Industrial camera average quantum efficiency measurement method based on white light source

Abstract

The invention discloses an industrial camera average quantum efficiency measurement method based on a white light source, and belongs to the technical field of image sensor performance evaluation. Firstly, a stable white light source is used as a light irradiation system, and the dynamic range of an industrial camera is covered by adjusting light intensity; then, placing the industrial camera under the irradiation of a light source, collecting a plurality of groups of exposure images, and calculating the average value of digital signals output by image signals, noise variance and the number of incident photons under corresponding conditions by combining the incident light intensity recorded by the light intensity standard measuring device; furthermore, a global system gain value is fitted based on an experimental data curve, and the average quantum efficiency of the camera is determined in combination with a measurement model of the average quantum efficiency. The accuracy and stability of the method are verified by comparing measurement results of various white light sources and industrial cameras of different models. The method is high in testing efficiency, simple and convenient to operate and capable of comprehensively reflecting the photoelectric conversion performance of the industrial camera in an actual application scene.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement and image sensor performance evaluation, and relates to a method for measuring the average quantum efficiency of an industrial camera based on a white light source. By controlling a test instrument to collect images and process and analyze photoelectric response data, an average quantum efficiency measurement model is constructed to achieve efficient and accurate measurement of the average quantum efficiency of the industrial camera. Background Art

[0002] Quantum efficiency is one of the important parameters for evaluating the performance of industrial cameras, and its measurement results directly affect the performance of the camera in practical applications. With the widespread application of industrial cameras in fields such as automated inspection, precision measurement, and scientific research, higher requirements are placed on the accuracy and efficiency of their quantum efficiency measurements. However, the existing quantum efficiency measurement methods are mainly based on monochromatic light sources. Although this method has a certain measurement accuracy, it has limitations in actual operation: the monochromatic light source test process is complicated, the test efficiency is low, and it cannot fully reflect the actual photoelectric response performance of industrial cameras under multi-wavelength light source conditions. In addition, since monochromatic light testing requires frequent switching of the light source wavelength, it is easy to cause the accumulation of equipment calibration errors, further affecting the accuracy and repeatability of the measurement.

[0003] At present, in order to solve the above-mentioned problems, a Chinese patent with publication number CN 112492300 A) discloses a polarization spectrum camera detector and detection method, including a light source generation module, a light source modulation module, a data acquisition and processing module, a power control module, and an optical darkroom. When working, step 1, initialize the camera and the optical path; step 2, modulate the intensity and wavelength of the incident light source of the camera; step 3, collect image data; step 4, calculate the quality parameters of the camera using an algorithm based on the image data collected in step 3; step 5, change the polarization state of the incident light and the intensity and wavelength of the light source, repeat steps 3 and 4, and complete the quality parameter detection of the camera under the polarized light state. The device improves the quality and type of the detection light source, but it has the following limitations: due to the use of a monochromatic light source and a single wavelength point-by-point scanning method, the test efficiency is low; at the same time, the camera quality parameters measured under monochromatic light conditions are difficult to directly reflect the performance of industrial cameras in actual wide spectrum or white light source environments. The standardized quantum efficiency measurement methods widely used in the industry include the test process based on the EMVA1288 standard, which specifies the method and process for testing the quantum efficiency of industrial cameras using a monochromatic light source. However, in actual application scenarios, industrial cameras usually work under a wide spectrum or white light source environment, and the monochromatic light test results are difficult to directly apply to evaluate the actual performance of the camera. Therefore, studying the quantum efficiency measurement method of industrial cameras based on white light sources can not only improve the test efficiency, but also more comprehensively characterize the optoelectronic performance of the camera, thereby providing more reliable data support for its performance optimization in complex application scenarios.

[0004] At present, there are few studies on quantum efficiency measurement methods based on white light sources, and its testing technology and theoretical models still need to be further explored and improved. Compared with the monochromatic light source method, white light source testing can avoid the operational complexity of frequent switching of light source wavelengths, while reducing the impact of accumulated calibration errors. However, this method also faces many challenges, such as how to achieve precise control of light source intensity, how to ensure the repeatability of camera test data, and how to establish an efficient and reliable measurement model. Therefore, a method for measuring the quantum efficiency of industrial cameras based on white light sources is proposed, which is of great significance to the technical improvement and innovation in the field of industrial camera performance testing. Summary of the invention

[0005] The purpose of the present invention is that the current method for measuring the quantum efficiency of industrial cameras based on monochromatic light sources is complex to operate, has low efficiency, and cannot fully reflect the photoelectric response performance of industrial cameras under wide-spectrum light sources. In order to solve the above problems, we propose a new method for measuring the quantum efficiency of industrial cameras based on white light sources. This method controls the white light source and the industrial camera to collect image signals, and combines the relationship between the incident light intensity and the photoelectric response of the camera output to construct a quantum efficiency measurement model, thereby achieving efficient and accurate measurement of the average quantum efficiency of industrial cameras.

