System and method for calibrating intrinsic parameters of a camera using optical ray tracing techniques

Abstract

A method of calibrating intrinsic parameters associated with a camera includes positioning the camera to receive collimated light from a rotatable collimator, wherein the collimated light is provided to the camera via a target having a central target aperture and a plurality of peripheral target apertures located at a periphery of the target. The method further includes rotating the collimator along a first axis extending through an entrance pupil location of the camera and recording spot locations associated with the collimated light provided through one or more target apertures of the target at each first axis interval, and determining a distortion profile associated with the camera based on the recorded spot locations measured at a plurality of first axis intervals.

Description

Technical Field

[0001] This disclosure generally relates to camera calibration, and more specifically to camera calibration using optical ray tracing technology. Background Technology

[0002] Camera calibration is the process of estimating intrinsic and / or extrinsic parameters. In particular, intrinsic parameters address the camera's internal characteristics, such as its focal length, skew, distortion, and image centering. Intrinsic parameters are used to establish a distortion profile, which is stored in the camera's non-volatile memory and used to correct distortion caused by the camera's intrinsic parameters.

[0003] Typically, camera calibration relies on fixing the camera in a given location and providing a target image with known parameters (e.g., a checkerboard pattern). The camera takes multiple images at different orientations and angles, and these images are analyzed to determine the inherent parameters associated with the camera. However, this type of calibration requires a significant amount of space (e.g., 3–10 meters) to collect image data encompassing the entire field of view of the camera. Developing a system and method that provides camera calibration while reducing the amount of space required would be beneficial. Summary of the Invention

[0004] According to some aspects, a method for calibrating inherent parameters associated with a camera includes: positioning the camera to receive collimated light from a rotatable collimator, wherein the collimated light is provided to the camera via a target having a central target aperture and a plurality of peripheral target apertures located on the periphery of the target. The method further includes: rotating the collimator along a first axis extending through an entrance pupil position of the camera; recording spot positions associated with the collimated light provided through one or more target apertures of the target at each first axis interval; and determining a distortion distribution associated with the camera based on the recorded spot positions measured at the plurality of first axis intervals.

[0005] According to another aspect, a camera calibration system is provided, comprising a rotatable collimator and a camera fixing device. The rotatable collimator includes a tube and a target located within the tube, the target having a central target aperture and a plurality of peripheral target apertures located radially outward of the central target aperture, wherein the rotatable collimator is rotatable about a first axis. The camera fixing device is configured to receive the camera and position the camera's entrance pupil position via the first axis of the rotatable collimator. Attached Figure Description

[0006] Figure 1 It is a diagram illustrating the definitions of the image plane, optical axis, focal length, and camera sensor.

[0007] Figure 2 This is a block diagram of a camera calibration system according to some embodiments.

[0008] Figure 3 This is a front view of a target having multiple peripheral apertures and a central aperture according to some embodiments.

[0009] Figure 4 This is a cross-sectional view of a collimating light source, a target, and a tube for providing collimated light to a lens aperture, according to some embodiments.

[0010] Figure 5a This is a block diagram illustrating the rotation of a collimator according to some embodiments about an axis extending through the position of the camera's entrance pupil, and Figure 5b This is a ray tracing diagram showing the path of collimated light rays provided at different angles through the lens of a camera according to some embodiments.

[0011] Figure 6 This is a front view of a plurality of magnetic switches for selectively opening and closing apertures on a target, according to some embodiments.

[0012] Figure 7 This is a flowchart illustrating a method for calibrating inherent parameters of a camera using ray tracing according to some embodiments. Detailed Implementation

[0013] This disclosure relates to an optical ray tracing method for calibrating the inherent parameters of a camera. The system includes a target backlit by a collimating light source, the target having a central aperture and a plurality of peripheral apertures, each of which can be selectively opened and closed. The collimator and the target are rotatable about an axis that extends through the camera's entrance pupil and is substantially perpendicular to the camera's optical axis.

