A minimum resolvable contrast testing device and method for a low-light-level night vision system

Abstract

The application provides a minimum distinguishable contrast test device and method for a low-light-level night vision system, wherein the device comprises a light source system, an aperture diaphragm system, an illumination collimation system, a main integrating sphere, a fine adjustment assembly system, a foreground integrating sphere, a foreground monitoring illuminometer, a background integrating sphere, a background monitoring illuminometer, a target wheel system, a beam combining box system, a collimator system, a measured low-light-level night vision product, an upper computer system and a light supplementing system. In the case of using a single light source, the fine adjustment assembly system and the aperture diaphragm and integrating sphere are used to realize wide-range continuous and accurate control of the illumination of each single integrating sphere, so that the functions of wide-range continuous adjustment of the illumination of the measuring system and contrast are realized. The method overcomes the shortcomings that the optical contrast range of the target cannot be precisely and continuously adjusted by the voltage adjustment method and the measuring brightness is not uniform by using the multi-light-source method.

Description

Technical Field

[0001] The present application relates to the field of optical imaging and measurement technology, and in particular to a device and method for testing the minimum resolvable contrast of a low-light-level night vision system. Background Art

[0002] Low-light-level night vision systems enhance the collection and processing of weak light, enabling the human eye to clearly observe and identify objects in low-light conditions. Their performance is crucial for determining the range and accuracy of optoelectronic imaging systems, making accurate measurement and evaluation of their imaging performance essential.

[0003] Minimum Resolvable Contrast (MRC) quantitatively defines the threshold contrast that a low-light-level night vision system can resolve. It integrates factors such as system sensitivity and noise, target spatial frequency, and human visual characteristics, comprehensively reflecting the ultimate performance of an optoelectronic imaging system. Therefore, MRC is a key metric for evaluating imaging system performance.

[0004] Regarding MRC measurement, Chinese patent ZL 201410353411.9 discloses a minimum resolvable contrast (MRC) test system for near-infrared cameras. This test system uses a single integrating sphere as the target light source and adjusts the target contrast through a steady-state current source and an aperture. However, this device's shortcomings include uncontrolled background brightness, making it difficult to simulate the variable target and background conditions found in real-world applications. Furthermore, the test system's applicability is limited, making it unsuitable for testing devices such as television sighting systems and low-light cameras.

[0005] In the Journal of Metrology, Vol. 27, No. 1, 2006, pp. 32-35, Li Wenjuan et al. developed a portable, contrast-adjustable target source generator using the overlapping integrating sphere method. The device primarily consists of a background integrating sphere, a target integrating sphere, and a spectroscopic system. A single light source illuminates each integrating sphere through spectroscopic illumination. The device utilizes an external adjustable rheostat to adjust the luminance of the integrating sphere's light source within a range of 0.3 to 200 cd / m² by varying the voltage. However, the device's main shortcomings are:

[0006] Since the target optical contrast is adjustable by adjusting the light source voltage and optical devices (such as attenuators), the color temperature stability of the target source lacks effective guarantees, and the range of variation of the target optical contrast cannot be precisely and continuously adjusted.

[0007] In order to solve the above problems, and with the continuous improvement of tracking and accuracy requirements of low-light-level night vision systems, it is urgent to develop a new minimum resolvable contrast measurement device for low-light-level night vision systems to improve the accuracy of imaging quality evaluation in actual applications of low-light-level night vision systems. Summary of the Invention

[0008] In order to solve the problem in the prior art that the minimum resolvable contrast of a low-light-level night vision system cannot be adjusted continuously and accurately, the present invention proposes a device for testing the minimum resolvable contrast of a low-light-level night vision system.

[0009] The present application provides a device for testing the minimum resolvable contrast of a low-light-level night vision system, the device comprising a light source system, an aperture stop system, an illumination collimation system, a main integrating sphere, a fine-tuning component system, a foreground integrating sphere, a foreground monitoring illuminometer, a background integrating sphere, a background monitoring illuminometer, a target wheel, a beam combining box system, a collimator system, a low-light-level night vision product to be tested, a host computer system, and a fill light component;

[0010] The main integrating sphere is used to receive the light emitted by the light source system. The light emitted by the light source system is attenuated by the aperture diaphragm system and converged by the illumination collimation system. The aperture diaphragm system includes apertures of different sizes, which makes the illumination of the main integrating sphere stable.

[0011] The main integrating sphere has three holes, one of which is connected to the light source system, and the other two are connected to the foreground integrating sphere and the background integrating sphere respectively. The center of the main integrating sphere is taken as the origin, and the line connecting the center line of the light source system opening and the origin is taken as the directrix. The center line of the foreground integrating sphere opening is taken as the directrix and rotated 135° clockwise. The center line of the background integrating sphere opening is taken as the directrix and rotated 135° counterclockwise. The directrixes of the two integrating spheres are 90° apart and are vertically distributed.