[0006] The principle of the present invention is: using a stable white light source as the lighting system, and adjusting the light intensity to cover the dynamic range of the industrial camera. The industrial camera is placed in an illumination environment of a white light source, the light intensity of the light source is gradually changed, and multiple sets of exposure images output by the camera are synchronously collected, while the incident light intensity value measured by a standard photometer is recorded. The average quantum efficiency of the camera is determined by combining the photoelectric response characteristics of the industrial camera and the global system gain value of the experimental data curve fitting, and combining the measurement model of the average quantum efficiency.

[0007] The objectives of the present invention are achieved through the following technical solutions.

[0008] A device and method for measuring the average quantum efficiency of an industrial camera based on a white light source, comprising a white light LED light source, a program-controlled constant current source, a light homogenizing device, a closed cavity with an aperture, a fiber optic spectrometer, an industrial camera to be tested, a computer and a control circuit.

[0009] The process of measuring quantum efficiency using the above device is as follows:

[0010] Step 1: Install the white light LED light source at the light entrance of the closed cavity, and stabilize the light source current through a programmable constant current source. The white light source is processed by the light homogenization device to form a uniform surface light source. The light beam enters from one end of the closed cavity, and the light exit of the cavity is connected to the industrial camera to be tested. Adjust the light source current to fully cover the dynamic range of the image sensor.

[0011] Step 2: Use a fiber optic spectrometer to measure the spectral irradiance distribution of the light source at the image sensor position to ensure the uniformity and light intensity accuracy of the light source. The spectral irradiance data is transferred to a computer for storage.

[0012] Step 3: Control the industrial camera to be tested to gradually collect multiple sets of images under different light intensity conditions. The computer extracts the grayscale signal value of the image and removes the dark current signal, and calculates the digital signal mean μ by the variable illumination method. y -μ y.dark .

[0013] Step 4: Based on the experimental data curve fitting, the global system gain K is obtained and the number of incident photons μ corresponding to different light intensity conditions is calculated. p , combined with the measurement model of average quantum efficiency, the average quantum efficiency of the camera is determined.

[0014] Beneficial Effects

[0015] The present invention has the following significant advantages over the existing technologies at home and abroad:

[0016] 1. Easy operation and avoid waste of resources. This method uses white light source to test the average quantum efficiency of industrial cameras, without complex monochromatic light source adjustment and tedious sample processing. The device has a simple structure and clear operation process, which significantly reduces the preparation cost of equipment and samples and reduces waste of resources.

[0017] 2. Wide applicability and comprehensive performance evaluation. This method is based on a white light source, covers a wide spectral range, and can more comprehensively reflect the photoelectric response characteristics of industrial cameras in practical applications. Compared with the traditional test method based on monochromatic light, this invention not only improves the measurement efficiency, but also is closer to the actual use scenario, enhancing the applicability of the test results.

[0018] 3. Efficient measurement with reliable accuracy. This method uses a precisely controlled uniform white light source and a measurement process that complies with the EMVA1288 standard. It calculates the average quantum efficiency through an efficient data processing algorithm, with high measurement accuracy and strong repeatability. The system is low-cost and suitable for efficient testing and performance optimization of industrial cameras.

[0019] 4. Strong innovation and excellent scalability. The present invention has made innovative improvements on the traditional variable illumination method and constructed a quantum efficiency measurement model based on a white light source. The model has good scalability and can be further applied to the performance evaluation of other optoelectronic devices, providing new ideas for the field of optical measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the average quantum efficiency measurement method for industrial cameras with white light sources.

[0021] Figure 2 Equipment diagram for the average quantum efficiency measurement method for industrial cameras with white light sources.

