CN112288822A - Camera active alignment method combined with calibration - Google Patents
Camera active alignment method combined with calibration Download PDFInfo
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- CN112288822A CN112288822A CN202011004423.2A CN202011004423A CN112288822A CN 112288822 A CN112288822 A CN 112288822A CN 202011004423 A CN202011004423 A CN 202011004423A CN 112288822 A CN112288822 A CN 112288822A
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- 238000000034 method Methods 0.000 title claims abstract description 22
- 238000012360 testing method Methods 0.000 claims abstract description 81
- 230000002093 peripheral effect Effects 0.000 claims abstract description 12
- 238000003384 imaging method Methods 0.000 claims description 13
- 238000012937 correction Methods 0.000 claims description 6
- 239000011521 glass Substances 0.000 claims description 4
- 239000003292 glue Substances 0.000 claims description 4
- 230000003287 optical effect Effects 0.000 description 3
- 238000001723 curing Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 241001237160 Kallima inachus Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
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- 238000004364 calculation method Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/80—Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/10—Image acquisition modality
- G06T2207/10016—Video; Image sequence
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Abstract
The invention discloses a camera active alignment method combined with calibration, which comprises the following steps: providing a test chart; acquiring image information of a test graphic card through a camera, determining the position of a central view field test pattern, and moving a lens or an image sensor until an angular point of the central view field test pattern is positioned in the center of an image; obtaining definition change curves of a central view field test pattern and a plurality of peripheral view field test patterns by scanning a camera in a focal length direction, calculating an inclination angle between a lens and an image sensor according to the definition change curves, and adjusting the lens to be parallel to the image sensor; and calibrating a distortion center of the camera through the checkerboard, and adjusting the relative horizontal position of the lens and the image sensor according to the difference between the distortion center and the image center to correct the deviation. The invention can greatly improve the center deviation of the long-focus camera by combining with the calibrated active camera alignment method, so that the center of the camera reference is closer to the image center, and the alignment precision is greatly improved.
Description
Technical Field
The invention relates to the technical field of active alignment of cameras, in particular to a camera active alignment method combined with calibration.
Background
With the development of technologies such as intelligent auxiliary driving and automatic driving in the automobile industry, the camera is used as one of main vehicle-mounted sensors, and the application field of the camera is more and more extensive. Especially, the forward-looking camera can be used for distance measurement, collision avoidance and the like, has a long focal length and higher requirements on camera parameters, and otherwise, the calculation precision can be reduced.
The traditional active alignment algorithm of the camera determines the horizontal positions of the lens and the image sensor by using the imaging positions of the corner points of the test pattern in the central area, and the central test pattern is considered to be optimal when being imaged on the image center. With the optical axis tilted by the same angle, the increase in the focal length of the lens causes the deviation in the center of the camera to increase proportionally. If the alignment is done in the conventional manner, the center of the produced camera may deviate from the center of the image by tens of pixels. For a camera with a focal length of around 16mm, the deviation may be more than fifty pixels, as a practical experience.
Disclosure of Invention
The invention aims to provide the active alignment method of the camera, which is high in feasibility and alignment precision and combines calibration.
In order to solve the above problems, the present invention provides an active alignment method for a camera combined with calibration, which includes:
providing a test chart, wherein the test chart is integrated with a checkerboard, a central view field test pattern and a plurality of peripheral view field test patterns, the central view field test pattern is embedded in the checkerboard, and the angular points of the central view field test pattern are superposed with the angular points of the checkerboard;
acquiring image information of the test graphic card through a camera, determining the position of the central view field test pattern, and moving a lens or an image sensor until the corner point of the central view field test pattern is positioned in the center of the image;
obtaining definition change curves of the central view field test pattern and the peripheral view field test patterns through scanning of a camera in the focal length direction, calculating the inclination angle of a lens and an image sensor according to the definition change curves, and adjusting the parallelism of the lens and the image sensor;
and calibrating a distortion center of the camera through the checkerboard, and adjusting the relative horizontal position of the lens and the image sensor according to the difference between the distortion center and the image center so as to correct the deviation.