[0012] The foreground monitoring illuminance meter is located above the foreground integrating sphere, and the background monitoring illuminance meter is located above the background integrating sphere. One fine-tuning component system is located between the main integrating sphere and the foreground integrating sphere, and another fine-tuning component system is located between the main integrating sphere and the background integrating sphere. By controlling the fine-tuning component system, the illumination control of the foreground integrating sphere and the background integrating sphere is achieved;

[0013] The main integrating sphere, foreground integrating sphere and background integrating sphere each consist of two hemispherical shells with inner walls coated with a white diffuse reflection layer;

[0014] The collimator system is located at the light outlet of the beam combiner system. It is used to project the image on the beam combiner into the field of view of the low-light-level night vision product being tested, and is supplemented by a fill light component to compensate for the imaging defects caused by the collimator system.

[0015] The low-light-level night vision product to be tested is used to receive the parallel light output by the collimator system and determine the minimum resolvable contrast; the low-light-level night vision product to be tested is placed in the collimated light path of the collimator system;

[0016] The host computer system is connected to the minimum resolvable contrast test device of the low-light-level night vision system and performs control operations.

[0017] Furthermore, the target wheel is located between the foreground integrating sphere and the beam combining box system; after the target image is illuminated by the foreground integrating sphere and the background integrating sphere, the required contrast target is generated on the beam combining mirror in the beam combining box system; the target wheel includes multiple groups of targets with alternating black and white, equal line width, different spatial frequencies and different sizes, and the targets with corresponding frequencies are selected according to the test requirements and rotated to the light-transmitting position between the foreground integrating sphere and the beam combining box system.

[0018] Furthermore, the target in the target wheel uses the USAF1951 resolution target with 6 groups of target line units, that is, light and dark stripes of equal width and equal spacing are formed on the target surface. Each group of target line units includes three horizontal target lines and three vertical target lines of equal length. The length of the target line is five times the target line width, the target line width and the interval between adjacent target lines are equal, and the interval between horizontal target lines and vertical target lines is twice the target line width. Starting from the largest group of target line units, every two groups of target line units with similar sizes are reduced in proportion.

[0019] Furthermore, the color temperature and color coordinates of the light source in the light source system are calibrated and verified, and the preset spectral power distribution and color temperature are output through power control.

[0020] Furthermore, the illumination collimation system includes an aperture stop, a collimating lens barrel, and a collimating lens; the exit position of the main integrating sphere (4) is located at the focal plane position of the collimating lens;

[0021] The collimating lens barrel in the illumination collimation system is made of aluminum alloy, and the inner wall is oxidized and blackened; the collimating lens is made of BaF7 optical glass, the focal length of the collimating lens is 350mm, the relative aperture D / F is 1 / 7, the effective aperture is 45mm, the surface is coated with anti-reflection film, and an anti-scattering aperture is added in front of the lens.

[0022] Furthermore, the foreground integrating sphere and the background integrating sphere have the same structure, and the diameters of the light entrance and light exit are the same; the inner diameter of the foreground integrating sphere and the background integrating sphere is 220 mm, and the opening diameter is 50 mm.

[0023] Furthermore, the fine adjustment component systems of the two controls have the same structure, including an aperture diaphragm, a stepper motor, and a guide rail;

[0024] The opening and closing degree of the diaphragm is controlled by a stepper motor, which controls the illumination of the light source entering the integrating sphere, thereby achieving continuous adjustment of the output illumination of the integrating sphere.

[0025] The fine-tuning component system is controlled by a stepper motor to drive the two aperture blades to move so that the central aperture is enlarged or reduced, and the illumination of the main integrating sphere is distributed to the foreground integrating sphere and the background integrating sphere.

[0026] Furthermore, the stepper motor model is LMA-TR-200-G10, the step angle is 1.8°, the maximum subdivision of the stepper motor driver is 128, and the wheel radius is 54.2 mm.

[0027] Furthermore, the aperture diaphragm system includes 6 single apertures and 3 combined aperture diaphragms. The single aperture includes 6 first-order attenuation diaphragms with apertures ranging from Ф1 to Ф50, which are specifically divided into Ф1.0, Ф2.2, Ф4.8, Ф10.5, Ф22.9 and Ф50; the combined aperture is divided into three A secondary attenuation diaphragm is installed behind the primary diaphragm, and three Ф1.0 light-transmitting holes are set on the surface of the secondary attenuation diaphragm. The aperture diaphragm system controls the aperture target wheel to rotate to the appropriate aperture through a stepping motor to form illumination.

[0028] This application also provides a method for testing the dynamic minimum resolvable contrast ratio of a low-light-level night vision system. The method is implemented based on the device provided in this application and includes:

[0029] The first step is to input the preset illumination value and contrast value into the host computer system according to the measurement conditions;

[0030] In the second step, according to the contrast control principle, the contrast is controlled by controlling the aperture diaphragm and the light transmission size of the fine-tuning component system to form a preset contrast value in the host computer. The output illumination of the foreground integrating sphere is set to L t , the output illumination of the background integrating sphere is L b , the target contrast C1 is determined by the following method:

[0031]

[0032] Therefore, the corresponding target to be measured is selected in the target wheel and rotated to the light-transmitting position, and a pattern of a preset contrast target can be generated in the beam combining box system.

