A method and device for small target infrared diffusion imaging based on point source blackbody

Abstract

The present invention discloses a method and device for infrared diffusion imaging of small targets based on a point source blackbody. First, based on the principle of small target infrared imaging diffusion, a small target diffusion imaging model is constructed to obtain a theoretical diffusion area that varies with distance. The constructed small target diffusion imaging model is calibrated based on dynamic test performance to obtain a small target diffusion calibration area. The small target diffusion calibration area is then compared with the actual diffusion area of ​​the small target measured to verify whether the derived diffusion calibration area conforms to the small target imaging diffusion size. This method and device overcome the problem in the prior art that the target imaging principle is not suitable for small target imaging ambiguity. It can effectively improve the accurate measurement of small target imaging size and provide a testing basis for target recognition in future infrared imaging systems.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a small target infrared diffusion imaging method and device based on a point source blackbody. Background Art

[0002] Due to the precise need for infrared imaging systems to detect targets, infrared imaging of targets has become a key task in weapon system development. For infrared imaging targets in complex scenes, the diffusion phenomenon in the image causes small targets in the scene to appear blurred. Accurately measuring the actual size of small targets in the image requires in-depth research into the imaging principles of infrared targets and detector effects. When detecting small targets using infrared detectors, the thermal radiation information of the small targets forms grayscale information at the detector imaging interface. These grayscale features represent the diffraction-limited light intensity distribution formed on the image plane after the target passes through the optical system. Under ideal conditions, the light intensity distribution before and after the image plane is symmetrical, varying with the field of view. However, in actual optical imaging, this symmetry is disrupted by factors such as distortion, coma, and aberration.

[0003] For the measurement research of infrared radiation characteristics of small point source targets, it is necessary to determine the actual diffusion size of the target based on the transmission characteristics of its optical system. To this end, factors such as the imaging mechanism of optical diffusion, detector effect, and main performance parameters of target imaging need to be taken into account. The target imaging mechanism is experimentally verified using a blackbody, and a new target diffusion imaging model is constructed based on the characteristic effect of the detector itself to achieve accurate measurement of the diffusion phenomenon and provide a test basis for target identification in future infrared imaging systems. Summary of the Invention

[0004] The purpose of the present invention is to provide a small target infrared diffuse imaging method and device based on a point source blackbody. This method and device overcome the problem in the prior art that the target imaging principle is not suitable for the fuzzy imaging of small targets, can effectively improve the accurate measurement of the imaging size of small targets, and provide a test basis for target identification in future infrared imaging systems.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A small target infrared diffusion imaging method based on a point source blackbody, the method comprising:

[0007] Step 1: Based on the diffusion principle of small target infrared imaging, a small target diffusion imaging model is constructed to obtain the theoretical diffusion area that varies with distance;

[0008] Step 2: calibrate the small target diffusion imaging model constructed according to the dynamic test performance to obtain the small target diffusion calibration area;

[0009] The dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference and minimum resolvable temperature difference;

[0010] Step 3: Compare the small target diffusion calibration area with the actual measured small target diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0011] A small target infrared diffusion imaging device based on a point source blackbody, the device comprising:

[0012] A model building unit is used to build a small target diffusion imaging model based on the diffusion principle of small target infrared imaging, and obtain a theoretical diffusion area that varies with distance;

[0013] A model calibration unit is configured to calibrate the constructed small target diffusion imaging model according to dynamic test performance to obtain a small target diffusion calibration area; wherein the dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference, and minimum resolvable temperature difference;

[0014] The verification unit is used to compare the small target diffusion calibration area with the actual measured small target diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0015] An electronic device includes a memory and a processor, wherein a computer program is stored in the memory and the processor is configured to run the computer program to perform the above method.

[0016] A computer storage medium is characterized in that the computer storage medium stores multiple instructions, and the instructions are suitable for being loaded by a processor to execute the above method.

