CN116719160A - Asymmetric penta-mirror single-view point refraction and reflection infrared peripheral vision system and method - Google Patents

Abstract

The application relates to an asymmetric penta-mirror single-viewpoint refraction and reflection infrared peripheral vision system and method, wherein the method comprises the following steps: selecting proper infrared imaging components and lens parameters thereof according to the requirements of spatial resolution and action distance aiming at the temperature difference between a target and a background in a specific task; determining the precise position of the infrared imaging assembly; determining the specific size of an asymmetric pentad reflector; analyzing whether the view field is blocked or not according to the obtained structural parameters; and optimizing the structure according to the non-shielding analysis result of the field of view until a non-shielding asymmetric pentad reflecting mirror is obtained. The application can realize non-shielding, seamless and non-blind area infrared imaging of horizontal 360 DEG and pitching + -29 DEG visual fields, provides an omnibearing and large-pitching vehicle-mounted real-time Zhou Shigong external image, and can be used in the civil and military fields of intelligent transportation, automatic driving, military reconnaissance and the like.

Description

Asymmetric penta-mirror single-view point refraction and reflection infrared peripheral vision system and method

Technical Field

The application relates to the field of vehicle-mounted peripheral vision infrared imaging application, in particular to an asymmetric five-mirror single-viewpoint refraction and reflection infrared peripheral vision system and method.

Background

The infrared imaging is not influenced by environmental illumination change, glare, backlight, smoke dust and the like, has certain capability of resisting small rain, snow and mist, is a main technical means for sensing scenes all the day under the conditions of night and low visibility, and can obviously enhance the safe driving capability of vehicles. In recent years, the infrared focal plane detector in China is developed greatly, the performances of pixel size, dimension, thermal sensitivity and the like are advanced internationally, the infrared focal plane detector has an important role in international market share, and the scale application of the low-cost infrared focal plane detector in China in vehicle driving is also on a daily basis. The infrared peripheral vision system can provide surrounding 360-degree scene infrared images, eliminates visual blind areas of vehicle driving, can realize functions of positioning, map building, obstacle avoidance, path planning, navigation and the like by means of an algorithm, and meets urgent requirements of intelligent driving and autonomous driving.

According to the technical route, the infrared peripheral vision systems can be divided into three categories:

(1) a time-sharing multi-view infrared peripheral vision system. The infrared optical system and the infrared focal plane detector (the infrared imaging component are called as infrared imaging components) rotate 360 degrees around a fixed shaft vertical to the optical axis, or the optical scanner rotates 360 degrees to reflect incident radiation to the infrared imaging component, and then video sequences with partial overlapping contents are spliced to obtain a panoramic image. Typical examples are infrared search tracking systems, such as the VAMPIR system in France, the SPIR-TAS system in Israel, the SIRIUS system in Netherlands, etc.;

(2) a split aperture multi-view infrared peripheral vision system. The integrated or distributed arrangement of the plurality of infrared imaging assemblies covers the 360-degree azimuth view field, and video images output by the imaging assemblies are spliced. A typical example is an on-board panoramic situation awareness system, such as DVE WIDE from leonado DRS company, usa, that compactly integrates 3 infrared imaging assemblies together to obtain a large field of view of 321 ° (107 ° ×3) ×30 °;

(3) a single viewpoint catadioptric infrared peripheral vision system. The quadric surface reflector is combined with a conventional refractive infrared optical system and an infrared focal plane detector, and gaze imaging of a 360-degree azimuth view field can be realized by using only a single area array detector without a motion scanning mechanism. A typical example is an infrared periscope, such as the us naval laboratory, using a single 2048 x 2048 mid-wave infrared focal plane detector, which has been developed to provide a 360 ° horizontal field of view, -10 ° to +30° pitch field of view. However, due to the non-linearity of quadric mirrors, the detection distance of such systems varies with pitch angle, and the detection distance is closely related to the size of a single focal plane detector.

Currently, foreign researchers have developed four-sided, five-sided and ten-sided single-view constraint catadioptric periscope systems working in the visible light band, which have the following common characteristics: the polygon mirror forms a regular polyhedron with a symmetrical structure and a bottom angle of 45 degrees; the focal length of the camera lens corresponding to each mirror is the same (namely, the angle of view is equal); the vertical distance between each camera viewpoint and the bottom surface, and the horizontal distance to the central axis are the same, and the camera viewpoint is the lens center (when the lens is a thin lens) or the principal point of the object side of the lens (when the lens is a lens group). The essence of the symmetrical polygon mirror single-view-point constraint catadioptric structure is that virtual images formed by a plurality of camera view points with the same focal length are overlapped on the same point by utilizing a regular polygon mirror.