[0033] The third step is to use a standard luminance meter to measure the contrast of the target image formed in the device to verify the target contrast; the maximum value L in the target contrast is measured. max and the minimum value L min and determine the contrast measurement C2 by:

[0034]

[0035] When C1=C2 and the control error is within 5%, the test device test is completed.

[0036] The fourth step is to record the target line unit number (i, j) corresponding to the thinnest target pattern that can be clearly separated. By creating a table of target pattern data, the line width of the target line unit corresponding to the serial number (i, j) is obtained by looking up the table. The corresponding spatial frequency f is determined by the following method, with the unit being line pairs per millimeter (lp / mm):

[0037] f(lp / mm)=2 i+(j-1) / 6

[0038] Where i and j are the number of groups and units corresponding to the target respectively;.

[0039] Step 5: According to the target line unit number selected in step 4, the spatial frequency f is obtained, and the average brightness of the scene L is obtained according to the preset input illumination value. m =L b +L t , according to f and L m The minimum resolvable contrast ratio (MRC) of the tested low-light-level night vision product (13) is (f, L m );.

[0040] Step 6: Change the illumination of the foreground integrating sphere and the background integrating sphere within the working range of the low-light-level night vision system, repeat steps 1 to 5, and obtain the MRC value under the average brightness of different scenes.

[0041] The overall effect of the present invention is embodied in the following aspects:

[0042] (1) The present invention optimizes the aperture diaphragm system and the fine-tuning component system structure to achieve independent, continuous, and precise control of illuminance over a wide range when a single light source is used, thereby realizing the function of continuously adjusting the illumination of the measurement system and the contrast of the target over a wide range, overcoming the shortcomings of methods such as adjusting the voltage, such as the inability to accurately and continuously adjust the range of the target optical contrast and the uneven brightness caused by multiple light sources.

[0043] (2) The present invention places the low-light-level night vision product to be measured in a collimator optical system to simulate the measurement of targets of arbitrary illumination and contrast at infinity. The optical band of the measuring equipment ranges from near-infrared to visible light, meeting the current requirements for the performance evaluation of dual-band fusion military optoelectronic equipment.

[0044] (3) The present invention adopts a triple integrating sphere structure design, which makes the entire system lightweight and miniaturized, and is convenient for real-time carrying and measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the minimum resolvable contrast test device of the present invention;

[0046] Figure 2 Schematic diagram of the aperture stop system structure of the minimum resolvable contrast test device of the present invention;

[0047] Figure 3 Schematic diagram of the target wheel of the minimum resolvable contrast test device of the present invention and the commonly used USAF1951 test target;

[0048] Figure 4 Schematic diagram of the fill light component of the minimum resolvable contrast test device of the present invention;

[0049] Figure 5 It is a schematic diagram of the contrast control principle of the minimum resolvable contrast test device of the present invention. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0051] A device for testing the minimum resolvable contrast of a low-light-level night vision system includes a light source system 1, an aperture diaphragm system 2, an illumination collimation system 3, a main integrating sphere 4, a fine-tuning component system 5, a foreground integrating sphere 6, a foreground monitoring illuminometer 7, a background integrating sphere 8, a background monitoring illuminometer 9, a target wheel 10, a beam combining box system 11, a collimator system 12, a low-light-level night vision product to be tested 13, a host computer system 14, and a fill light component 15.

[0052] The main integrating sphere 4 is used to receive the light emitted by the light source system 1. The light emitted by the light source system 1 is attenuated by the aperture diaphragm system 2 and converged by the illumination collimation system 3. The aperture diaphragm system 2 includes apertures of different sizes, thereby achieving a wide range of continuously adjustable stable illumination in the main integrating sphere 4.

[0053] The main integrating sphere 4 has three holes, one of which is connected to the light source system 1, and the other two are connected to the foreground integrating sphere 6 and the background integrating sphere 8 respectively. Taking the top view as the cross section, with the center of the main integrating sphere 4 as the origin, and the line connecting the center line of the opening of the light source system 1 and the origin as the directrix, the center line of the opening of the foreground integrating sphere 6 is used as the directrix and rotated 135° clockwise, and the center line of the opening of the background integrating sphere 8 is used as the directrix and rotated 135° counterclockwise. The directrixes of the two integrating spheres are 90° apart and are vertically distributed.

