CN109782380B - Iris imaging system and iris identification module - Google Patents
Iris imaging system and iris identification module Download PDFInfo
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- CN109782380B CN109782380B CN201910196142.2A CN201910196142A CN109782380B CN 109782380 B CN109782380 B CN 109782380B CN 201910196142 A CN201910196142 A CN 201910196142A CN 109782380 B CN109782380 B CN 109782380B
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Abstract
The invention discloses an iris imaging system, which comprises a front component, a zoom component and a rear component; the iris imaging optical system is an imaging system combining a traditional optical system and a liquid optical system, and has good imaging quality and low distortion characteristic in a short-distance wide working range; the diopter of the zooming component is changed through the driving of an external voltage signal, the automatic focusing is realized by combining an image intelligent algorithm, the focusing speed is high, and the service life is long; the imaging system has simple and compact structure, convenient installation and adjustment and low cost.
Description
Technical Field
The invention relates to the field of biological identification, in particular to an iris imaging system and an iris identification module.
Background
Iris recognition belongs to the field of biological recognition, and is a biological recognition technology based on the iris of eyes, and the iris image texture information is collected by an optical system and processed to authenticate the identity of a user. Compared with other biological identification technologies, such as fingerprints, the method has the remarkable advantages of non-contact property, good stability and the like, and becomes one of the accurate identification technologies in the current identity characteristics. The difficulty in realizing the iris recognition technology lies in how to acquire clear and high-quality iris images on the premise of comfort of different users, so that an optical system for acquiring the high-quality iris images becomes a key point of iris recognition equipment.
The existing iris collecting optical system mainly comprises three types of fixed-focus optical systems, a traditional zooming optical system and a liquid optical system. The fixed-focus optical system has the advantages of good imaging quality, simple system and low cost, but has single working distance and limited application range. The traditional zoom optical system can meet the requirements of different working distance ranges, but the system has the defects of large volume, complex structure, high manufacturing cost, easy mechanical zooming, short abrasion life and the like, and is not beneficial to popularization. In a specific embodiment, the iris imaging lens comprises two lenses, but the iris imaging lens has low optical design freedom, is not easy to control optical aberration, and has poor lens imaging quality. In another specific embodiment, the iris imaging lens comprises three lenses, wherein the first lens and the second lens are cemented lenses, and the third lens is a rotationally symmetric aspherical lens. Compared with an iris imaging lens with a two-lens structure, the iris imaging lens with three lenses has the advantages that the optical design freedom degree is increased, the spherical aberration of an optical imaging system is controlled to a certain degree by adopting the aspheric lens, the imaging quality is improved, the lens processing technology is complex, the total length of the whole optical imaging system is too long, and the occupied space is large.
Although liquid optics can achieve the advantages of both systems, conventional liquid optics have the following problems: the working distance range is expanded to some extent but still is small, the imaging quality is poor, the image is dark, the exposure time is long and the volume is large under the adoption of an external light source. Therefore, the liquid optical system with good imaging quality, high image repeated acquisition times, simple structure, low cost, wide working distance range, large luminous flux, compact size and small volume becomes the key point of the current research.
Disclosure of Invention
The invention provides an iris imaging system combining a traditional optical system and a liquid optical system, which is an iris imaging system and an iris identification module with wide working distance range, good imaging quality and high cost performance.
The technical scheme of the invention is as follows: an iris imaging system comprises, arranged in order from an object side to an image side: a front component, a zoom component and a rear component;
the front component comprises a first lens with positive focal power, a second lens with positive focal power and a third lens with negative focal power, which are sequentially arranged from the object side to the image side;
the zoom component consists of a liquid lens with variable focal power;
the rear component comprises a fifth lens with negative optical focal length, a sixth lens with positive optical focal length, a seventh lens with negative optical focal length and an eighth lens with positive optical focal length which are arranged from the object side to the image side in sequence;
and the fifth lens, the sixth lens and the seventh lens are cemented to form a first cemented lens group.
Preferably, the focal length of said front component is fG1, the focal length of said zoom component is fG2, the focal length of said rear component is fG3, and when the optical focal length of zoom component is 0, the focal length of optical system is f, and it satisfies 5< | fG1/f |,0.4< | fG3/f | <1.0, | fG2| > 40.
