to the first camera 3a side, and this deviation is obtained. A correction parameter for correction is calculated.

  Thus, since the corresponding position difference with respect to each of the first and second corresponding points D1 and D2 can be acquired in the entire center area of the imaged screen, the first and second values can be obtained from the variation in the values of the acquired corresponding position differences. The inclination and flatness of the test charts 2a and 2b can be easily grasped and readjusted with high accuracy. Thereby, each corresponding position difference can be acquired as highly reliable data.

  Further, by taking the positions of the first and second corresponding points D1 and D2 in the entire center area of the imaged screen, it is possible to suppress the influence on the curvature of the imaging lens 8 and the local change in optical characteristics. it can. Thereby, the calculation accuracy of the corresponding position difference with respect to each of the first and second corresponding points D1 and D2 can be increased.

  In addition, although the pattern of 1st, 2nd test chart 2a, 2b of each above-described embodiment was a checker pattern, it is not limited to this, For example, a circular pattern etc. may be sufficient.

1 Stereo Camera Inspection Device 2 Test Chart (Inspection Tool)
2a First test chart (first inspection tool)
2b Second test chart (second inspection tool)
DESCRIPTION OF SYMBOLS 3 Stereo camera 3a 1st camera 3b 2nd camera 4 Image processing part 4a Corresponding point search part 4b Position shift calculation part 5 Correction parameter calculation part 6 Correction parameter recording part 7 Control part 8 Imaging lens 9 Imaging element 12 Reflecting plate

JP 2004-132870 A

Claims (10)

An inspection tool used for inspecting a relative positional shift between a pair of cameras constituting a stereo camera arranged with a gap corresponding to a baseline length,
A first inspection tool having a first pattern formed on a surface disposed at a predetermined distance on the imaging direction side of the pair of cameras;
A second inspection tool in which a second pattern is formed on a surface arranged at a predetermined distance on the opposite side of the pair of cameras or the pair of cameras with respect to the first inspection tool;
A part of the second pattern of the second inspection tool is included in the first pattern of the first inspection tool on the screen imaged by the pair of cameras when captured by the pair of cameras. Pattern reflecting means for making it appear, and
Each of the first pattern and the second pattern has a characteristic region that serves as an inspection point when a stereo camera inspection apparatus inspects a relative positional shift between the pair of cameras. Inspection tool to do.   The pattern reflection means is one or more openings formed in the first inspection tool, and the second inspection tool is located behind the pair of cameras on the rear side of the first inspection tool. The inspection tool according to claim 1, wherein the inspection tool is arranged.   The pattern imprinting means is a reflecting plate disposed on a part of the surface of the first inspection tool on the pair of cameras side, and the second inspection tool in front of the pair of cameras on the first test chart. The inspection tool according to claim 1, wherein the inspection tool is disposed.   The pair of cameras, the reflector, and the second inspection tool are arranged at positions where the second inspection tool is reflected on the reflector and the pair of cameras are not reflected. The inspection tool according to claim 3.   5. The inspection tool according to claim 1, wherein a distance between the pair of cameras and the first inspection tool is in the vicinity of a minimum distance at which the pair of cameras are focused.   The inspection tool according to any one of claims 1 to 5, wherein the first inspection tool is larger than an imaging range of the pair of cameras in the vicinity of a minimum distance where the pair of cameras are in focus. A stereo camera inspection device that inspects a relative positional deviation between a pair of cameras constituting a stereo camera arranged with an interval by a base line length,
A first inspection tool in which a first pattern is formed on a surface disposed at a predetermined distance on the imaging direction side of the pair of cameras, and the opposite side of the pair of cameras with respect to the first inspection tool Alternatively, the images were picked up by the pair of cameras when picked up by the second inspection tool having the second pattern formed on the surface disposed at a predetermined distance on the pair of cameras and the pair of cameras. An inspection tool provided with a pattern reflection means for causing a part of the second pattern of the second inspection tool to be reflected in the first pattern of the first inspection tool on the screen When,
A pair of cameras in which an image signal output from the pair of cameras is captured when the inspection tool is imaged by the pair of cameras, and a part of the second pattern is reflected in the first pattern. Image processing means for generating an image;
Corresponding to search each of the first and second corresponding points on the pair of images in each feature region that is an inspection point of the first and second patterns from the generated screen of the pair of images Point search means;
A corresponding position difference at each of the searched first and second corresponding points on the pair of images is calculated, and a relative position shift between the pair of cameras is calculated from the calculated corresponding position difference. Misalignment calculating means for
A stereo camera inspection apparatus comprising: correction parameter calculation means for calculating a correction parameter for correcting the calculated positional deviation.   The stereo camera inspection apparatus according to claim 7, further comprising recording means for recording the correction parameter calculated by the correction parameter calculation means.   The stereo camera inspection apparatus according to claim 7, wherein the positional shift calculated by the positional shift calculation unit is a vertical position shift of the pair of cameras. An inspection method for inspecting a relative positional deviation between a pair of cameras constituting a stereo camera arranged with an interval of a base line length,
A first inspection tool in which a first pattern is formed on a surface disposed at a predetermined distance on the imaging direction side of the pair of cameras, and the opposite side of the pair of cameras with respect to the first inspection tool Alternatively, the images were picked up by the pair of cameras when picked up by the second inspection tool having the second pattern formed on the surface disposed at a predetermined distance on the pair of cameras and the pair of cameras. An inspection tool provided with a pattern reflection means for causing a part of the second pattern of the second inspection tool to be reflected in the first pattern of the first inspection tool on the screen using,
A pair of image signals output from the pair of cameras when the inspection tool is imaged by the pair of cameras, and a part of the second pattern is reflected in the first pattern. Generating an image of
Searching each of the first and second corresponding points on the pair of images in each feature region serving as an inspection point of each of the first and second patterns from the generated screen of the pair of images. When,
A corresponding position difference at each of the searched first and second corresponding points on the pair of images is calculated, and a relative position shift between the pair of cameras is calculated from the calculated corresponding position difference. And steps to
Calculating a correction parameter for correcting the calculated misregistration.