[0054] A foreground monitoring illuminometer 7 is located above the foreground integrating sphere 6 and a background monitoring illuminometer 9 is located above the background integrating sphere 8. A fine adjustment component system 5 is located between the main integrating sphere 4 and the foreground integrating sphere 6, and another fine adjustment component system 5 is located between the main integrating sphere 4 and the background integrating sphere 8. By controlling the fine adjustment component systems 5, continuous and precise control of the illumination of the foreground integrating sphere 6 and the background integrating sphere 8 is achieved over a wide range. The main integrating sphere 4, the foreground integrating sphere 6, and the background integrating sphere 8 each include two hemispherical shells with an inner wall coated with a white diffuse reflection layer.

[0055] The target wheel 10 is located between the foreground integrating sphere 6 and the beam combining box system 11. After the target image is illuminated by the foreground integrating sphere 6 and the background integrating sphere 8, the required contrast target is generated on the beam combining mirror in the beam combining box system 11. The target wheel 10 includes multiple groups of targets with alternating black and white colors, equal line widths, different spatial frequencies, and different sizes. Targets with corresponding frequencies are selected according to test requirements and rotated to the light-transmitting position between the foreground integrating sphere 6 and the beam combining box system 11.

[0056] The target in the target wheel 10 uses the USAF1951 resolution target with 6 groups of target line units, that is, light and dark stripes of equal width and equal spacing are formed on the target surface. Each group of target line units includes three horizontal target lines and three vertical target lines of equal length. The length of the target line is five times the target line width, the target line width and the interval between adjacent target lines are equal, and the interval between horizontal target lines and vertical target lines is twice the target line width. Starting from the largest group of target line units, every two groups of target line units of similar size are reduced in proportion.

[0057] The collimator system 12 is located at the light outlet of the beam combiner system 11 and is used to project the image on the beam combiner into the field of view of the low-light-level night vision product 13 to be tested, and is assisted by the fill light component 15 to compensate for the imaging defects caused by the collimator system;

[0058] The low-light-level night vision product 13 to be tested is used to receive the parallel light output by the collimator system 12, and the minimum resolvable contrast is determined by the human eye or computer software;

[0059] The host computer system 14 is connected to the minimum resolvable contrast test device of the low-light-level night vision system and performs control operations.

[0060] The color temperature and color coordinates of the light source in the light source system 1 are calibrated and verified, and the output spectral power distribution and color temperature output are stable through the control of a precise voltage and current stabilizing power supply.

[0061] The illumination collimation system 3 includes an aperture stop, a collimating lens barrel, and a collimating lens; the exit position of the main integrating sphere 4 is located at the focal plane position of the collimating lens.

[0062] The foreground integrating sphere 6 and the background integrating sphere 8 have the same structure, and the diameters of the light entrance and light exit are the same; the inner diameter of the foreground integrating sphere 6 and the background integrating sphere 8 is 220 mm, and the opening diameter is 50 mm;

[0063] The two controlled fine-tuning assembly systems 5 have the same structure, including an aperture diaphragm, a stepper motor, and a guide rail. The stepper motor controls the opening and closing of the diaphragm, thereby controlling the illumination of the light source entering the integrating sphere, thereby achieving continuous adjustment of the sphere's output illumination. Fine-tuning assembly system 5 uses a stepper motor to drive the movement of two diaphragm blades to expand or contract the central diaphragm, distributing the illumination from the main integrating sphere to the foreground integrating sphere 6 and the background integrating sphere 8. The stepper motor model is LMA-TR-200-G10, with a step angle of 1.8°, a maximum subdivision of the stepper motor driver of 128, and a wheel radius of 54.2 mm.

[0064] A collimator system 12 is installed at the light outlet of the beam combining box system 11 to project the preset contrast target pattern, which is then filled with light by the fill light component 15 to solve the gain saturation problem that may occur in some large-field-of-view low-light-level night vision products.

[0065] The low-light-level night vision product 13 to be tested is placed in the collimated light path of the parallel light tube system 12 , and the human eye can distinguish a clear pattern of the imaging target through the low-light-level night vision product to be tested.

[0066] The aperture diaphragm system 2 includes 6 single apertures and 3 combined aperture diaphragms. The single apertures include 6 first-order attenuation diaphragms with apertures ranging from Ф1 to Ф50, specifically divided into Ф1.0, Ф2.2, Ф4.8, Ф10.5, Ф22.9 and Ф50; the combined apertures are in three A secondary attenuation diaphragm is installed after the primary diaphragm, and three 1.0 diameter light-transmitting holes are set on the secondary attenuation diaphragm surface; the aperture diaphragm system 2 controls the aperture target wheel to rotate to the appropriate aperture through a stepping motor to form illumination;

[0067] The collimating lens barrel in the illumination collimation system 3 is made of aluminum alloy, and the inner wall is oxidized and blackened; the collimating lens is made of BaF7 optical glass, with a focal length of 350mm, a relative aperture D / F of 1 / 7, an effective aperture of 45mm, an anti-reflection coating on the surface, and an anti-scattering aperture added in front of the lens;

[0068] The method for testing the dynamic minimum resolvable contrast ratio of a low-light-level night vision system using the above-mentioned device includes the following steps:

[0069] The first step is to input the preset illumination value and contrast value into the host computer system 14 according to the measurement conditions;

[0070] In the second step, according to the contrast control principle, the contrast is controlled by controlling the aperture diaphragm and the light transmission size of the fine-tuning component system to form a preset contrast value in the host computer. The output illumination of the foreground integrating sphere 6 is set to L t , the output illumination of the background integrating sphere 8 is L b , the target contrast C1 is determined by the following method:

[0071]

[0072] Therefore, the corresponding target to be measured is selected in the target wheel and rotated to the light-transmitting position, and a pattern of a preset contrast target can be generated in the beam combining box system 11.

