Internal Parameter Test

Abstract

To provide an intrinsic parameter testing tool and method for intrinsic parameters of a camera under test, which addresses problems of prior arts.SOLUTION: The intrinsic parameter testing apparatus and method may variously shorten process time by using a plurality of collimators capable of azimuthal rotation, and address chromatic aberration by providing independently actuable illumination means associated with the collimator or each collimator, for selectively supplying light of various wavelength ranges.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an intrinsic parameter testing tool and method for the intrinsic parameters of a camera under test. [Background technology]

[0002] The present invention relates to the measurement or determination of camera intrinsic parameters (i.e., parameters related to the camera itself, as opposed to "extrinsic parameters," e.g., related to the camera's pose or position), and to the independent verification of previously determined intrinsic parameters. Throughout this document, the term "intrinsic parameter testing" will be used to refer both to the measurement or determination of intrinsic parameters and also to the verification of previously determined intrinsic parameters. Measurement of such intrinsic parameters can be used, for example, to assess whether a camera under test meets required quality thresholds, and may also be used for subsequent calibration or correction of the camera.

[0003] Conventional intrinsic parameter testing systems use at least one optical target having optically identifiable features, and the testing process requires precise knowledge of the location of the features relative to the camera being measured.

[0004] A conventional process involves placing two targets with a known angular separation relative to a camera whose intrinsic parameters are being tested, and this process is shown diagrammatically in FIG. 1. For example, if the test involves verifying previously measured intrinsic parameters, one image from the camera under test (1) verifies a small portion of the camera's total field of view by comparing the actual distance between the two targets (2, 3) with a calculated value using the camera's (1) intrinsic parameters. In this conventional method, the angular separation θ between the targets (2, 3) is determined by measuring the distance from the camera (1) to each of the targets (2, 3), which is measured using a laser. To verify the entire camera field of view, the camera (1) is rotated (the rotation can be considered above, below, left, right, or around its lens pupil) so that the targets (2, 3) appear in different regions of the image. The resulting set of images can be used to verify the accuracy of the camera's (1) intrinsic parameters across its total field of view. However, there are various problems associated with such a process. For example, such a testing process typically requires a setup with targets 2, 3 approximately 10 m apart, with each target 2, 3 located approximately 15 to 20 m from the camera 1 under test. Because the resulting large footprint makes it impractical to design a testing machine, the process is instead typically carried out on some kind of open floor plan. The large footprint itself can hinder automation of the testing process and can also introduce issues with lighting and image quality that affect testing. Testing just one camera 1 can take up to an hour, and switching between cameras can be difficult due to the required rotation mechanism.

[0005] An alternative apparatus, or intrinsic parameter testing tool, that addresses some of these issues is shown schematically in FIG. 2. Here, the camera under test 1 is supported on an azimuth rotation table 4 so that it is positioned below an infinity-focusing collimator 5, which is mounted on an elevation rotation support 6 that allows the collimator 5 to move ±100 degrees across the field of view of the camera 1 about a rotation axis substantially perpendicular to the optical axis 7 of the camera 1, which extends outward in a predetermined direction—here, vertically upward. This rotation is caused by an elevation rotation actuator 8. The azimuth rotation table 4 can be rotated by an azimuth rotation actuator 9 about an azimuth rotation axis substantially parallel to and coincident with the optical axis 7 to change the elevation scan position. By using an infinity-focusing collimator 5 on the rotation table 4, the angular separation between targets can be precisely controlled between images obtained from the camera under test 1 simply by rotating the collimator 5 using the elevation rotation actuator 8. The infinity-focusing collimator 5 contains a backlit reticle with a focusing lens that projects the reticle as if it were infinitely far away. This eliminates all effects of linear translation on the image. An angular separation equal to the angular separation θ shown in FIG. 1 is created by rotating the collimator 5 using the lift rotation actuator 8. Two image captures are required to create a pair of images. An example of a scan of the image target location is shown in FIG. 3, where several image pairs are created. Actuating the azimuth rotation actuator 9 causes azimuth rotation between the images, allowing the scan to be performed over a larger region of interest in the camera image. An example of such a scan is shown in FIG. 4.

[0006] This provides a way to test the internal parameters of a particular camera 1 within a much smaller footprint than using a physical target, making full automation of the process practical.