Taking a fully symmetrical penta-mirror as an example, as shown in FIG. 1 (a), P ₁ 、P ₂ 、P ₃ 、P ₄ 、P ₅ The camera view point simplified by adopting the pinhole imaging model has the view point directionVertically downward. Each prism face corresponding to the view point is a plane reflecting mirror with a mirror face facing outwards, and an included angle of 45 degrees is formed between the plane reflecting mirror and the plane. All the viewpoints are positioned on the intersection line of the horizontal plane where the pyramid vertex is positioned and the vertical plane where the angular bisector of the corresponding prismatic surface is positioned, virtual viewpoints obtained by imaging the viewpoints in different directions through the plane mirror are overlapped to be the same point, and the point P' becomes the unique viewpoint of the system. Assuming that the observer is located at point P', a peripheral seamless panoramic image can be observed from this point by a plurality of cameras of different imaging directions. FIG. 1 (b) is a front projection view of two adjacent mirrors of FIG. 1 (a), P ₁ And P ₂ Virtual images of the two viewpoints, which are axisymmetric with respect to the mirror plane, are positioned on a vertical line OO ' between the vertex O ' and the bottom surface, and are overlapped at a point P ', and single viewpoint constraint can be realized by constructing a constraint relation between the plane mirror and the camera.

The dual-band split aperture multi-viewpoint periscope system WolfPack developed by Tonbo Imaging corporation of the united states uses 9 sets of low-light CMOS and uncooled infrared Imaging components, respectively. Compared with the split-aperture and multi-view periscope system, the split-aperture and single-view periscope system constructed by introducing the reflecting surface has the advantages that:

(1) Parallax between different cameras can be effectively eliminated;

(2) The panoramic image of the horizontal 360-degree view field can be directly obtained without image stitching;

(3) The imaging method can ensure that the object images in the horizontal 360-degree view field correspond to each other one by one, the imaging of the same object is unique, the problem of cross-mirror tracking is avoided, the credibility of the target in the panoramic image is improved, the identification and tracking of the target of interest are facilitated, and the quantitative measurement of the direction and the motion state of the target is facilitated.

Based on the prior art, how to integrate the advantages of the split-aperture multi-viewpoint periscope and the single-viewpoint catadioptric periscope, and according to the actual conditions of high requirements on the front detection distance and low requirements on the rear detection distance in vehicle-mounted application, the improvement on the periscope system is worth researching.

Disclosure of Invention

In order to solve the problems, the application provides an asymmetric five-mirror single-view point refraction and reflection infrared peripheral vision system and method, which are designed for a split-aperture single-view point asymmetric five-mirror refraction and reflection infrared peripheral vision system according to the practical situations of high requirements on front detection distance and low requirements on rear detection distance in vehicle-mounted application.

The technical scheme of the application is as follows:

a design method of an asymmetric pentad reflector comprises the following steps:

aiming at the temperature difference between a target and a background in a specific task, selecting a proper infrared imaging assembly and lens parameters thereof according to the requirements of spatial resolution and action distance;

step (2) selecting a proper combination of the height m of the virtual viewpoint P ', the distance d from the center point of the bottom surface to the side length, the height h of the tailorable mirror surface, the height l of the equivalent viewpoint P of the imaging component, the horizontal distance l between the equivalent viewpoint P and the structural vertex O', the vertical field angle 2 epsilon of the imaging component and the lens diameter k, and the inclination angle theta of the lens according to the virtual viewpoint P ', the height h of the equivalent viewpoint P of the infrared imaging component and the horizontal distance l between the equivalent viewpoint P and the structural vertex O', so as to determine the accurate position of the infrared imaging component, and then determining the distance d from the center point of the bottom of the structure to the side length and the tailorable mirror surface height s according to the reflection field, thereby determining the specific size of the asymmetric pentad reflecting mirror;

step (3) analyzing whether the view field is blocked or not according to the structural parameters obtained in the step (2);

and (4) optimizing the structure according to the unobstructed analysis result of the field of view until an unobstructed asymmetric penta-prismatic table reflector is obtained.

Further, in the step (2), according to the combination of different mirror inclination angles θ and virtual viewpoint heights m, a horizontal distance l from the central axis to the infrared imaging component and a vertical height h from the bottom surface are determined, where the expression is:

l＝2(dtanθ-m)sinθcosθ；

h＝2dsinθcosθ+(sin ² θ-cos ² θ)m；

the expression for the tailorable mirror height s is:

further, in step (3), the unobstructed analysis includes:

when calculating the current parameters, the infrared imaging component just does not image the vertical field angle epsilon of the infrared imaging component ₁ '、ε ₂ ' if epsilon is compared with the actual vertical angle epsilon ₁ '＜ε＜ε ₂ ' the non-shielding imaging can be realized under the structure; wherein:

wherein:

the application also relates to an application of the asymmetric pentad reflecting mirror, the asymmetric pentad reflecting mirror meeting single-viewpoint constraint and the infrared lenses with different focal lengths reflect and converge scene radiation in five directions to five sets of vertically placed infrared focal plane detectors, and the optical center of the infrared lens coincides with the center of the infrared focal plane detector, so that the center point (C _x ,C _y ) Satisfy the following requirements

The coordinates of the image (x, y) are projected as cylindrical surfaces, and the coordinates are (x ', y');

front and left and right side view field focal length f ₁ Conversion formula at=5.8 mm:

left rear, right rear field of view focal length f ₂ Conversion formula at=4.1 mm:

the application also relates to an asymmetric pentad reflecting mirror which is obtained according to the design method.