[0073] The third step is to use a standard luminance meter to measure the contrast of the target image formed in the device to verify the target contrast; the maximum value L in the target contrast is measured. max and the minimum value L min and determine the contrast measurement C2 by:

[0074]

[0075] When C1=C2 and the control error is within 5%, the test device test is completed.

[0076] In the fourth step, the human eye observes the pattern generated by the test device through the low-light-level night vision product, and subjectively distinguishes the thinnest target pattern that can be clearly separated, recording the corresponding target line unit serial numbers i and j. By creating a table of target pattern data, the line width of the target line unit corresponding to serial numbers i and j is obtained by looking up the table, and the corresponding spatial frequency f is determined by the following method, with the unit of line pairs per millimeter lp / mm:

[0077] f(lp / mm)=2 i+(j-1) / 6

[0078] Where i and j are the number of groups and units corresponding to the target respectively;.

[0079] Step 5: According to the target line unit number selected in step 4, the spatial frequency f is obtained, and the average brightness of the scene L is obtained according to the preset input illumination value. m =L b +L t , according to f and L m The minimum resolvable contrast ratio (MRC) of the tested low-light-level night vision product 13 is f, L m ;.

[0080] Step 6: Change the illumination of the foreground integrating sphere 6 and the background integrating sphere 8 within the working range of the low-light-level night vision product 13, and repeat steps 1 to 5 to obtain the MRC values ​​under different scene average brightness.

[0081] The present application will be further described below with reference to the accompanying drawings.

[0082] like Figure 1 As shown, the minimum resolvable contrast test device in this embodiment includes a light source system 1, an aperture stop system 2, an illumination collimation system 3, a main integrating sphere 4, a fine adjustment component system 5, a foreground integrating sphere 6, a foreground monitoring illuminometer 7, a background integrating sphere 8, a background monitoring illuminometer 9, a target wheel 10, a beam combining box system 11, a collimator system 12, a low-light-level night vision product to be tested 13, a host computer system 14, and a fill light component 15.

[0083] The light source system 1 adopts an external lighting method to adjust the illumination by controlling the aperture diaphragm system 2 to stabilize the color temperature. In this embodiment, the light source is a 40W halogen tungsten lamp with a spectral range of 380-1100nm, which meets the measurement requirements from the near-infrared to the visible light band.

[0084] The aperture stop system 2 controls the aperture target wheel to rotate to a suitable aperture through a stepping motor to form illumination; in this preferred embodiment, refer to Figure 2 The aperture diaphragm system 2 includes 6 single apertures and 3 combined aperture diaphragms to meet the requirements of the dynamic range of illumination. The single aperture includes 6 first-level attenuation diaphragms with apertures ranging from Ф1 to Ф50, specifically divided into Ф1.0, Ф2.2, Ф4.8, Ф10.5, Ф22.9 and Ф50; the combined aperture is in three A secondary attenuation diaphragm is installed after the first-level diaphragm, and three 1.0-diameter light holes are set on the surface of the secondary attenuation diaphragm. The light is attenuated by staggering the double-layer diaphragms. By switching different aperture diaphragms, the maximum measured illumination can reach 645lx and the minimum can reach 0.000172lx. The dynamic range of illumination reaches 10 6 , achieving a wide range of continuous adjustment of illumination.

[0085] The illumination collimation system 3 utilizes the light converging effect of the lens to place the light source at the focus of the lens, allowing the divergent light beam emitted by the light source to become parallel light and irradiate into the main integrating sphere, thereby achieving the effect of simulating an infinitely distant target. In this preferred embodiment, the collimating lens barrel is made of aluminum alloy, and the inner wall is oxidized and blackened in the process to reduce reflection from the inner wall of the optical lens barrel, reduce light energy loss, and enhance the ability to absorb stray light, thereby improving the system's anti-interference ability. The collimating lens is made of BaF7 optical glass, with a focal length of 350mm, a relative aperture D / F of 1 / 7, an effective clear aperture of 45mm, an anti-reflection film on the surface, and a stray light stop added in front of the lens to reduce the influence of stray light.

