JP2012002612A - Calibration board and calibration apparatus equipped with this calibration board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a calibration board excelling in planarity and pattern accuracy, and a calibration apparatus facilitated in picture acquisition for calibrating optical equipment and enabled to accomplish highly accurate calibration by being equipped with this calibration board.SOLUTION: A calibration apparatus 100 for optical equipment comprises a board body 11, a checker pattern 12 formed on one face of this board body 11, a calibration board 10 having at least two reference units 13 formed symmetrically with respect to the origin P of this checker pattern 12, an illumination device 20, and a universal head 40 that holds a camera body 30, which is an optical equipment item arranged on the reverse side to the illumination device 20 with respect to the calibration board 10, and enables the camera body 30 to be shifted relative to the calibration board 10.

Description

  The present invention relates to a calibration board and a calibration apparatus including the calibration board.

  When performing optical device calibration (camera calibration) such as camera lens distortion correction and stereo camera parallelization, a calibration checker pattern as shown in FIG. It is very important to photograph 1) and measure the position of the pattern 1 in a wide range and with high accuracy from the obtained image. Further, it is desirable that as many patterns 1 as possible be included in one image. In order to realize this, a calibration device capable of obtaining an image suitable for measurement is required. Conventionally, in order to cover a wide angle of view, a large calibration board is created and a calibration image is acquired (see, for example, Patent Document 1). Alternatively, pattern 1 is displayed on the liquid crystal display, and an image is acquired by bringing the camera closer.

JP 2008-193188 A

  However, it has been very difficult to maintain the flatness of the conventional large calibration board. In addition, there has been a problem that the calibration apparatus is enlarged. On the other hand, when a pattern is displayed on the display, there is a problem that the camera body is reflected on the surface of the display. In addition, when the detection wavelength range of the camera is in the infrared region, there is a problem that the pattern displayed on the display cannot be captured. In addition, since the liquid crystal display has glass on the surface, there is a problem that the pattern to be photographed becomes a pattern affected by refraction by the glass on the surface. Accordingly, there is a need for a calibration board and a calibration apparatus that are small in size, cover a wide angle of view, can easily obtain an angle of view for camera calibration, and can perform more accurate calibration.

  The present invention has been made in view of such a problem, and is for calibrating an optical apparatus (a camera or the like) having an optical system with a wide angle of view, and has a high flatness and a highly accurate pattern. It is an object of the present invention to provide a calibration board and a calibration apparatus that can easily acquire an image for calibrating an optical device and can perform high-accuracy calibration by providing the calibration board.

  In order to solve the above-mentioned problems, a calibration board according to the present invention is used for calibration of optical equipment, and is a flat plate board body that transmits light, and a grid-like structure on one surface of the board body. A plurality of rectangular areas obtained by dividing the checker pattern into vertical and horizontal colors are alternately colored, so that the checker pattern of the checker pattern is formed at the intersection of the checker pattern in which the colored portions and the colorless portions are alternately formed and the checker pattern lattice. And at least two reference portions formed so as to sandwich an intersection defined as an origin.

  In such a calibration board, it is preferable that the colored portion of the checker pattern blocks the light and the colorless portion transmits the light.

  In such a calibration board, the reference portion is preferably formed at least one of a colored portion and a colorless portion that form an intersection defined as the origin.

  In such a calibration board, the reference portion can be a black dot.

  In such a calibration board, the colored portion is preferably formed by applying chromium.

  Further, a calibration apparatus according to the present invention includes any one of the above-described calibration boards, an illumination apparatus that irradiates the calibration board with illumination light emitted from the light source, and an illumination apparatus for the calibration board. And a pan head for holding the optical device for imaging the checker pattern and moving the optical device relative to the calibration board.

  Such a calibration apparatus detects a reference part of a checker pattern from an image captured by an optical device, and further processes the image based on the origin by detecting the origin of the checker pattern from the reference part. It is preferable to have a control unit.

  In such a calibration apparatus, it is preferable that the illumination apparatus has a diffusion unit that diffuses illumination light between the light source and the calibration board.

  Furthermore, it is preferable that such a calibration apparatus has a plurality of the above-described illumination apparatuses and is configured to irradiate the calibration board with illumination light from a plurality of directions.

  When the present invention is configured as described above, a calibration board having a high flatness and a highly accurate checker pattern, and the calibration board, and irradiating illumination light from the back surface, a wide-angle optical system is provided. Therefore, it is possible to obtain a calibration apparatus that can easily acquire an image for calibrating an optical apparatus having a high accuracy and that can perform high-precision calibration.

