Camera calibration tool and calibration method

Abstract

The invention belongs to the technical field of machine vision, and discloses a camera calibration tool and a calibration method.The camera calibration tool comprises a body, the body is located below a lens of a camera, the surface of the body is horizontal, and the body is used for placing a calibration plate; the positioning assembly is arranged on the body and is used for positioning the body and a camera lens; the calibration mechanism is arranged on the body and located in the range of the positioning assembly; the calibration mechanism comprises a first calibration assembly, a second calibration assembly, a third calibration assembly and a fourth calibration assembly which are arranged on the body, and the calibration plates are respectively positioned in the first calibration assembly, the second calibration assembly, the third calibration assembly and the fourth calibration assembly for positioning and shooting. The device is simple in structure and convenient to use, the calibration plate can be conveniently positioned, the positioning precision is improved, the calibration error is reduced, the calibration efficiency of the camera is improved, and the convenience and operability of the calibration process are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of machine vision, and in particular relates to a camera calibration tool and a calibration method. Background Art

[0002] Camera calibration is an important process in computer vision and image processing. It is mainly used to establish the relationship between the pixel positions of camera images and the positions of scene points in three-dimensional space. Zhang's camera calibration is a commonly used camera calibration method. By photographing a specific calibration plate pattern and analyzing the captured pattern, the camera's internal and external parameters can be solved.

[0003] In the solution process, theoretically, three calibration plate patterns are needed to complete the calibration. However, in actual use, in order to better correct distortion, reduce noise and error, and improve the robustness of calibration, multiple calibration plate patterns are used to complete the calibration. Therefore, in order to obtain a more accurate calibration effect, more calibration plates are generally used to calibrate the camera. However, using more calibration plates for calibration will increase the calibration workload and reduce the calibration efficiency. At the same time, when calibrating with multiple calibration plates, the calibration plate posture needs to be changed frequently, which is inconvenient for calibration. Random placement of calibration plates will lead to reduced calibration accuracy.

[0004] Therefore, it is urgent to design a camera calibration tooling and calibration method to solve the above technical methods. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a camera calibration tool that can use fewer calibration plate images and obtain calibration results more quickly and conveniently.

[0006] To achieve the above objectives, the present invention provides a camera calibration tool, comprising:

[0007] A body, located below the camera lens and having a horizontal surface, for placing a calibration plate;

[0008] A positioning component is provided on the body and is used to realize the positioning of the body and the camera lens;

[0009] A calibration mechanism is provided on the main body and is located within the range of the positioning component; the calibration mechanism includes a first calibration component, a second calibration component, a third calibration component and a fourth calibration component provided on the main body, and the calibration plate is respectively positioned in the first calibration component, the second calibration component, the third calibration component and the fourth calibration component for positioning and shooting.

[0010] Preferably, the first calibration component includes two right-angled ribs and two straight ribs arranged on the main body, the two right-angled ribs are symmetrically arranged, the two straight ribs are symmetrically arranged, one corner of the calibration plate abuts against the inner wall of the right-angled rib, and the straight ribs on the same side abut against the edge of the calibration plate.

[0011] Preferably, the second calibration component includes a placement groove provided on the main body and adapted to the calibration plate, the four corners of the bottom end of the placement groove are respectively fixed with small planes, and the calibration plate is embedded in the placement groove and abuts against the top ends of several of the small planes.

[0012] Preferably, a concave hole is formed through the main body, and the middle portion of the concave hole coincides with any edge position of the placement slot, so as to facilitate taking out the calibration plate from the placement slot.

[0013] Preferably, the third calibration component includes two wide inclined surfaces symmetrically arranged in the placement groove, and the wide inclined surface is set between the two small planes on the same side; the calibration plate is tilted and attached to the two wide inclined surfaces.

[0014] Preferably, the fourth calibration component includes two long inclined surfaces symmetrically arranged at the bottom end of the placement groove, the long inclined surfaces are inclined from the middle to both sides, and the calibration plate is obliquely attached to the long inclined surfaces.

[0015] Preferably, the positioning assembly includes an annular groove formed on the top surface of the body, and the annular groove is arranged corresponding to the shooting range of the camera lens.

[0016] Preferably, the positioning assembly includes lugs fixedly connected to both sides of the body, and the lugs are provided with a plurality of long holes for fixing.