As a further improvement of the present invention, the calibrating a distortion center of the camera by the checkerboard, and adjusting a relative horizontal position of the lens and the image sensor according to a difference between the distortion center and the image center, then further includes: and determining a correction result through calibration again, and continuing correction if the deviation does not meet the requirement.
As a further improvement of the present invention, the calibrating a distortion center of the camera by the checkerboard, and adjusting a relative horizontal position of the lens and the image sensor according to a difference between the distortion center and the image center, then further includes: and determining the positions of the lens and the image sensor through glue curing.
As a further improvement of the present invention, the marking out the distortion center of the camera by the checkerboard specifically includes: and calibrating the distortion center of the camera by utilizing the characteristic that an image obtained by imaging the checkerboard in an ideal small hole is parallel to the actual imaging of the checkerboard and utilizing the antipodal geometric relation.
As a further improvement of the present invention, the calibrating the distortion center of the camera by using the epipolar geometry relationship specifically includes: and determining the distortion center of the camera through the epipolar points determined by the image obtained by imaging the ideal small holes by the checkerboard and the actual imaging of the checkerboard.
As a further improvement of the invention, the test chart is film printed or glass etched.
As a further improvement of the present invention, the film printed test card is attached or pressed onto a flat carrying surface.
As a further improvement of the invention, the test chart is of a transmission type or a reflection type.
As a further improvement of the present invention, the central field-of-view test pattern and the plurality of peripheral field-of-view test patterns are based on the ISO12233 standard, and are both black and white edges inclined by 5 degrees, including both horizontal and vertical directions.
As a further improvement of the invention, each grid in the chessboard is square, and the number of the grids is equal to or more than 4x4 between black and white in the transverse direction and the longitudinal direction.
The invention has the beneficial effects that:
the invention can greatly improve the center deviation of the long-focus camera by combining with the calibrated active camera alignment method, so that the center of the camera reference is closer to the image center, and the alignment precision is greatly improved.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the content of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following preferred embodiments are described in detail with reference to the accompanying drawings.
Drawings
FIG. 1 is a flow chart of an active alignment method for a camera incorporating calibration in a preferred embodiment of the present invention;
FIG. 2 is a first schematic diagram of the structure of a test card according to the preferred embodiment of the present invention;
FIG. 3 is a second schematic structural diagram of a test card according to a preferred embodiment of the present invention.
Detailed Description
The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.
As shown in fig. 1, an active alignment method for a camera combined with calibration in a preferred embodiment of the present invention includes the following steps:
and S10, providing a test chart, wherein the test chart is integrated with a checkerboard, a central view field test pattern and a plurality of peripheral view field test patterns, and the central view field test pattern is embedded in the checkerboard and the corner points of the central view field test pattern coincide with the corner points of the checkerboard.
Referring to fig. 2 and 3, for two different test cards according to the preferred embodiment of the present invention, in fig. 2, the black grids in the checkerboard of the test card are all filled, and two white circles are added to the diagonal black grids beside the central view test pattern, so that the software can locate the corner positions of the central view test pattern by recognizing the two circles. In fig. 3, the interior of the black lattices in the checkerboard of the test card is all in a hollowed structure, and only a circle of narrow black edges are left, so that the test card does not influence the search of the checkerboard angular points in the calibration algorithm, but the active alignment algorithm does not identify the angular points of the checkerboard, and the position identification error of the central view field test pattern can also be avoided.
Preferably, the test chart is film printed or etched glass. The film printed test card is attached or pressed on the flat bearing surface. The bearing surface can be selected from glass and the like.
In this embodiment, the test card is transmissive or reflective.