It is the schematic which shows the structure of the apparatus for calibration provided with the board for calibration which concerns on this embodiment. It is the schematic which shows the structure of the board for a calibration concerning this embodiment. It is a flowchart which shows the calibration method. It is explanatory drawing for demonstrating the pattern of the board for conventional calibration.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of a calibration apparatus 100 for calibrating a camera body 30 that is an optical device that includes a calibration board and has a detection wavelength range of infrared light will be described with reference to FIG. As shown in FIG. 1, the calibration device 100 according to the present embodiment includes a calibration board 10, a lighting device 20, a camera platform 40 that supports the camera body 30, a mounting table 50, and a control unit 60. And a storage unit 70. The control unit 60 is provided in a distance measuring device (not shown), and performs calculation and image conversion for measuring the distance (spatial coordinates) to the subject based on the image data (test image) from the camera body 30. In this embodiment, the later-described pan head moving means 41 for operating the pan head 40 is also controlled. The control unit 60 can be implemented as a program executed by a CPU in a computer including a processing unit such as a CPU, ROM, and RAM incorporated in the distance measuring device and a storage unit 70 such as a hard disk. The storage unit 70 stores parameter information used at the time of image conversion by the control unit 60, actual coordinate values of intersections 14 of the calibration board 10 described later, and the like.

  The calibration board 10 has a board body 11 made of a glass substrate used for a photomask substrate or the like, and one surface of the boat body 11 is divided into a grid to create a rectangular area. As shown in FIG. 2, the checker pattern 12 in which black portions (colored portions) 12a and white portions (colorless portions) 12b are alternately arranged is formed. Here, for the black portion 12a, for example, chromium having a low reflectance with respect to the wavelength of infrared light is used. Since the calibration board 10 according to the present embodiment is made of a glass substrate used for a photomask substrate, the flatness is very high, and the accuracy of the checker pattern 12 made of chromium may be very high. it can. Hereinafter, the surface on which the checker pattern (hereinafter may be simply referred to as “pattern”) 12 is drawn is called the front surface of the calibration board 10, and the surface on which the checker pattern is not drawn is called the back surface. In the following description, as shown in FIGS. 1 and 2, the horizontal direction when the calibration board 10 is viewed from the front side is defined as the X axis, and the vertical direction is defined as the Y axis. The optical axis direction of the camera body 30, that is, the normal direction of the surface of the calibration board 10, will be described as the Z axis.

  When a pattern is displayed on a liquid crystal display as in the past, a material with a refractive index different from that of air, that is, the glass of the liquid crystal display, exists between the pattern and the camera body. Although there is a problem that cannot be measured, the calibration board 10 according to the present embodiment directly measures (images) the checker pattern 12 on the surface, so that such a problem does not occur. Further, the calibration board 10 is mounted and fixed substantially vertically on the mounting table 50, and stability is maintained so that there is no blurring, rattling or tilting.

  In addition, since the black portion 12a of the checker pattern 12 has a low reflectance because it is drawn with chrome, the camera body 30 itself has the black portion 12a even in a location where the positional relationship between the calibration board 10 and the camera body 30 is close. Can be reduced. The reflection of the camera body 30 means that the illumination light that has passed through the white portion 12b from the back surface of the calibration board 10 is irradiated and reflected on the surface of the camera body 30, and the surface of the calibration board 10 (the black portion). 12a) means that this reflected light is generated by reflection.

  The calibration board 10 is further drawn in the vicinity of the intersection P, which is the center of the board body 11, among the intersections (cross points) 14 of the checker pattern 12 so as not to interfere with the measurement of the checker pattern 12. A reference portion 13 composed of two black dots is provided. The reference unit 13 is used for detecting the position of the center P. In the present embodiment, as shown in FIG. 2, a small black dot is drawn at the center of two white portions 12 b that are arranged point-symmetrically with respect to the center P as the reference portion 13. In this way, by detecting the cross position of the checker pattern 12 sandwiched between the reference portions 13 composed of two black circle points, the center P of the checker pattern 12, that is, the origin, can be detected quickly and accurately. The reference portion 13 is not limited to the one in the present embodiment, and a white circle may be drawn on the two black portions 12a arranged with the center P in between, and the reference portion 13 may be drawn. The shape of the checker pattern 12 is not limited as long as it does not interfere with the measurement of the checker pattern 12. Further, for each intersection (cross point) 14 of the checker pattern 12, coordinate information (X, Y) is stored in the storage unit 70 with the center P as the origin.