[0017] The present invention also discloses a camera calibration method, comprising the following steps:

[0018] Prepare calibration fixtures and standard calibration plates;

[0019] Positioning the calibration fixture body below the calibrated camera through the positioning component;

[0020] Place the calibration plates in the first calibration component, the second calibration component, the third calibration component, and the fourth calibration component respectively, and perform calibration by taking photos with a camera;

[0021] The photo information of the calibration plate taken at different orientations and angles is processed to complete the camera calibration.

[0022] Preferably, when photographing the calibration plate, the calibration plate is placed twice in the first calibration component and twice in the fourth calibration component, and photographed and calibrated.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects: the present invention discloses a camera calibration tool and a calibration method, the positioning component on the main body is accurately positioned with the camera, so that the camera's shooting range is fixed at the specified position of the camera, thereby improving the positioning accuracy; at the same time, the positioning component can also fix the calibration tool of the present application at the specified position so that it will not move, thereby avoiding errors caused by misalignment of the calibration tool and avoiding repeated positioning during batch calibration, reducing workload, improving calibration accuracy, and improving calibration efficiency; the positioning mechanism is divided into a first calibration component, a second calibration component, a third calibration component and a fourth calibration component, and the first calibration component, the second calibration component, the third calibration component and the fourth calibration component are respectively adapted to the calibration plate. During calibration, the position and angle of the calibration plate are directly restricted, so that the calibration plate can be positioned and placed according to a fixed position and angle, thereby reducing calibration errors, improving positioning accuracy, reducing the number required for calibration, improving the efficiency of camera calibration, and improving the convenience and operability of the calibration process.

[0024] The present invention has a simple structure and is easy to use, can conveniently realize the positioning of the calibration plate, improves the positioning accuracy, reduces the calibration error, improves the calibration efficiency of the camera, and improves the convenience and operability of the calibration process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0026] Figure 1 Axis view of the camera calibration fixture of the present invention;

[0027] Figure 2 A top view of the camera calibration tooling of the present invention;

[0028] Figure 3 For the present invention Figure 2 Schematic cross-section of the middle AA;

[0029] Figure 4 For the present invention Figure 2 Schematic cross-section of the middle BB;

[0030] Figure 5 This is a schematic diagram of the calibration plate of the present invention being installed in a first placement mode within the first calibration assembly;

[0031] Figure 6 This is a schematic diagram of the second placement of the calibration plate in the first calibration assembly of the present invention;

[0032] Figure 7 This is a schematic diagram of the installation of the calibration plate of the present invention in the second calibration assembly;

[0033] Figure 8 Schematic diagram of the installation of the calibration plate of the present invention in the third calibration assembly;

[0034] Figure 9 This is a schematic diagram of the first installation arrangement of the calibration plate of the present invention within the fourth calibration assembly;

[0035] Figure 10 Schematic diagram of the second installation arrangement of the calibration plate of the present invention within the fourth calibration assembly;

[0036] Figure 11 The relationship between the number of images of the calibration plate of the present invention and the evaluation factor;

[0037] Figure 12 The process of collecting images of the calibration plate in different positions of the present invention;

[0038] Figure 13 The calculation process of the images collected in different postures of the present invention;

[0039] In the figure: 1. Straight rib; 2. Groove; 3. Right-angle rib; 4. Lug; 5. Long hole; 6. Small plane; 7. Placement slot; 8. First edge line; 9. Wide bevel; 10. Second edge line; 11. Long bevel; 12. Main body; 13. Concave hole; 14. Calibration plate. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] Reference Figures 1-13 As shown, this embodiment provides a camera calibration tool, including:

[0043] The body 12 is located below the camera lens and has a horizontal surface, and is used to place a calibration plate 14;

[0044] A positioning component is provided on the body 12 and is used to realize the positioning of the body 12 and the camera lens;

[0045] The calibration mechanism is provided on the main body 12 and is located within the range of the positioning component; the calibration mechanism includes a first calibration component, a second calibration component, a third calibration component and a fourth calibration component provided on the main body 12, and the calibration plate 14 is respectively positioned in the first calibration component, the second calibration component, the third calibration component and the fourth calibration component for positioning and shooting.