[0007] An alternative device that attempts to address such problems is known from US Pat. No. 5,649,999, in which a number of collimators are provided which project a number of markers onto a target surface, and a camera under test captures a number of images of the target surface, the camera rotating between each image capture.

[0008] Even with all of these systems, lighting can be very difficult to control. Often, the process is performed in any available open space, where fluorescent lighting or other ambient light can be used for various purposes. This can affect the quality of the image of the target. Also, camera lenses can exhibit chromatic aberration, so the test results can be affected by the color of the ambient light. Specifically, lateral color from chromatic aberration causes the light to be focused at slightly different points on the camera sensor depending on the color. This will affect the accuracy of any distortion calculations.

[0009] The expected accuracy of such a testing process is approximately 0.05%, with a typical goal of better than 0.3% calibration accuracy. In some automotive camera lenses, chromatic aberration can result in a 0.15% difference between red and green light. This reduces the expected accuracy of the measurement, which can result in false positives or false negatives. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2021 / 150689 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention seeks to address these problems. [Means for solving the problem]

[0012] In accordance with the present invention, this object is achieved by a novel intrinsic parameter testing apparatus and method that can provide various processing time reductions by using multiple collimators that can be azimuthally rotated, and that can address chromatic aberrations by providing independently operable illumination means to selectively provide light in various wavelength ranges.

[0013] According to a first aspect of the present invention, there is provided an intrinsic parameter test tool for measuring intrinsic parameters or for verifying intrinsic parameter calibration of a camera under test, comprising: a camera support for mounting the camera under test with its optical axis extending outward therefrom in a predetermined direction; an infinity-focusing collimator positioned relative to the camera support such that the camera mounted on the camera support can obtain an image of a target surface from light passing through the collimator; the collimator includes a first illumination means and a second illumination means for projecting an image of a reticle associated with the collimator onto a camera while the collimator is mounted on a camera support, the first illumination means being configured to emit light within a first wavelength range and the second illumination means being configured to emit light within a second wavelength range, the first wavelength range and the second wavelength range being different; An internal parameter testing tool is provided.

[0014] According to a second aspect of the present invention, there is provided a method for testing a camera under test, for measuring or verifying measured internal parameters of the camera under test, comprising the steps of: i) providing an internal parametric test tool, the internal parametric test tool including a camera support and an infinity-focusing collimator, the collimator including first and second illumination means for projecting respective images of a reticle associated with the collimator onto the camera while the collimator is mounted on the camera support, the first illumination means configured to emit light within a first wavelength range and the second illumination means configured to emit light within a second wavelength range, the first wavelength range and the second wavelength range being different; ii) mounting the camera on the camera support with its optical axis extending outward therefrom in a predetermined direction; iii) obtaining a first image of the target surface using a camera via a collimator while the first combination of the first illumination means and the second illumination means is turned on; iv) obtaining a second image of the target surface using a camera via a collimator while a second combination of first and second illumination means is turned on, the second combination being different from the first and second combinations; v) comparing the first image and the second image of the target surface with the actual target surface; A method is provided, including:

[0015] According to a third aspect of the present invention, there is provided an intrinsic parameter test tool for measuring intrinsic parameters or verifying intrinsic parameter calibration of a camera under test, comprising: a camera support for mounting the camera under test with its optical axis extending outward therefrom in a predetermined direction; A collimator support; a plurality of infinitely focusing collimators mounted on the collimator support, each collimator of the plurality of collimators positioned relative to the collimator support such that a camera mounted on the camera support can obtain an image of a target surface, the image including a plurality of sub-images corresponding to sub-regions of the target surface, each sub-image being obtained from light passing through a respective collimator of the plurality of collimators; Including, the collimator support is movably mounted such that it can rotate independently about two axes of rotation, and when mounted on the camera support, the first azimuthal axis of rotation is parallel to the optical axis of the camera and the second axis of rotation is substantially orthogonal to the first axis of rotation; An internal parameter testing tool is provided.