[0086] Fine adjustment assembly system 5, controlled by a stepper motor, drives the movement of two aperture blades to enlarge or reduce the central aperture, precisely distributing the illumination from the main integrating sphere to the foreground integrating sphere 6 and the background integrating sphere 8, achieving continuous adjustment of the output illumination of the foreground integrating sphere 6 and the background integrating sphere 8. The structure and function of the foreground integrating sphere 6 are identical to those of the background integrating sphere 8. In this embodiment, the stepper motor model is LMA-TR-200-G10, with a step angle of 1.8°. The stepper motor driver has a maximum subdivision of 128, and its wheel radius is 54.2 mm. This results in a minimum adjustment distance S of the fine adjustment assembly of 0.01324 mm, and a ratio P of the minimum adjustable illumination to the maximum illumination of the fine adjustment assembly system 5 of 0.0133%. A smaller P ensures a finer adjustment range for the fine adjustment assembly, further improving the accuracy of illumination control by the fine adjustment aperture, thereby improving contrast control.

[0087] The main integrating sphere 4, foreground integrating sphere 6, and background integrating sphere 8 are key to forming a diffusely reflected light source. They consist of two hemispherical shells with inner walls coated with a white diffuse reflective layer. In this invention, the main integrating sphere is designed with an inner diameter of 160 mm and an opening diameter of 50 mm; the background and target integrating spheres are designed with inner diameters of 220 mm and an opening diameter of 50 mm. In this preferred embodiment, the illumination uniformity at the exits of the foreground and background integrating spheres 6 and 8 can reach 5%, and the local uniformity can reach 2%, effectively reducing MRC processing errors caused by temporal and spatial instability or unevenness of the light source. Furthermore, the individual integrating spheres are designed to be compact and close together, meeting the requirements of a lightweight and miniaturized measurement device.

[0088] The target wheel 10 is located between the foreground integrating sphere 6 and the beam combining box system 11. After the target image is illuminated by the foreground integrating sphere 6 and the background integrating sphere 8, the required contrast target is generated on the beam combining mirror in the beam combining box system 11. In this preferred embodiment, Figure 3 The target uses the USAF1951 resolution target, which has 6 groups of target line units, that is, light and dark stripes of equal width and equal spacing formed on the target surface. Each group of target line units is composed of three horizontal target lines and three vertical target lines of equal length. The length of the target line is five times the target line width, the target line width and the interval between adjacent target lines are equal, and the interval between horizontal target lines and vertical target lines is twice the target line width. Starting from the largest group of target line units, every two groups of target line units with similar sizes are reduced in proportion.

[0089] The beam combining box system 11 has a semi-transparent and semi-reflective mirror installed in the beam combining box. The beam combining box system is designed to prevent external environmental factors from interfering with imaging. In this preferred embodiment, in areas with large stray light such as the beam combining mirror group, a vapor deposition film layer that eliminates stray light is used to reduce the diffuse reflectivity of the structural parts to below 0.5%.

[0090] The collimator system 12 is connected to the beam combiner system 11, and projects the preset contrast target formed on the beam combiner into an infinitely distant target. In this preferred embodiment, the collimator system adopts a Cassegrain structure with a focal length of 1600 mm, a field of view of ±1°, and an F # =8. Also refer to Figure 4 , design a fill light component 15 with a circular structure and LED light sources distributed at 90°. In this preferred case, a fill light component with a field of view angle of 50° and a central field of view blind area of ​​2° is designed. It can fill light in the range of 1 to 0.001lx, and illuminate the edge area of ​​the field of view of the tested low-light level night vision product 13 with adjustable brightness to solve the gain saturation problem that may occur in some large-field-of-view products. Through the parallel light tube system, the function of infinite imaging of the tested product is realized.

[0091] The tested low-light-level night vision product 13 is identified by the human eye. The tested low-light-level night vision product 13 receives the parallel light output by the collimator system, outputs the target image into the field of view of the low-light-level night vision product 13, and the human eye determines the minimum resolvable contrast.

[0092] The host computer system 14 is connected to the measuring device and is used to send instructions to the measuring device and control the measuring device.

[0093] A method for measuring MRC using a dynamic minimum resolvable contrast test device for a low-light-level night vision system is characterized in that the method comprises the following steps:

[0094] In the first step, according to the measurement conditions, the tester inputs the preset illumination value and contrast value into the host computer system 14;

[0095] In the second step, according to the contrast control principle, the contrast is controlled by controlling the aperture diaphragm and the light transmission size of the fine-tuning component system to form a preset contrast value in the host computer. The output illumination of the foreground integrating sphere 6 is set to L t , the output illumination of the background integrating sphere 8 is L b , the following formula is the principle formula for generating target contrast C1:

[0096]

[0097] Therefore, the corresponding target to be measured is selected in the target wheel and rotated to the light-transmitting position, and a pattern of a preset contrast target can be generated in the beam combining box system (11).