Preferably, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, and the focal length of the optical system when the zoom component power is 0 is f, which satisfies 0.8< | f1/f | <1.2, 0.8< | f2/f | <1.3, and 0.05< | f3/f | < 0.7.
Preferably, the value of the outer diameter of the eighth lens element is D8, and the diameter of the exit pupil of the optical system is EP, which satisfies 0.5< D8/EP < 1.6.
Preferably, a diaphragm used for controlling the amount of light energy passing through is arranged between the third lens and the fifth lens, and the diaphragm can indirectly influence the resolving power of the optical system by controlling the intensity of light, so that certain image resolution capability is ensured.
Preferably, the refractive index parameters of the first lens and the second lens are nd1 and nd2 respectively, and satisfy 0.95< nd1/nd2< 1.15.
Preferably, a band-pass filter capable of enhancing near infrared light transmission and reducing visible light transmission is arranged between the front end of the first lens or the eighth lens and the imaging surface, so that the transmission rate of the lens in a near infrared band is improved, a response curve of a spectrum on the image sensor is most consistent with a spectrum curve of a light source, and the best iris image imaging quality is achieved.
The iris identification module comprises the iris imaging system and is characterized in that the iris identification module comprises the iris imaging system, and a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) image sensor is arranged at the image surface of the iris imaging system.
The invention has the beneficial effects that: the iris imaging system combining the traditional optical system and the liquid optical system has the advantages of wide working distance range, good imaging quality and high cost performance, and meanwhile, the iris imaging optical system still has good imaging quality and low distortion characteristic in a short-distance wide working range; the diopter of the zooming component is changed through the driving of an external voltage signal, and the automatic focusing can be realized by combining an image intelligent algorithm, and the focusing speed is high and the service life is long; the imaging system has simple and compact structure, convenient installation and adjustment and low cost; and the imaging module can be matched with near-infrared LED light sources with different frequency spectrums and different CMOS image sensing devices, so that iris identification application under different environmental occasions is met.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Drawings
Further objects, features and advantages of the present invention will become apparent from the following description of embodiments of the invention, with reference to the accompanying drawings, in which:
fig. 1 schematically shows a structural view of an imaging system of the present invention.
Fig. 2a to 2b are schematic diagrams showing optical performance of an embodiment of the imaging system of the present invention at a working distance of 1000mm, wherein fig. 2a is a graph showing MTF transfer function characteristics of the embodiment, and fig. 2b is a graph showing field distortion of the embodiment.
Fig. 3 a-3 b schematically show optical performance graphs of an embodiment of the imaging system of the present invention at a working distance of 612mm, wherein fig. 3a is a graph of MTF transfer function characteristics of the embodiment, and fig. 3b is a graph of field distortion of the embodiment.
Fig. 4a to 4b are schematic diagrams showing optical performance of an embodiment of the imaging system of the present invention at a working distance of 297mm, wherein fig. 4a is a graph showing MTF transfer function characteristics of the embodiment, and fig. 4b is a graph showing field distortion of the embodiment.
Detailed Description
The objects and functions of the present invention and methods for accomplishing the same will be apparent by reference to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it can be implemented in different forms. The nature of the description is merely to assist those skilled in the relevant art in a comprehensive understanding of the specific details of the invention.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals denote the same or similar parts, or the same or similar steps.
The invention provides an iris imaging system, as shown in fig. 1, comprising, arranged in order from an object side to an image side: a front cell G1, a zoom cell G2 and a rear cell G3.
The front component G1 comprises a first lens 1 with positive focal power, a second lens 2 with positive focal power and a third lens 3 with negative focal length, which are arranged in sequence from the object side to the image side.
The zoom component G2 is constituted by a variable power liquid lens 4.
The rear component G3 includes a fifth lens 5 having a negative optical focal length, a sixth lens 6 having a positive optical focal length, a seventh lens 7 having a negative optical focal length, and an eighth lens 8 having a positive optical focal length, which are arranged in order from the object side to the image side.
The fifth lens 5, the sixth lens 6, and the seventh lens 7 are cemented to form a first cemented lens group C1.