[0014] During calibration, collimated light is supplied to the camera through one or more apertures in the target (i.e., target apertures). The camera is aligned such that the optical center of the camera sensor is aligned with the central target aperture, while collimated light from each peripheral target aperture remains visible and focused on the image plane. The camera orientation is adjusted (via a six-axis alignment controller) until the light spots produced by the collimated light through the multiple target apertures (i.e., LX, RX, LY, and UY) are focused and reach maximum intensity. Once each is visible and focused, the peripheral target apertures are turned off (i.e., closed), and the principal point (PP) is determined based on the collimated light supplied through the OA aperture.

[0015] After aligning the collimator with the camera and identifying the principal point, the collimator and the target are rotated together about an axis extending through the camera's entrance pupil (and approximately perpendicular to the camera's optical axis), and the distortion at multiple points is measured (i.e., the positions of these points on the sensor). Multiple measurements are used to construct a distortion distribution that defines the camera's inherent parameters. In this way, the principal point (PP), distortion center (COD), focal length (FL), and the camera's distortion distribution can be determined. The distortion distribution can be stored in non-volatile memory associated with the camera. Specifically, the FL is determined based on the lateral displacement of the OA spot when the collimator rotates over a small portion of the paraxial field (i.e., rotation about the paraxial axis, perpendicular to the x- and y-axis).

[0016] Figure 1 This is a diagram illustrating the definitions of optical terms used throughout the application. A 3D orthogonal coordinate system x, y, z is centered at point O, which represents the lens entrance or aperture. The image plane 106 lies behind the lens entrance defined by point O. The center point of the image plane 106 is aligned with the lens entrance. However, due to distortion in the lens system, the optical axis 102 is not perfectly aligned with the center point of the image plane 106 (referred to herein as O'). The point where the optical axis 102 intersects the image plane 106 is called the principal point PP. The distance 108 from point O to the principal point PP represents the focal length of the camera system. Distortion in the lens system causes the principal point PP to shift from the center point of the image plane (represented by point O'). As discussed in more detail below, the calibration of the camera's inherent parameters requires identifying the principal point PP and the optical axis 102 of the camera system.

[0017] refer to Figures 2-6 The diagram illustrates components of a camera calibration system 200 according to some embodiments. Generally, the camera calibration system 200 is configured to calibrate the inherent parameters of a camera 218. Figure 2 In the block diagram shown, the camera calibration system 200 includes a collimator 202, a target 204, a collimator / target fixing device 206, a camera fixing device 208, a collimator position controller 210, a target controller 212, a camera alignment controller 214, and a computer / processor system 216.

[0018] Collimator / target fixation device 206 is configured to hold collimator 202 and target 204. In some embodiments, collimator / target fixation device 206 is rotatable about axis 226. In some embodiments, axis 226 extends through aperture / incident pupil position 228 of camera 218, wherein axis 226 is substantially perpendicular to optical axis 224 of camera 218. Collimator position controller 210 is configured to control rotation of collimator / target fixation device 206. Similarly, camera fixation device 208 is configured to hold camera 218, and camera alignment controller 214 is configured to modify the position / orientation of camera 218. In some embodiments, camera alignment controller 214 modifies the position / orientation of camera 218 with six degrees of freedom. Target controller 212 is configured to selectively open / close the target aperture associated with target 204.

[0019] refer to Figure 3 The diagram shows a front view of target 204, illustrating a plurality of target apertures labeled UY, LY, RX, LX, and OA. In some embodiments, the plurality of peripheral target apertures (e.g., UY, LY, RX, LX) are equidistantly spaced around target 204, wherein the positions of the peripheral target apertures are defined by a circle 302 having a first diameter d1. As discussed in more detail below, in some embodiments, each of the plurality of target apertures is selectively opened / closed by a target controller 212. In some embodiments, the first diameter d1 is approximately equal to the net aperture diameter d3 at the optical axis of lens aperture 228 (e.g., ...). Figure 4 (As shown). In other embodiments, the first diameter d1 is slightly smaller than the net aperture diameter d3 of the lens aperture 228. As discussed in more detail below, in some embodiments, each of a plurality of target apertures UY, LY, RX, LX, and OA can be selectively turned on / off to determine the collimated light supplied to the lens aperture 228 of the camera 218. In some embodiments, the target controller 212 is configured to selectively turn on / off the plurality of target apertures UY, LY, RX, LX, and OA based on commands provided by the computer / processor system 216. In some embodiments, for example, as referenced Figure 6 As shown, a switching magnet is used to selectively open / close multiple target apertures UY, LY, RX, LX and OA.