[0017] It can be seen from the technical solution provided by the above-mentioned present invention that the above-mentioned method and device overcome the problem that the target imaging principle in the prior art is not suitable for the fuzzy imaging of small targets, can effectively improve the accurate measurement of the imaging size of small targets, and provide a test basis for target identification in future infrared imaging systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A schematic flow chart of a small target infrared diffusion imaging method based on a point source blackbody provided in an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the mapping relationship between the infrared image of the target and the detector according to an embodiment of the present invention;

[0021] Figure 3 Schematic diagram of the relationship between the total imaging modulation transfer function and the optical spatial frequency and the cutoff frequency according to an embodiment of the present invention;

[0022] Figure 4 Schematic diagram showing the comparison between the theoretical area of ​​diffusion imaging and the actual area varying with temperature and distance according to an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of the comparison between the actual imaging area of ​​a small target and the model calibration area according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments, and do not constitute a limitation of the present invention. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0025] The embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings. The contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art. In the embodiments of the present invention, if specific conditions are not specified, the conditions are carried out according to conventional conditions in the art or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used in the embodiments of the present invention, they are all conventional products that can be purchased commercially.

[0026] like Figure 1 FIG2 is a flow chart of a method for small target infrared diffusion imaging based on a point source blackbody according to an embodiment of the present invention. The method includes:

[0027] Step 1: Based on the diffusion principle of small target infrared imaging, a small target diffusion imaging model is constructed to obtain the theoretical diffusion area that varies with distance;

[0028] In this step, the image of the target obtained after passing through the infrared detection system conforms to the principle of optical refraction. The factors affecting the target imaging size are the target's true size and diffusion size, such as Figure 2 The figure shows the mapping relationship between the target infrared image and the detector according to the embodiment of the present invention, with reference to Figure 2 , if d is the actual size of the target, L is the distance between the target and the infrared detector, F is the focal length, and r is the radius of the diffusion circle, then the theoretical area s obtained on the imaging surface of the infrared detector is:

[0029]

[0030] Since the target will be diffused on the imaging surface, the obtained diffuse area is different from the actual theoretical area. The target diffuse size formed on the imaging surface is calculated according to the detection effective field of view angle:

[0031]

[0032] a is the effective field of view angle, expressed in radians or degrees, and α = nD / F, where D is the pixel size, n is the number of pixels after the target is imaged, and F is the focal length;

[0033] Substituting a into formula (2) yields:

[0034]

[0035] Then the actual imaging target diffusion size is:

[0036] nD=arctan(d / 2L)·F(4)

[0037] Therefore, the theoretical diffusion area formula without considering the detector effect is as follows:

[0038]

[0039] S L is the theoretical diffusion area obtained as the distance L changes.

[0040] Step 2: calibrate the small target diffusion imaging model constructed according to the dynamic test performance to obtain the small target diffusion calibration area;

[0041] In this step, the small target radiates light onto the focal plane array through the imaging detector, which is then converted into an electrical signal. The grayscale radiation field of the small target is reproduced in the imaging software. During the entire link process, the intrinsic characteristics of the small target, the path transmission, the imaging front end, the signal processing, and the arrival at the imaging interface will all affect the imaging characteristics of the small target. Dynamic test performance includes noise equivalent temperature difference (NETD), modulation transfer function (MTF), minimum detectable temperature difference (MDTD), and minimum resolvable temperature difference (MRTD). Specifically:

[0042] The noise equivalent temperature difference (NETD) is the equivalent temperature difference caused by the temperature difference between the target and the background after imaging being the same as the root mean square value of the detector noise. It reflects the sensitivity of the detection system and is defined as:

[0043]

[0044] Where V is the root mean square of the detector output voltage; F# is the optical F number of the detector; A dis the imaging area at the front end of the detector; λ is the wavelength; T is the temperature value within the wavelength range; τ is the atmospheric transmittance; M is the radiation emittance; R is the optical system response rate;

[0045] The modulation transfer function (MTF) includes the diffraction transfer function and the aberration transfer function. The diffraction transfer function depends on the aperture and wavelength and is expressed as:

[0046]

[0047] is the diffraction transfer function; f x is the frequency in the x direction of the imaging system space; f y is the frequency in the y direction of the imaging system space; f c is the cutoff frequency;

[0048] The energy distribution caused by aberration is a circularly symmetric Gaussian distribution, and the aberration transfer function is:

[0049] MTF(f)=exp(-2(π) 2 σ 2 f 2 )(8)

[0050] MTF(f) is the aberration transfer function; σ is the standard deviation; f is the optical spatial frequency;

[0051] The total modulation transfer function MTF is the product of the diffraction transfer function and the aberration transfer function, expressed as:

[0052]

[0053] In specific implementation, the total transfer function of the imaging system is generally between 0 and 1, such as Figure 3 FIG2 is a schematic diagram showing the relationship between the total imaging modulation transfer function and the optical spatial frequency and the cutoff frequency according to an embodiment of the present invention.

[0054] The minimum resolvable temperature difference (MRTD) is the minimum temperature difference between the target and the background after imaging at a fixed spatial frequency. It is used to evaluate the spatial resolution and temperature resolution of the system and is expressed as:

[0055]

[0056] Where, SNR TH The threshold signal-to-noise ratio for identifying 4 target features; σ tvh is the spatiotemporal random noise; k z (f) is the correction factor; MTF is the modulation transfer function; E t is the time integral function of the human eye; E h (f) and E v (f) is the spatial integration function for the human eye;

[0057] The minimum detectable temperature difference MDTD indicates the temperature difference between the target and the background at which a target of a specific size can be detected on the imaging interface, and is expressed as:

[0058]

[0059] Where MTF is the modulation transfer function, MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging, expressed as:

[0060]

[0061] Where W T is the horizontal size of the target; H T is the vertical size of the target; a is the horizontal instantaneous field of view; β is the vertical instantaneous field of view.

[0062] The following specific experiments verify the difference between the theoretical area of ​​diffusion imaging and the actual area that varies with temperature and distance:

[0063] The experiment used a point-source cavity blackbody with a temperature range of 30°C to 1250°C, a point source diameter of 0.25 inches, and a temperature resolution of 0.1°C. The point source blackbody had a uniformity greater than 95% and an emissivity of 0.999. The imaging detector used was the IRCAMEquus 327km, with a medium-wavelength range of 3.7µm to 5µm, a resolution of 640 x 512, a focal length of 50mm, a pixel size of 15µm, and an F / 2 aperture.

[0064] The experiment raised the temperature of the point source blackbody to 100°C, with the heat source emitted from a 0.25-inch aperture. A detector was then used to acquire the point source target on the blackbody. As the distance between the detector and the blackbody target gradually increased, the change in the point source target image size with distance could be obtained on the software interface.

[0065] Therefore, the focal length is selected as 25mm, the integration time is 20us, and the temperature is set at 100℃, 200℃, 300℃, 400℃, 500℃, and 600℃.

[0066] From the images of small point source targets on the detector at different distances, we can see that the size of the small target is getting smaller as the distance from the detector increases, and the pixels it occupies in the image are gradually decreasing. Using MATLAB to remove the background information of each image, we can get the pixel values ​​occupied by the small target imaging, as shown in Table 1:

[0067] Table 1 Imaging area of ​​small targets at different temperatures and distances (unit: mm 2 )

[0068]

[0069] According to the theoretical model of small target diffuse imaging derived in step 1, the actual area of ​​the blackbody point source small target temperature changes with distance in the range of 100℃-600℃ is compared, as shown in Figure 2. Figure 4 The figure shows a comparison diagram of the theoretical area of ​​diffusion imaging and the actual area that changes with temperature and distance according to an embodiment of the present invention. By comparing the change curves of the two, it can be seen that the theoretical area curve of diffusion imaging of a small target and the actual area curve show a certain similarity. Figure 4 The actual area between 100℃ and 600℃ is larger than the theoretical area and is regularly distributed. Due to the dynamic imaging mechanism, the theoretical area is obtained without considering the modulation transfer function, noise equivalent temperature difference, minimum detectable temperature difference and other factors of the imaging detector, resulting in the theoretical area being smaller than the actual area. Therefore, it is necessary to calibrate the constructed small target diffusion imaging model based on the dynamic test performance. The specific process is as follows:

[0070] According to the theoretical diffusion area formula (5) of small target imaging obtained in step 1, by studying the dynamic imaging mechanism of the imaging system, the small target imaging area is obtained after preliminary correction:

[0071] S=(1+NETD)·S L +MDTD(13)

[0072] Right now:

[0073] S is the calibration area value obtained according to the distance change after the small target is imaged; NETD is the noise equivalent temperature difference; S L is the theoretical diffusion area obtained by varying the distance L; MTF is the modulation transfer function; MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging;

[0074] At the same time, the relationship between the small target imaging area and temperature can be seen:

[0075]

[0076] …

[0077]

[0078] The calibration imaging diffusion area obtained with temperature change is:

[0079]

[0080] Where S1 is the calibrated diffuse area imaged at a temperature of 100°C; n is the value obtained by dividing the measured small target temperature by 100; T n is the small target temperature; Sn The calibration area obtained for different temperatures of the small target;

[0081] Then the small target diffusion calibration area S derived as the temperature and distance change is:

[0082]

[0083] Step 3: Compare the small target diffusion calibration area with the actual measured small target diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0084] For example, in order to verify that the calibrated small target diffusion calibration area is consistent with the actual measured area, the selected parameters are substituted into the calibration area model. The imaging detector used has a spatial resolution (MRTD) of 0.6 mrad, a noise equivalent temperature difference (NETD) of 25 mk, and a FOV of 21.7° × 17.5°. By adding each parameter to the formula (18) of the small target diffusion calibration area S, we obtain:

[0085]

[0086] At the same time, the field of view of the small blackbody point source target in the detector is 7.24°×7.24°. Substituting it into formula (12), we get I=0.138.

[0087] Substituting the detector parameters into equations (7), (8) and (9), we obtain MTF = 0.5.

[0088] Therefore, the small target diffusion calibration area S is:

[0089]

[0090] Compare the area obtained based on the above formula and parameter calibration with the actual area, and use MATLAB to process the comparison results, such as Figure 5 FIG. 1 is a schematic diagram showing a comparison between the actual imaging area of ​​a small target and the model calibration area according to an embodiment of the present invention. Figure 5 The small target diffusion calibration area that changes with temperature and distance is basically consistent with the actual imaging area. Even if there is a slight difference, it objectively verifies that the derived diffusion calibration area meets the requirements, providing authenticity for subsequent verification of simulation data.

[0091] It should be noted that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0092] Based on the method described in the embodiment of the present invention, the embodiment of the present invention further provides a small target infrared diffusion imaging device based on a point source blackbody, the device comprising:

[0093] A model building unit is used to build a small target diffusion imaging model based on the diffusion principle of small target infrared imaging, and obtain a theoretical diffusion area that varies with distance;

[0094] A model calibration unit is configured to calibrate the constructed small target diffusion imaging model according to dynamic test performance to obtain a small target diffusion calibration area; wherein the dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference, and minimum resolvable temperature difference;

[0095] The verification unit is used to compare the small target diffusion calibration area with the actual measured small target diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0096] The specific implementation process of each unit in the above device is described in the above method embodiment.

[0097] An embodiment of the present invention further provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor is configured to run the computer program to perform the steps in the above method embodiment.

[0098] An embodiment of the present invention further provides a computer storage medium, characterized in that the computer storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor to execute the steps of the above method embodiment. The above-mentioned storage medium can be a read-only memory, a magnetic disk, or an optical disk.

[0099] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or any form of implication that the information constitutes prior art already known to those skilled in the art.

Claims

1. A small target infrared diffusion imaging method based on point source blackbody, characterized in that: The method comprises: Step 1: Based on the diffusion principle of small target infrared imaging, a small target diffusion imaging model is constructed to obtain the theoretical diffusion area that varies with distance; Step 2: calibrate the small target diffusion imaging model constructed according to the dynamic test performance to obtain the small target diffusion calibration area; The dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference and minimum resolvable temperature difference; Step 3: Compare the small target diffusion calibration area with the actual measured small target diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

2. The small target infrared diffusion imaging method based on point source blackbody according to claim 1 is characterized in that: In step 1, the image of the target obtained after passing through the infrared detection system conforms to the principle of optical refraction. The factors affecting the target imaging size are the target's true size and diffusion size. If d is the target's true size, L is the distance between the target and the infrared detector, F is the focal length, and r is the radius of the diffusion circle, then the theoretical area s obtained on the infrared detector imaging surface is: Since the target will be diffused on the imaging surface, the obtained diffuse area is different from the actual theoretical area. The target diffuse size formed on the imaging surface is calculated according to the detection effective field of view angle: α is the effective field of view angle, expressed in radians or degrees, and α = nD / F, where D is the pixel size, n is the number of pixels after the target is imaged, and F is the focal length; Substituting α into formula (2) yields: Then the actual imaging target diffusion size is: nD=arctan(d / 2L)·F(4) Therefore, the theoretical diffusion area formula without considering the detector effect is as follows: S L is the theoretical diffusion area obtained as the distance L changes.