[0046] The present invention discloses a camera calibration tool and a calibration method. The positioning component on the main body 12 is accurately positioned with the camera, so that the camera's shooting range is fixed at the specified position of the camera, thereby improving the positioning accuracy. At the same time, the positioning component can also fix the calibration tool of the present application at the specified position so that it will not move, thereby avoiding errors caused by misalignment of the calibration tool and avoiding repeated positioning when performing batch calibration, reducing workload, improving calibration accuracy, and improving calibration efficiency. The positioning mechanism is divided into a first calibration component, a second calibration component, a third calibration component, and a fourth calibration component, and the first calibration component, the second calibration component, the third calibration component, and the fourth calibration component are respectively adapted to the calibration plate 14. During calibration, the position and angle of the calibration plate 14 are directly restricted, so that the calibration plate 14 can be positioned and placed according to a fixed position and angle, thereby reducing calibration errors, improving positioning accuracy, reducing the number required for calibration, improving the efficiency of camera calibration, and improving the convenience and operability of the calibration process. The present invention has a simple structure and is easy to use, can conveniently realize the positioning of the calibration plate, improves the positioning accuracy, reduces the calibration error, improves the calibration efficiency of the camera, and improves the convenience and operability of the calibration process.

[0047] The technical solution of the present application is a tool based on the Zhang Zhengyou calibration method, wherein the Zhang Zhengyou calibration method is a camera calibration method based on a two-dimensional plane target (such as a chessboard). The camera is used to capture multiple images of the plane target (such as chessboard images) at different angles, and then the camera is calibrated by performing calculation and analysis on the corner points of the chessboard, that is, solving the internal and external parameters of the camera, providing strong support for related tasks in the field of computer vision; this calibration method is between the traditional calibration method and the self-calibration method, overcoming the disadvantage of the traditional calibration method requiring high-precision calibration objects, while improving the accuracy and operability compared to self-calibration.

[0048] This method uses multiple images of a two-dimensional planar target (chessboard) to solve the camera's intrinsic and extrinsic parameters and distortion parameters. In the field of computer vision and optical measurement, in order to accurately measure the actual state of an object, it is necessary to establish the relationship between the spatial coordinate system and the camera's pixel coordinate system. Accurate modeling of the camera's intrinsic and extrinsic parameters and distortion parameters is an important step in this process and directly determines the measurement accuracy.

[0049] The calibration process includes the following steps:

[0050] Printing a checkerboard: Print an A4 paper with a checkerboard pattern of known black and white spacing and tape it to a flat plate.

[0051] Capture images: Use a camera to capture images of the checkerboard from multiple different angles.

[0052] Compute the homography matrix: For each image, calculate the homography matrix H from the chessboard plane to the image plane. This involves the relationship between a 3D point (a point on the chessboard) and its projection point on the image.

[0053] Solving for intrinsic parameters: Using the constraint relationship between the homography matrix H and the camera's intrinsic parameter matrix A, linearly solve the intrinsic parameter matrix A. The intrinsic parameter matrix A contains information such as the camera's focal length, principal point coordinates, and the perpendicularity of the image coordinate axes.

[0054] Solving extrinsic parameters: When the intrinsic parameter matrix A and the homography matrix H are known, the extrinsic parameter matrix (rotation matrix R and translation vector t) can be calculated, which describes the position and posture of the camera relative to the world coordinate system.

[0055] Optimize parameters: The maximum likelihood estimation method is used to optimize the above parameters to improve the calibration accuracy. This involves minimizing an error function that includes all images and calibration points.

[0056] The application and characteristics of this calibration method: Only a printed chessboard is needed as the calibration object, which reduces the calibration cost. Compared with the traditional calibration method, it improves the accuracy and operability. Compared with the self-calibration method, it is easier to implement and the results are more stable.

[0057] Zhang Zhengyou calibration method is widely used in camera calibration, 3D reconstruction, augmented reality and other tasks in the field of computer vision. It is also one of the standard methods for camera calibration in many computer vision software and libraries (such as OpenCV).

[0058] When performing the Zhang Zhengyou calibration method, it is necessary to ensure the accuracy of the chessboard and the clarity of the image.

[0059] When shooting checkerboard images, you should shoot from as many different angles as possible to obtain richer coordinate information.

[0060] When optimizing parameters, it is necessary to select appropriate initial values and iterative algorithms to ensure the stability and accuracy of the optimization results.