[0098] In the third step, the tester uses a standard luminance meter to measure the contrast of the target image formed in the device to verify the target contrast. The maximum value L max and the minimum value L min , and calculate C2 using the following contrast measurement formula:

[0099]

[0100] When C1=C2 and the control error is within 5%, the test device test is completed.

[0101] In the fourth step, the human eye observes the pattern generated by the test device through the low-light-level night vision product. The tester subjectively distinguishes the thinnest target strip that can be clearly separated and records the corresponding target line unit number (i, j). By creating a table of target pattern data, the line width of the target line unit corresponding to the serial number (i, j) is obtained by looking up the table. The corresponding spatial frequency f is calculated using the following formula, with the unit of line pairs per millimeter (lp / mm):

[0102] f(lp / mm)=2 i+(j-1) / 6

[0103] Where i and j are the number of groups and units corresponding to the target respectively;.

[0104] Step 5: According to the target line unit number selected in step 4, the spatial frequency f is obtained, and the average brightness of the scene L is obtained according to the preset input illumination value. m =L b +L t , combining the above f and L m Then the minimum resolvable contrast ratio MRC of the tested low-light-level night vision product (13) is (f, L m );.

[0105] In the sixth step, the illumination of the foreground integrating sphere (6) and the background integrating sphere (8) is changed within the working range of the low-light-level night vision product (13), and steps 1 to 5 are repeated to obtain a series of MRC values ​​under different scene average brightness. This series of MRC values ​​can then be used to provide support for estimating the effective range of the low-light-level night vision system.

[0106] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the dynamic minimum resolvable contrast ratio of a low-light-level night vision system, characterized in that: The method is implemented based on a minimum resolvable contrast test of a low-light-level night vision system. A minimum resolvable contrast test device for a low-light-level night vision system comprises a light source system (1), an aperture diaphragm system (2), an illumination collimation system (3), a main integrating sphere (4), a fine-tuning component system (5), a foreground integrating sphere (6), a foreground monitoring illuminometer (7), a background integrating sphere (8), a background monitoring illuminometer (9), a target rotating wheel (10), a beam combining box system (11), a collimator system (12), a low-light-level night vision product to be tested (13), a host computer system (14), and a fill light component (15); The main integrating sphere (4) is used to receive light emitted by the light source system (1). The light emitted by the light source system (1) is sequentially attenuated by the aperture stop system (2) and converged by the illumination collimation system (3). The aperture stop system (2) includes apertures of different sizes, so that the illumination of the main integrating sphere (4) is stable. The main integrating sphere (4) has three holes, one of which is connected to the light source system (1), and the other two are connected to the foreground integrating sphere (6) and the background integrating sphere (8), respectively. The center of the main integrating sphere (4) is taken as the origin, and the line connecting the center line of the opening of the light source system (1) and the origin is taken as the directrix. The center line of the opening of the foreground integrating sphere (6) is taken as the directrix and rotated 135° clockwise. The center line of the opening of the background integrating sphere (8) is taken as the directrix and rotated 135° counterclockwise. The directrixes of the two integrating spheres are 90° apart and are vertically distributed. In the foreground integrating sphere (6) and the background integrating sphere (8), a foreground monitoring illuminometer (7) is located above the foreground integrating sphere, and a background monitoring illuminometer (9) is located above the background integrating sphere (8). A fine adjustment component system (5) is located between the main integrating sphere (4) and the foreground integrating sphere (6), and another fine adjustment component system (5) is located between the main integrating sphere (4) and the background integrating sphere (8). By controlling the fine adjustment component system (5), illumination control of the foreground integrating sphere (6) and the background integrating sphere (8) is achieved. The main integrating sphere (4), the foreground integrating sphere (6) and the background integrating sphere (8) each comprise two hemispherical shells with inner walls coated with a white diffuse reflection layer; The collimator system (12) is located at the light outlet of the beam combining box system (11), and is used to project the image on the beam combining mirror into the field of view of the low-light-level night vision product (13) to be tested, and is assisted by a fill light component (15) to compensate for the imaging defects caused by the collimator system (12); The low-light-level night vision product (13) to be tested is used to receive the parallel light output by the collimator system (12) and to determine the minimum resolvable contrast; the low-light-level night vision product (13) to be tested is placed in the collimated light path of the collimator system (12); The host computer system (14) is connected to the minimum resolvable contrast test device of the low-light-level night vision system and performs control operations; The method comprises: The first step is to input the preset illumination value and contrast value into the host computer system (14) according to the measurement conditions; In the second step, according to the contrast control principle, the contrast is controlled by controlling the aperture diaphragm and the light transmission size of the fine-tuning component system to form a preset contrast value in the host computer. The output illumination of the foreground integrating sphere (6) is set to L t , the output illumination of the background integrating sphere (8) is L b , the target contrast C1 is determined by the following method: Therefore, the corresponding target to be measured is selected in the target wheel and rotated to the light-transmitting position, and a pattern of a preset contrast target can be generated in the beam combining box system (11). The third step is to use a standard luminance meter to measure the contrast of the target image formed in the device to verify the target contrast; the maximum value L in the target contrast is measured. max and the minimum value L min and determine the contrast measurement C2 by: When C1=C2 and the control error is within 5%, the test device test is completed; The fourth step is to record the target line unit number (i, j) corresponding to the thinnest target pattern that can be clearly separated. By creating a table of target pattern data, the line width of the target line unit corresponding to the serial number (i, j) is obtained by looking up the table. The corresponding spatial frequency f is determined by the following method, with the unit being line pairs per millimeter (lp / mm): f(lp / mm)=2 i+(j-1) / 6 Where i and j are the number of groups and units corresponding to the target, respectively; Step 5: According to the target line unit number selected in step 4, the spatial frequency f is obtained, and the average brightness of the scene L is obtained according to the preset input illumination value. m =L b +L t , according to f and L m The minimum resolvable contrast ratio (MRC) of the tested low-light-level night vision product (13) is (f, L m ); Step 6: Change the illumination of the foreground integrating sphere (6) and the background integrating sphere (8) within the working range of the low-light-level night vision product (13), repeat steps 1 to 5, and obtain the MRC values ​​under the average brightness of different scenes.