Further, the device comprises a disc platform, a specular reflection area, an infrared imaging component and a central column shaft;

the infrared imaging assemblies are fixed on the disc platform, a certain horizontal distance and a certain vertical distance are kept between the infrared imaging assemblies and the central column shaft, and the specular reflection areas are arranged around the central column shaft;

the mirror reflection area is separated and comprises a reflector bracket and a reflector surface; or the mirror reflection area is integral, and a high-reflectivity film is plated on the surface after the mirror reflection area is processed in an integral molding mode;

the reflecting mirror surfaces correspond to the infrared imaging components and form a certain included angle; each infrared imaging component collects infrared radiation reflected by the corresponding reflecting mirror surface to form a 360-degree infrared peripheral vision image.

Further, different numbers of first adjusting rings are placed on the central column shaft, and the heights of the infrared imaging assemblies are adjusted; and the connection part of the single infrared imaging component and the disc platform is provided with different numbers of second adjusting rings, so that the vertical height of the single infrared imaging component is adjusted.

The application also relates to an asymmetric pentahedron single-view point refraction and reflection infrared peripheral vision system which comprises the asymmetric pentahedron reflector.

The application also relates to application of the asymmetric pentahedron single-view point refraction and reflection infrared peripheral vision system, and 360-degree peripheral vision field is obtained by using the asymmetric pentahedron reflector.

The application also relates to an image processing method, which is used for obtaining an image according to the asymmetric penta-mirror single-viewpoint refraction and reflection infrared peripheral vision system and comprises the following steps:

firstly, one of the focal lengths of the image is zoomed, the front, left and right side view field information is reserved, and after cylindrical projection, one of the focal lengths is zoomedIs scaled and sampled, and the scaling factor gamma is the vertical field angle epsilon of the infrared imaging component corresponding to the first focal length and the second focal length ₁ 、ε ₂ The decision, the formula is:

in order to obtain a seamless infrared peripheral vision image, the image of the second focal length is aligned with the center of the image of the first focal length after being amplified, and redundant fields of view are matched and cut, so that the seamless peripheral vision infrared image can be obtained;

carrying out uniform gray balance on the peripheral infrared image; taking infrared images collected simultaneously in five directions, and respectively calculating average value mu of the infrared images _i (i=1, 2,3,4, 5) and variance σ _i (i=1, 2,3,4, 5), the average value μ of the 5 frames of infrared images is obtained _average Mean variance sigma _average The expression is as follows:

respectively for 5 frames of image I _i (i=1, 2,3,4, 5) gray balance, output result is O _i (i=1, 2,3,4, 5) with the expression:

most of the time, a driver ensures safe driving by observing the front side, the left side and the right side of a road, so that a front view camera, a left side camera and a right side camera in a peripheral view system are required to have a longer action distance, so that road surface information can be perceived as early as possible, obstacle avoidance operation can be performed quickly, and the action distance requirement on a rear view camera is relatively low.

According to the practical situations of high requirements on front detection distance and low requirements on rear detection distance in vehicle-mounted application, the design scheme of the split-aperture single-viewpoint asymmetric five-mirror refraction and reflection infrared peripheral vision system is provided, the front view field and the left view field are 64 degrees, the rear view field is two 84-degree view fields, and the front view field and the left view field and the right view field are combined to form a peripheral view field with 360 degrees in horizontal direction and +/-29 degrees in pitching direction. Aiming at uncooled infrared imaging assemblies with different focal lengths, the structural design of an asymmetric pentahedron is completed, and an asymmetric refraction and reflection periscope structural theoretical model meeting single-viewpoint constraint is established; the system mechanical structure with adjustable and aligned view points is designed, the elements of projection conversion and image processing of the system are analyzed, and the comprehensiveness, the authenticity and the credibility of the system are improved.

Drawings

FIG. 1 is a prior art diagram of a single viewpoint constraint of a fully symmetric penta-mirror; wherein, (a) represents a fully symmetrical penta-mirror; (b) a front projection of adjacent mirrors;

FIG. 2 is a graph of MRTD calculation results according to an embodiment of the present application; wherein, (a) represents detection distances of the infrared lenses with focal lengths of 4.1mm, 5.8mm and 9.1mm at 50% detection probability; (b) Representing the horizontal field angle corresponding to the infrared lens with focal length of 4.1mm, 5.8mm and 9.1 mm;

FIG. 3 is a schematic view of the field of view composition of a system according to an embodiment of the present application;

FIG. 4 is a schematic diagram of the geometry of an asymmetric penta-mirror of an embodiment of the present application;

FIG. 5 is a schematic diagram of the parameter definition of an asymmetric penta-mirror structure according to an embodiment of the present application; wherein, (a) is a three-dimensional map; (b) a side projection two-dimensional map;

FIG. 6 is a non-occlusion imaging analysis of an embodiment of the present application;

FIG. 7 is a flow chart of a design of an asymmetric penta-mirror structure according to an embodiment of the present application;

FIG. 8 is a schematic representation of the conversion of a planar projection to a panoramic image in accordance with an embodiment of the present application; wherein, (a) is a planar image in five directions; (b) is a panoramic image after cylindrical projection;

FIG. 9 is a schematic diagram of the structure of one of the asymmetric penta-mirrors according to the embodiment of the present application;

FIG. 10 is a schematic view of a part of a non-fully symmetrical penta-mirror according to an embodiment of the present application;

FIG. 11 is a diagram showing the relationship between the center principal axis of an asymmetric penta-mirror and the mirror support in accordance with one embodiment of the present application;

FIG. 12 is a schematic view of the center principal axis of one of the asymmetric penta-mirrors according to an embodiment of the present application;

fig. 13 is a schematic diagram of imaging results of an embodiment of the present application.