[0061] In the prior art, reprojection error is an important indicator for judging the accuracy of camera calibration results. It evaluates the accuracy of calibration by comparing the difference between the positions of points in 3D space projected onto the image plane by the calibrated projection matrix and the actual positions of these points in the image. Inverse reprojection error is a variant of reprojection error. It is used to evaluate the accuracy of camera calibration. Unlike forward reprojection error, inverse reprojection residual evaluates the accuracy of calibration by comparing the difference between the theoretical position of 2D image points in 3D space and the actual position after back-projection using calibration parameters. It reflects the error in three-dimensional space.

[0062] In the prior art, the calibration plate 14 is a device used in the fields of machine vision, image measurement, photogrammetry, etc. Its main functions are to correct lens distortion, determine the conversion relationship between physical size and pixels, and determine the relationship between the three-dimensional geometric position of a point on the surface of a spatial object and its corresponding point in the image.

[0063] There are many types of camera calibration plates 14, including commonly used solid circle array pattern calibration plates 14, chessboard pattern calibration plates 14, April calibration plates 14, checkerboard calibration plates 14, aruco_marker calibration plates 14, V-shaped / inverted calibration plates 14, and vertical calibration plates 14. These calibration plates 14 typically have a high-precision manufactured fixed-pitch pattern array, such as black and white squares or circles, which play a key role in the calibration process.

[0064] During the calibration process, a calibration plate 14 is placed in the camera's field of view and multiple images are captured. By mapping the characteristic points in the images to known points on the calibration plate 14, the camera's intrinsic parameter matrix, such as focal length and principal point coordinates, and extrinsic parameters, such as the rotation matrix and translation vector, can be calculated. These parameters are crucial for correcting lens distortion, improving measurement accuracy, and reconstructing accurate results.

[0065] The camera calibration plate 14 is widely used in scenarios requiring high-precision cameras, such as robotic vision, autonomous driving, and 3D reconstruction. In the autonomous driving field, the calibration plate 14 is an essential tool for experiments, mass production, and after-sales service. It can improve the accuracy and reliability of perception data, thereby ensuring the safety and reliability of autonomous driving systems.

[0066] In one embodiment of the present application, the calibration plate 14 selected for camera calibration of the present application is a square panel with a fixed size.

[0067] In one embodiment of the present application, the calibration tooling of the present application is integrally printed using 3D printing and is made of flexible materials such as nylon and resin to prevent scratching the surface of the calibration plate 14 .

[0068] In one embodiment of the present application, there is no restriction on the color of the surface of the calibration tool and the table on which the tool is placed, but the contrast between the two must be sufficient. For example, if the color of the calibration tool is black, the surface of the table on which the tool is placed can be designed to be white to prevent recognition failure when identifying the surface features of the calibration plate.

[0069] In one embodiment of the present application, the sizes of the first calibration component, the second calibration component, the third calibration component and the fourth calibration component are all designed according to the calibration plate 14, so as to directly limit the position of the calibration plate 14 and facilitate precise positioning.

[0070] A further optimized solution is that the first calibration component includes two right-angled ribs 3 and two straight ribs 1 provided on the body 12. The two right-angled ribs 3 are symmetrically arranged, and the two straight ribs 1 are symmetrically arranged. One corner of the calibration plate 14 abuts against the inner wall of the right-angled rib 3, and the straight rib 1 on the same side abuts against the edge of the calibration plate 14. As shown in Reference 2, a right-angled rib 3 and a straight rib 1 on the same side form a calibration position as a group. Therefore, during calibration, the calibration plate 14 can be positioned at two calibration positions respectively; during positioning, the patterned side of the calibration plate 14 faces the camera lens, and then any right-angle position of the calibration plate 14 abuts against the inner corner position of the right-angled rib 3, and then the edge abuts and fits against the inner wall of the straight rib 1, so that different calibration plates 14 can be positioned.

[0071] In one embodiment of the present application, when the calibration plate 14 is photographed to calibrate the camera through the first calibration component, the calibration plate 14 can be clamped at two symmetrical calibration positions to take photos and obtain calibration information.

[0072] As a further optimization, the second calibration component includes a placement slot 7 on the body 12 that matches the calibration plate 14. A small flat surface 6 is fixed to the four corners of the bottom end of each placement slot 7. The calibration plate 14 is embedded in the placement slot 7 and abuts against the top of several small flat surfaces 6. The size of the placement slot 7 is adapted to the calibration plate 14, and the four corners of its bottom section are respectively set on the small flat surfaces 6 with the top surface horizontal. During calibration, the image surface of the calibration plate 14 faces upward and is embedded in the placement slot 7. The bottom surface of the calibration plate 14 abuts against the small flat surfaces 6, achieving horizontal positioning of the calibration plate 14 and facilitating camera calibration.

