Infrared radiation inversion method for small targets at long distances

Abstract

The present invention relates to the field of target infrared radiation inversion, and in particular to a method for inverting infrared radiation of a small, distant target. The method comprises the following steps: S1: imaging the small, distant target using an infrared imaging system to obtain an original image; S2: performing grayscale segmentation on the target region and the background region in the original image to extract the target region; S3: calculating the gradient amplitude distribution within the extracted target region; S4: obtaining an ideal imaging region of the target based on the gradient amplitude distribution within the target region; S5: calculating the target equivalent grayscale based on the ideal imaging region; and S6: inverting the target radiance based on the target equivalent grayscale. The method uses the gradient amplitude distribution calculation method to effectively estimate the theoretical image plane size of the small, distant target, and inverts the target radiance of the small, distant target based on the theoretical image plane size. The method does not rely on the actual size of the small target as a priori information and is applicable to small targets of unknown size.

Description

Technical Field

[0001] The present invention belongs to the technical field of target infrared radiation inversion, and in particular relates to a method for inverting infrared radiation of a small target at a long distance. Background Art

[0002] As infrared imaging systems improve in performance, detection ranges are increasing. When detecting long-range targets, small targets appear as small surface sources in the image. Due to image degradation caused by optical, mechanical, and atmospheric factors, the high-frequency edge information of the small target image plane is smoothed, causing the energy of the small target image plane to diffuse outward, resulting in a grayscale characteristic similar to a Gaussian distribution. Therefore, grayscale correction of the small target image plane is necessary. Because the small target image plane lacks sharp edges, its ideal image plane size cannot be effectively extracted. In this case, the actual size of the small target must be used as a priori to invert the small target's radiant brightness. Otherwise, significant errors will be introduced, seriously affecting the accuracy of small target radiometric measurements.

[0003] Existing small target radiance inversion methods mainly rely on the known physical area of ​​the small target and restore the grayscale of the small target image based on the energy conservation method. However, this method is not applicable to small targets of unknown size. Summary of the Invention

[0004] In view of this, the present invention aims to provide a method for infrared radiation inversion of small targets at a long distance, so as to solve the technical problem that the radiation brightness inversion cannot be achieved when the size of the small target is unknown.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] A method for inverting infrared radiation of a small target at a long distance includes the following steps:

[0007] S1: Use the infrared imaging system to image a small target at a long distance and obtain the original image;

[0008] S2: Perform grayscale segmentation on the target area and background area in the original image to extract the target area;

[0009] S3: Based on the extracted target area, calculate the gradient amplitude distribution within the target area;

[0010] S4: obtaining a target ideal imaging area based on the gradient amplitude distribution within the target area;

[0011] S5: Calculate the target equivalent grayscale based on the target ideal imaging area;

[0012] S6: Invert the target radiance based on the target equivalent grayscale.

[0013] Furthermore, step S2 specifically includes the following steps:

[0014] S21: Select the background area in the original image and calculate the background grayscale mean within the background area and background area noise ;

[0015] S22: The target area and background area in the original image are segmented by grayscale based on the segmentation threshold, thereby extracting the target area.

[0016] Furthermore, in step S3, the gradient amplitude distribution The calculation formula is as follows:

[0017] ;

[0018] ;

[0019] ;

[0020] in, represents the horizontal gradient, represents the vertical gradient, Indicates the i +1 row, j The pixel value at column , Indicates the i Row, No. j The pixel value at column , Indicates the j +1 row, i The pixel value at column.

[0021] Furthermore, in step S4, based on the gradient amplitude distribution within the target area, the extreme gradient amplitude at the edge of the target is determined, and the area surrounded by the extreme gradient amplitude is the target ideal imaging area.

[0022] Furthermore, in step S5, the target equivalent grayscale The calculation formula is as follows:

[0023] ;

[0024] ;

[0025] in, Indicates the distance between the target and the infrared imaging system, represents the focal length of the infrared imaging system, Indicates the pixel size of the detector in the infrared imaging system, represents the target ideal imaging area, Represents the total grayscale of the target area, Indicates the target energy diffusion area within the target area, Indicates the target grayscale within the target energy diffusion area, Represents the background grayscale mean in the background area.

[0026] Furthermore, the area within the target area except the target ideal imaging area is the target energy diffusion area.

[0027] Furthermore, in step S6, the target radiance The inversion formula is as follows:

[0028] ;

[0029] in, and represents the radiation calibration coefficient of the infrared imaging system, represents the atmospheric transmittance, represents atmospheric radiation, represents the target emissivity, represents the ambient radiation, Indicates the target equivalent grayscale.

[0030] Furthermore, after step S6, the following steps are further included:

[0031] S7: Inversion of target apparent temperature based on target equivalent grayscale , the inversion formula is as follows:

[0032] ;

[0033] in, represents the target emissivity, and represents the response band of the infrared imaging system, Represents any wavelength within the working band of the infrared imaging system, and represents the radiation constant, Indicates the target temperature.