[0022] Among them, 1-white light source; 2-light homogenizing device; 3-closed cavity with aperture; 4-industrial camera to be tested; 5-fiber optic spectrometer; 6-computer; 7-programmable constant current source. DETAILED DESCRIPTION

[0023] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0024] The basic principle of the present invention is based on the measurement of the response characteristics of industrial cameras under white light. The working principle of digital cameras is: the image sensor converts the photons incident on the pixel area during the exposure time into a certain number of electrons, which are converted into a voltage signal of a certain amplitude through the capacitor storing these charges. The signal is amplified and quantized and finally becomes the grayscale value of the digital image. Figure 1 As shown, according to the EMVA1288 standard, when monochromatic light is incident, the number of photons with a wavelength of λ1 received by a single pixel during the exposure time of the image sensor is These photons are converted into The quantum efficiency of electrons in the single wavelength case is The number is The number of electrons and The dark electrons (the number of electrons generated in the absence of light) are converted by the system gain K and superimposed on the noise source σ distributed in the quantization interval. q , and finally outputs the digital signal y.

[0025] For a white light source, it is assumed that there are n n The total number of photons under the condition of white light incident is μ p , the total number of photogenerated electrons is μ e , then the average quantum efficiency That is μ e With μ p Ratio of:

[0026]

[0027] in

[0028] exist Figure 2 In the system structure equipment diagram, the industrial camera 4 to be tested converts the photogenerated electrons into digital values ​​y. In the linear model, this process can be described by the global system gain K, with the unit of DN / e -(DN is a dimensionless digital code value), which represents the change in digital output caused by each electron. The mean value of the output digital signal y can be expressed as:

[0029] μ y =K(μ e +μ d ) (2)

[0030] where μ d It is the average number of electrons generated by the thermal effect of the circuit in the absence of light. These electrons are eventually transformed into the average dark signal μ under zero irradiation. y.dark =Kμ d (Unit: DN). Substituting into formula 2, we get:

[0031] μ y -μ y.dark =Kμ e (3)

[0032] Substituting formula (3) into formula (1), we have:

[0033]

[0034] That is, to calculate the average quantum efficiency, the corresponding values ​​of the three parameters need to be obtained respectively:

[0035] 1) The mean value μ of the digital signal generated by the photogenerated electrons through the system gain y -μ y.dark ;

[0036] 2) Global system gain K;

[0037] 3) Number of incident photons μ p .

[0038] For the digital signal mean μ y -μ y.dark , respectively, in bright field and dark field, the computer 6 controls the state of the white light source 1 through the program-controlled constant current source 7 to continuously collect images. For a bright field image y with a size of M×N A With y B , dark field image y A.dark With y B.dark , the signal mean is calculated by formula (5) (6).

[0039]

[0040] For the global system gain K, by fitting the variance of the digital image The average gray value (μ y -μ y.dark ), whose slope is the desired value, as shown in formula (7).

[0041]

[0042] Bright field variance Calculated by formula (10). Dark field variance Calculated by formula (11):

[0043]

[0044] For the total number of incident photons μ p According to the EMVA1288 standard, at exposure time t exp The wavelength is λ i The number of photons incident on a pixel with an area of ​​A is The irradiance E that can pass through the sensor surface i , photon energy hν i Work out:

[0045]

[0046] Formula (10) is for monochromatic light sources. If a white light source is used, the spectral irradiance data of the light source measured in real time by the fiber optic spectrometer 5 should be used (using the common units of sensor parameters, A: μm 2 ,t exp :ms,λ i λ i+1 :μm,E i E i+1 :μW / cm 2 / nm) to calculate the total number of photons and substitute the parameter light speed c = 2.99792458×10 8 m / s, Planck constant h=6.6260755×10-34Js:

[0047]

[0048] Among them, λ i represents the starting wavelength of the ith interval among the total number of n discretized intervals, is the central wavelength of this interval, E i Represents the wavelength λ in the spectral irradiance data i The corresponding unit irradiance value.

[0049] The average quantum efficiency measurement method of the industrial camera based on the white light source of the present invention is as follows:

[0050] The first step is to deploy the measuring device. The structure of the measuring device is as follows: Figure 2As shown, it includes a white light source 1, a light homogenizing device 2, a closed cavity with an aperture 3, an industrial camera to be tested 4, a fiber optic spectrometer 5, a computer 6, and a program-controlled constant current source 7. The white light source forms a uniform surface light source through the light homogenizing device, and irradiates the light through the light inlet of the closed cavity to the light outlet, which is connected to the industrial camera to be tested. The entire system is controlled by a computer to achieve light source adjustment, image acquisition, and data processing.