  The illumination device 20 includes a light source 21 that emits infrared light, a condensing lens 22 that condenses the infrared light emitted from the light source 21, and a diffusion unit 23 that diffuses the infrared light emitted from the condensing lens 22. And is configured. The illumination device 20 is installed on the back side of the calibration board 10 and is configured to be able to adjust the illumination intensity (brightness) by controlling the voltage applied to the light source 21, for example. In FIG. 1, only one set of the illumination device 20 is illustrated, but actually, a plurality of sets are installed, and the illumination position is adjusted so that the illumination intensity distribution on the calibration board 10 is as uniform as possible. When the luminance value of the test image acquired by the camera body 30 is saturated or the contrast is low, the illumination intensity is adjusted so that appropriate illumination can be performed. The diffusing unit 23 is disposed between the light source 21 and the back surface of the calibration board 10 and diffuses infrared light that is illumination light to irradiate the calibration board 10 with illumination light (infrared light). For example, it is desirable to install a material that does not block infrared light such as imitation paper.

  In this way, by performing illumination from the back side of the calibration board 10, it is possible to perform illumination capable of obtaining a good test image even when the camera body 30 and the calibration board 10 are close to each other. Further, when the illumination is performed from the front side of the calibration board 10 as in the prior art, it is difficult for the camera body to obstruct the area to be photographed, and the back surface as in the present embodiment. Such a problem can be solved by illuminating from the side. The illumination device 20 is not limited to the above-described configuration, and any conventionally known device may be used.

  The camera body 30 includes an imaging optical system 31 and an image sensor 32 made of a CCD, a CMOS, or the like, and is installed on the camera platform 40 by a tripod 33. Note that the test image picked up by the image pickup device 32 is sent to the control unit 60, and the calibration processing described below is performed based on the test image.

  Further, the pan head 40 on which the camera body 30 is installed mounts the above-described calibration board 10 so that the camera body 30 and the calibration board 10 can be photographed by arranging them in a positional relationship controlled with high accuracy. It is installed on the mounting table 50. The pan head 40 includes a pan head moving means 41, and the position of the pan head 40 is moved in the X, Y, and Z directions under the control of the control unit 60 to change the shooting position of the camera body 30. Fine adjustment of the installation position can be performed. With such a configuration, there is an advantage that a test image can be acquired in a positional relationship that facilitates obtaining calibration accuracy. Furthermore, since images can always be taken with the same positional relationship, the reproducibility is excellent, and the calibration performance during mass production of the camera body 30 can be stabilized. In this embodiment, the movement of the camera platform 40 by the camera platform moving means 41 is configured to be automatically performed by the control unit 60, but may be configured to be performed manually. In addition, the camera body 30 can be removed from the camera platform 40 and replaced with another camera body 30, and the camera body 30 after the replacement can be calibrated. In the calibration apparatus 100, since it is necessary to change the relative positional relationship between the camera body 30 and the calibration board 10, not only the camera body 30 is moved by the camera platform 40 as described above. The calibration board 10 may be configured to move with respect to the camera body 30.

  For example, when the calibration apparatus 100 configured as described above is used, for example, calibration of parameter information for acquiring (ranging) the relative coordinates of the subject by the control unit 60 from the image captured by the camera body 30 is performed. Will be described. First, the pan head 40 is moved by the pan head moving means 41 to adjust the position of the camera body 30 and the position of the calibration board 10 to a predetermined positional relationship. Next, infrared light is emitted as illumination light from the light source 21 of the illumination device 20 arranged on the back surface of the calibration board 10. The illumination light is condensed by the condenser lens 22, diffused by the diffusion unit 23, and applied to the calibration board 10. As a result, the image of the checker pattern 12 is formed on the image sensor 32 by the imaging optical system 31 of the camera body 30, and a test image is output from the image sensor 32. As described above, the checker pattern 12 has a very high degree of flatness, and the use of chrome makes the checker pattern 12 very accurate. Therefore, the image sensor 32 can easily and accurately obtain a test image. Can do. However, depending on the camera body 30, distortion or the like may occur in the test image acquired due to the aberration of the imaging optical system 31 or the like. In order to perform highly accurate distance measurement in consideration of such distortion, calibration of parameter information is performed.

