Calibration method and calibration device

Abstract

The embodiment of the present invention discloses a calibration method and a calibration device. The calibration method comprises: fixing a plurality of camera assemblies on a calibration fixture, and fixing a calibration plate at a certain distance from the calibration fixture; a plurality of cameras take pictures of the calibration plate at the same time; rotating the calibration plate and / or rotating the calibration fixture, and a plurality of cameras continue to take pictures of the calibration plate to a predetermined number of times; inputting the images obtained after multiple pictures into a calibration calculation module, and performing calibration calculations through the calibration calculation module to obtain calibration parameters. The calibration device comprises a plurality of camera assemblies, a calibration plate, a calibration fixture and a calibration module; the calibration module is communicatively connected with a plurality of camera assemblies, and is used to calibrate a plurality of camera assemblies according to the calibration method. The technical solution provided by the embodiment of the present invention not only improves the calibration accuracy of the lens, but also can be compatible with simultaneous calibration of different field of view angles in a multi-camera system while ensuring high calibration accuracy, thereby improving the calibration efficiency and simplifying the structure of the calibration device.

Description

[Technical field]

[0001] The present invention relates to the technical field of mobile phone optical cameras, and in particular to a calibration method and a calibration device. [Background technology]

[0002] As one of the device methods for implementing depth calculation, optical camera is already the most common method in the mobile phone industry. With the increasing demand for shooting effects, shooting performance has gradually become the main selling point of various manufacturers, and multi-camera combination has become the mainstream design of current high-end mobile phones.

[0003] The camera system has key applications in scene blur, 3D reconstruction, motion capture, and many other aspects. Camera calibration, that is, determining the internal and external parameters of each camera, is a key and necessary link for the application of these scenarios. It determines whether the system can calculate effectively.

[0004] The mainstream combination of multi-cameras in current high-end mobile phones is a combination of main camera + wide-angle + telephoto lens. The main difference between the three lenses is the focal length and field of view (FOV). When shooting objects at the same distance, the field of view content of the lenses with different field of view angles varies greatly. Figure 1 These are the imaging contents of the wide-angle, main camera and telephoto lenses at the same distance.

[0005] The calibration process is simply that the camera shoots the calibration plate and uses the correspondence between the coordinates of the feature points on the captured image in the image coordinate system (image coordinates) and the coordinates of these feature points in the actual space (world coordinates) to calculate the corresponding parameters.

[0006] According to the traditional Zhang Zhengyou calibration method, it does not matter whether the calibration plate fills the entire image or the number of "corner points" in the field of view ("corner points" can be the corner points of square grids on a chessboard, or dots on a dot board, etc., in any form). It only needs to meet the minimum four points required by Zhang Zhengyou calibration.

[0007] The entire lens is not filled with "corner points", and the accuracy of the calibration parameters, especially the distortion data, is low, which cannot meet the calibration accuracy requirements of the large aperture and other characteristics of the mobile phone back end.

[0008] Use calibration boards that fill the entire lens market. According to the backend feature usage scenario requirements, the usual calibration requirements for multi-camera calibration are to calibrate the main camera lens + wide-angle lens together, and the main camera lens + telephoto lens together. The multi-camera calibration process can be decomposed into multiple dual-camera calibrations. After decomposing the multi-camera calibration into multiple dual-camera calibrations, you can follow the traditional dual-camera calibration ideas. Use equipment and methods that meet the requirements when calibrating the main camera + wide-angle lens and the main camera + telephoto lens to ensure sufficient accuracy.

[0009] In order to ensure the calibration accuracy and effect, two sets of calibration devices are required at the same time or two calibration plates are installed in the device for use by different cameras. This equipment is redundant and affects efficiency. [Summary of the invention]

[0010] In view of this, an embodiment of the present invention provides a calibration method and a calibration device to solve the above-mentioned technical problems existing in the prior art.

[0011] In a first aspect, an embodiment of the present invention provides a calibration method, which includes: fixing multiple camera assemblies on a calibration fixture, and fixing a calibration plate at a certain distance from the calibration fixture; multiple cameras taking pictures of the calibration plate at the same time; rotating the calibration plate and / or rotating the calibration fixture, and the multiple cameras continue to take pictures of the calibration plate for a predetermined number of times; inputting the images obtained after multiple pictures into a calibration calculation module, and performing calibration calculations through the calibration calculation module to obtain calibration parameters.