[0051] Step 2: Collect spectrum and image data. Turn on the white light source and adjust the input current of the light source through the programmable constant current source. Use the fiber optic spectrometer to measure the spectral irradiance distribution at the position of the industrial camera sensor. The industrial camera to be tested collects image data under different illuminations, and the computer synchronously records the spectral irradiance and image signal.

[0052] Step 3: Data processing and quantum efficiency measurement. Calculate the digital signal mean μ according to formula (5) (6): y -μ y.dark Based on the experimental data curve, the noise variance is calculated and the global system gain K is obtained by fitting according to (7), (8), and (9). The number of incident photons μ corresponding to different light intensities is calculated according to formula (11). p , and the average quantum efficiency of the camera is determined by combining the measurement model of the average quantum efficiency and formula (4).

[0053] This method is not only applicable to quantum efficiency measurement in the visible light band, but can also be applied to measurement in the ultraviolet and infrared bands by replacing the light source, homogenizing device and spectrometer of the corresponding band, thus meeting the performance evaluation requirements of industrial cameras under different spectral conditions.

[0054] The specific implementation modes of the present invention are described above in conjunction with the accompanying drawings, but these descriptions cannot be understood as limiting the scope of the present invention. The protection scope of the present invention is defined by the attached claims, and any changes based on the claims of the present invention are within the protection scope of the present invention.

Claims

1. A method for measuring the average quantum efficiency of an industrial camera based on a white light source, which is characterized by the following steps: The first step is to deploy an average quantum efficiency measurement device for an industrial camera based on a white light source, which is characterized by comprising a white light source 1, a light homogenizing device 2, a closed cavity with an aperture 3, an industrial camera to be tested 4, a fiber optic spectrometer 5, a computer 6, and a program-controlled constant current source 7; The second step is to turn on the white light source 1, adjust the input current through the program-controlled constant current source 7, use the optical fiber spectrometer 5 to measure the spectral irradiance distribution at the sensor position of the industrial camera 4 to be tested, collect image data under different illuminations of the industrial camera 4 to be tested, and the computer 6 synchronously records the spectral irradiance and image signal; The second step is to turn on the white light source 1, adjust the input current through the program-controlled constant current source 7, use the optical fiber spectrometer 5 to measure the spectral irradiance distribution at the sensor position of the industrial camera 4 to be tested, collect image data under different illuminations of the industrial camera 4 to be tested, and the computer 6 synchronously records the spectral irradiance and image signal; The third step is to collect the bright field image y of size M×N collected by the industrial camera 4 to be tested. A With y B , dark field image y A.dark With y B.dark The digital signal is sent to the computer 6 for processing and the mean value μ of the digital signal output by the camera is calculated. y -μ y.dark And the noise variance The formula is as follows; By fitting the image The average gray value (μ y -μ y.dark ), the global system gain K can be obtained from its slope; The third step is to extract the irradiance data recorded by the fiber spectrometer 5, and calculate the number of photons μ incident on the industrial camera 4 under different illumination conditions of the white light source 1 based on the calculation formula of the incident photons of monochromatic light. p , at exposure time t exp The wavelength is λ i The number of photons incident on a pixel with an area of ​​A is The irradiance E that can pass through the sensor surface i , photon energy hν i work out; If a white light source is used, the spectral irradiance data of the light source measured in real time by the fiber optic spectrometer 5 should be used (using the common units of sensor parameters, A: μm 2 ,t exp :ms,λ i λ i+1 :μm,E i E i+1 :μW / cm 2 / nm) to calculate the total number of photons and substitute the parameter light speed c = 2.99792458×10 8 m / s, Planck constant h = 6.6260755 × 10-34 Js; Among them, λ i represents the starting wavelength of the ith interval among the total number of n discretized intervals, is the central wavelength of this interval, E i Represents the wavelength λ in the spectral irradiance data i The corresponding unit irradiance value; The fourth step is to obtain the calculation formula of average quantum efficiency through the average quantum efficiency measurement model under white light source; The digital signal mean μ calculated in the third step is y -μ y.dark , global system gain K, total number of incident photons μ p Substituting into the formula, the average quantum efficiency of the camera 4 under test under the white light source 1 can be obtained:

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