[0034] Furthermore, when the infrared imaging system is a mid-infrared imaging system, the response band is 3.7μm~4.8μm; when the infrared imaging system is a long-wave infrared imaging system, the response band is 7.7μm~9.5μm.

[0035] Furthermore, the size of the target ideal imaging area is in the range of 9 to 81 pixels.

[0036] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0037] (1) The present invention uses the method of calculating the gradient amplitude distribution to effectively estimate the theoretical image plane size of a small target at a long distance, and performs target radiance inversion for the small target at a long distance based on the theoretical image plane size. This method does not need to rely on the actual size of the small target as a priori and is suitable for small targets of unknown size.

[0038] (2) The present invention can achieve effective inversion of target radiance based on a single-band target infrared image, thereby reducing the cost of the infrared imaging system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0040] Figure 1 A schematic diagram of the process of inverting infrared radiation of a small target at a distance according to an embodiment of the present invention;

[0041] Figure 2 A schematic diagram showing the distribution of the background area, the target energy diffusion area, and the target ideal imaging area in the target area according to an embodiment of the present invention;

[0042] Figure 3 A schematic diagram of the gradient amplitude distribution within the target area described in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0044] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0045] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0046] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "assemble," "connect," and "connect" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0047] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0048] like Figure 1 As shown, the present invention provides a method for inverting infrared radiation of a small target at a long distance, including the following steps:

[0049] S1: Use the infrared imaging system to image a small target at a long distance and obtain the original image.

[0050] The infrared imaging system is an air-based infrared imaging system or a ground-based infrared imaging system. When the infrared imaging system is an air-based infrared imaging system, the long-distance small target is a ground-based target; when the infrared imaging system is a ground-based infrared imaging system, the long-distance small target is an air-based target.

[0051] The infrared imaging system adopts a medium-wave infrared imaging system or a long-wave infrared imaging system. The response band of the medium-wave infrared imaging system is 3.7μm~4.8μm, and the response band of the long-wave infrared imaging system is 7.7μm~9.5μm.

[0052] The infrared imaging system has completed absolute radiation calibration before detecting small targets at long distances.

[0053] S2: Perform grayscale segmentation on the target area and background area in the original image to extract the target area.

[0054] Step S2 specifically includes the following steps:

[0055] S21: Select the background area in the original image and calculate the background grayscale mean within the background area and background area noise .

[0056] S22: The target area and background area in the original image are segmented by grayscale based on the segmentation threshold, thereby extracting the target area.

[0057] like Figure 2 As shown, the original image includes the target area and the background area. The area outside the target area in three rows and three columns is used as the background area. The background grayscale mean value in the background area is calculated. and background area noise , thereby extracting the target area, which includes the target ideal imaging area and the target energy diffusion area, and the target energy diffusion area is located between the background area and the target ideal imaging area.

[0058] S3: Based on the extracted target region, calculate the gradient amplitude distribution within the target region.

[0059] Gradient amplitude distribution Including horizontal gradient and vertical gradient .

[0060] Horizontal gradient The calculation formula is:

[0061] ;

[0062] in, Indicates the i +1 row, j The pixel value at column , Indicates the i Row, No. j The pixel value at column.

[0063] Vertical gradient The calculation formula is:

[0064] ;

[0065] in, Indicates the j +1 row, i The pixel value at column.

[0066] Gradient amplitude distribution The calculation formula is:

[0067] .

[0068] Gradient amplitude distribution Indicates the intensity of pixel value changes in the target area. The larger the gradient amplitude, the more intense the pixel value changes in the target area and the more obvious the grayscale changes; the smaller the gradient amplitude, the more gradual the pixel value changes in the target area and the more blurred the grayscale changes. Figure 3 As shown, the boundary between the target ideal imaging area and the target energy diffusion area can be determined by the gradient amplitude distribution of the target area.

[0069] S4: Acquire a target ideal imaging area based on the gradient amplitude distribution within the target area.

[0070] According to the image degradation model ,in, For degraded images, is the original image, is the degradation function, is a noise function. Without considering the noise, the degraded image is the convolution of the original image and the degradation function. For an ideal uniform radiation source, it has a clear edge in a rational imaging system. The edge feature of the uniform radiation source can be described as a step function in one dimension. :

[0071] ;

[0072] Where, is the target response value, is the background response value, is the target edge position.

[0073] For an infrared imaging system with good focus and stable target tracking, at a higher frame rate, assuming that image degradation is mainly due to atmospheric effects, the degradation function uses the atmospheric point spread function, which has a Gauss-like distribution characteristic:

[0074] ;

[0075] Derivative the one-dimensional form of the degraded image:

[0076] ;

[0077] The derivative of is the Dirichlet function, and the convolution of any function with the Dirichlet function is equal to itself. Therefore, the above formula is finally expressed as:

[0078] .