[0016] According to a fourth aspect of the present invention, there is provided a method for testing a camera under test, for measuring or verifying measured internal parameters of the camera under test, comprising the steps of: i) providing an intrinsic parametric test tool, the intrinsic parametric test tool including a camera support, a collimator support, and a plurality of infinity-focusing collimators mounted on the collimator support; ii) mounting the camera on the camera support so that its optical axis extends outward therefrom in a predetermined direction; iii) using a camera to obtain an image of the target surface through each of the plurality of collimators while rotating the collimator support about an axis of rotation orthogonal to the optical axis; iv) rotating the collimator support about an azimuthal rotation axis parallel to the optical axis; v) using a camera to obtain additional images of the target surface through each of a plurality of collimators while rotating the collimator support about an axis of rotation perpendicular to the optical axis; vi) comparing said image of the target surface with the actual target surface; A method is provided, including:

[0017] Other particular aspects and features of the present invention are set forth in the appended claims.

[0018] The invention will now be described with reference to the accompanying drawings (not to scale). [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram of a known intrinsic parameter test setup; [Figure 2] 1 is a schematic perspective view from above of a known internal parameter testing tool; [Figure 3] 1A-1C are diagrams of images obtained using various internal parameter testing tools. [Figure 4] 1A-1C are diagrams of images obtained using various internal parameter testing tools. [Figure 5] 1A-1C are diagrams of images obtained using various internal parameter testing tools. [Figure 6] FIG. 1 is a schematic perspective view of a collimator support fitted with five collimators for use with the internal parameter testing tool of the present invention. [Figure 7] 1 is a schematic side view of an internal parameter testing tool according to an embodiment of the present invention. [Figure 8] 1 is a schematic cross-sectional side view of a collimator equipped with two different illumination means for use with the internal parameter testing tool of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0020] A first embodiment of the present invention, which provides much faster scanning, is described with reference to FIGS.

[0021] In this embodiment, an internal parameter test tool 10 is used that includes multiple infinity-focusing collimators 11. Each infinity-focusing collimator 11 includes a backlit reticle with a focusing lens that projects the reticle as if it were infinitely far away. As shown in FIG. 6, five collimators 11 are used here, each mounted to a collimator support 12, so that rotation of the collimator support 12 causes all of the collimators 11 to rotate in unison. FIG. 7 shows a schematic diagram of the internal parameter test tool 10 in detail and how the collimator supports 12 are likely to be mounted therein. The camera under test 1 is mounted on a camera support 16 with its optical axis 7 extending outward therefrom in a predetermined direction, here vertically upward. A rigid frame 13 supports the collimator arrangement. The collimator support 12 is attached to an elevation / rotation actuator 14 that is operable to rotate the collimator support 12 about an elevation / rotation axis that is substantially perpendicular to the optical axis 7, i.e., horizontally as shown. The lift rotation actuator 14 is mounted to depend from an azimuth rotation actuator 15 which is supported by the frame 13. The azimuth rotation actuator 15 is adapted to cause rotation of the lift rotation actuator 14, and hence the collimator support 12, about an azimuth axis of rotation substantially parallel to the optical axis 7. The collimator support 12 is movably mounted such that it can rotate independently about these two axes of rotation 17, 18.

[0022] Each collimator 11 of the plurality of collimators mounted on the collimator support 12 is positioned relative to the collimator support 12 so that a camera 1 mounted on the camera support 16 can obtain an image of the target surface, the image including a plurality of sub-images corresponding to sub-regions of the target surface, each sub-image being obtained from light passing through a respective collimator 11 of the plurality of collimators.

[0023] Once camera 1 is mounted on camera support 16 with its optical axis 7 extending outward therefrom in a predetermined direction, camera 1 is used to obtain an image of the target surface through each of the plurality of collimators 11 while collimator support 12 is rotated about elevation rotation axis 17. Collimator support 12 may then be rotated about azimuthal rotation axis 18, and camera 1 is used to obtain further images of the target surface through each of the plurality of collimators 11 while collimator support 12 is so rotated. The images so obtained of the target surface, shown in FIG. 5, may then be compared to the actual target surface to either measure internal parameters or determine the accuracy of previously measured internal parameters.

[0024] The use of multiple infinity-focusing collimators 11 allows scans to be performed over more of the camera's field of view with the same number of images. The use of these additional collimators 11 allows testing of internal parameters over the entire field of view in less than 20 seconds.

[0025] This method significantly reduces the footprint, setup effort, and time for testing internal parameter camera calibration while improving accuracy. The footprint of the internal parameter testing tool 10 can be less than one square meter. Furthermore, there is very little dependency on the camera under test 1; the tool 10 can accommodate cameras 1 with fields of view ranging from 20 degrees to 180 degrees without requiring setup changes. The use of an infinity-focused collimator 11 results in very precise angular displacement; in fact, this can be much more accurate than can be achieved using lasers that measure physical targets 2, 3 and the distance between them.