Detailed Description

The following description of the embodiments will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the application. Based on the embodiments, all other embodiments that may be obtained by a person of ordinary skill in the art without making any inventive effort are within the scope of the present application.

Unless otherwise defined, technical or scientific terms used in the embodiments of the present application should be given the ordinary meaning as understood by one of ordinary skill in the art. The terms "first," "second," and the like, as used in this embodiment, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that elements or items preceding the word are included in the element or item listed after the word and equivalents thereof, but does not exclude other elements or items. "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. "upper", "lower", "left", "right", "transverse", and "vertical", etc. are used only with respect to the orientation of the components in the drawings, these directional terms are relative terms, which are used for descriptive and clarity with respect thereto and which may vary accordingly with respect to the orientation in which the components are disposed in the drawings.

Example 1

The design of the asymmetric penta-mirror single-viewpoint refraction and reflection infrared peripheral vision system of the embodiment is as follows:

first, an appropriate infrared lens is selected according to a pedestrian detection distance when the vehicle is driven. Assume that the pedestrian size is 0.5×1.7m ² When the detection probability is calculated by using a Minimum Resolvable Temperature Difference (MRTD) formula and 50% of the detection probability, the temperature 333K, the background temperature 298K, the infrared detector pixel size 640×512, the pixel size 12 μm and the Noise Equivalent Temperature Difference (NETD) 40mk, the curve delta T '(R) of the equivalent blackbody temperature difference delta T' between the pedestrian and the background and the distance R and the MRTD (R) are shown as the graph in fig. 2 (a), at this time, the detection distances of the infrared lenses with focal lengths of 4.1mm, 5.8mm and 9.1mm are 145m, 200m and 320m respectively, and the corresponding horizontal field angles are 86 DEG, 67 DEG and 46 DEG respectively, as shown in the graph in fig. 2 (b). The MRTD calculation process is as follows:

when the vehicle runs at night and under the condition of low visibility, the surrounding objects can be effectively detected by utilizing the infrared imaging technology. And using pedestrians as detection objects, analyzing the detection distance of the infrared imaging assembly, and designing or selecting corresponding parameters of the infrared imaging assembly according to actual detection requirements.

In an infrared imaging system, evaluating the temperature resolution and the spatial resolution of the system by using the MRTD, wherein the expression of the MRTD is as follows:

in the formula (1), NETD is the noise equivalent temperature difference, SNR _TH For the observer to distinguish the threshold signal-to-noise ratio of the band, alpha, beta are the instantaneous angles of view in the horizontal and vertical directions, t _e For human eye integration time, f _p For frame rate τ _d For dwell time, Δf is the noise equivalent bandwidth. MTF is the modulation transfer function of an infrared optoelectronic system, where the diffraction effects in the optical system are mainly considered, so the MTF of the system can be expressed as:

wherein f _c D/λ, which represents the spatial cut-off frequency of the optical system, D is the effective aperture of the optical system, and λ is the average operating wavelength. Using a radiation emittance M meterShowing the radiant power emitted to the hemispherical space by the unit surface area of the radiation target, the emittance of the gray body with epsilon and the temperature T is as follows:

c in formula (3) ₁ ＝3.7418×10 ⁸ W·μm ⁴ /m ² ，c ₂ ＝1.4388×10 ⁴ μm.K. Infrared radiation is affected by absorption and scattering by the atmosphere, and changes in temperature are a function of distance R due to changes in radiant energy. The transmittance of infrared radiation through the atmosphere can be expressed as:

τ(R)＝exp(-p·R) (4)

where p is the atmospheric attenuation coefficient, related to the wavelength of the infrared radiation, the geographic location where it is located, the atmospheric pressure, temperature, humidity, season, climate conditions, etc. The radiation emergent degree M '(T') of the radiation target after the radiation target is transmitted by the atmosphere is as follows:

M'(T')＝τ(R)·M(T) (5)

in practical application, the background temperature is usually at 220K-320K, and c is the value of infrared band of 8-12 μm ₂ > λT, equation (5) can be expressed as:

assuming the target temperature is T _t The background temperature is T _b Then the equivalent blackbody temperature difference Δt' to the detector target and background is:

ΔT'＝T _t '-T _b ' (7)

wherein T is _t '、T _b ' represents the equivalent blackbody temperature of the radiation of the target and background, respectively, after atmospheric transmission. When the target width is W and the target height is H, the target equivalent line pair number n can be divided according to the Johnson criterion _e Dividing the object into widths H/2n _e The aspect ratio of the target in the MRTD formula of the distance performance is corrected, and the corrected MRTD _target The method comprises the following steps:

where γ is the aspect ratio of the target equivalent stripe, expressed as:

at the detection distance R, the limit spatial frequency f of the target _T Can be expressed as:

let the acting distance of the infrared system be R, the energy radiated by the target and the background will be affected by the atmospheric attenuation, and there is a relation curve delta T' (R) between the equivalent temperature difference and the acting distance R. MRTD after correction according to detection probability, observation level and actual target size _target (f) The corresponding limit spatial frequency f can be obtained _T The function with R is thus obtained, which, in combination with DeltaT' (R), can be used to solve the range of the infrared system.