[0012] Through the solution provided in this embodiment, under the premise of ensuring high precision, that is, ensuring high precision of internal and external parameters and distortion parameters, multiple camera lenses with different field of view angles can be calibrated at one time. In addition, multiple camera components can be calibrated at one time.

[0013] In a preferred embodiment, in the calculation module, the calibration calculation includes the following steps: obtaining coordinate pairs of dots and feature points on the calibration plate; matching corresponding feature points according to the size of the field of view angle θ of the camera; calculating initial calibration parameters using the coordinate pairs of feature points; calculating output calibration parameters using the coordinate pairs of dots; wherein the feature points include inner circle feature points and outer circle feature points.

[0014] Through the solution provided in this embodiment, the multi-camera images collected by the multiple camera assemblies are processed to obtain images of appropriate sizes, and then the coordinate pairs of the required feature points are obtained. After the initial calibration parameters are obtained, the calibration parameters are further optimized using all the dots and feature points in the entire image, thereby improving the parameter accuracy.

[0015] In a preferred embodiment, the matching includes the following steps: searching and distinguishing dots without circular ring features and inner circle feature points and outer circle feature points with circular ring features on the calibration plate; if the camera assembly includes a main camera lens and a telephoto lens, determining the correct inner circle feature points and assigning first index numbers based on the image position of each outer circle feature point or the positional relationship between the outer circle feature points and the inner circle feature points; if the camera assembly includes a main camera lens and a wide-angle lens, finding all outer circle feature points and assigning second index numbers based on absolute and relative position relationships; calculating the initial matrix using the inner circle feature points with the first index number, and calculating the initial matrix using the outer circle feature points with the second index number.

[0016] Through the solution provided in this embodiment, since the fields of view of lenses with different field of view angles differ greatly, in order to adapt to the characteristics of the large field of view of wide-angle lenses and the small field of view of telephoto lenses, the feature points on the calibration plate are designed into two layers, the inner circle feature points are used for the calibration of telephoto lenses, and the outer circle feature points are used for the calibration of wide-angle lenses, thereby achieving high-precision calibration while improving calibration efficiency.

[0017] In a preferred embodiment, the inner circle feature points and the outer circle feature points both include three-layer circular rings as special position marks and ordinary two-layer circular rings.

[0018] Through the solution provided in this embodiment, the number of layers of circular rings and the absolute and relative position relationship of each circular ring are utilized so that the dots, inner circle feature points, and outer circle feature points can be easily distinguished, which is beneficial for calibrating lenses with large field of view angles and lenses with small field of view angles at the same time. The inner circle feature points close to the center area can be used for the calibration of lenses with small field of view angles, and the outer circle feature points on the periphery can be used for the calibration of lenses with large field of view angles. There will be no mismatch between lenses and feature points, thus achieving high-precision calibration and also helping to improve the efficiency of calibration.

[0019] In the second aspect, an embodiment of the present invention discloses a calibration device, which includes: multiple camera assemblies, a calibration plate, a calibration fixture and a calibration module; the calibration plate and the calibration fixture are respectively fixed at two places, the center of the calibration fixture is aligned with the center of the calibration plate, and the calibration plate and the calibration fixture can both rotate; multiple camera assemblies are fixed on the calibration fixture, and the camera assemblies can receive light from the effective field of view area on the calibration plate; the calibration module is communicatively connected to the multiple camera assemblies, and is used to calibrate the multiple camera assemblies according to the calibration method described in the first aspect.

[0020] Through the solution provided in this embodiment, the camera assembly fixed in the calibration fixture is aligned with the calibration plate, and the images containing partial areas on the calibration plate acquired by different camera assemblies are transmitted to the calibration module. The multiple camera assemblies are calibrated simultaneously through the calibration method described above, thereby achieving high-precision calibration when dealing with camera assemblies with different fields of view, different models, and used in different devices, and the calibration device has a simple structure and high calibration efficiency.

[0021] In a preferred embodiment, the lateral length of the calibration plate is greater than the lateral length of the effective field of view area, and the longitudinal height of the calibration plate is greater than the longitudinal height of the effective field of view area.

[0022] Through the solution provided in this embodiment, the camera component can obtain an image containing most of the area on the calibration plate, the coordinates of the feature points can be calculated more accurately during calibration, and when the calibration parameters are finally output, the more dots the acquired image contains, the higher the accuracy of the calibration parameters.

[0023] In a preferred embodiment, the calibration plate is arranged with array-arranged dots, inner circle feature points and outer circle feature points, the inner circle feature points are arranged close to the central area of ​​the calibration plate, and the outer circle feature points are arranged away from the central area of ​​the calibration plate.