[0026] There are various advantages to rotating the collimator rather than the camera. For example, it simplifies interaction with the camera, since the wiring required to interconnect the camera 1 with processing means (not shown), such as a computer, used to analyze the acquired images does not have to pass through any rotating support. Furthermore, it is relatively easy to balance the lifting support mass and improve motion stability.

[0027] A second embodiment of the present invention, which enables testing of chromatic aberration, is described with reference to FIG. 8 . This figure schematically illustrates an infinity-focusing collimator 20 having a reticle 21 and a focusing lens 22 in a manner similar to the known collimator 5 described with reference to FIG. 2 . The collimator 20 may be provided in an internal parameter testing tool, such as the tool 10 of FIG. 7 or the tool shown in FIG. 2 . Furthermore, the collimator 20 includes first and second illumination means, here a first LED 23 and a second LED 24, for projecting an image of the reticle 21 onto the camera 1 while the collimator 20 is mounted on the camera support of the internal parameter testing tool. The first illumination means is configured to emit light within a first wavelength range, and the second illumination means is configured to emit light within a second wavelength range, which are different from the first and second wavelength ranges. Although not shown in FIG. 8 , the collimator optionally includes additional illumination means, such as an LED, configured to emit light within another, different wavelength range. The illumination means are independently controllable, and as a result the wavelength of the light generated by the collimator 20 is controllable, which allows the collimator 20 to project images of the reticle 21 onto the camera 1 in different colors, which allows evaluation of the effect of chromatic aberration on the accuracy of intrinsic parameter testing.

[0028] For example, if the test involves verifying a previously measured intrinsic parameter, the intrinsic parameter verification test uses the positions on the camera image of the image capture of two collimator positions. The distance between these points (which can conveniently be measured in pixels) is converted to an angular distance that is compared to the actual angular distance the collimator travels between the two images. Chromatic aberration (or lateral color) causes the distance between collimator images to vary in image space (i.e., pixels) depending on the color of the light. For example, two collimator images with the same angular distance between the physical collimator positions may have a separation of 1000 pixels in green light (560 nm), but 1001 pixels in red light (650 nm). This is a difference of 0.1%, which can be very impactful for error budgets that are often less than 0.3%.

[0029] To understand the impact of lateral color, the intrinsic parameter testing tool can be tested using various colors of light. In the previous example using red and green light instead of two images of one color, four images can be taken, with two images of green and two images of red. This allows for quantification of the performance of the intrinsic parameters for both green and red, and a difference of 0.1% would be understood. This can be extended to as many image pairs and colors as the user requires. Users could use different sets of intrinsic parameters for various colors, or (more likely) they could ensure they use one set of intrinsic parameters that provides acceptable performance across all wavelengths and color spectrums of interest.

[0030] Ideally, the collimator 20 would provide illumination in a variety of colors to simulate possible lighting conditions that could be seen by the camera under test 1. This would enable the tool to test the effect of chromatic aberration on the accuracy of the intrinsic parameters. Current intrinsic parameter testing schemes have little or no control over lighting, and chromatic aberration can have a significant impact on the overall accuracy of the measurements. It is contemplated that the illumination means could include several colors, e.g., red, near-infrared, and white, corresponding to real-world lighting conditions such as noon and sunrise.

[0031] More specifically, this device can be used to ensure that the internal parameter measurements of the camera under test 1 are accurate across the anticipated conditions under which the camera will be used. For example, such cameras are often used in automotive applications where a wide range of lighting conditions must be tested. In such applications, the internal parameters must be accurate to see red taillights and traffic lights (650 nm) or green traffic lights (560 nm). In some cases, cameras are also used in near-infrared (850 nm to 1000 nm) applications for driver monitoring. The camera is also expected to accurately reflect the environment under various daylight conditions with a variety of color temperature spectrums. For example, at dusk (approximately 3400 K), at noon (approximately 5500 K), or even on a bright, snowy day (8000 K).

[0032] In some settings, it may be useful to create certain lighting effects by turning on different combinations of lighting means. For example, if a first lighting means produces essentially white light and a second lighting means produces colored light, the first lighting means may be turned on continuously, while the second lighting means is turned on as needed to evaluate the effect of changing colors throughout the day.

[0033] Various extensions or alternatives are possible. For example, if such a collimator is used in a multi-collimator arrangement such as that shown in Figures 6 and 7, it may be possible to include illumination means of the same color or illumination means of different colors in each collimator of the multiple collimators.

[0034] However, in all cases, the basic method is similar: whatever type of internal parameter testing tool is provided, a camera will be mounted on the tool's camera support with its optical axis extending outward therefrom in a predetermined direction. While a first combination of first and second illumination means is switched on, the camera is then used to obtain a first image of the target surface via a collimator. While a second combination of the first and second illumination means is switched on, the camera is then used to obtain a second image of the target surface via a collimator, which is different from the first and second combinations. The first and second images of the target surface thus obtained are then compared to the actual target surface to either measure an internal parameter or determine the accuracy of a previously measured internal parameter.

[0035] The foregoing embodiments are merely exemplary and other possibilities and alternatives that fall within the scope of the present invention will be apparent to those skilled in the art. [Explanation of symbols]

[0036] 1 camera 2, 3 targets, physical targets 4 Azimuth angle rotation table 5 Infinity focusing collimator 6. Lifting and rotating support 7 Optical axis 8, 14 Elevating and rotating actuator 9, 15 Azimuth rotation actuator 10 Internal parameter test tool 11 (Multiple) collimators, (Multiple) infinity-focusing collimators 12 Collimator support 13 Frame, Rigid Frame 16 Camera support 17 Elevating rotation axis 18 Azimuth rotation axis 20 collimators, infinity focusing collimators 21 Reticle 22 focusing lens 23 First LED 24 Second LED θ angle separation

Claims

1. 1. An intrinsic parameter test tool for measuring intrinsic parameters or verifying intrinsic parameter calibration for a camera under test, comprising: a camera support for mounting the camera under test with its optical axis extending outward therefrom in a predetermined direction; an infinity-focusing collimator positioned relative to the camera support such that the camera mounted on the camera support can obtain an image of a target surface from light passing through the collimator; Including, the collimator includes first and second illumination means for projecting an image of a reticle associated with the collimator onto the camera while the collimator is mounted on the camera support, the first illumination means configured to emit light within a first wavelength range and the second illumination means configured to emit light within a second wavelength range, the first wavelength range and the second wavelength range being different; Internal parameter testing tool.

2. The intrinsic parametric test tool of claim 1 , wherein the collimator includes the reticle.

3. The intrinsic parametric testing tool of claim 1 , wherein the first illumination means and the second illumination means are independently controllable.

4. 10. The intrinsic parametric test tool of claim 1, wherein the first illumination means and the second illumination means include respective LEDs.

5. 2. The intrinsic parameter test tool of claim 1, including a collimator support, the infinity-focusing collimator mounted on the collimator support, the collimator support being movably mounted such that the collimator support can rotate about an axis of rotation substantially perpendicular to the optical axis of the camera when mounted on the camera support.

6. 6. The intrinsic parameter test tool of claim 5, wherein the collimator support is movably mounted such that when mounted on the camera support, it can independently rotate about an azimuthal axis of rotation substantially parallel to the optical axis of the camera.

7. 6. The intrinsic parameter test tool of claim 5, including at least one additional infinity-focusing collimator mounted on the collimator support, the at least one additional collimator positioned relative to the camera support such that the camera mounted on the camera support can obtain an image of a target surface from light passing through the at least one additional collimator.

8. 8. The intrinsic parametric testing tool of claim 7, wherein the additional collimator includes an additional first illumination means and an additional second illumination means for projecting an image of a reticle associated with the additional collimator onto the camera while the additional collimator is mounted on the camera support, the additional first illumination means being configured to emit light within a first wavelength range and the additional second illumination means being configured to emit light within a second wavelength range, the first wavelength range and the second wavelength range being different.

9. 1. A method for testing a camera under test, comprising measuring or verifying measured internal parameters of said camera under test, said method comprising: i) providing an intrinsic parametric test tool, the intrinsic parametric test tool including a camera support and an infinity-focusing collimator, the collimator including first and second illumination means for projecting an image of a reticle associated with the collimator onto the camera while the collimator is mounted on the camera support, the first illumination means configured to emit light within a first wavelength range and the second illumination means configured to emit light within a second wavelength range, the first wavelength range and the second wavelength range being different; ii) mounting said camera on said camera support so that its optical axis extends outward therefrom in a predetermined direction; iii) obtaining a first image of a target surface using the camera through the collimator while the first illumination means and the second illumination means are turned on in a first combination of on / off patterns; iv) using the camera to obtain a second image of the target surface through the collimator while the first illumination means and the second illumination means are turned on in a second combination, the second combination being different from the first combination; v) comparing the first and second images of the target surface with the actual target surface; A method comprising:

10. 10. The method of claim 9, wherein steps iii) and iv) each include rotating the collimator about a rotation axis perpendicular to the optical axis, and wherein each of the first image and the second image is obtained while rotating the collimator.

11. 10. The method of claim 9, further comprising, after step iv), relatively rotating the camera and the collimator about an azimuthal rotation axis parallel to the optical axis, and repeating steps iii) and iv).

12. 10. The method of claim 9, wherein the internal parametric testing tool includes a collimator support, the infinity-focusing collimator mounted on the collimator support, and at least one additional infinity-focusing collimator mounted on the collimator support, the at least one additional collimator positioned relative to the camera support such that the camera mounted on the camera support can obtain an image of a target surface from light passing through the at least one additional collimator.

13. 1. An intrinsic parameter test tool for measuring intrinsic parameters or verifying intrinsic parameter calibration for a camera under test, comprising: a camera support for mounting the camera under test with its optical axis extending outward therefrom in a predetermined direction; A collimator support; a plurality of infinitely focusing collimators mounted on the collimator support, each collimator of the plurality of collimators positioned relative to the collimator support such that the camera mounted on the camera support can obtain an image of a target surface, the image including a plurality of sub-images corresponding to sub-regions of the target surface, each sub-image obtained from light passing through a respective collimator of the plurality of collimators; Including, the collimator support is movably mounted so as to be independently rotatable about a first azimuthal axis of rotation that is parallel to the optical axis of the camera when mounted on the camera support, and a second axis of rotation that is substantially orthogonal to the first azimuthal axis of rotation; Internal parameter testing tool.

14. 14. The intrinsic parameter testing tool of claim 13, including respective actuators adapted to rotate the collimator support about the first azimuthal axis of rotation and the second axis of rotation.

15. 14. The intrinsic parametric test tool of claim 13, wherein at least one collimator of the plurality of collimators includes first and second illumination means for projecting an image of a reticle associated with the collimator onto the camera while the collimator is mounted on the camera support.

16. 16. The intrinsic parametric testing tool of claim 15, wherein the first illumination means and the second illumination means are independently controllable.

17. 16. The intrinsic parametric testing tool of claim 15, wherein the first illumination means emits light within a first wavelength range and the second illumination means emits light within a second wavelength range, the first wavelength range and the second wavelength range being different.

18. 16. The intrinsic parametric testing tool of claim 15, wherein the first illumination means and the second illumination means include respective LEDs.

19. 1. A method for testing a camera under test, comprising measuring an intrinsic parameter of the camera under test or verifying a measured intrinsic parameter of the camera, the method comprising: i) providing an intrinsic parametric test tool, said intrinsic parametric test tool including a camera support, a collimator support, and a plurality of infinity-focusing collimators mounted on said collimator support; ii) mounting said camera on said camera support so that its optical axis extends outward therefrom in a predetermined direction; iii) using the camera to obtain an image of a target surface through each of the plurality of collimators while rotating the collimator support about an axis of rotation orthogonal to the optical axis; iv) rotating the collimator support about an azimuthal rotation axis parallel to the optical axis; v) using the camera to obtain additional images of the target surface through each of the plurality of collimators while rotating the collimator support about an axis of rotation orthogonal to the optical axis; vi) comparing the image of the target surface with an actual target surface; A method comprising:

20. 20. The method of claim 19, wherein at least one collimator of the plurality of collimators includes a first illumination means and a second illumination means for projecting an image of a reticle associated with the collimator onto the camera while it is mounted on the camera support, and wherein step iii) includes: obtaining a first image of the target surface through the collimator using the camera while the first illumination means and the second illumination means are turned on in a first combination of on / off pattern combinations; and obtaining a second image of the target surface through the collimator using the camera while the first illumination means and the second illumination means are turned on in a second combination, the first combination and the second combination being different.

Images