[0073] As a further optimization, a recessed hole 13 is formed through the body 12, and the middle portion of the recessed hole 13 coincides with any edge of the placement slot 7, making it easy to remove the calibration plate 14 from the placement slot 7. The recessed hole 13 is located in the middle of the edge of the placement slot 7, and its size is about the thickness of a human index finger, making it easy to remove the calibration plate 14 from the placement slot 7.

[0074] In one embodiment of the present application, each placement groove 7 is provided in a lower limit area on the main body 12 , and the edges of each placement groove 7 are a first edge line 8 and a second edge line 10 .

[0075] Further optimizing the solution, the third calibration component includes two wide bevels 9 symmetrically arranged in the placement groove 7, and the wide bevel 9 is set between the two small planes 6 on the same side; the calibration plate 14 is tilted and attached to the two wide bevels 9. The wide bevel 9 is arranged between the two small planes 6 on the same side, and the slope of the wide bevel 9 rises toward the second edge line 10, and the two wide slopes are arranged symmetrically; when placed for calibration, the calibration is tilted and attached to the two wide bevels 9, and the input image of the calibration plate 14 faces the lens of the camera, which is convenient for calibration; after the calibration plate 14 is placed in place, the back of the calibration plate 14 abuts against the second edge line 10, thereby ensuring the stable positioning of the calibration plate 14 and improving the convenience and accuracy of positioning.

[0076] As a further optimization, the fourth calibration component includes two long inclined surfaces 11 symmetrically arranged at the bottom of the placement slot 7. The long inclined surfaces 11 are inclined from the middle to the sides, and the calibration plate 14 is tilted and attached to the long inclined surfaces 11. The high ends of the two long inclined surfaces 11 are located at the midline of the placement slot 7, and then tilt downward to the sides. When the calibration plate 14 is positioned, the back of the calibration plate 14 is attached to the long inclined surfaces 11, and at the same time, the back of the calibration plate 14 is in contact with the first edge line 8, thereby ensuring the stable positioning of the calibration plate 14 and improving the convenience and accuracy of positioning.

[0077] In one embodiment of the present application, the edge of the small plane 6 facing the long inclined surface 11 is also designed to be an inclined surface. When the calibration plate 14 is positioned and placed, its back surface also fits on the inclined surface, further improving the positioning stability.

[0078] In one embodiment of the present application, when calibration and positioning are performed by the fourth calibration component, the calibration plate 14 needs to be tilted to both sides and photographed for calibration.

[0079] To sum up, when calibrating the camera in this application, the first calibration component and the fourth calibration component are calibrated using two calibration plates 14 respectively, and the second calibration component and the third calibration component are calibrated using one calibration plate 14. That is, when using the calibration tooling of this application for calibration, precise positioning can be completed using six calibration plates 14.

[0080] In one embodiment of the present application, in order to further improve the accuracy of calibration, more calibration plates 14 may be used for calibration. The calibration plates 14 may be rotated in the same calibration assembly to change the pattern of the calibration plates 14 .

[0081] In a further optimization, the positioning assembly includes an annular groove 2 formed on the top surface of the body 12. The groove 2 is configured to correspond to the camera's field of view. The groove 2 is formed on the body 12 and its dimensions correspond to the camera's field of view. This is used to adjust the calibration fixture's position so that it coincides with the camera's field of view.

[0082] In one embodiment of the present application, there is color in the groove 2 to facilitate observation of whether they overlap.

[0083] As a further optimization, the positioning assembly includes lugs 4 fixed to both sides of the body 12, and provided with a plurality of slots 5 for fixing. The lugs 4 are fixed to both sides of the body 12 and extend outward, and are provided with a plurality of slots 5 for fixing the fixture to prevent passive misalignment when the calibration plate 14 is placed.

[0084] The present invention also discloses a camera calibration method, comprising the following steps:

[0085] Prepare a calibration tool and a standard calibration plate 14; design the size of the tool according to the size of the calibration plate 14, and then use 3D printing to complete the calibration preparation work;

[0086] Use the positioning assembly to position the calibration fixture body 12 below the calibration camera. Place the fixture below the camera lens and adjust the position so that the camera's field of view is flush with the area of the groove 2. Then, secure the fixture body 12 using the long hole 5 on the lug 4. It should be noted that when adjusting the fixture's position, the actual movement direction of the fixture is opposite to the movement direction observed by the camera.

