CN111273438B - Optical device and method for eliminating trapezoidal distortion based on micro-reflector array - Google Patents
Optical device and method for eliminating trapezoidal distortion based on micro-reflector array Download PDFInfo
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- CN111273438B CN111273438B CN201811474298.4A CN201811474298A CN111273438B CN 111273438 B CN111273438 B CN 111273438B CN 201811474298 A CN201811474298 A CN 201811474298A CN 111273438 B CN111273438 B CN 111273438B
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Abstract
An optical device and method based on micro-mirror array belongs to the technical field of optical imaging, and aims to solve the problem of trapezoidal distortion in the prior art, the device comprises a diaphragm, an imaging system, a semi-transparent semi-reflective mirror, a micro-mirror array, a collimation system and secondary imagingA system; light emitted by an object plane passes through a diaphragm and is incident to an imaging system, the light is converged on a semi-transparent and semi-reflective mirror through the imaging system, the light is transmitted by the semi-transparent and semi-reflective mirror and then imaged at a primary image surface position, a micro-mirror array is arranged at a primary image surface, the light is incident to a micro-mirror array, the light is reflected by the micro-mirror array, the reflected light is reflected to a collimation system through the semi-transparent and semi-reflective mirror, the light is incident to a secondary imaging system after passing through the collimation system, and finally the light is imaged at a secondary image surface; the method is to adjust the inclination angle theta of the micro-reflector arraybAnd the distance d' between the exit pupil of the collimation system and the main plane of the secondary imaging system, the size of the additional introduced trapezoidal distortion is controlled, and the trapezoidal distortion in the oblique imaging is compensated.
Description
Technical Field
The invention relates to an optical device and method for eliminating trapezoidal distortion in oblique imaging, in particular to an optical device and method for compensating trapezoidal distortion by a micro-reflector array, and belongs to the technical field of optical imaging.
Background
In traffic monitoring, license plate recognition is widely applied to the fields of traffic violation monitoring and inquiry, flow monitoring, intelligent access of parking lots, social security, public safety and the like. However, because the license plate recognition cameras are all installed in a downward inclined mode, the shot pictures have trapezoidal distortion in the vertical direction, and the accurate recognition of the license plate is adversely affected. Therefore, the research on the method for eliminating the trapezoidal distortion has very important significance, and domestic researchers make a lot of researches on the method for reducing the trapezoidal distortion.
The Chinese patent publication No. CN108241859A, named as license plate correction method and device, adopts digital image processing technology to correct the keystone distortion of the image, and the method has large load and poor algorithm adaptability, and all processes are carried out after the image is acquired, so that the real-time property is poor.
In the Chinese patent publication No. CN102663381A entitled "Low distortion Single finger fingerprint acquisition System and method for reducing trapezoidal distortion", an object space near telecentric optical path is used to reduce the trapezoidal distortion of the system, and the specific implementation is that an aperture diaphragm is positioned at the focus position of an optical system in front of the aperture diaphragm, so the effect is obvious. However, the object space near telecentric optical path can only be used for an optical system with an object plane size approximately equal to the system aperture and a small object distance, in traffic monitoring, the working distance is approximately 16-100m, and the field of view is large, so that the imaging object plane is far larger than the camera aperture, the system cannot realize object space telecentric, and trapezoidal distortion is difficult to eliminate.
Disclosure of Invention
The invention provides an optical device and method based on a micro-reflector array, aiming at solving the problem of trapezoidal distortion in the inclined imaging of a long distance, a large view field and a large working area in the prior art, and improving the identification reliability, stability and practicability of a system.
The technical scheme for solving the problems is as follows:
an optical device for eliminating trapezoidal distortion based on a micro-reflector array is characterized by comprising a diaphragm, an imaging system, a semi-transparent semi-reflecting mirror, the micro-reflector array, a collimation system and a secondary imaging system; the light that the object plane sent passes through the diaphragm, incides imaging system, and the light passes through imaging system and converges on the half mirror, and light is imaged in primary image plane position after the half mirror transmission, places a little mirror array in primary image plane department, and light incides on the little mirror array, and light is reflected through little mirror array, and the reflected light is on half mirror reflection of half mirror is to collimation system, incides secondary imaging system after the light is through collimation system, finally is imaged in secondary image plane.