[0024] Through the solution provided in this embodiment, three types of image points are used to calibrate the lens with a small field of view angle and the lens with a large field of view angle at the same time, the inner circle feature points are matched to the calibration of the lens with a small field of view angle, and the outer circle feature points are matched to the calibration of the lens with a large field of view angle. When calibrating lenses with different field of view angles at the same time, different image points can be effectively distinguished, and the calibration of the lens with a large field of view angle and the calibration of the lens with a small field of view angle can be minimized from interfering with each other, and finally high-precision calibration parameters are obtained.

[0025] In a preferred embodiment, the maximum horizontal spacing between two of the inner circle feature points and between two of the outer circle feature points is smaller than the lateral length of the effective field of view area, and the maximum vertical spacing is smaller than the longitudinal height of the effective field of view area.

[0026] Through the solution provided by this embodiment, when the camera assembly has a combination of a main camera lens and a wide-angle lens, the initial monoreflective matrix is ​​calculated using the outer circle feature points, and when the camera assembly has a combination of a main camera lens and a telephoto lens, the initial monoreflective matrix is ​​calculated using the inner circle feature points. In this way, the accuracy of the matrix obtained by the camera assembly in different lens combination scenes can be guaranteed, and multi-camera calibration can be implemented in one calibration device.

[0027] In a preferred embodiment, the calibration plate and the calibration fixture are respectively provided with a horizontal rotation axis and a vertical rotation axis.

[0028] Through the solution provided in this embodiment, the user can fix the calibration fixture and only rotate the calibration plate, or fix the calibration plate and only rotate the calibration fixture, which improves the user's freedom and flexibility when calibrating the lens of the camera assembly.

[0029] In a preferred embodiment, a central area of ​​the calibration fixture is provided with a plurality of slots, and the camera assembly is fixed in the slots.

[0030] The solution provided in this embodiment can improve the calibration efficiency of the calibration device, and can also be applied to a multi-camera system with lenses of various field of view angles. The user can determine the number, shape and arrangement of the slots based on external factors such as the site, the overall size of the calibration equipment, and the cost-benefit ratio.

[0031] Compared with the prior art, this technical solution has at least the following beneficial effects:

[0032] The calibration method and calibration device disclosed in the embodiment of the present invention not only improve the calibration accuracy of the lens, but also can be compatible with the simultaneous calibration of different field angles in a multi-camera system while ensuring high calibration accuracy, thereby improving the calibration efficiency and simplifying the structure of the calibration device. In addition, the technical solution of the embodiment of the present invention can perform full-image calibration, and the accuracy of parameters such as distortion is greatly improved.

Brief Description of the Drawings

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 This is a comparison diagram of imaging under lenses with different field of view angles in the prior art;

[0035] Figure 2 is a flow chart of the calibration method provided in Example 1 of the present invention;

[0036] Figure 3 is a schematic diagram of a calibration calculation flow in the calibration method provided in Example 1 of the present invention;

[0037] Figure 4 is a flow chart of the matching step of the calibration calculation in the calibration method provided in Embodiment 1 of the present invention;

[0038] Figure 5aThis is a schematic diagram of a calibration method provided in Embodiment 1 of the present invention, in which an image acquired by a lens with a small field of view and requiring inner circle feature points for calculation contains some outer circle feature points that need to be eliminated;

[0039] Figure 5b It is a schematic diagram of an image acquired by a lens with a large field of view and requiring outer circle feature points for calculation, which includes inner circle feature points to be removed in the calibration method provided in Example 1 of the present invention;

[0040] Figure 6 is a schematic diagram of the structure of a calibration device provided in Example 2 of the present invention;

[0041] Figure 7 is a schematic diagram of the size relationship between the calibration plate and the effective field of view area in the calibration device provided in Example 2 of the present invention;

[0042] Figure 8 is a schematic diagram of the arrangement of the dots, inner circle feature points and outer circle feature points on the calibration plate in the calibration device provided in Example 2 of the present invention;

[0043] Figure 9a It is an image acquired by a camera assembly consisting of a main camera lens and a wide-angle lens at the same distance in the calibration device provided in Embodiment 2 of the present invention;

[0044] Figure 9b It is an image acquired by a camera assembly consisting of a main camera lens and a telephoto lens at the same distance in the calibration device provided in Embodiment 2 of the present invention;

[0045] Fig.10 It is a structural schematic diagram of a calibration fixture with multiple slots applied to a multi-camera system in the calibration device provided in Example 2 of the present invention.