3. The small target infrared diffusion imaging method based on point source blackbody according to claim 2 is characterized in that: In step 2, The noise equivalent temperature difference (NETD) is the equivalent temperature difference caused by the temperature difference between the target and the background after imaging being the same as the root mean square value of the detector noise. It reflects the sensitivity of the detection system and is defined as: Where V is the root mean square of the detector output voltage; F# is the optical F number of the detector; A d is the imaging area at the front end of the detector; λ is the wavelength; T is the temperature value within the wavelength range; τ is the atmospheric transmittance; M is the radiation emittance; R is the optical system response rate; The modulation transfer function (MTF) includes the diffraction transfer function and the aberration transfer function. The diffraction transfer function depends on the aperture and wavelength and is expressed as: is the diffraction transfer function; f x is the frequency in the x direction of the imaging system space; f y is the frequency in the y direction of the imaging system space; f c is the cutoff frequency; The energy distribution caused by aberration is a circularly symmetric Gaussian distribution, and the aberration transfer function is: MTF(f)=exp(-2(π) 2 s 2 f 2 (8) MTF(f) is the aberration transfer function; σ is the standard deviation; f is the optical spatial frequency; The total modulation transfer function MTF is the product of the diffraction transfer function and the aberration transfer function, expressed as: The minimum resolvable temperature difference (MRTD) is the minimum temperature difference between the target and the background after imaging at a fixed spatial frequency. It is used to evaluate the spatial resolution and temperature resolution of the system and is expressed as: Where, SNR TH The threshold signal-to-noise ratio for identifying 4 target features; σ tvh is the spatiotemporal random noise; k z (f) is the correction factor; MTF is the modulation transfer function; E t is the time integral function of the human eye; E h (f) and E v (f) is the spatial integration function for the human eye; The minimum detectable temperature difference MDTD indicates the temperature difference between the target and the background at which a target of a specific size can be detected on the imaging interface, and is expressed as: Where MTF is the modulation transfer function; MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging, expressed as: Where W T is the horizontal size of the target; H T is the vertical size of the target; a is the horizontal instantaneous field of view; β is the vertical instantaneous field of view.

4. The small target infrared diffusion imaging method based on point source blackbody according to claim 3 is characterized in that: The process of step 2 is specifically as follows: According to the theoretical diffusion area formula (5) of small target imaging obtained in step 1, by studying the dynamic imaging mechanism of the imaging system, the small target imaging area is obtained after preliminary correction: S=(1+NETD)·S L +MDTD(13) Right now: S is the calibration area value obtained according to the distance change after the small target is imaged; NETD is the noise equivalent temperature difference; S L is the theoretical diffusion area obtained by varying the distance L; MTF is the modulation transfer function; MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging; At the same time, the relationship between the small target imaging area and temperature can be seen: The calibration imaging diffusion area obtained with temperature change is: Where S1 is the calibrated diffuse area imaged at a temperature of 100°C; n is the value obtained by dividing the measured small target temperature by 100; T n is the small target temperature; S n The calibration area obtained for different temperatures of the small target; Then the small target diffusion calibration area derived with the change of temperature and distance is: S is the small target diffusion calibration area derived with temperature and distance changes.

5. A small target infrared diffusion imaging device based on a point source blackbody, characterized in that: The device comprises: A model building unit is used to build a small target diffusion imaging model based on the diffusion principle of small target infrared imaging, and obtain a theoretical diffusion area that varies with distance; A model calibration unit is configured to calibrate the constructed small target diffusion imaging model according to dynamic test performance to obtain a small target diffusion calibration area; wherein the dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference, and minimum resolvable temperature difference; The verification unit is used to compare the small target diffusion calibration area with the actual measured small target diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

6. An electronic device comprising a memory and a processor, characterized in that: A computer program is stored in the memory, and the processor is configured to run the computer program to perform the method according to any one of claims 1 to 4.

7. A computer storage medium, characterized in that The computer storage medium stores a plurality of instructions, and the instructions are suitable for being loaded by a processor and executing the method according to any one of claims 1 to 4.

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