In the present embodiment, the central field-of-view test pattern and the plurality of peripheral field-of-view test patterns are based on the ISO12233 standard, and each of the central field-of-view test pattern and the plurality of peripheral field-of-view test patterns is a black-and-white edge inclined by 5 degrees, and includes both horizontal and vertical directions. The distribution of the test patterns can be adjusted according to the field angle of the camera and the test field requirements of customers, a central field test pattern is arranged in the central area of the image, and four or eight peripheral field test patterns are arranged.
In other embodiments, the test pattern has slits, has a star pattern, has a dead-leaf pattern, and the like.
In the present embodiment, each of the checkerboards is square, and the number of the checkerboards is equal to or greater than 4 × 4 between black and white in the horizontal direction and the vertical direction.
S20, acquiring image information of the test chart through a camera, determining the position of the central view field test pattern, and moving a lens or an image sensor until the corner point of the central view field test pattern is located at the center of the image. Specifically, for the test chart in fig. 2, two circles are identified first, the position of the central view field test pattern can be determined according to the positions of the two circles, and the corner point of the central view field test pattern is moved to the center of the image. For the test chart in fig. 3, because the black lattices of the checkerboard are hollowed, the definition algorithm cannot grab the corner points of the checkerboard, only grabs the corner points of the central view field test pattern, and directly moves the corner points of the central view field test pattern to the center of the image. This step is to ensure that the test pattern is in the required field of view or in close proximity when focusing, and does not define the center position of the final camera parameters.
S30, obtaining definition change curves of the central view field test pattern and the peripheral view field test patterns through scanning of the camera in the focal length direction, calculating the inclination angle of the lens and the image sensor according to the definition change curves, and adjusting the parallelism of the lens and the image sensor.
The lens and the image sensor are not parallel, and the definition curve of each test pattern is visually represented as that the peak value is scattered on different scanning steps before adjustment, and the peak value of the definition curve is basically simultaneously located at one position after the parallelism is adjusted. Because the lens is equivalent to a black box, the position of the principal point of the lens cannot be accurately known, and the actual lens generally cannot reach the ideal state in design because of assembly errors and the like, when the lens and the image sensor are parallel in this way, the optical axis of the lens may be actually inclined due to the characteristics of the lens.
In one embodiment, the method further comprises the following steps: after leveling, scanning once again in the focal length direction, returning to a definition peak point, and determining the horizontal relative position of the lens and the image sensor by taking the principle that the corner point of the central visual field test pattern is imaged in the center of the image. However, since the optical axis of the lens itself in this state may have an inclination angle, which is about 46 pixels from the center of the lens with a larger focal length, for example, a 16mm long focal length, if the inclination angle is 0.5 degrees and the pixel size is 3um, the deviation is out of the allowable range for the vehicle-mounted camera and the like requiring precise measurement, not to mention that the introduction of the variable during the thermal curing of the glue may cause more deviation.
And S40, calibrating the distortion center of the camera through the checkerboard, and adjusting the relative horizontal position of the lens and the image sensor according to the difference between the distortion center and the image center to correct the deviation. The purpose is to make the distortion center coincide with the image center as far as possible, reduce the deviation, promote the precision.
Specifically, the distortion center of the camera is calibrated by utilizing the characteristic that an image obtained by imaging the checkerboard in an ideal small hole is parallel to the actual imaging of the checkerboard and utilizing the relation of epipolar geometry. More specifically, the distortion center of the camera is determined by the epipolar point determined by the image obtained after the ideal pinhole imaging is carried out on the checkerboard and the actual imaging of the checkerboard.
In this embodiment, the calibration is based on a single image, so that the calibration efficiency is greatly improved, and the alignment precision is ensured.
In one embodiment, the following steps are further included after step S40:
and determining a correction result through calibration again, and continuing correction if the deviation does not meet the requirement. This process can be repeated depending on the different requirements for precision and production efficiency.
In one embodiment, the following steps are further included after step S40: and determining the positions of the lens and the image sensor through glue curing.
The above embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.