[0046] Reference numerals:

[0047] 1- Camera assembly;

[0048] 2- Calibration plate;

[0049] 21-dot;

[0050] 22-inner circle feature points;

[0051] 23-outer circle feature points;

[0052] 3- Calibration fixture;

[0053] 31- slot;

[0054] 4- Calibration module;

[0055] 5-Horizontal rotation axis;

[0056] 6-Vertical axis. [Specific implementation method]

[0057] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0058] It should be clear that 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 creative work are within the scope of protection of the present invention.

[0059] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0060] like Figures 1 to 10 As shown, Figure 1 This is a comparison diagram of imaging under lenses with different field of view angles in the prior art; Figure 2 is a flow chart of the calibration method provided in Example 1 of the present invention; Figure 3 is a schematic diagram of a calibration calculation flow in the calibration method provided in Example 1 of the present invention; Figure 4 is a flow chart of the matching step of the calibration calculation in the calibration method provided in Embodiment 1 of the present invention; Figure 5a This is a schematic diagram of a calibration method provided in Embodiment 1 of the present invention, in which an image acquired by a lens with a small field of view and requiring inner circle feature points for calculation contains some outer circle feature points that need to be eliminated; Figure 5b It is a schematic diagram of an image acquired by a lens with a large field of view and requiring outer circle feature points for calculation, which includes inner circle feature points to be removed in the calibration method provided in Example 1 of the present invention; Figure 6 is a schematic diagram of the structure of a calibration device provided in Example 2 of the present invention; Figure 7 is a schematic diagram of the size relationship between the calibration plate and the effective field of view area in the calibration device provided in Example 2 of the present invention; Figure 8 is a schematic diagram of the arrangement of the dots, inner circle feature points and outer circle feature points on the calibration plate in the calibration device provided in Example 2 of the present invention; Figure 9a It is an image acquired by a camera assembly consisting of a main camera lens and a wide-angle lens at the same distance in the calibration device provided in Embodiment 2 of the present invention; Figure 9b It is an image acquired by a camera assembly consisting of a main camera lens and a telephoto lens at the same distance in the calibration device provided in Embodiment 2 of the present invention; Fig.10It is a structural schematic diagram of a calibration fixture with multiple slots applied to a multi-camera system in the calibration device provided in Example 2 of the present invention.

[0061] Example 1

[0062] like Figure 2 As shown, embodiment 1 of the present invention discloses a calibration method, which includes: fixing multiple camera assemblies 1 on a calibration fixture 3, and fixing a calibration plate 2 at a certain distance from the calibration fixture 3; multiple cameras simultaneously take pictures of the calibration plate 2; rotating the calibration plate 2 and / or rotating the calibration fixture 3, and multiple cameras continue to take pictures of the calibration plate 2 for a predetermined number of times; inputting the images obtained after multiple pictures into a calibration calculation module, and performing calibration calculations through the calibration calculation module to obtain calibration parameters.

[0063] In the calibration method of Example 1 of the present invention, the first three steps in the process mainly involve equipment and software processes, and the fourth step is the algorithm process.

[0064] By adopting the calibration method of Example 1 of the present invention, under the premise of ensuring high precision, that is, ensuring high precision of internal and external parameters and distortion parameters, multiple camera lenses with different field of view angles can be calibrated at one time. In addition, multiple camera assemblies 1 can be calibrated at one time.

[0065] like Figure 3 As shown, in the calibration method of Example 1 of the present invention, in the calculation module, the calibration calculation includes the following steps: obtaining the coordinate pair of the dot 21 and the feature point on the calibration plate 2; matching the corresponding feature point according to the size of the field of view angle θ of the camera; calculating the initial calibration parameters using the coordinate pair of the feature point; calculating the output calibration parameters using the coordinate pair of the dot 21; wherein the feature point includes an inner circle feature point 22 and an outer circle feature point 23.

[0066] In the calculation module of step 4, the first thing to do is to process the collected multi-camera images to obtain images of appropriate size, and then obtain the coordinate pairs of the required feature points 22 and 23. According to Zhang's calibration principle, it is necessary to calculate the internal and external parameters at least four pairs of image points taken at three angles and the corresponding world point coordinates. Embodiment 1 of the present invention will be described by taking the high-precision dot 21 calibration plate 2 as an example. In order to improve the accuracy of the parameters, after the initial calibration parameters are obtained, the calibration parameters are further optimized using all the image points of the entire image.

[0067] Using the calibration method of embodiment 1 of the present invention, the multi-camera images collected by the multiple camera assemblies 1 are processed to obtain images of appropriate sizes, and then the coordinate pairs of the required feature points 22 and 23 are obtained. After the initial calibration parameters are obtained, the calibration parameters are further optimized using all the dots 21 and feature points 22 and 23 in the entire image, thereby improving the parameter accuracy.

[0068] like Figure 4 As shown, in the calibration method of embodiment 1 of the present invention, matching includes the following steps: searching and distinguishing the circular point 21 without circular ring features and the inner circle feature points 22 and outer circle feature points 23 with circular ring features on the calibration plate 2, wherein the inner circle feature points 22 and the outer circle feature points 23 are respectively divided into two layers of circular rings and three layers of circular rings; if the camera assembly 1 includes a main camera lens and a telephoto lens, then according to the image position of each outer circle feature point 23 or the positional relationship between the outer circle feature point 23 and the inner circle feature point 22, the correct required inner circle feature point 22 is determined and assigned a first index number. Specifically, for the found The required inner three-layer circular rings are determined according to the absolute and relative position relationship of all the three-layer circular rings, and then all the required correct inner circle feature points 22 are found according to the absolute position of each two-layer circular ring and the relative position relationship with the correct inner three-layer circular ring that has been obtained, and a first index number is assigned to all the inner circle feature points 22; if the camera assembly 1 includes a main camera lens and a wide-angle lens, all the outer circle feature points 23 are found according to the absolute and relative position relationship and assigned a second index number; the initial matrix is ​​calculated using the inner circle feature points 22 with the first index number, and the initial matrix is ​​calculated using the outer circle feature points 23 with the second index number.

[0069] like Figure 5a and Figure 5b As shown, a lens with a large field of view will inevitably include inner circle feature points 22 in addition to the outer circle feature points 23 required by itself, and a lens with a small field of view will also include some outer circle feature points 23 when the calibration plate 2 rotates. Therefore, the algorithm design in the calculation module of step 4 needs to select the correct ring in the image as the input of different scenes.

[0070] The calibration method of Example 1 of the present invention is adopted. Since the fields of view of lenses with different field of view angles differ greatly, in order to adapt to the characteristics of the wide-angle lens with a large field of view and the telephoto lens with a small field of view, the feature points 22 and 23 on the calibration plate 2 are designed to be two layers, the inner circle feature points 22 are used for the calibration of the telephoto lens, and the outer circle feature points 23 are used for the calibration of the wide-angle lens, thereby achieving high-precision calibration while improving the calibration efficiency.

[0071] In the calibration method of Example 1 of the present invention, the inner circle feature points 22 and the outer circle feature points 23 respectively include three-layer circular rings and ordinary two-layer circular rings as special position marks.

[0072] By adopting the calibration method of Example 1 of the present invention, the number of layers of circular rings and the absolute and relative positions of each circular ring are utilized, so that the three-layer circular rings and the two-layer circular rings in the circular point 21, the inner circle feature point 22 and the outer circle feature point 23 can be easily distinguished. This is beneficial when calibrating a lens with a large field of view angle and a lens with a small field of view angle at the same time. The inner circle feature points close to the center area can be used for the calibration of the lens with a small field of view angle, and the outer circle feature points on the periphery can be used for the calibration of the lens with a large field of view angle. There will be no mismatch between the lens and the feature points 22 and 23, thereby achieving high-precision calibration and also helping to improve the efficiency of calibration.

[0073] The fields of view of lenses with different field of view angles differ greatly. In order to adapt to the characteristics of telephoto and small field of view, the feature points 22 and 23 on the calibration plate 2 can only be centered and closely spaced. At this time, due to distortion, equipment and other reasons, the calculated initial matrix cannot represent the conversion relationship between the entire image point coordinates of the camera assembly 1 with a large field of view and the respective world point coordinates of the combined lens of the main camera lens and the wide-angle lens, which will affect the accuracy and precision of the camera assembly 1 with a combined lens of the main camera lens and the wide-angle lens. Therefore, the calibration method of embodiment 1 of the present invention is a technical solution that is compatible with the calibration of lenses with large field of view angles and lenses with small field of view angles, which can not only ensure accuracy, but also only need to use the same calibration device in the application scenario of the multi-camera system, thereby improving the calibration efficiency.

[0074] To this end, corresponding to the calibration method disclosed in Example 1 of the present invention, a calibration device disclosed in Example 2 of the present invention is specially designed, wherein the calibration plate 2 and the calibration fixture 3 are both uniquely designed.

[0075] Example 2

[0076] like Figure 6 As shown, Embodiment 2 of the present invention discloses a calibration device, which includes: multiple camera assemblies 1, a calibration plate 2, a calibration fixture 3 and a calibration module 4; the calibration plate 2 and the calibration fixture 3 are fixed at two locations respectively, the center of the calibration fixture 3 is aligned with the center of the calibration plate 2, and both the calibration plate 2 and the calibration fixture 3 can rotate; multiple camera assemblies 1 are fixed on the calibration fixture 3, and the camera assemblies 1 can receive light from the effective field of view area on the calibration plate 2; the calibration module 4 is connected to the multiple camera assemblies 1 in communication, and is used to calibrate the multiple camera assemblies 1 according to the calibration method of Embodiment 1. The calibration device disclosed in Embodiment 2 of the present invention omits some structures such as a box body and a transmission device.

[0077] In the calibration device of the second embodiment of the present invention, the calibration plate 2 and the calibration fixture 3 are respectively provided with a horizontal rotation axis 5 and a vertical rotation axis 6. The calibration fixture 3 and the calibration plate 2 do not need to be provided with dual rotation axes at the same time, and can even be provided with a single rotation axis.

[0078] By using the calibration device of Example 2 of the present invention, the user can fix the calibration fixture 3 and only rotate the calibration plate 2, or fix the calibration plate 2 and only rotate the calibration fixture 3, thereby improving the user's freedom and flexibility in calibrating the lens of the camera assembly 1.

[0079] The calibration device of Example 2 of the present invention is used to align the camera assembly 1 fixed in the calibration fixture 3 with the calibration plate 2, and the images containing partial areas on the calibration plate 2 acquired by different camera assemblies 1 are transmitted to the calibration module 4. The multiple camera assemblies 1 are calibrated simultaneously using the calibration method described above, thereby achieving high-precision calibration when dealing with camera assemblies 1 with different fields of view, different models, and used in different devices, and the calibration device has a simple structure and high calibration efficiency.

[0080] like Figure 7 As shown, in the calibration device of embodiment 2 of the present invention, the lateral length of the calibration plate 2 is greater than the lateral length of the effective field of view area, and the longitudinal height of the calibration plate 2 is greater than the longitudinal height of the effective field of view area.

[0081] By using the calibration device of Example 2 of the present invention, the camera assembly 1 can obtain an image containing most of the area on the calibration plate 2. During calibration, the coordinates of the feature points 22 and 23 can be calculated more accurately. When the calibration parameters are finally output, the more dots 21 are contained in the acquired image, the higher the accuracy of the calibration parameters.

[0082] like Figure 8 As shown, in the calibration device of embodiment 2 of the present invention, the calibration plate 2 is arranged with array-arranged dots 21, inner circle feature points 22 and outer circle feature points 23, the inner circle feature points 22 are arranged close to the central area of ​​the calibration plate 2, and the outer circle feature points 23 are arranged away from the central area of ​​the calibration plate 2. There are two types of image points on the calibration plate 2: one type is the inner circle feature points 22 and outer circle feature points 23, which are designed to each contain a 3-layer circular ring and a plurality of 2-layer circular rings, the inner circle feature points 22 are used as the initial monoscopic matrix feature points of the camera assembly 1 of the combination lens of the main camera lens and the telephoto lens, and the outer circle feature points 23 are used as the initial monoscopic matrix feature points of the camera assembly 1 of the combination lens of the main camera lens and the wide-angle lens; the other type is ordinary dots 21, which are used to calculate the final calibration output parameters.

[0083] By using the calibration device of Example 2 of the present invention, the lens with a small field of view angle and the lens with a large field of view angle are calibrated simultaneously, the inner circle feature points 22 are matched to the calibration of the lens with a small field of view angle, and the outer circle feature points 23 are matched to the calibration of the lens with a large field of view angle. When the lenses with different field of view angles are calibrated at the same time, different image points can be effectively distinguished, and the calibration of the lens with a large field of view angle and the calibration of the lens with a small field of view angle can be minimized from interfering with each other, and finally high-precision calibration parameters are obtained.

[0084] like Figure 9a and Figure 9b As shown, in the calibration device of Example 2 of the present invention, the maximum horizontal spacing between the two inner circle feature points 22 and the maximum vertical spacing between the two outer circle feature points 23 are both smaller than the lateral length of the effective field of view area, and the maximum vertical spacing are both smaller than the longitudinal height of the effective field of view area.

[0085] Using the calibration device of Embodiment 2 of the present invention, when the camera assembly 1 has a combination of a main camera lens and a wide-angle lens, the initial monoscopic matrix is ​​calculated using the outer circle feature points 23, and when the camera assembly 1 has a combination of a main camera lens and a telephoto lens, the initial monoscopic matrix is ​​calculated using the inner circle feature points 22. In this way, the accuracy of the matrix obtained by the camera assembly 1 in scenes with different combinations of lenses can be guaranteed, and multi-camera calibration can be implemented in one calibration device.

[0086] When designing the calibration board 2, the calibration board 2 needs to meet two conditions:

[0087] 1: The effective field of view of the lens of the entire camera assembly 1 is filled with the calibration plate 2, that is, the calibration plate 2 is larger than the size of the effective field of view seen by the lens.

[0088] 2: The inner circle feature points 22 used to calculate the initial matrix must be within the effective field of view of the lens with a small field of view angle, and the outer circle feature points 23 used to calculate the initial matrix must be within the effective field of view of the lens with a large field of view angle.

[0089] To improve the calibration accuracy, the calibration plate 2 needs to cover the entire effective field of view of the entire multi-camera system. Assume that the center of the camera assembly 1 is aligned with the center of the calibration plate 2, the distance between the camera assembly 1 and the calibration plate 2 is D, the diagonal field of view of the lens of the camera assembly 1 is θ, and the resolution of the image of the camera assembly 1 is the common 4:3 ratio.

[0090] Depend on Figure 7 The relationship between the horizontal length and vertical height of the calibration plate 2 and the effective field of view can be calculated:

[0091]

[0092]

[0093] To meet condition 1: the lateral length and longitudinal height of the calibration plate 2 are respectively parallel to the long and short sides of the image of the camera assembly 1, and the lateral length and longitudinal height of the entire calibration plate 2 are respectively greater than the length v and height h of the effective field of view area;

[0094] To satisfy condition 2: the horizontal spacing and vertical spacing between the two inner circle feature points 22 are respectively smaller than the length v and height h of the effective field of view area; the horizontal spacing and vertical spacing between the two outer circle feature points 23 are respectively smaller than the length v and height h of the effective field of view area.

[0095] Therefore, the initial monoscopic matrix of the camera assembly 1 having a combination of a main camera lens and a wide-angle lens is calculated using the outer circle feature points 23, and the initial monoscopic matrix of the camera assembly 1 having a combination of a main camera lens and a telephoto lens is calculated using the inner circle feature points 22. This ensures the accuracy of the matrices obtained in each scene, and allows the multi-camera system to be calibrated together using the same device.

[0096] Here, the calibration plate 2 takes the dot 21 calibration plate 2 as an example, but it is not limited to this in actual operation. The calibration plate 2 can have other characteristic patterns, and these characteristic patterns are used as characteristic points of cameras with large and small field of view angles respectively.

[0097] like Fig.10 As shown, in the calibration device of embodiment 2 of the present invention, a plurality of slots 31 are provided in the central area of ​​the calibration fixture 3 , and the camera assembly 1 is fixed in the slots 31 .

[0098] For a multi-camera system application scenario, it is obviously impossible to align the center of each lens with the center of the calibration plate 2. At the same time, in order to improve efficiency, a calibration fixture 3 (as a fixing device for the multi-camera system) can be designed with multiple slots 31. Taking the currently more common matrix multi-camera system as an example, the design is as follows Fig.10 The design principles of the four-slot 31-position fixture shown are as follows:

[0099] a. The opening shape of each slot 31 may be square or L-shaped, that is, conforming to the lens distribution shape of the multi-camera system;

[0100] b. The center of the calibration fixture 3 is aligned with the center of the calibration plate 2, and the opening position of each slot 31 is close to the center of the calibration fixture 3, which saves equipment waste caused by unreasonable layout to the greatest extent.

[0101] c. The shape of each slot 31 ensures that after the multi-camera system is placed in the slot 31, the long side direction of the image of the camera assembly 1 is parallel to the horizontal length direction of the calibration plate 2, and the purpose is the same as the design principle b.

[0102] exist Fig.10 In the figure, each lens in the camera assembly 1 and the center of the calibration fixture 3 are displaced. Therefore, this factor needs to be considered when designing the calibration plate 2. The corresponding displacement is added in the horizontal length and vertical height directions of the calibration plate 2 to match the displacement of the center of the lens and the calibration fixture 3.

[0103] It should be understood that in actual use, the calibration fixture 3 is not limited to a four-slot structure. The arrangement and structure of the slots 31 of the calibration fixture 3 can also be determined based on external factors such as the site, the overall size of the calibration device, and the benefit-cost ratio. However, the core idea in designing the calibration fixture 3 is the same as the design principles described above.

[0104] The calibration device of Example 2 of the present invention can improve the calibration efficiency of the calibration device, and can also be applied to a multi-camera system with lenses of various field of view angles. The user can determine the number, shape and arrangement of the slots 31 based on external factors such as the site, the overall size of the calibration equipment, and the cost-benefit ratio.

[0105] The calibration method and calibration device disclosed in the embodiment of the present invention not only improve the calibration accuracy of the lens, but also can be compatible with the simultaneous calibration of different field angles in a multi-camera system while ensuring high calibration accuracy, thereby improving the calibration efficiency and simplifying the structure of the calibration device. In addition, the technical solution of the embodiment of the present invention can perform full-image calibration, and the accuracy of parameters such as distortion is greatly improved.

[0106] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A calibration method, characterized in that: The calibration method comprises: Fixing a plurality of camera assemblies on a calibration fixture, and fixing a calibration plate at a certain distance from the calibration fixture; Multiple cameras take photos of the calibration plate simultaneously; Rotate the calibration plate and / or the calibration fixture, and the plurality of cameras continue to take pictures of the calibration plate for a predetermined number of times; The images obtained after multiple shots are input into a calibration calculation module, and calibration calculation is performed by the calibration calculation module to obtain calibration parameters; In the calculation module, the calibration calculation includes the following steps: Obtaining coordinate pairs of the circle points and feature points on the calibration plate; Matching corresponding feature points according to the size of the field of view angle of the camera; Calculate the initial calibration parameters using the coordinate pairs of feature points; Use the coordinates of the dots to calculate the output calibration parameters; Wherein, the characteristic points include inner circle characteristic points and outer circle characteristic points; The matching comprises the following steps: Searching and distinguishing the circular points without circular ring features and the inner circle feature points and the outer circle feature points with circular ring features on the calibration plate; If the camera assembly includes a main camera lens and a telephoto lens, all inner circle feature points are found and assigned a first index number according to the image position of each outer circle feature point or the positional relationship between the outer circle feature point and the inner circle feature point; If the camera assembly includes a main camera lens and a wide-angle lens, all outer circle feature points are found according to the absolute and relative position relationship and assigned a second index number; The initial matrix is ​​calculated using the inner circle feature points of the first index number, and the initial matrix is ​​calculated using the outer circle feature points of the second index number.

2. The calibration method according to claim 1, characterized in that: The inner circle feature points and the outer circle feature points both include three-layer circular rings as special position marks and ordinary two-layer circular rings.

3. A calibration device, characterized in that: The calibration device comprises: Multiple camera assemblies, calibration plates, calibration fixtures, and calibration modules; The calibration plate and the calibration fixture are fixed at two locations respectively, the center of the calibration fixture is aligned with the center of the calibration plate, the calibration plate and the calibration fixture can both rotate and the relative distance between the two can be adjusted; A plurality of the camera assemblies are fixed on the calibration fixture, and the camera assemblies are capable of receiving light from an effective field of view area on the calibration plate; The calibration module is communicatively connected to the plurality of camera assemblies, and is used to calibrate the plurality of camera assemblies according to the calibration method according to claim 1 or 2.

4. The calibration device according to claim 3, characterized in that: The lateral length of the calibration plate is greater than the lateral length of the effective field of view area, and the longitudinal height of the calibration plate is greater than the longitudinal height of the effective field of view area.

5. The calibration device according to claim 3, characterized in that: The calibration plate is arranged with dots, inner circle feature points and outer circle feature points in an array, the inner circle feature points are arranged close to the central area of ​​the calibration plate, and the outer circle feature points are arranged away from the central area of ​​the calibration plate.

6. The calibration device according to claim 5, characterized in that: The maximum horizontal spacing between two of the inner circle feature points and between two of the outer circle feature points is smaller than the lateral length of the effective field of view area, and the maximum vertical spacing is smaller than the longitudinal height of the effective field of view area.

7. The calibration device according to claim 3, characterized in that: The calibration plate and the calibration fixture are respectively provided with a horizontal rotating shaft and a vertical rotating shaft.

8. The calibration device according to claim 3, characterized in that: A central area of ​​the calibration fixture is provided with a plurality of slots, and the camera assembly is fixed in the slots.

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