[0087] The calibration plate 14 is placed in the first calibration component, the second calibration component, the third calibration component and the fourth calibration component respectively, and the calibration is carried out by taking pictures with the camera; the calibration plate 14 is placed in the calibration position in two directions composed of the right-angle ribs 3 and the straight ribs 1 on the same side of the first calibration component, and then pictures are taken respectively; the calibration plate 14 is clamped in the placement groove 7 of the second calibration component so that the calibration plate 14 falls on the small plane 6, and then pictures are taken; the calibration plate 14 is tilted and placed between the two wide inclined surfaces 9 and the second edge line 10, and then pictures are taken; the calibration plate 14 is tilted and placed along the long inclined sides and the first edge line 8 on both sides of the fourth calibration component, and then pictures are taken respectively; the above steps can be performed in a random order until six different photo information is obtained;

[0088] The photographic information of the calibration plate 14 taken at different orientations and angles is processed to complete the camera calibration.

[0089] After research, it was found that when performing camera calibration, the lighting environment, the number of patterns on the calibration plate 14, and the position of the calibration plate 14 all have an impact on the calibration results.

[0090] When performing camera calibration, a camera calibration result evaluation criterion based on inverse reprojection residual is specially proposed: all images in a set of calibration plate 14 images are used to calculate the camera calibration results, and only all feature points of the first image in this set of calibration plate 14 images are used to evaluate the camera calibration results using inverse reprojection residual. The purpose of this is to prevent low-quality calibration plate 14 images from interfering with the evaluation results.

[0091]

[0092] Among them, K -1 It is the inverse matrix of the intrinsic parameter matrix in the calibration result.

[0093] [R|t] -1 It is the inverse matrix of the external parameter matrix in the calibration result.

[0094] n is the number of feature points in the first calibration plate image.

[0095] It is the evaluation factor, the unit is mm. The camera calibration result can be judged by this value. The smaller the value, the more accurate the camera calibration result.

[0096] When considering the effect of the image brightness of the calibration plate 14 on the camera calibration results, a ring light source was placed in front of the camera and the brightness of the light source was adjusted to ensure that there was no difference in each set of images except for the brightness. The evaluation factors were compared. As can be seen from Table 1, the brightness of the calibration plate 14 image has an impact on the calibration results. Therefore, when setting the light source brightness and camera exposure, it is necessary to ensure that the image brightness is uniform and there is no dark field.

[0097] Table 1 Comparison of evaluation factors for brightness of different light sources

[0098]

[0099] The following experiments were conducted to investigate the effect of the number of images on the calibration plate 14 on the calibration results. The specific experimental methods are as follows:

[0100] Let G i Represents the set of the i-th group of images, where i∈(1,m), and each group of images G i Contains n images, denoted as G i ={I i，1, I i，2 ,…,I i，n}

[0101] For each set of images G i Do the following:

[0102] For k from 4 to 20:

[0103] Calculate the calibration results of the first k images

[0104] Through calibration results Calculate the first image I among these k images i，1 The judging factor

[0105] A total of more than 1200 images of 14 calibration plates were collected, divided into m = 60 groups, with n = 20 images in each group.

[0106] The final experimental results are as follows Figure 11 As shown, the conclusions are as follows:

[0107] 1. Too many images involved in the calculation will make the judgment factor Increase.

[0108] 2. When the number of images involved in the calculation is 3-6, the evaluation factor After 6 pictures, the judging factor The changes are no longer noticeable.

[0109] 3. Judgment Factor The minimum value of mostly occurs when the number of images is 6.

[0110] 4. Although the minimum judgment factor in some groups It appears after the 6th image, but the judgment factor at the 6th image is only within 0.001mm of the minimum judgment factor.

[0111] Theoretically, the change of the calibration plate 14 posture will definitely affect the calibration results. We want to explore which postures can obtain better calibration results with fewer calibration plate 14 images.

[0112] Specific experimental methods such as Figure 12 As shown, after the experiment, multiple groups of data were analyzed and their mean values were obtained. The results are as follows Figure 13 As shown;

[0113] x corrected =x+[2p1xy+p2(r 2 +2x2 )]

[0114] y corrected =y+[p1(r 2 +2y 2 )+2p2xy]

[0115]

[0116] x and y are the original coordinates of a point in the image; corrected and y corrected is the coordinate of a point after distortion correction; p1 and p2 are the distortion coefficients.