As shown in fig. 2, according to the calculation result, in order to obtain 360 ° peripheral view field by using five asymmetric reflectors, the front view and the left and right sides are 64 ° view field (focal length 5.8 mm), and the back view is regarded as two 84 ° view fields (focal length 4.1 mm), and the view field is shown in fig. 3.

The traditional vehicle-mounted vision exists Blind area detection area, mainly is that windshield both sides slope A post shelters from A post Blind area (see the blank Spot I in FIG. 3) and rear-view mirror Blind area (see the blank Spot II in FIG. 3) that causes, and these Blind areas can effectively be eliminated to the system of this embodiment design. The parameters of the infrared detector component selected by the system are shown in table 1.

Table 1 performance parameters of infrared imaging assemblies used in the system of this example

Based on detection distance analysis and spatial resolution requirements, an infrared imaging assembly is selected, and the structural design of the asymmetric pentahedron is carried out according to single-viewpoint constraint requirements. Three sets of focal lengths f ₁ Equivalent viewpoint P of=5.8mm ₁ 、P ₂ 、P ₃ The included angle of alpha is formed between the corresponding prismatic surface and the horizontal plane, namely the inclination angle of the mirror surface; two sets of focal lengths f ₂ Equivalent viewpoint of=4.1 mm is P ₄ And P ₅ The corresponding prism face forms a mirror inclination angle beta with the horizontal plane. The different focal length lens combinations make the bottom of the penta-mirror structure appear as asymmetric pentagons with equal vertex-to-center distances and unequal side lengths and inner angles, and the infrared imaging assemblies are at different heights in the vertical direction, as shown in fig. 4. The structural design key point of the single-viewpoint constraint asymmetric penta-mirror is to adjust the spatial positions of different mirror inclination angle combinations (alpha, beta) and infrared imaging components so that the viewpoint P ₁ 、P ₂ 、P ₃ 、P ₄ 、P ₅ The resulting virtual image coincides with point P'.

In order to facilitate calculation of the structural parameters of the asymmetric penta-mirror under the single viewpoint constraint, the infrared imaging assembly in one direction in fig. 4 is selected for analysis. For the sake of no loss of generality, let the equivalent viewpoint of the imaging component be P, the corresponding mirror tilt be θ, and other structural parameter definitions as shown in fig. 4 and 5 and listed in table 2, including: virtual viewpoint P 'height m, bottom center point to side length distance d, tailorable mirror height s (height above red virtual line in fig. 5 (b)), height h of imaging element equivalent viewpoint P, and horizontal distance l from structure vertex O', vertical field angle 2 epsilon of imaging element, lens diameter k.

TABLE 2 structural parameters of asymmetric penta-mirrors

The overall size of the penta-mirror structure is determined by the mirror tilt angle θ, the distance d from the bottom center point to the side length, and the virtual viewpoint height m. Assuming that the left-hand edge ray of the vertical field angle 2ε is located just at the bottom C of the structure, the mirror facet corresponding to the point of view P is the plane ABO 'in FIG. 5 (a), and the side projection of this mirror facet is CO' in FIG. 5 (b). According to the combination of different mirror inclination angles theta and virtual viewpoint heights m, the horizontal distance (approximately equal to the horizontal distance l between the equivalent viewpoint P and the structural vertex O') and the vertical height (approximately equal to the height h of the equivalent viewpoint P) from the bottom surface of the infrared imaging component can be determined, and the expression is as follows:

l＝2(dtanθ-m)sinθcosθ (11)

h＝2dsinθcosθ+(sin ² θ-cos ² θ)m (12)

assuming that the right boundary line of the vertical viewing angle intersects the reflecting surface at the point Q when the formulas (1) and (2) are satisfied, the mirror surface area above the horizontal plane where the point Q is located, that is, the area above the red imaginary line in fig. 5 (b) does not participate in imaging, and is tailorable in actual use, therefore, the actual usable structure is represented as an asymmetric pentagonal frustum, while the plane mirror is represented as an isosceles trapezoid, and the expression of the tailorable mirror surface height s is:

the small mirror inclination angle theta or the high virtual viewpoint height m can lead to the image shielding of the reflection prism surface reflection imaging component to image surrounding scenes; when the inclination angle θ of the mirror surface is too large or the virtual viewpoint height m is too low, the size of the prism table needs to be increased to ensure the integrity of imaging, so that imaging analysis is required to be carried out without shielding the lens to compromise the adjustment of the values of θ and m.

According to the critical angle of the field of view when the infrared imaging assembly just does not image itself by the reflection analysis of the light in the geometrical optics, as shown in fig. 6, the lens diameter k of the infrared imaging assembly corresponding to the equivalent viewpoint P is made to be a line segment MN, the critical incident light Ray i (Ray i in fig. 6) just passes through the lens boundary point M, and the incident angle phi is used at the point Q ₁ The reflected light enters the infrared imaging assembly after passing through the lens boundary point N; critical incident Ray II (Ray II in FIG. 6) at C with incident angleφ ₂ The reflected light enters the infrared imaging assembly after passing through the lens boundary point M. Under this condition, let angle ++mpn=2ε'.