The micro-mirror array is composed of a plurality of rows of micro-mirrors, the width of each row is d, the magnitude of 10um is obtained, the inclined planes of the plurality of rows of micro-mirrors are reflecting surfaces, and the inclination angle is thetabLight normally incident on the micromirror array at an angle of 2 θbAnd (7) emitting.
The inclination angle thetab＝10-20°。
The method for eliminating the trapezoidal distortion based on the micro-reflector array is characterized in that the method utilizes the secondary imaging of the micro-reflector array to eliminate the trapezoidal distortion, and comprises the following specific steps:
designing a collimation system according to the size of a primary image surface;
designing a secondary imaging system according to the size of the field of view of the collimation system;
step three, selecting the inclination angle thetabThe micromirror array of (a);
placing the micro-mirror array at the primary image surface, reflecting the light by the micro-mirror array, reflecting the reflected light by the semi-transparent semi-reflective mirror to the collimation system, and then, emitting the light to the secondary imaging system after passing through the collimation system, and finally imaging the light on the secondary image surface;
step five, adjusting the inclination angle theta of the micro-reflector arraybAnd the distance d' between the exit pupil of the collimation system and the main plane of the secondary imaging system, the size of the additional introduced trapezoidal distortion is controlled, and the trapezoidal distortion in the oblique imaging is compensated.
Theta isb＝10-20°。
The invention has the advantages and beneficial effects that:
1. the invention provides an optical device and method for eliminating trapezoidal distortion under a long distance and a large view field.
2. The invention can obtain low-distortion and high-resolution images, and the system is more durable and has better real-time property due to the adoption of the optical structure.
3. The micro-mirror array for eliminating keystone distortion in the invention can be produced in mass production in a grading way.
Drawings
Fig. 1 is a schematic diagram of an optical device based on micro-mirror array keystone distortion elimination according to the present invention.
Fig. 2 is a schematic view of a micromirror array structure according to the present invention.
Fig. 3 is a schematic diagram of distortion of a conventional traffic monitoring camera during normal imaging.
FIG. 4 shows the inventionbDistortion at 10 ° and d' 18.802 mm.
FIG. 5 shows the inventionbDistortion at 15 ° and d' 28.6735 mm.
Fig. 6 is a graph of the relationship of trapezoidal distortion to zero in an example of a traffic monitoring camera.
In the figure: 1. an object surface; 2. a diaphragm; 3. an imaging system; 4. a semi-transparent semi-reflective mirror; 5. a primary image plane; 6. a micro-mirror array; 7. a collimating system; 8. a collimating system exit pupil; 9. a secondary imaging system; 10. a secondary image plane;
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, the optical device for eliminating keystone distortion based on micro-mirror array comprises a diaphragm 2, an imaging system 3, a half-mirror 4, a micro-mirror array 6, a collimation system 7 and a secondary imaging system 9; the light that the object plane 1 sent passes through diaphragm 2, incide imaging system 3, the light converges on semi-transparent semi-reflecting mirror 4 through imaging system 3, the light is imaged in a 5 position on image planes after the semi-transparent semi-reflecting mirror 4 transmission, place micro mirror array 6 in a 5 department on image planes, the light incides on micro mirror array 6, the light reflects through micro mirror array 6, the reflected light is on semi-transparent semi-reflecting mirror 4 reflects collimating system 7, the light incides secondary imaging system 9 after passing collimating system 7, finally image on secondary image planes 10.
As shown in fig. 2, the micromirror array 6 comprises a plurality of rows of micromirrors, each row having a width d and an order of magnitude of 10um, the inclined planes of the micromirrors being reflective surfaces and having an inclination angle θbLight rays perpendicularly incident on the micromirror array 6 are at an angle of 2 thetabAnd (7) emitting. ThetabThe optimal angle range is 10-20 degrees.
The invention relates to a method for eliminating trapezoidal distortion based on a micro-reflector array, which is characterized in that light emitted by an object plane 1 is incident to an imaging system 3 through a diaphragm 2, the light is converged on a semi-transparent semi-reflecting mirror 4 through the imaging system 3, and the light is transmitted through the semi-transparent semi-reflecting mirror 4 and then imaged at a primary image plane 5 position, and the method utilizes a micro-reflector array 6 for secondary imaging to eliminate trapezoidal distortion, and comprises the following specific steps:
firstly, designing a collimation system 7 according to the size of a primary image surface 5;
designing a secondary imaging system 9 according to the size of the field of view of the collimation system 7;
step three, selecting the inclination angle thetab Micro mirror array 6, thetabThe optimal angle range is 10-20 degrees;
and fourthly, placing the micro-mirror array 6 at the primary image surface 5, reflecting the light by the micro-mirror array 6, reflecting the reflected light to the collimation system 7 by the semi-transparent semi-reflective mirror 4, making the light enter the secondary imaging system 9 after passing through the collimation system 7, and finally imaging the light on the secondary image surface 10.