2. The method according to claim 1, characterized in that The target rotating wheel (10) is located between the foreground integrating sphere (6) and the beam combining box system (11); after the target image is illuminated by the foreground integrating sphere (6) and the background integrating sphere (8), the required contrast target is generated on the beam combining mirror in the beam combining box system (11); the target rotating wheel (10) includes multiple groups of targets with alternating black and white, equal line width, different spatial frequencies and different sizes, and the targets with corresponding frequencies are selected according to the test requirements and rotated to the light-transmitting position between the foreground integrating sphere (6) and the beam combining box system (11).

3. The method according to claim 2, characterized in that The target in the target wheel (10) is a USAF1951 resolution target with 6 groups of target line units, i.e., light and dark stripes of equal width and equal spacing are formed on the target surface. Each group of target line units includes three horizontal target lines and three vertical target lines of equal length. The length of the target line is five times the width of the target line. The width of the target line and the interval between adjacent target lines are equal. The interval between the horizontal target line and the vertical target line is twice the width of the target line. Starting from the largest group of target line units, every two groups of target line units with similar sizes are reduced in proportion.

4. The method according to claim 1, wherein The color temperature and color coordinates of the light source in the light source system (1) are calibrated and verified, and the preset spectral power distribution and color temperature are output through power control.

5. The method according to claim 1, wherein The illumination collimation system (3) includes an aperture stop, a collimating lens barrel, and a collimating lens; the exit position of the main integrating sphere (4) is located at the focal plane position of the collimating lens; The collimating lens barrel in the illumination collimating system (3) is made of aluminum alloy, and the inner wall is oxidized and blackened; the collimating lens is made of BaF7 optical glass, the focal length of the collimating lens is 350mm, the relative aperture D / F is 1 / 7, the effective aperture is 45mm, the surface is coated with anti-reflection film, and an anti-scattering aperture is added in front of the lens.

6. The method according to claim 1, characterized in that The foreground integrating sphere (6) and the background integrating sphere (8) have the same structure, and the diameters of the light inlet and the light outlet are the same; the inner diameter of the foreground integrating sphere (6) and the background integrating sphere (8) is 220 mm, and the opening diameter is 50 mm.

7. The method according to claim 1, characterized in that The two controlled fine adjustment component systems (5) have the same structure, including an aperture diaphragm, a stepping motor, and a guide rail; The opening and closing degree of the diaphragm is controlled by a stepper motor, which controls the illumination of the light source entering the integrating sphere, thereby achieving continuous adjustment of the output illumination of the integrating sphere. The fine adjustment component system (5) drives the two aperture blades to move by controlling the fine adjustment component system through a stepping motor so as to enlarge or reduce the central aperture, thereby distributing the illumination from the main integrating sphere to the foreground integrating sphere (6) and the background integrating sphere (8).

8. The method according to claim 7, characterized in that The stepper motor model is LMA-TR-200-G10, the step angle is 1.8°, the maximum subdivision of the stepper motor driver is 128, and the wheel radius is 54.2mm.

9. The method according to claim 8, characterized in that The aperture diaphragm system (2) includes 6 single apertures and 3 combined aperture diaphragms. The single apertures include 6 first-order attenuation diaphragms with apertures ranging from Ф1 to Ф50, which are specifically divided into Ф1.0, Ф2.2, Ф4.8, Ф10.5, Ф22.9 and Ф50; the combined apertures are arranged in three A secondary attenuation diaphragm is installed behind the primary diaphragm, and three Φ1.0 light-transmitting holes are respectively set on the secondary attenuation diaphragm surface; the aperture diaphragm system (2) controls the aperture target wheel to rotate to a suitable aperture through a stepping motor to form illumination.

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