Obtaining phi according to geometric relation ₁ ＝θ-ε'、φ ₂ =θ+ε', the following geometric relationship is also satisfied:

two values of ε' can be solved according to equation (4), respectively let ε be ₁ ' and ε ₂ ' obtaining:

wherein the method comprises the steps of

When the current parameters are calculated according to the formula (5) and the formula (6), the infrared imaging component just does not image the vertical field angle epsilon of the infrared imaging component ₁ '、ε ₂ ' when compared with the actual vertical angle epsilon (the numerical value is shown in Table 1) ₁ '＜ε＜ε ₂ ' the system under this architecture enables occlusion free imaging.

In summary, as shown in fig. 7, the main steps of designing the asymmetric penta-mirror structure according to the single viewpoint constraint include:

(1) Selecting a proper infrared imaging assembly and lens parameters thereof according to the requirements of spatial resolution and action distance aiming at the temperature difference between a target and a background in a specific task, as shown in a table 1;

(2) Selecting a proper combination of the viewpoint height m and the mirror inclination angle theta according to the vertical field angle 2 epsilon, the lens diameter k and the like, determining the accurate position of the infrared imaging assembly by solving the height h of the equivalent viewpoint P of the infrared imaging assembly and the horizontal distance l between the equivalent viewpoint P and the structural vertex O', and determining the distance d from the central point of the bottom of the structure to the side length and the tailorable mirror surface height s according to the reflection field, thereby determining the specific size of the asymmetric pentad reflecting mirror;

(3) Analyzing whether the view field is blocked or not according to the system structure parameters obtained in the last step;

(4) And optimizing the system structure according to the non-shielding analysis result of the view field until the non-shielding asymmetric pentad reflecting mirror with small structure size and easy processing is obtained.

The asymmetric penta-mirror and the infrared lenses with different focal lengths meeting the single-view constraint reflect and converge scene radiation in five directions to five sets of vertically placed infrared focal plane detectors, as shown in fig. 8, and as the axis where the virtual view point P' is located can be used as a rotation axis, cylindrical projection is adopted to convert the planar images in the five directions in fig. 8 (a) into seamless panoramic images, as shown in fig. 8 (b).

The solid line and the dotted line in FIG. 8 respectively represent the focal length f ₁ ＝5.8mm、f ₂ Infrared imaging assembly =4.1 mm.

In addition, to keep the front and left and right side view field information as much as possible, the focal length f is set ₁ Circumferential image projection was performed with a cylindrical projection radius of =5.8mm. At the same time, three focal lengths f ₁ =5.8 mm and two f ₂ Images of =4.1 mm can also be saved as large field of view images and recalled by the user.

For simplicity of description, let one image in FIG. 8 (a) be W in width and H in height, and let the infrared lens center of light coincide with the infrared focal plane detector center, then the image center point (C _x ,C _y ) Satisfy the following requirements

The coordinates of the image coordinates (x, y) projected as the cylindrical surface in fig. 8 (b) are given by the coordinates (x ', y'), and then the conversion formula from coordinates (x, y) to coordinates (x ', y') needs to be discussed in two cases:

(1) Front and left and right side view field focal length f ₁ Conversion formula at=5.8 mm:

(2) Left rear, right rear field of view focal length f ₂ Conversion formula at=4.1 mm:

as a specific implementation manner, in this embodiment, the ProE software is used to perform simulation design on the system, and a mechanical structure scheme capable of adjusting and aligning the viewpoints is provided, so that the viewpoints of the infrared imaging components with different focal lengths can be accurately overlapped to the same point, as shown in fig. 9, 10, 11 and 12. The periscope system comprises a disc platform 1, a specular reflection area 6, an infrared imaging assembly 3 and a central column shaft 2.

The infrared imaging assembly 3 is fixed on the disc platform 1 and keeps a certain horizontal distance and a certain vertical distance with the central column shaft 2, the specular reflection area 6 is arranged around the central column shaft, the specular reflection area 6 is separated and mainly comprises a reflector bracket and a reflector surface, the plane bracket is added in the horizontal direction and the vertical direction to ensure the stability and the accuracy of the inclination angle, and grooves are engraved on the surface of the bracket to ensure the fit of the two. The reflecting mirror surface is composed of float glass with certain thickness, uniform inside and smooth and flat front surface, and is favorable for specular reflection of infrared radiation. Each infrared imaging component 3 collects the infrared radiation reflected by the corresponding reflecting mirror surface to form a 360-degree infrared peripheral vision image together.

To align multiple viewpoints with a single virtual viewpoint to ensure single viewpoint constraints, a mechanical structure with adjustable spatial positions of the infrared imaging assembly may be designed.