[0020] Reference Figure 4 A cross-sectional view of the collimated light 222 provided by target 204 to camera 218 through aperture 228 is shown. Figure 4 In the illustrated embodiment, the collimated light source 222 is incident on the target 204, wherein the collimated light passes through multiple open target apertures – such as in Figure 4In the illustrated embodiment, UY, OA, and LY are provided. As a result, multiple collimated beams are provided to the lens aperture 228 via the target apertures UY, OA, and LY. Figure 4 In the illustrated embodiment, tube 205 guides collimated light to lens aperture 228 and prevents stray light from other sources from incident on lens aperture 228. In some embodiments, the diameter d2 of tube 205 is approximately equal to the net aperture diameter d3 of lens aperture 228. In some embodiments, diameters d2 and d3 are larger than the diameter d1 of the peripheral target apertures UY, LY, RX, and LX located on target 204. As described in more detail below, camera 218 is positioned such that camera aperture 228 is aligned with collimator 202, target 204, and tube 205, such that collimated light sources provided via each of the target apertures are incident on camera aperture 228.

[0021] Reference Figure 5a Collimator 202 is shown in a first position and a second position. As discussed in more detail below, during calibration, collimator 202 and target 204 are rotated by collimator / target fixing device 206 (not shown) about axis 226, which extends through the entrance pupil position 228 of camera 218 (axis 226 shown extends to...). Figure 5a (In the page). After the collimator 202 and target 204 are initially aligned with the camera 218, the rotation of the collimator 202 and target 204 about axis 226 (extending into the page) ensures that the collimated light is incident on the entrance pupil position 228 of the camera 218. For example, in Figure 5a In the illustrated embodiment, the collimator 202 and the target 204 rotate about axis 226 (into the page) through the entrance pupil position 228. Because the axis of rotation 226 passes through the center of the entrance pupil position 228, the collimated light provided by the collimator 202 and the target 204 is incident on the entrance pupil position 228 at both the first and second positions (albeit at different incident angles).

[0022] Reference Figure 5b The diagram illustrates the components of camera 218 receiving collimated light from collimator 202 at first and second positions. The components shown here include a camera lens 512 and an image sensor 510, where the camera lens 512 focuses the incident light onto the surface of the image sensor 510. Because the angle of incidence of the collimated light on lens 512 is known, and the intersection point of the collimated light with the image sensor 510 is known, the path of the collimated light through lens 512 and to the image sensor 510 can be determined. In this way, ray tracing techniques are used to determine the distortion associated with lens 512.

[0023] also, Figure 5bThe diagram illustrates the rotation of collimator 202 and target 204 from a first position to a second position, and the corresponding effect on the light supplied to image sensor 510. For example, when collimator 202 and target 204 are in the first position, collimated light 520a, 520b, and 520c from multiple target apertures is supplied to camera lens 512, which focuses the multiple light rays 520a, 520b, and 520c onto the surface of image sensor 510. Because the light incident on camera lens 512 is collimated, an ideal lens would focus light rays (e.g., rays 520a, 520b, and 520c) supplied from each of the multiple target apertures onto the same point on image sensor 510. Distortion in camera lens 512 would cause the projection of light onto image sensor 510 to not be perfectly focused at a single location. Collimator 202 and target 204 are rotated to a second position, and collimated beams 522a, 522b, and 522c are provided to camera lens 512, but at an angle different from that provided in the first position. As a result, collimated beams 522a, 522b, and 522c are focused onto image sensor 510 at slightly different positions. In an ideal lens, collimated beams 522a, 522b, and 522c would be focused onto the same position on image sensor 510—albeit at a different position compared to the collimated beams provided from the first position. Distortion in camera lens 512 causes collimated beams 522a, 522b, and 522c to be imperfectly focused at a single position. As discussed in more detail below, the inherent parameters of the camera system (including the camera lens 512) are determined based on the knowledge of the positions of the collimator 202 and the target 204 (i.e., the angular intervals of movement) and the position of the collimating light on the monitored image sensor 510.

[0024] Reference Figure 6A system for selectively opening / closing multiple target apertures UY, LY, RX, LX, and OA is illustrated. This system utilizes switching magnets 602a, 602b, 602c, 602d, and 602e, multiple fixed magnets 604a, 604b, 604c, 604d, and 604e, and multiple baffles 606a, 606b, 606c, 606d, and 606e. In some embodiments, the baffles 606a-606e are positioned relative to each of the multiple target apertures UY, LY, RX, LX, and OA, and have a first position and a second position. In the first position, the baffle is positioned above the corresponding target aperture, thereby effectively blocking the transmission of collimated light. In the second position, the baffle moves toward the switching magnet, thereby exposing the corresponding aperture. The positions of the baffles 606a-606e are determined based on the magnetism of the switching magnets 602a-602e, respectively. The magnetism of the switching magnets 602a-602e is determined and selectively controlled by the target controller 212. For example, to close the target aperture OY, the switching magnet 602a is controlled such that the portions of the magnet facing the fixed magnet 604a have the same polarity, thereby removing the fixed magnet 604a and the baffle 606a from the switching magnet 602a. As a result, the baffle 606a moves to a position above the aperture OY, thereby covering the aperture and preventing collimated light from passing through. Regarding the aperture RX, the switching magnet 602b is controlled such that the portions closest to the fixed magnet 604b have different polarities, thereby moving the fixed magnet 604b toward the switching magnet 602b, and thus exposing the baffle 606b to the target aperture RX. In this way, the target controller 212 can selectively control the positions of multiple baffles, thereby allowing the target controller 212 to control which of the multiple target apertures provides collimated light to the camera 218.

[0025] Continue to refer to Figures 2-6 , refer to Figure 7 The flowchart shown describes the process of calibrating the inherent parameters of camera 218.

[0026] In step 700, camera 218 is placed in camera mounting 208 to receive collimated light from collimator 202. Specifically, camera 218 is positioned such that the lens entrance pupil is located at the hinge axis of collimator 202. In this manner, the axis of rotation of the collimator extends through the lens entrance pupil of the camera. Target 204 is located between the light source for generating collimated light and camera 218. In some embodiments, in step 700, via alignment controller 214 ( Figure 2 (As shown) The position of the camera mounting device 208 is selectively controlled, and thus the position of the camera 518 is selectively controlled, to provide focused collimated light to the center position of the image sensor 510 (e.g., Figure 5b(As shown). In some embodiments, during the initial alignment of camera 218 with collimator 202 and target 204, only the central target aperture OA is opened. Image processor 220 ( Figure 2 The system (shown) receives an image captured by the image sensor 510 and calculates one or more attributes of the captured image (e.g., spot position, spot intensity, etc.). The computer / processor system 216 receives feedback from the image sensor 510 and uses this information to provide control signals to the alignment controller 214 and the target controller 212.

[0027] In some embodiments, in step 702, multiple peripheral target apertures UY, LY, RX, and LX are selectively opened and closed to ensure that each of the multiple peripheral light spots is visible to the camera. At this time, the position of the light spot on the image sensor 510 is not important. However, if a target aperture (e.g., UY) is opened and the image sensor 510 does not detect the corresponding light spot, this indicates a misalignment between the collimator 202 and the camera 218. In step 702, if the image sensor 510 does not detect the peripheral light spot, the alignment controller 214 modifies the position of the camera 218 until each of the multiple peripheral light spots is detected at a specific orientation of the camera 218.

[0028] In step 704, the target controller 212 controls multiple target apertures UY, LY, RX, LX, and OA to the open position, and the image processor 220 measures the size and / or intensity of the corresponding light spot on the image sensor 510. The alignment controller 214 selectively modifies the position of the camera mounting device 208, and thus selectively modifies the position of the camera 218 (e.g., pan / tilt) to minimize the size of the light spot and / or maximize the intensity of the light spot generated by the collimated light provided via the multiple target apertures UY, LY, RX, LX, and OA. The minimum light spot size and / or maximum intensity light spot indicate that the camera 218 is well aligned with the collimator 202 and the target 204. In some embodiments, the size of the light spot (e.g., measured by the image processor 220 and / or the computer / processor system 216) is compared with a minimum size threshold to determine whether proper alignment has been achieved. In other embodiments, the spot intensity (again, measured by image processor 220 and / or computer processor system 216) is compared to a maximum spot intensity threshold to determine if proper alignment has been achieved. In other embodiments, the position of camera 218 is modified via panning / tilting operations, and measurements are taken until a minimum size (while ensuring all peripheral spots remain visible) and / or maximum intensity are achieved relative to adjacent positions.

[0029] After aligning the camera 218 with the collimator 202 and the target 204 in steps 702 and 704, in step 706, the collimator assembly 206 is rotated about one or more of the x-axis and z-axis (e.g., ...). Figure 1 (As shown). In some embodiments, the rotation of the collimator assembly 206 is controlled to the same value (e.g., 1 degree) in both directions. In some embodiments, the collimator assembly 206 rotates only about one axis at a time (e.g., the x-axis or z-axis). The position, intensity, and / or size of the light spot projected onto the image sensor 510 is measured by the image processor 220, and the computer / processor system 216 uses this position, intensity, and / or size to determine the relationship with the camera 218 (particularly the camera lens 512, such as...). Figure 5b (As shown) the associated symmetry.

[0030] In step 708, it is determined whether proper alignment of camera 218 and collimator 202 has been achieved. If proper alignment of camera 218 and collimator 202 has not yet been achieved, steps 702, 704, and 706 are repeated until proper alignment is achieved. In some embodiments, proper alignment is determined based on a comparison of the measured spot size, intensity, and / or position with respect to a threshold. In other embodiments, proper alignment is determined based on a comparison of the measured spot size, intensity, and / or position with respect to adjacent positions of camera 218, wherein the best fit is selected as proper alignment. In some embodiments, a combination of comparison with a threshold and comparison with position is used to determine whether proper alignment has been achieved.

[0031] In step 710, after determining that the camera 218 is properly aligned with the collimator 202 and the target 204, the target controller 212 selectively closes a plurality of peripheral target apertures UY, LY, RX, and LX located on the target 204, and selectively opens or holds the central target aperture OA in the open position. The position of the light spot generated on the image sensor 510 by the collimated light provided via the central target aperture OA (i.e., a specific pixel or group of pixels associated with the image sensor) is identified as the principal point of the optical system. As discussed above, the principal point represents the point where the optical axis of the system (i.e., the camera lens 512) intersects the image plane (i.e., the image sensor 510). The position of the principal point is stored by the computer / processor system 216.

[0032] In step 712, the computer / processor system 216 instructs the target controller 212 to open multiple peripheral target apertures UY, LY, RX, and LX. In step 714, the computer / processor system 216 instructs the collimator position controller 210 to rotate the collimator assembly 206 along the x-axis (i.e., the horizontal direction) by a defined angular interval, and records the position, size, and / or intensity of the resulting light spot on the image sensor 510. For example, Figure 5aThe illustrated embodiment shows a defined angular interval for the collimator assembly 206 to rotate. In some embodiments, this step may be repeated multiple times in the positive and negative x-axis directions, wherein the position, size, and / or intensity of the light spot are recorded relative to each angular interval or position of the collimator assembly 206. In step 716, the same process is repeated, but relative to the z-interval (i.e., the vertical direction). Based on the feedback received from steps 714 and 716, a distortion distribution with respect to camera 218 is constructed.

[0033] In step 718, the distortion center (COD) associated with camera 218 is determined based on the following location on the image plane: at this location, the intensity symmetry of the light spots is uniform among the plurality of peripheral light spots corresponding to the collimated light provided through the plurality of peripheral target apertures UY, LY, RX, and LX. In some embodiments, this requires the central target aperture OA to be selectively closed. In other embodiments, the central target aperture may remain open during COD determination. In some embodiments, in addition to COD, the focal length FL of camera 218 is determined based on the lateral displacement x of the OA light spot measured when collimator 202 rotates through a known angle Θ. FL is given by the following formula:

[0034] FL = x / tanΘ

[0035] For example, the collimator 202 is used to measure the OA spot at a first position. The collimator 202 is then rotated by an interval Θ to a second position, and the OA spot is measured again. The distance between the first and second OA spots is distance x. Based on these inputs, the focal length FL can be determined.

[0036] As a reference Figure 7 The described method results in the determination of one or more inherent parameters associated with camera 218, including principal point (PP), distortion center, distortion distribution, and focal length. In some embodiments, these inherent parameters of camera 218 are used to construct a distribution for correcting distortion in captured images. In some embodiments, this distribution is stored in the memory of camera 218.

[0037] Discussion of possible embodiments

[0038] The following is a non-exclusive description of possible embodiments of the present invention.

[0039] According to one aspect, a method for calibrating inherent parameters associated with a camera includes: positioning the camera to receive collimated light from a rotatable collimator, wherein the collimated light is provided to the camera via a target having a central target aperture and a plurality of peripheral target apertures located on the periphery of the target. The method further includes: rotating the collimator along a first axis extending through an entrance pupil position of the camera, and recording spot positions associated with the collimated light provided through one or more target apertures of the target at each first axis interval, and determining a distortion distribution associated with the camera based on the recorded spot positions measured at the plurality of first axis intervals.

[0040] The methods described in the preceding paragraphs may optionally include (additionally and / or alternatively) any one or more of the following features, configurations, and / or additional components.

[0041] For example, in some embodiments, the central target aperture and a plurality of peripheral target apertures are selectively opened and closed, wherein the spot position recorded at each first axial interval may include a peripheral spot position associated with collimated light provided by the selected peripheral target aperture, an OA spot position associated with collimated light provided by the central target aperture, or a spot position associated with collimated light provided by both the central target aperture and the plurality of peripheral target apertures.

[0042] In some embodiments, the method further includes aligning the camera with a rotatable collimator.

[0043] In some embodiments, aligning the camera with a rotatable collimator includes selectively opening / closing a plurality of peripheral target apertures to ensure that each peripheral target aperture is visible to the camera.

[0044] In some embodiments, aligning the camera with a rotatable collimator includes modifying the camera's position by selectively panning / tilting the camera to minimize the size of the light spot generated by collimating light provided through a plurality of peripheral target apertures and a central target aperture.

[0045] According to some embodiments, the method further includes: selectively closing a plurality of peripheral target apertures and measuring the position of the OA spot generated by collimated light provided through the central target aperture.

[0046] According to some embodiments, the method further includes determining the distortion center (COD) based on a comparison of the uniformity of the intensity symmetry between the light spots generated by collimated light provided through a plurality of peripheral target apertures.

[0047] According to some embodiments, the method further includes: selectively opening a central target aperture and closing a plurality of peripheral target apertures, and subsequently recording a first position of the OA spot generated by the collimated light provided through the central target aperture. The method may further include: rotating the collimator by an angular interval to a second position, and recording the second position of the OA spot generated by the collimated light provided through the central target aperture. The lateral displacement of the OA spot relative to the first and second positions is measured and used to determine the focal length of the camera.

[0048] According to some embodiments, the method further includes: rotating a collimator along a second axis extending through the entrance pupil position of the camera and perpendicular to the first axis; and recording the position of one or more provided light spots through a central target aperture and a plurality of peripheral target apertures at each second axis interval, wherein the distortion distribution of the camera is further determined based on the recorded positions of the light spots measured at the plurality of second axis intervals.

[0049] According to some embodiments, rotating the collimator along a second axis extending through the camera's entrance pupil position and perpendicular to the first axis further includes rotating the camera ninety degrees relative to the rotatable collimator.

[0050] According to another aspect, a camera calibration system includes a rotatable collimator and a camera fixing device. The rotatable collimator includes a tube and a target located within the tube, the target having a central target aperture and a plurality of peripheral target apertures located radially outward of the central target aperture, wherein the rotatable collimator is rotatable about a first axis. The camera fixing device is configured to receive the camera and position the camera's entrance pupil via the first axis of the rotatable collimator.

[0051] The camera calibration system described in the preceding paragraph may optionally include (additionally and / or alternatively) any one or more of the following features, configurations, and / or additional components.

[0052] For example, in some embodiments, the peripheral target apertures include four target apertures equidistant from each other along the periphery of the target.

[0053] In some embodiments, each peripheral target aperture includes a magnetic shutter that can be selectively controlled to open and close a shutter associated with each target aperture.

[0054] In some embodiments, each central target aperture includes a magnetic shield that can be selectively controlled to open and close a shield associated with the central target aperture.

[0055] In some embodiments, the tube has a first inner diameter.

[0056] In some embodiments, the camera mounting device mounts a camera having a lens aperture with a diameter approximately equal to a first inner diameter.

[0057] In some embodiments, the camera calibration system further includes a control system, wherein the control system includes one or more of an alignment controller and a rotary stage controller. The alignment controller may be configured to control the alignment of the camera relative to a rotatable collimator. The rotary stage controller may be configured to control the rotation of the rotatable collimator about a first axis.

[0058] In some embodiments, the camera calibration system further includes a computer including a processor and a computer-readable medium, the computer communicating with an alignment controller, a rotary stage controller, and an image processor, wherein the processor executes instructions stored on the computer-readable medium to: modify the position of the camera using the alignment controller based on feedback received from the image processor to align the camera with a rotatable collimator, modify the angular position of the rotatable collimator, and record one or more light spots associated with collimated light provided through one or more apertures of the target at each angular position of the rotatable collimator.

[0059] In some embodiments, the processor executes instructions stored on a computer-readable medium to further: determine the principal point (PP) based on the position of the OA spot provided by the central target aperture of the target after the camera is aligned with the rotatable collimator, and determine the distortion distribution of the camera based on the spot recorded at each of a plurality of angular positions of the rotatable collimator.

Claims

1. A method for calibrating inherent parameters associated with a camera, the method comprising: Positioning a camera to receive collimated light from a rotatable collimator, wherein the collimated light is provided to the camera via a target having a central target aperture and a plurality of peripheral target apertures; The collimator is rotated along a first axis extending through the entrance pupil position of the camera, and the spot positions associated with the collimated light provided by one or more target apertures of the target at multiple first axis intervals are recorded. The distortion distribution associated with the camera is determined based on the recorded spot positions measured at the intervals of the plurality of first axes.

2. The method as described in claim 1, characterized in that, The central target aperture and the plurality of peripheral target apertures are selectively opened and closed.

3. The method as described in claim 1, characterized in that, The spot positions recorded at each first axis interval include peripheral spot positions associated with collimated light provided by a selected peripheral target aperture, OA spot positions associated with collimated light provided by the central target aperture, or spot positions associated with collimated light provided by both the central target aperture and the plurality of peripheral target apertures.

4. The method as described in claim 1, characterized in that, This further includes aligning the camera with the rotatable collimator.

5. The method as described in claim 4, characterized in that, Aligning the camera with the rotatable collimator includes selectively opening / closing the plurality of peripheral target apertures to ensure that each peripheral target aperture is visible to the camera.

6. The method as described in claim 5, characterized in that, Aligning the camera with the rotatable collimator includes modifying the position of the camera by selectively panning / tilting it to minimize the size of the light spot generated by the collimating light provided through the plurality of peripheral target apertures and the central target aperture.

7. The method as described in claim 1, characterized in that, Further includes: The plurality of peripheral target apertures are selectively closed, and the position of the OA spot generated by the collimated light provided through the central target aperture is measured.

8. The method as described in claim 7, characterized in that, Further includes: The distortion center (COD) is determined by comparing the uniformity of the intensity symmetry between the light spots generated by the collimated light provided through the plurality of peripheral target apertures.

9. The method as described in claim 1, characterized in that, Further includes: Selectively open the central target aperture and close the plurality of peripheral target apertures; Record the first position of the OA spot generated by the collimated light provided through the central target aperture; Rotate the collimator by an angle to the second position; Record the second position of the OA spot generated by the collimated light provided through the central target aperture; Measure the lateral displacement of the OA spot relative to the first position and the second position; as well as The focal length of the camera is determined based on the lateral displacement and the angular interval.

10. The method as described in claim 1, characterized in that, Further includes: The collimator is rotated along a second axis extending through the entrance pupil position of the camera and perpendicular to the first axis, and the positions of light spots provided by one or more of the central target aperture and the plurality of peripheral target apertures are recorded at each second axis interval, wherein the distortion distribution of the camera is further determined based on the recorded positions of the light spots measured at the plurality of second axis intervals.

11. A camera calibration system, comprising: A rotatable collimator includes a tube and a target located within the tube, the target having a central target aperture and a plurality of peripheral target apertures located radially outside the central target aperture, wherein the rotatable collimator is rotatable about a first axis; and A camera mounting device is configured to receive a camera and align the camera with the rotatable collimator, wherein the first axis extends through the entrance pupil of the camera and is approximately perpendicular to the optical axis of the camera.

12. The camera calibration system as described in claim 11, characterized in that, The peripheral target apertures include four target apertures that are equidistant from each other along the periphery of the target.

13. The camera calibration system as described in claim 11, characterized in that, Each peripheral target aperture includes a magnetic shield that can be selectively controlled to open and close the shield associated with each target aperture.

14. The camera calibration system as described in claim 13, characterized in that, The central target aperture includes a magnetic shield that can be selectively controlled to open and close the shield associated with the central target aperture.

15. The camera calibration system as described in claim 11, characterized in that, The tube has a first inner diameter.

16. The camera calibration system as described in claim 15, characterized in that, The camera mounting device is used to mount a camera with a lens aperture whose diameter is approximately equal to the first inner diameter.

17. The camera calibration system as described in claim 11, characterized in that, Further includes: Control system, including: An alignment controller is configured to control the alignment of the camera relative to the rotatable collimator; as well as A collimator position controller is configured to control the rotation of the rotatable collimator about the first axis.

18. The camera calibration system as described in claim 17, characterized in that, The collimator position controller is further configured to control the rotation of the rotatable collimator about a second axis perpendicular to the first axis, wherein the second axis extends through the entrance pupil position of the camera and is approximately perpendicular to the optical axis of the camera.

19. The camera calibration system as described in claim 17, characterized in that, The system further includes a computer comprising a processor and a computer-readable medium, the computer communicating with the alignment controller, the collimator position controller, and the image processor, wherein the processor executes instructions stored on the computer-readable medium to: The alignment controller is used to modify the position of the camera based on feedback received from the image processor so that the camera is aligned with the rotatable collimator; Modify the angular position of the rotatable collimator and record one or more light spots associated with the collimated light provided through one or more apertures of the target at each angular position of the rotatable collimator.

20. The camera calibration system as described in claim 19, characterized in that, The processor executes instructions stored on the computer-readable medium to further: After the camera is aligned with the rotatable collimator, the principal point (PP) is determined based on the position of the OA spot provided by the central target aperture of the target. as well as The distortion distribution of the camera is determined based on the light spot recorded at each of the plurality of angular positions of the rotatable collimator.

21. The camera calibration system as described in claim 20, characterized in that, The processor executes instructions stored on the computer-readable medium to determine the focal length of the camera based on the lateral displacement of the OA spot measured in response to a known angle Θ change in the angular position of the rotatable collimator.

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