The focal length of front component G1 is fG1, the focal length of zoom component G2 is fG2, the focal length of rear component G3 is fG3, when the optical focal length of zoom component G2 is 0, the focal length of the optical system is f, and the optical system satisfies 5< | fG1/f |,0.4< | fG3/f | <1.0, | fG2| >40
The focal length of the first lens 1 is f1, the focal length of the second lens 2 is f2, the focal length of the third lens 3 is f3, and the focal length of the optical system when the focal power of the zoom component G2 is 0 is f, which satisfies 0.8< | f1/f | <1.2, 0.8< | f2/f | <1.3, and 0.05< | f3/f | <0.7
The value of the outer diameter of the lens of the eighth lens 8 is D8, the diameter of the exit pupil of the optical system is EP, and the requirement that the diameter of the exit pupil is 0.5< D8/EP <1.6 is met. When the imaging system satisfies the above relationship, the volume of the imaging lens can be made compact and small, the system manufacturing cost can be reduced, and the miniaturization of the iris recognition device can be realized.
Preferably, a diaphragm is arranged between the third lens 3 and the fifth lens 5 for controlling the amount of light energy passing through. The diaphragm can indirectly influence the resolving power of the optical system by controlling the intensity of light rays, thereby ensuring certain image resolution capability.
The refractive index parameters of the first lens 1 and the second lens 2 are nd1 and nd2 respectively, and 0.95< nd1/nd2<1.15 is satisfied. When the optical system adopts the refractive index ratio, the spherical aberration changes under different working distances can be balanced to obtain good imaging quality under different working distances, and the material taking cost is low.
A band-pass filter capable of enhancing the transmission of near infrared light and reducing the transmission of visible light is arranged at the front end of the first lens 1 or between the eighth lens 8 and an imaging surface of the imaging system, so that the transmission rate of the lens in a near infrared band is improved, the response curve of a spectrum on the image sensor is most consistent with the spectrum curve of a light source, and the best imaging quality of an iris image is achieved.
An iris identification module comprises the iris imaging system, and a CCD or CMOS image sensor is arranged on an image surface of the iris imaging system.
Examples
The practical effects achieved by the embodiments of the iris imaging system of the present invention are illustrated by taking the working distances of 1000mm, 612mm and 297mm as examples.
When the working distance is 1000mm, it can be seen from fig. 2a that the lens MTF transfer function curves are compact and straight, all the field curves are less than 1 lattice scattered on the ordinate axis corresponding to 80lp/mm, and the lowest MTF curve is greater than 0.5 at 80 lp/mm. And the area enclosed by the ordinate of the modulation transfer function value (module of the OTF) on the left side and the abscissa of the line pair frequency (spatial frequency in cycles per mm) below is as much as possible, which shows that the system has excellent imaging quality and good consistency under all fields of view, and the iris image is uniform and has no particularly poor area. From fig. 2b it can be seen that the field curvature of the imaging system is significantly less than 0.1mm, the optical relative distortion curves are superimposed and the maximum optical relative distortion is also significantly less than 1%.
When the working distance is 612mm, it can be seen from fig. 3a that the lens MTF transfer function is compact and straight relative to the curves, all the field curves are less than 1.5 grids scattered on the ordinate axis corresponding to 80lp/mm, and the lowest MTF curve is greater than 0.5 at 80 lp/mm. And the area enclosed by the ordinate of the modulation transfer function value (module of the OTF) on the left side and the abscissa of the line pair frequency (Spatial frequency in cycles per mm) below is as much as possible, which shows that the system has excellent imaging quality and good consistency under all fields of view, and the iris image is uniform and has no particularly poor area. From fig. 3b it can be seen that the field curvature of the imaging system is significantly less than 0.1mm, the optical relative distortion curves are superimposed and the maximum optical relative distortion is also significantly less than 1%.
At a working distance of 297mm, it can be seen from fig. 4a that the lens MTF transfer function curves are relatively compact and straight, all the field curves are less than 1.5 grids scattered on the ordinate axis corresponding to 80lp/mm, and the lowest MTF curve is greater than 0.5 at 80 lp/mm. And the area enclosed by the ordinate of the modulation transfer function value (module of the OTF) on the left side and the abscissa of the line pair frequency (Spatial frequency in cycles per mm) below is as much as possible, which shows that the system has excellent imaging quality and good consistency under all fields of view, and the iris image is uniform and has no particularly poor area. From fig. 4b, it can be seen that the field curvature of the imaging system is significantly less than 0.1mm, the coincidence degree of each spectral curve of the field curvature is good, the optical relative distortion curves are coincident together, and the maximum optical relative distortion is also significantly less than 1%.