Claims (10)
1. A camera active alignment method combined with calibration is characterized by comprising the following steps:
providing a test chart, wherein the test chart is integrated with a checkerboard, a central view field test pattern and a plurality of peripheral view field test patterns, the central view field test pattern is embedded in the checkerboard, and the angular points of the central view field test pattern are superposed with the angular points of the checkerboard;
acquiring image information of the test graphic card through a camera, determining the position of the central view field test pattern, and moving a lens or an image sensor until the corner point of the central view field test pattern is positioned in the center of the image;
obtaining definition change curves of the central view field test pattern and the peripheral view field test patterns through scanning of a camera in the focal length direction, calculating the inclination angle of a lens and an image sensor according to the definition change curves, and adjusting the parallelism of the lens and the image sensor;
and calibrating a distortion center of the camera through the checkerboard, and adjusting the relative horizontal position of the lens and the image sensor according to the difference between the distortion center and the image center so as to correct the deviation.
2. The active camera alignment method with calibration as claimed in claim 1, wherein the chessboard pattern is used to calibrate the distortion center of the camera and adjust the relative horizontal position of the lens and the image sensor according to the difference between the distortion center and the image center, and then further comprising: and determining a correction result through calibration again, and continuing correction if the deviation does not meet the requirement.
3. The active camera alignment method with calibration as claimed in claim 1, wherein the chessboard pattern is used to calibrate the distortion center of the camera and adjust the relative horizontal position of the lens and the image sensor according to the difference between the distortion center and the image center, and then further comprising: and determining the positions of the lens and the image sensor through glue curing.
4. The active alignment method for a camera in combination with calibration according to claim 1, wherein the calibration of the distortion center of the camera through the checkerboard concretely comprises: and calibrating the distortion center of the camera by utilizing the characteristic that an image obtained by imaging the checkerboard in an ideal small hole is parallel to the actual imaging of the checkerboard and utilizing the antipodal geometric relation.
5. The active alignment method for a camera with calibration according to claim 4, wherein the calibrating the distortion center of the camera by using the epipolar geometry relationship comprises: and determining the distortion center of the camera through the epipolar points determined by the image obtained by imaging the ideal small holes by the checkerboard and the actual imaging of the checkerboard.
6. The active camera alignment method in combination with calibration according to claim 1, wherein the test card is film printed or glass etched.
7. The active alignment method for camera head with calibration according to claim 6, wherein the film printed test card is attached or pressed on the flat carrying surface.
8. The active camera alignment method in combination with calibration of claim 1, wherein the test card is transmissive or reflective.
9. The active camera alignment method in combination with calibration according to claim 1, wherein the central view field test pattern and the plurality of peripheral view field test patterns are based on the ISO12233 standard, and are both black and white edges inclined by 5 degrees, including both horizontal and vertical directions.
10. The active alignment method for camera head with calibration combination according to claim 1, wherein each grid in the checkerboard is square, and the number of grids is equal to or greater than 4x4 between black and white in the horizontal direction and the vertical direction.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202011004423.2A CN112288822A (en) | 2020-09-22 | 2020-09-22 | Camera active alignment method combined with calibration |
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| CN202011004423.2A CN112288822A (en) | 2020-09-22 | 2020-09-22 | Camera active alignment method combined with calibration |
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Cited By (4)
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| CN113766210A (en) * | 2021-07-21 | 2021-12-07 | 歌尔光学科技有限公司 | Test method and device |
| CN115361497A (en) * | 2022-08-01 | 2022-11-18 | 歌尔股份有限公司 | Method, device and equipment for measuring inclination angle of camera module and storage medium |
| CN116320747A (en) * | 2023-05-19 | 2023-06-23 | 四川华鲲振宇智能科技有限责任公司 | Method for horizontally checking image sensor and lens |
| CN115361497B (en) * | 2022-08-01 | 2024-06-07 | 歌尔股份有限公司 | Method, device, equipment and storage medium for measuring inclination angle of camera module |
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