[0117] By analyzing the distortion model, it can be seen that the farther away from the center point of the image, the greater the distortion. Therefore, in order to better correct the distortion of the image, it is necessary to have calibration plates 14 placed around the image.

[0118] After experiments, the following conclusions were obtained:

[0119] 1. The images used for calibration must contain at least 1-2 images of the calibration plate 14 in pitch position.

[0120] 2. The positional relationship between the images used for calibration should not only have translation changes, or the posture differences should be large.

[0121] 3. The image used for calibration should contain images of calibration plates 14 distributed around the image as much as possible.

[0122] 4: When using this calibration tool for calibration, you only need to collect 6 calibration plate images, which can achieve the effect of collecting more than ten calibration plate images without the tool.

[0123] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0124] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A camera calibration tool, characterized in that: include: A body (12), the body (12) is located below the camera lens and has a horizontal surface, and is used to place a calibration plate (14); A positioning component, the positioning component is arranged on the body (12) and is used to realize the positioning of the body (12) and the ground camera lens; A calibration mechanism is provided on the body (12) and is located within the range of the positioning component; the calibration mechanism comprises a first calibration component, a second calibration component, a third calibration component, and a fourth calibration component provided on the body (12); the calibration plate (14) is positioned in the first calibration component, the second calibration component, the third calibration component, and the fourth calibration component, respectively, for positioning and photographing.

2. The camera calibration tool according to claim 1, characterized in that: The first calibration component comprises two right-angled ribs (3) and two straight ribs (1) provided on the body (12); the two right-angled ribs (3) are symmetrically arranged, and the two straight ribs (1) are symmetrically arranged; one corner of the calibration plate (14) abuts against the inner wall of the right-angled rib (3), and the straight rib (1) on the same side abuts against the edge of the calibration plate (14).

3. The camera calibration tool according to claim 1, characterized in that: The second calibration component comprises a placement groove (7) provided on the body (12) and adapted to the calibration plate (14); small planes (6) are fixedly connected to the four corners of the bottom end of the placement groove (7); the calibration plate (14) is embedded in the placement groove (7) and abuts against the top ends of several of the small planes (6).

4. The camera calibration tool according to claim 3, characterized in that: A concave hole (13) is provided through the body (12), and the middle portion of the concave hole (13) coincides with any edge position of the placement groove (7), making it easy to remove the calibration plate (14) from the placement groove (7).

5. The camera calibration tool according to claim 3, characterized in that: The third calibration component comprises two wide inclined surfaces (9) symmetrically arranged in the placement groove (7), and the wide inclined surfaces (9) are arranged between the two small planes (6) on the same side; the calibration plate (14) is tilted and attached to the two wide inclined surfaces (9).

6. The camera calibration tool according to claim 3, characterized in that: The fourth calibration component comprises two long inclined surfaces (11) symmetrically arranged at the bottom end of the placement groove (7), the long inclined surfaces (11) are inclined from the middle to both sides, and the calibration plate (14) is inclined and attached to the long inclined surfaces (11).

7. The camera calibration tool according to claim 3, characterized in that: The positioning component comprises an annular groove (2) provided on the top surface of the body (12), and the annular groove (2) is arranged corresponding to the shooting range of the camera lens.

8. The camera calibration tool according to claim 7, characterized in that: The positioning assembly comprises lugs (4) fixedly connected to both sides of the body (12), and the lugs (4) are provided with a plurality of long holes (5) for fixing.

9. A camera calibration method, comprising the camera calibration tool according to any one of claims 1 to 8, characterized in that The following steps are involved: Preparing a calibration tool and a standard calibration plate (14); Positioning the calibration tool body (12) below the calibrated camera through a positioning assembly; The calibration plate (14) is sequentially placed in the first calibration component, the second calibration component, the third calibration component and the fourth calibration component, and calibration is performed by taking photos with a camera; The photographic information of the calibration plate (14) taken at different orientations and angles is processed to complete the camera calibration.

10. The camera calibration method according to claim 9, wherein: When photographing the calibration plate (14), the calibration plate (14) is placed twice in each of the first calibration component and the fourth calibration component, and photographing and calibration are performed.

Images