[0079] According to the Gauss distribution characteristics, at the edge At is an extreme value, corresponding to the maximum gradient point at the edge of the degraded image. Therefore, The extreme value of directly reflects the extreme gradient amplitude at the edge of the degraded image. For a two-dimensional image, this represents the degraded image. At the edge of the original image, the gradient amplitude has an extreme value. The area enclosed by the extreme gradient amplitude is the target ideal imaging area. The pixel size of the target ideal imaging area represents the theoretical image size of a small target at a distance, preferably within the range of 9 to 81 pixels. The area outside the target ideal imaging area is the target energy dispersion area.

[0080] S5: Calculate the target equivalent grayscale based on the target ideal imaging area.

[0081] Target equivalent grayscale The calculation formula is as follows:

[0082] ;

[0083] in, Indicates the distance between the target and the infrared imaging system, represents the focal length of the infrared imaging system, Indicates the pixel size of the detector in the infrared imaging system, represents the target ideal imaging area, Represents the total grayscale of the target area, and the calculation formula is as follows:

[0084] ;

[0085] in, Indicates the target energy diffusion area within the target area, Indicates the target grayscale within the target energy diffusion area, Represents the background grayscale mean in the background area.

[0086] S6: Invert the target radiance based on the target equivalent grayscale.

[0087] Target radiance The inversion formula is as follows:

[0088] ;

[0089] in, and represents the radiation calibration coefficient of the infrared imaging system, represents the atmospheric transmittance, represents atmospheric radiation, and Calculated using atmospheric model calculation software, represents the target emissivity, represents the ambient radiation, Indicates the target equivalent grayscale.

[0090] After step S6, the following steps are also included:

[0091] S7: Inversion of target apparent temperature based on target equivalent grayscale , the inversion formula is as follows:

[0092] ;

[0093] in, represents the target emissivity, and represents the response band of the infrared imaging system, Represents any wavelength within the working band of the infrared imaging system, and represents the radiation constant, Indicates the target temperature.

[0094] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0095] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for inverting infrared radiation of a small target at a long distance, characterized in that: The steps include: S1: Use the infrared imaging system to image a small target at a long distance and obtain the original image; S2: Perform grayscale segmentation on the target area and background area in the original image to extract the target area; S3: Based on the extracted target area, calculate the gradient amplitude distribution within the target area; S4: obtaining a target ideal imaging area based on the gradient amplitude distribution within the target area; S5: Calculate the target equivalent grayscale based on the target ideal imaging area; In step S5, the target equivalent grayscale The calculation formula is as follows: ； ； in, Indicates the distance between the target and the infrared imaging system, represents the focal length of the infrared imaging system, Indicates the pixel size of the detector in the infrared imaging system, represents the target ideal imaging area, Represents the total grayscale of the target area, Indicates the target energy diffusion area within the target area, Indicates the target grayscale within the target energy diffusion area, Represents the background grayscale mean value in the background area; the area outside the target ideal imaging area in the target area is the target energy diffusion area; S6: Invert the target radiance based on the target equivalent grayscale; in step S6, the target radiance The inversion formula is as follows: ； in, and represents the radiation calibration coefficient of the infrared imaging system, represents the atmospheric transmittance, represents atmospheric radiation, represents the target emissivity, represents the ambient radiation, Indicates the target equivalent grayscale.

2. The infrared radiation inversion method for a small target at a long distance according to claim 1, characterized in that: Step S2 specifically includes the following steps: S21: Select the background area in the original image and calculate the background grayscale mean within the background area and background area noise ; S22: The target area and background area in the original image are segmented by grayscale based on the segmentation threshold, thereby extracting the target area.

3. The infrared radiation inversion method for a small target at a long distance according to claim 1, characterized in that: In step S3, the calculation formula of the gradient amplitude distribution is as follows: ； ； ； in, represents the horizontal gradient, represents the vertical gradient, Indicates the i +1 row, j The pixel value at column , Indicates the i Row, No. j The pixel value at column , Indicates the j +1 row, i The pixel value at column.

4. The infrared radiation inversion method for a small target at a long distance according to claim 1, characterized in that: In step S4, the gradient amplitude extreme value at the target edge position is determined according to the gradient amplitude distribution within the target area, and the area surrounded by the gradient amplitude extreme value is the target ideal imaging area.

5. The infrared radiation inversion method for a small target at a long distance according to claim 1, characterized in that: After step S6, the following steps are also included: S7: Inversion of target apparent temperature based on target equivalent grayscale , the inversion formula is as follows: ； in, represents the target emissivity, and represents the response band of the infrared imaging system, Represents any wavelength within the working band of the infrared imaging system, and represents the radiation constant, Indicates the target temperature.

6. The infrared radiation inversion method for a small target at a long distance according to claim 5, characterized in that: When the infrared imaging system is a mid-infrared imaging system, the response band is 3.7μm~4.8μm; when the infrared imaging system is a long-wave infrared imaging system, the response band is 7.7μm~9.5μm.

7. The infrared radiation inversion method for a small target at a long distance according to claim 1, characterized in that: The size of the target ideal imaging area ranges from 9 to 81 pixels.

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