Compared with the experimental results, the iris imaging system and the iris identification module thereof expand the working distance of the iris identification device from the general 1000mm to the range of 297-1000mm, the range is a main use area, the imaging quality at each working distance is excellent, the lens MTF transfer function curve is relatively compact and straight, the lowest MTF curve is more than 0.5 at the position of 80lp/mm, the field curvature of the imaging system is obviously less than 0.1mm, the optical relative distortion is obviously less than 1%, and the iris identification requirement of an iris identification algorithm on an iris image acquired at the front end of the device is met. In addition, the imaging device can well image when the imaging depth is less than 297mm or more than 1000mm, so that the working range is enlarged, the use feeling of a user is improved, and a required space is provided for upgrading and updating software and hardware of equipment in the later period.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like, which are within the spirit and principle of the present invention, will be apparent to those skilled in the art and are included in the scope of the present invention.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
Claims (7)
1. An iris imaging system comprises, arranged in order from an object side to an image side: a front component, a zoom component and a rear component;
the front component comprises a first lens with positive focal power, a second lens with positive focal power and a third lens with negative focal power, which are sequentially arranged from the object side to the image side;
the zoom component consists of a liquid lens with variable focal power;
the rear component comprises a fifth lens with negative optical focal length, a sixth lens with positive optical focal length, a seventh lens with negative optical focal length and an eighth lens with positive optical focal length which are arranged from the object side to the image side in sequence;
the fifth lens, the sixth lens and the seventh lens are cemented to form a first cemented lens group, wherein,
the focal length of the front component is fG1, the focal length of the zoom component is fG2, the focal length of the rear component is fG3, and when the optical focal length of the zoom component is 0, the focal length of the optical system is f, which meets the requirements of 5< | fG1/f |,0.4< | fG3/f | <1.0, and | fG2| > 40.
2. The iris imaging system of claim 1, wherein the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, and the focal length of the optical system at the time of zoom component power of 0 is f, which satisfies 0.8< | f1/f | <1.2, 0.8< | f2/f | <1.3, and 0.05< | f3/f | < 0.7.
3. The iris imaging system of claim 1, wherein the outer diameter value of the eighth lens element is D8, the exit pupil diameter of the optical system is EP, and 0.5< D8/EP <1.6 is satisfied.
4. The iris imaging system as claimed in claim 1, wherein a diaphragm for controlling the amount of light energy passing through is disposed between the third lens and the fifth lens, and the diaphragm can indirectly influence the resolving power of the optical system by controlling the intensity of light, thereby ensuring a certain image resolution capability.
5. The iris imaging system of claim 1, wherein the refractive index parameters of the first lens and the second lens are nd1 and nd2 respectively, and satisfy 0.95< nd1/nd2< 1.15.
6. The iris imaging system of claim 1, wherein a band pass filter capable of enhancing the transmission of near infrared light and reducing the transmission of visible light is arranged between the front end of the first lens or the eighth lens and the imaging surface, so as to improve the transmission rate of the lens in the near infrared band, so that the response curve of the spectrum on the image sensor is most consistent with the spectrum curve of the light source, thereby achieving the best iris image imaging quality.
7. An iris identification module of an iris imaging system as claimed in any one of claims 1 to 6, wherein the iris identification module comprises the iris imaging system, and a CCD or CMOS image sensor is arranged at an image plane of the iris imaging system.
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| TWI701474B (en) | 2019-07-17 | 2020-08-11 | 大立光電股份有限公司 | Optical imaging lens assembly, image capturing unit and electronic device |
| TWI704389B (en) | 2019-08-14 | 2020-09-11 | 大立光電股份有限公司 | Optical photographing lens assembly, image capturing unit and electronic device |
| KR20210099916A (en) * | 2020-02-05 | 2021-08-13 | 엘지이노텍 주식회사 | Imaging lens |
| CN113885167B (en) * | 2021-09-01 | 2023-02-03 | 苏州协尔智能光电有限公司 | Fixed-focus imaging system and fixed-focus imaging lens |
| CN114924376B (en) * | 2022-06-13 | 2023-12-08 | 苏州协尔智能光电有限公司 | Barrel lens optical system |
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