  A calibration method performed by the control unit 60 using the test image acquired by the imaging element 32 will be described with reference to the flowchart of FIG. First, when acquiring a test image from the image sensor 32 (step S100), the control unit 60 detects two black circle points that are the reference unit 13 of the calibration board 10 from the test image (step S110). And if this reference | standard part 13 is detected, the origin of the board 10 for a calibration will be detected by image processing (step S120). For example, a virtual square region having a diagonal line connecting the two reference portions 13 is formed, and the intersection 14 of the checker pattern 12 included in the square region is the center P of the calibration board 10, that is, the origin. Become. In this way, by having the reference portion 13 composed of two black dots, the origin of the calibration board 10 can be detected quickly.

  Next, the control unit 60 trims the test image into a square or the like within a predetermined range around the origin P in the test image, and the coordinate values (x, y) is detected, and the space coordinate value (X, Y, Z) of this intersection is calculated from this coordinate value and the parameter information described above (step S130). Of course, it is also possible to calculate the spatial coordinate values for all the intersections in the test image without trimming the test image and use it as calibration data. Then, the actual coordinate value of each intersection 14 of the calibration board 10 stored in advance in the storage unit 70 is compared with the coordinate value of each intersection of the test image corresponding thereto (step S140). The control unit 60 can calculate the actual coordinate value of each intersection in the Z direction, that is, the distance between the camera body 30 and the calibration board 10 based on the position coordinates of the camera platform 40. As a result of the comparison, it is determined whether there is an error in the coordinate values (step S150). If there is an error due to distortion or the like, the parameter information in the parameter table is corrected (calibrated) (step S160). Alternatively, the conversion formula of the measurement data may be stored in advance in the parameter table in the storage unit 70, and the variable of the conversion formula may be corrected. When the calibration of one camera body 30 is completed, the camera body 30 is replaced, and the above-described series of operations are performed for each replacement, so that the calibration operation can be quickly performed.

  As described above, in the calibration apparatus 100 including the calibration board 10 according to the present embodiment, the calibration board 10 having the high flatness and the high-precision checker pattern 12 is used, and illumination light is emitted from the back surface of the calibration board 10. Therefore, it is possible to suppress the reflection of the camera body 30 and the unevenness of the brightness value of the image pickup, to easily obtain a test image, and to calibrate the camera with high accuracy. As a result, it is possible to improve the efficiency of calibration work and to mass-produce highly accurate cameras.

DESCRIPTION OF SYMBOLS 10 Board for calibration 11 Board body 12 Checker pattern 12a Black part (colored part) 12b White part (colorless part) 13 Reference part 14 Intersection 20 Illumination device 21 Light source 23 Diffusing part 30 Camera body (optical device) 40 Pan head 60 Control part 100 Calibration equipment

Claims (9)

A calibration board used for calibration of optical equipment,
A flat plate board that transmits light;
A checker pattern in which colored portions and colorless portions are alternately formed by coloring a plurality of quadrangular regions obtained by dividing into a lattice shape on one side of the board main body in a vertical and horizontal manner;
A calibration board comprising: at least two reference portions formed so as to sandwich an intersection defined as an origin of the checker pattern among intersections of the checker pattern lattice.   The calibration board according to claim 1, wherein the colored portion of the checker pattern blocks the light, and the colorless portion transmits the light.   The calibration board according to claim 1, wherein the reference part is formed in at least one of the colored part and the colorless part that form an intersection defined as the origin.   The calibration board according to claim 1, wherein the reference portion is a black dot.   The calibration board according to claim 1, wherein the colored portion is formed by applying chromium. The calibration board according to any one of claims 1 to 5,
An illumination device having a light source and irradiating the calibration board with illumination light emitted from the light source;
A pan head for holding an optical device for imaging the checker pattern on the opposite side of the illumination device of the calibration board and moving the optical device relative to the calibration board, Calibration equipment.   Control for processing the image based on the origin by detecting the reference portion of the checker pattern from the image captured by the optical device and further detecting the origin of the checker pattern from the reference portion. The calibration apparatus according to claim 6, further comprising a section.   The calibration apparatus according to claim 6, wherein the illumination apparatus includes a diffusion unit that diffuses the illumination light between the light source and the calibration board.   The calibration apparatus according to claim 6, wherein the calibration apparatus includes a plurality of the illumination apparatuses, and is configured to irradiate the calibration board with illumination light from a plurality of directions.

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