On the one hand, the first adjusting rings 4 with different numbers are placed on the central column shaft 2 to adjust the height and are fixed through the locking rings; on the other hand, the infrared imaging assembly 3 is fixed on the disc by a fixing seat assembly (such as a bolt, a screw and the like), and the assembly can move within a certain range to adjust the horizontal distance of the infrared imaging assembly, and a different number of second adjusting rings 5 are placed below the infrared imaging assembly to adjust the vertical height. The central column shaft 2 adjusting mechanism and the fixing seat adjusting mechanism ensure that the space position of the infrared imaging assembly can be manually adjusted, and the viewpoint position offset caused by structural processing and manual adjustment errors is avoided. The final structural parameters of the system of this example after mechanical design are shown in table 3.

TABLE 3 theoretical design values and actual values of the system structural parameters of the present embodiment

And processing, assembling and debugging to obtain the real object. When the system works, the five infrared imaging components collect video images simultaneously according to the external synchronous signals, and the size of one frame of image is 640 multiplied by 480.

This embodiment is due to the use of two focal lengths of infrared lens (f ₁ =5.8 mm and f ₂ =4.1 mm), an image of one of the focal lengths needs to be scaled first. To keep the front and left and right side view field information as much as possible, after cylindrical projection, the method is characterized by that ₂ The image of =4.1 mm is amplified and upsampled by an amplification factor γ defined by the focal length f ₁ =5.8 mm and f ₂ Infrared imaging assembly vertical field angle ε corresponding to =4.1mm ₁ 、ε ₂ The decision, the formula is:

the amplification factor γ=1.41 is obtained from equation (10).

Focal length f for obtaining seamless infrared peripheral vision image ₁ ＝5.8mm、f ₂ The redundant fields of view of a video image of=4.1 mm in the horizontal direction are 6.5% (640×6.5+.42 pixels) and 8.6% (640×8.6+.55 pixels), respectively, and therefore f ₂ Image magnification and f of =4.1 mm ₁ Images of 5.8mm are aligned in center, and redundant fields of view are matched and cut, so that a seamless panoramic infrared image can be obtained.

Due to exposure conditions and automatic gainDifferent, uniform gray balance is required for the peripheral infrared image. Taking infrared images collected simultaneously in five directions, and respectively calculating average value mu of the infrared images _i (i=1, 2,3,4, 5) and variance σ _i (i=1, 2,3,4, 5), the average value μ of the 5 frames of infrared images is obtained _average Mean variance sigma _average The expression is as follows:

taking this as a reference, respectively for 5 frames of image I _i (i=1, 2,3,4, 5) gray balance, output result is O _i (i=1, 2,3,4, 5) with the expression:

in summary, the image processing steps required for acquiring the infrared peripheral vision image of the system mainly include: cylindrical projection, scaling, center alignment, redundant partial cutting and gray balance, and finally, a complete and seamless infrared peripheral vision image is obtained, as shown in fig. 13, the front infrared imaging assembly and the left infrared imaging assembly and the right infrared imaging assembly have longer acting distances, the visual field of a driver is enlarged, and the observation requirement of no blind area in all days is met.

It can be seen that, in this embodiment, aiming at the difference of requirements of the front, the left, the right and the rear on the detection distance of pedestrians (200 m and 145m respectively) in the driving application of the vehicle, an asymmetric five-mirror single-view point refraction and reflection infrared peripheral vision system with 64-degree fields of view on the front, the left and the right and with two 84-degree fields of view is provided and realized, and three sets of focal lengths f are formed by utilizing the asymmetric five-mirror ₁ =5.8 mm and two sets f ₂ Virtual viewpoints of the infrared imaging assembly with the length of 4.1mm are overlapped to be the same point, a design flow of a single viewpoint constraint asymmetric pentahedron structure is established, namely, after a proper infrared imaging assembly and lens parameters thereof are selected according to the requirements of space resolution and action distance, the specific size of the asymmetric pentahedron reflector is determined according to the constraint condition of the single viewpoint structure, and then the view shielding analysis is carried out according to the system structure parametersAnd optimizing the system structure until an asymmetric pentad reflecting mirror which is free of shielding, small in structure size and easy to process is obtained. After finishing processing, assembling and adjusting the asymmetric pentahedral mirror refraction and reflection infrared peripheral vision prototype system, a peripheral vision infrared image processing flow comprising the steps of cylindrical projection, zooming, center alignment, redundant part cutting, gray balance and the like is provided, and finally, non-shielding, seamless and non-blind area infrared imaging of a horizontal 360 DEG pitching + -29 DEG visual field is realized. The system acquires the infrared image of the scene comprehensively, truly and credibly, is beneficial to eliminating the vehicle driving observation blind area, improves the intelligent driving capability, and has wide application prospect in civil and military fields.

Example 2

In this embodiment, the specular reflection area of the peripheral vision system is monolithic, and a high-reflectivity film is coated on the surface after processing by using an integral molding method. The remainder was the same as in example 1.

The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the application.