Step five, adjusting the inclination angle theta of the micro-reflector array 6bAnd the distance d' between the exit pupil 8 of the collimation system and the main plane of the secondary imaging system 9 controls the size of the additional introduced trapezoidal distortion to compensate the trapezoidal distortion in oblique imaging.
Example (b):
the optical device based on the micro-mirror array for eliminating the trapezoidal distortion is used for explaining a traffic monitoring camera, the traffic monitoring camera is generally installed in a mode of inclining downwards by 10-15 degrees and is described by 12 degrees, as shown in figure 1, an included angle between the traffic monitoring camera and a license plate is 12 degrees, an object plane 1 in the light path is 16m away from the traffic monitoring camera, the whole view field is 24 degrees, and the object height is +/-3.4 m.
When the existing traffic monitoring camera is used for imaging normally, light emitted by an object plane 1 passes through a diaphragm 2 and an imaging system 3 and then is imaged on a primary image plane 5, and parameters are shown in a table 1. As shown in fig. 3, there is approximately 4.5% keystone distortion.
TABLE 1
| Surface type | Focal length/mm | Thickness/mm | Pore diameter/mm | Bevel angle of inclination/° |
| Inclined object plane | \ | 16000 | 6800 | 12 |
| Diaphragm | \ | 50 | 20 | \ |
| Ideal lens | 50 | 50.16 | 42.32 | \ |
| Oblique image plane | \ | \ | 22.26 | -0.038 |
The invention relates to a method for eliminating trapezoidal distortion based on a micro-mirror array, which utilizes a micro-mirror array 6 to perform secondary imaging to eliminate trapezoidal distortion and comprises the following specific steps:
1) designing a collimation system 7 according to the size of the primary image surface 5; as can be seen from Table 1, the size of the primary image plane 5 is 22.26mm, a lens with the designed image plane size of 22.26mm is provided, the parameters are shown in Table 2, and the primary image plane is inverted to be used as the collimation system 7.
TABLE 2
2) Designing a secondary imaging system 9 according to the size of the field of view of the collimation system 7; as shown in table 2, the half field of view size is calculated from the image plane size and the focal length of the collimation system 7 to be 12.548 °, and a secondary imaging system with the half field of view of 12.548 ° is designed, and the parameters are as shown in table 3.
TABLE 3
| Surface type | Focal length/mm | Thickness/mm | Pore diameter/mm |
| Article surface | \ | ∞ | \ |
| Diaphragm/ideal lens | 50 | 50 | 60 |
| Image plane | \ | \ | 22.26 |
3) Selecting the angle of inclination as thetabThe micromirror array 6 of (1) is preferably 10 to 20 degrees.
4) The imaging system 3, the collimation system 7 and the secondary imaging system 9 are arranged as shown in fig. 1, and the selected micro lens array 6 is placed at the position of the primary image surface 5, wherein the half mirror 4 is used for deflecting the light path, so as to prevent the systems before and after the micro mirror array 6 from being inseparable, and the parameters are as shown in table 4.
TABLE 4
| Surface type | Focal length/mm | Thickness/mm | Pore diameter/mm | Bevel angle of inclination/° |
| Inclined object plane 1 | \ | 16000 | 6800 | 12 |
| |
\ | 50 | 20 | |
| Imaging system | ||||
| 3 | 50 | 25.16 | 42.32 | \ |
| Semi-permeable and semi-reflecting (permeable) 4 | \ | 25 | 32.71 | -20 |
| |
\ | -30.67 | 22.26 | 10(θb) |
| Semi-permeable and semi-reflecting (reflecting) 4 | \ | 19.33 | 47.03 | \ |
| Collimation system 7 | 50 | 50 | 42.43 | \ |
| Collimating system exit pupil 8 | \ | 18.802(d') | 20 | \ |
| |
50 | 50 | 27.71 | \ |
| |
\ | \ | 19.97 | -19.95 |
5) Adjusting the mirror tilt angle theta of the micromirror array 6bAnd the distance d' between the exit pupil 8 of the collimation system and the main plane of the secondary imaging system 9, the size of the additional introduced trapezoidal distortion is controlled, and the trapezoidal distortion of the oblique imaging is compensated. The optical parameters, tilt angle θ of micromirror array 6, are shown in Table 4bWhen d' is 18.802mm, the trapezoidal distortion becomes zero as shown in fig. 4. As shown in fig. 5, the inclination angle θ of the micromirror array 6b15 deg., when d' is 28.6735mm, the trapezoidal distortion becomes zero.
In this example, d' and θ when keystone distortion is approximately zerobThe expression is satisfied:
θbis the mirror tilt angle of the micro-mirror array 6, and d' is the distance between the exit pupil of the collimating system and the principal plane of the secondary imaging system.
The above relation is shown in FIG. 6, and it can be seen that the magnitude of the keystone distortion is represented by θbDetermined together with d', different tilt angles theta can be used in the same systembThe micro-mirror array 6 eliminates the trapezoidal distortion, and the inclination angle theta of the micro-mirror array 6 can be adjustedbDividing the lens into a grade at intervals of 2 degrees for mass production, and selecting the micro-mirror with reasonable inclination angle when actually designing the lensThe lens array 6 changes d' to achieve the purpose of eliminating keystone distortion.
Claims (5)
1. An optical device for eliminating trapezoidal distortion based on a micro-reflector array is characterized by comprising a diaphragm (2), an imaging system (3), a semi-transparent semi-reflecting mirror (4), a micro-reflector array (6), a collimation system (7) and a secondary imaging system (9); the light that the object plane (1) sent passes through diaphragm (2), incide imaging system (3), the light passes through imaging system (3) and converges on half mirror (4), the light is imaged in image plane (5) position once after half mirror (4) transmission, place micro mirror array (6) in image plane (5) department once, the light incides on micro mirror array (6), the light reflects through micro mirror array (6), the reflection light is on half mirror (4) reflection collimation system (7), incide secondary imaging system (9) after collimation system (7), finally image in secondary image plane (10).
2. The keystone-canceling optical device according to claim 1, wherein the micromirror array (6) comprises a plurality of rows of micromirrors, each row having a width d on the order of 10um, the rows of micromirror having a reflective surface with a reflective slope at an inclination angle θbThe light ray perpendicularly incident on the micromirror array (6) is at 2 theta relative to the incident light raybIs emitted.
3. The micro-mirror array based keystone distortion-reducing optical device of claim 2, wherein the tilt angle θb＝10-20°。
4. The method for eliminating the trapezoidal distortion based on the micro-reflector array is characterized in that the micro-reflector array (6) is used for secondary imaging to eliminate the trapezoidal distortion, and the method comprises the following specific steps:
firstly, designing a collimation system (7) according to the size of a primary image surface (5);
designing a secondary imaging system (9) according to the size of the field of view of the collimation system (7);
step three, selecting the inclination angle thetabA micromirror array (6);
placing the micro-mirror array (6) at the primary image surface (5), reflecting the light by the micro-mirror array (6), reflecting the reflected light to the collimation system (7) by the semi-transparent semi-reflective mirror (4), and making the light enter the secondary imaging system (9) after passing through the collimation system (7) and finally imaging on the secondary image surface (10);
step five, adjusting the inclination angle theta of the micro-reflector array (6)bAnd the distance d' between the exit pupil (8) of the collimation system and the main plane of the secondary imaging system (9) controls the size of the additional introduced trapezoidal distortion to compensate the trapezoidal distortion in the inclined imaging.
5. The method for keystone distortion removal based on a micro mirror array of claim 4, wherein θ isb＝10-20°。
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| JP3489171B2 (en) * | 1994-01-20 | 2004-01-19 | 松下電器産業株式会社 | License reading device |
| CN1641406B (en) * | 2004-01-15 | 2012-09-26 | 长春方圆光电技术有限责任公司 | Large view field distortion-free palm print collecting system |
| US20070058229A1 (en) * | 2005-09-15 | 2007-03-15 | Russell Hudyma | Volumetric Three-Dimensional Display System |
| US9607363B2 (en) * | 2012-06-19 | 2017-03-28 | Ricoh Company, Ltd. | Projector, trapezoidal distortion correction method, and storage medium storing trapezoidal distortion correction program |
| DE102016100252B4 (en) * | 2016-01-08 | 2020-01-16 | Sypro Optics Gmbh | Projection system for display applications |
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