Claims (10)

1. A design method of an asymmetric pentad reflector is characterized by comprising the following steps: the method comprises the following steps:

aiming at the temperature difference between a target and a background in a specific task, selecting a proper infrared imaging assembly and lens parameters thereof according to the requirements of spatial resolution and action distance;

step (2) selecting a proper combination of the height m of the virtual viewpoint P ', the distance d from the center point of the bottom surface to the side length, the height h of the tailorable mirror surface, the height l of the equivalent viewpoint P of the imaging component, the horizontal distance l between the equivalent viewpoint P and the structural vertex O', the vertical field angle 2 epsilon of the imaging component and the lens diameter k, and the inclination angle theta of the lens according to the virtual viewpoint P ', the height h of the equivalent viewpoint P of the infrared imaging component and the horizontal distance l between the equivalent viewpoint P and the structural vertex O', so as to determine the accurate position of the infrared imaging component, and then determining the distance d from the center point of the bottom of the structure to the side length and the tailorable mirror surface height s according to the reflection field, thereby determining the specific size of the asymmetric pentad reflecting mirror;

step (3) analyzing whether the view field is blocked or not according to the structural parameters obtained in the step (2);

and (4) optimizing the structure according to the unobstructed analysis result of the field of view until an unobstructed asymmetric penta-prismatic table reflector is obtained.

2. The design method according to claim 1, wherein: in the step (2), according to the combination of different mirror inclination angles theta and virtual viewpoint heights m, the horizontal distance l between the infrared imaging component and the central axis and the vertical height h between the infrared imaging component and the bottom surface are determined, and the expression is as follows:

l＝2(dtanθ-m)sinθcosθ；

h＝2dsinθcosθ+(sin ² θ-cos ² θ)m；

the expression for the tailorable mirror height s is:

3. the design method according to claim 1, wherein: in step (3), the unobstructed analysis includes:

when calculating the current parameters, the infrared imaging component just does not image the vertical field angle epsilon of the infrared imaging component ₁ '、ε ₂ ' if epsilon is compared with the actual vertical angle epsilon ₁ '＜ε＜ε ₂ ' the non-shielding imaging can be realized under the structure; wherein:

wherein:

4. an application of an asymmetric pentad reflector is characterized in that: reflecting and converging the scene radiation in five directions to five sets of vertically placed infrared focal plane detectors by the asymmetric pentad reflecting mirror meeting the single viewpoint constraint and the infrared lenses with different focal lengths according to any one of claims 1 to 3, wherein the optical center of the infrared lenses coincides with the center of the infrared focal plane detectors, and then the center point (C _x ,C _y ) Satisfy the following requirements

The coordinates of the image (x, y) are projected as cylindrical surfaces, and the coordinates are (x ', y');

front and left and right side view field focal length f ₁ Conversion formula at=5.8 mm:

left rear, right rear field of view focal length f ₂ Conversion formula at=4.1 mm:

5. an asymmetric pentad reflector, characterized in that: a design method according to any one of claims 1-3.

6. An asymmetric pentad mirror according to claim 5, wherein: the infrared imaging device comprises a disc platform, a specular reflection area, an infrared imaging component and a central column shaft;

the infrared imaging assemblies are fixed on the disc platform, a certain horizontal distance and a certain vertical distance are kept between the infrared imaging assemblies and the central column shaft, and the specular reflection areas are arranged around the central column shaft;

the mirror reflection area is separated and comprises a reflector bracket and a reflector surface; or the mirror reflection area is integral, and a high-reflectivity film is plated on the surface after the mirror reflection area is processed in an integral molding mode;

the reflecting mirror surfaces correspond to the infrared imaging components and form a certain included angle; each infrared imaging component collects infrared radiation reflected by the corresponding reflecting mirror surface to form a 360-degree infrared peripheral vision image.

7. An asymmetric pentad mirror according to claim 6, wherein: placing different numbers of first adjusting rings on the central column shaft, and adjusting the heights of a plurality of infrared imaging components; and the connection part of the single infrared imaging component and the disc platform is provided with different numbers of second adjusting rings, so that the vertical height of the single infrared imaging component is adjusted.

8. An asymmetric penta-mirror single-view point refraction and reflection infrared peripheral vision system is characterized in that: comprising an asymmetric pentad mirror as claimed in any one of claims 5 to 7.

9. The application of the asymmetric penta-mirror single-viewpoint refraction and reflection infrared peripheral vision system is characterized in that: a 360 ° periscope field obtained using the asymmetric pentad mirror of any one of claims 5-7.

10. An image processing method, characterized in that: the asymmetric penta-mirror single-view catadioptric infrared peripheral vision system of claim 9, comprising the steps of:

firstly, scaling an image with one focal length, reserving front, left and right side view field information, performing cylindrical projection, scaling and sampling the image with one focal length, wherein the scaling factor gamma is represented by the vertical field angle epsilon of an infrared imaging assembly corresponding to the first focal length and the second focal length ₁ 、ε ₂ The decision, the formula is:

in order to obtain a seamless infrared peripheral vision image, the image of the second focal length is aligned with the center of the image of the first focal length after being amplified, and redundant fields of view are matched and cut, so that the seamless peripheral vision infrared image can be obtained;

carrying out uniform gray balance on the peripheral infrared image; taking infrared images collected simultaneously in five directions, and respectively calculating average value mu of the infrared images _i (i=1, 2,3,4, 5) and variance σ _i (i=1, 2,3,4, 5), the average value μ of the 5 frames of infrared images is obtained _average Mean variance sigma _average The expression is as follows:

respectively for 5 frames of image I _i (i=1, 2,3,4, 5) gray balance, output result is O _i (i=1, 2,3,4, 5) with the expression: