High-dynamic infrared image contrast enhancement method suitable for aerospace background

Abstract

The invention discloses a high-dynamic infrared image contrast enhancement method suitable for an aerospace background, and relates to the technical field of infrared image contrast enhancement, and the method comprises the steps: constructing an upper limit intermediate parameter and a lower limit intermediate parameter based on a mean value, a standard deviation and a cumulative distribution function of a gray scale probability distribution function of each frame of infrared image; the upper limit intermediate parameter is used for suppressing a highlight target occupying a small number of pixels; the lower limit intermediate parameter is used for suppressing a background occupying a large number of pixels; converting the upper limit intermediate parameter and the lower limit intermediate parameter into an upper limit gray threshold and a lower limit gray threshold; calculating a target mapping coefficient based on the upper and lower limit gray threshold values; constructing a mapping function based on the target mapping coefficient and the lower limit gray threshold; and based on the target infrared image and the mapping coefficient, obtaining the target infrared image after contrast enhancement so as to solve the problem that a traditional histogram equalization method has an over-enhanced background in infrared image processing and cannot adapt to infrared background changes.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared image contrast enhancement, and in particular relates to a high dynamic infrared image contrast enhancement method suitable for air-sky background. Background Art

[0002] For long-distance space detection systems such as vehicle-mounted infrared search and tracking systems, the target image on the detector often occupies only a few pixels, lacking obvious target attitude information, and due to the interference of the imaging background and the influence of the internal noise of the detector system, the signal-to-noise ratio of the target infrared image is low. Therefore, enhancing the contrast of high-dynamic original infrared images plays a very important role in improving the target signal-to-noise ratio and enhancing the search and tracking capabilities.

[0003] At present, the most commonly used image contrast enhancement method is histogram equalization. The histogram equalization algorithm aims to stretch the grayscale distribution of the original image. Although it can effectively stretch the grayscale dynamic range of the image, the algorithm has the problem of excessive background contrast enhancement and insignificant target contrast enhancement. The conventional histogram equalization algorithm selects the cumulative distribution function as the mapping function, which can only achieve an approximate uniform distribution and often cannot adapt to the problem of infrared background changes.

[0004] Therefore, the traditional histogram equalization method has the problem of over-enhancing the background in infrared image processing and cannot adapt to the changes of infrared background. Summary of the invention

[0005] The purpose of the present invention is to provide a high dynamic infrared image contrast enhancement method suitable for sky and space backgrounds, so as to solve the problem that the traditional histogram equalization method has excessive background enhancement in infrared image processing and cannot adapt to infrared background changes.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] On the one hand, this specification provides a high dynamic infrared image contrast enhancement method applicable to an air-sky background, comprising:

[0008] Step 102, based on the mean, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image, construct an upper intermediate parameter and a lower intermediate parameter; the upper intermediate parameter is used to suppress the highlight target occupying a small number of pixels; the lower intermediate parameter is used to suppress the background occupying a large number of pixels;

[0009] Step 104, based on preset weights, converting the upper intermediate parameter and the lower intermediate parameter into an upper grayscale threshold and a lower grayscale threshold;

[0010] Step 106, calculating and obtaining a target mapping coefficient based on the upper grayscale threshold and the lower grayscale threshold;

[0011] Step 108, constructing a mapping function based on the target mapping coefficient and the lower grayscale threshold;

[0012] Step 110: obtaining a contrast-enhanced target infrared image based on the target infrared image and the mapping coefficients.

[0013] On the other hand, the present specification provides a high dynamic infrared image contrast enhancement device suitable for air and sky background, comprising:

[0014] An intermediate parameter construction module is used to construct an upper intermediate parameter and a lower intermediate parameter based on the mean value, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image; the upper intermediate parameter is used to suppress a highlight target that occupies a small number of pixels; the lower intermediate parameter is used to suppress a background that occupies a large number of pixels;

[0015] A grayscale threshold obtaining module, used for converting the upper limit intermediate parameter and the lower limit intermediate parameter into an upper limit grayscale threshold and a lower limit grayscale threshold based on a preset weight;

[0016] A mapping coefficient calculation module, used to calculate and obtain a target mapping coefficient based on an upper grayscale threshold and a lower grayscale threshold;

[0017] A mapping function building module, used to build a mapping function based on a target mapping coefficient and a lower grayscale threshold;

[0018] The contrast enhancement module is used to obtain a contrast-enhanced target infrared image based on the target infrared image and the mapping coefficient.

[0019] Based on the above technical solution, this specification can achieve the following technical effects:

[0020] This method calculates the upper and lower grayscale threshold parameters of each frame of infrared image according to the mean, standard deviation and grayscale cumulative distribution function of each frame of image, thereby constructing an exponential mapping function. Through this method, the high-dynamic infrared image with a quantization accuracy of 14 bits can be compressed and displayed as an 8-bit image, while the background occupying a large number of pixels and the highlighted target occupying a small number of pixels can be moderately suppressed, leaving room for target and detail enhancement, thereby overcoming the shortcoming of the traditional histogram equalization method in infrared image processing that over-enhances the background. Under different sky and space infrared backgrounds, the contrast of high-dynamic infrared images can be significantly enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flowchart of a method for contrast enhancement of high dynamic infrared images suitable for sky and space backgrounds in one embodiment of the present invention.

[0022] Figure 2 The present invention is a flowchart of a method for contrast enhancement of high dynamic infrared images suitable for sky and space backgrounds in one embodiment of the present invention.

[0023] Figure 3 This is a diagram showing the effect of an infrared image of a sky and space background after being processed by a traditional histogram equalization method in one embodiment of the present invention.

[0024] Figure 4 This is a rendering of an infrared image of a sky and space background processed by a high dynamic infrared image contrast enhancement method suitable for a sky and space background in one embodiment of the present invention.

[0025] Figure 5 The present invention is a schematic structural diagram of a high dynamic infrared image contrast enhancement device suitable for sky and space backgrounds in one embodiment of the present invention.

[0026] Figure 6 The figure is a schematic diagram of an electronic device according to the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims. It should be noted that the drawings are all in very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0028] It should be noted that, in order to clearly explain the content of the present invention, the present invention specifically cites multiple embodiments to further illustrate different implementations of the present invention, wherein the multiple embodiments are enumerated rather than exhaustive. In addition, for the sake of brevity of explanation, the contents mentioned in the previous embodiments are often omitted in the subsequent embodiments. Therefore, the contents not mentioned in the subsequent embodiments can refer to the previous embodiments accordingly.

[0029] Example 1

[0030] Please refer to Figure 1 , Figure 1 The figure shows a high dynamic infrared image contrast enhancement method applicable to sky and space background provided by this embodiment. In this embodiment, the method includes:

[0031] Step 102, based on the mean, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image, construct an upper intermediate parameter and a lower intermediate parameter; the upper intermediate parameter is used to suppress the highlight target occupying a small number of pixels; the lower intermediate parameter is used to suppress the background occupying a large number of pixels;

[0032] In this embodiment, one implementation of step 102 is:

[0033] Step 202, obtaining a lower limit intermediate parameter based on the mean and standard deviation of the infrared image of the current frame;

[0034] Step 204 : taking the grayscale corresponding to when the cumulative distribution function of the infrared image of the current frame is equal to the preset threshold as the upper limit intermediate parameter.

[0035] In this embodiment, the preset threshold is 0.95.

[0036] Step 104, based on preset weights, converting the upper intermediate parameter and the lower intermediate parameter into an upper grayscale threshold and a lower grayscale threshold;

[0037] In this embodiment, the preset weight includes the weight of the infrared image of the current frame and the weight of the infrared image of the previous frame, and the sum of the weight of the infrared image of the current frame and the weight of the infrared image of the previous frame is equal to 1.

[0038] In this embodiment, the upper grayscale threshold is the sum of the product of the current frame infrared image weight and the upper limit intermediate parameter of the current frame infrared image and the product of the previous frame infrared image weight and the upper limit intermediate parameter of the previous frame infrared image.

[0039] In this embodiment, the lower grayscale threshold is the sum of the product of the current frame infrared image weight and the lower intermediate parameter of the current frame infrared image and the product of the previous frame infrared image weight and the lower intermediate parameter of the previous frame infrared image.

[0040] In this embodiment, the weight of the infrared image of the current frame is 0.01; the weight of the infrared image of the previous frame is 0.99.

[0041] Step 106, calculating and obtaining a target mapping coefficient based on the upper grayscale threshold and the lower grayscale threshold;

[0042] In this embodiment, one implementation of step 106 is:

[0043] Step 302, based on the upper grayscale threshold, the lower grayscale threshold and the intermediate mapping coefficient calculation formula, calculate and obtain the intermediate mapping coefficient;

[0044] Step 304: Calculate and obtain the target mapping coefficient based on the upper grayscale threshold, the lower grayscale threshold and the intermediate mapping coefficient.

[0045] Step 108, constructing a mapping function based on the target mapping coefficient and the lower grayscale threshold;

[0046] Step 110: obtaining a contrast-enhanced target infrared image based on the target infrared image and the mapping coefficients.

[0047] Specifically, refer to Figure 2, which is a flow chart of a high dynamic infrared image contrast enhancement method suitable for sky background.

[0048] S1. Count the mean value E of each frame of infrared image n , standard deviation D r And the cumulative distribution function CDF(i) of the grayscale probability distribution function.

[0049] Calculate the intermediate parameter gmin for each frame of infrared image n and gmax n , where gmin n =En-3Dn;gm a x n It is the grayscale corresponding to when the cumulative distribution function CDF(i) of the grayscale probability distribution function of the frame infrared image is 0.95.

[0050] It should be noted that the optimal choice of the preset threshold in this embodiment is 0.95, which is an empirical value. If the value is higher than this value, the infrared detector may be a flash element. This value should be adjusted according to the actual situation when using different infrared detectors and optical structure combinations.

[0051] gmin n It is a key parameter that can effectively suppress the background that occupies a large number of pixels. However, in order to avoid image jumps caused by scene changes, gmin n The parameters are improved to Gminn.

[0052] Where Gmin n =0.01gmin n +0.99gmin n-1 , qmin n is the parameter of the frame image, gmin n-1 is the parameter of the previous frame.

[0053] gmax n It is a key parameter that can suppress highlight targets. However, in order to avoid image jumps caused by scene changes, gmax n Parameter improvement is Gmax n .

[0054] Where Gmax n =0.01gmax n +0.99gmax n-1 .gmax n is the parameter of the frame image, gmax n-1 is the parameter of the previous frame.

[0055] Constructing the mapping function Pic out =K*(Pic in -Gminn ).

[0056] in

[0057] According to the above mathematical model, we can find Pic out This is the image after contrast enhancement.

[0058] refer to Figure 3 , which is the effect of the sky and space background infrared image after being processed by the traditional histogram equalization method. Figure 4 , which is a high dynamic infrared image contrast enhancement method suitable for sky and space background. It can be seen that this method effectively suppresses the background that occupies a large number of pixels, leaving room for the target and details to be enhanced, thus overcoming the disadvantage of the traditional histogram equalization method in infrared image processing that the background is over-enhanced.

[0059] In the embodiment of the present invention, Gmin is creatively used n and Gmax n The upper and lower grayscale thresholds are set by parameters to moderately suppress the background that occupies a large number of pixels and the highlighted targets that occupy a small number of pixels, leaving room for enhancing the targets and details, thus overcoming the shortcoming of the traditional histogram equalization method in infrared image processing that over-enhances the background.

[0060] In the embodiment of the present invention, in order to overcome the sudden change of the image after mapping caused by scene changes, a weight distribution method is creatively used to construct Gmin n and Gmax n In order to prevent the image from jumping significantly, gmax calculated based on the previous frame is given n-1 and gmin n-1 Assign a weight coefficient of 0.99 to gmax calculated based on the current frame image n and gmin n Assign a weight coefficient of 0.01.

[0061] In the embodiment of the present invention, Pic is creatively constructed. out =K*(Pic in -Gmin n ) mapping function, which can compress and display the high dynamic infrared image with quantization accuracy of 14bit into an 8bit image. out -Gmin n Most of the background is filtered out, and the background grayscale that occupies a large number of pixels is compressed. The substantial compression of the actual grayscale mapping interval increases the percentage of target grayscale levels that originally accounted for a small proportion of pixels. Therefore, the grayscale of the target that occupies a small number of pixels can be stretched, which better meets the human eye observation needs during the search and tracking process.

[0062] In summary, this method calculates the upper and lower grayscale threshold parameters of each frame of infrared image according to the mean, standard deviation and grayscale cumulative distribution function of each frame image, and thus constructs an exponential mapping function. Through this method, the high dynamic infrared image with a quantization accuracy of 14 bits can be compressed and displayed as an 8-bit image, while the background occupying a large number of pixels and the highlighted target occupying a small number of pixels can be moderately suppressed, giving space for target and detail enhancement, thereby overcoming the shortcoming of the traditional histogram equalization method in infrared image processing that over-enhances the background, and can achieve significant enhancement of the contrast of high dynamic infrared images under different sky and space infrared backgrounds.

[0063] Example 2

[0064] Please refer to Figure 5 , Figure 5 The figure shows a high dynamic infrared image contrast enhancement device suitable for sky and space background provided by this embodiment. In this embodiment, the device includes:

[0065] An intermediate parameter construction module is used to construct an upper intermediate parameter and a lower intermediate parameter based on the mean value, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image; the upper intermediate parameter is used to suppress a highlight target that occupies a small number of pixels; the lower intermediate parameter is used to suppress a background that occupies a large number of pixels;

[0066] A grayscale threshold obtaining module, used for converting the upper limit intermediate parameter and the lower limit intermediate parameter into an upper limit grayscale threshold and a lower limit grayscale threshold based on a preset weight;

[0067] A mapping coefficient calculation module, used to calculate and obtain a target mapping coefficient based on an upper grayscale threshold and a lower grayscale threshold;

[0068] A mapping function building module, used to build a mapping function based on a target mapping coefficient and a lower grayscale threshold;

[0069] The contrast enhancement module is used to obtain a contrast-enhanced target infrared image based on the target infrared image and the mapping coefficient.

[0070] Optionally, the intermediate parameter building blocks include:

[0071] A lower limit intermediate parameter construction unit is used to obtain a lower limit intermediate parameter based on a mean value and a standard deviation of the infrared image of the current frame;

[0072] The upper limit intermediate parameter construction unit is used to take the grayscale corresponding to when the cumulative distribution function of the current frame infrared image is equal to the preset threshold as the upper limit intermediate parameter.

[0073] Optionally, the preset threshold is 0.95.

[0074] Optionally, the preset weight includes a weight of the infrared image of the current frame and a weight of the infrared image of the previous frame, and the sum of the weight of the infrared image of the current frame and the weight of the infrared image of the previous frame is equal to 1.

[0075] Optionally, the upper grayscale threshold is the sum of the product of the current frame infrared image weight and the upper limit intermediate parameter of the current frame infrared image and the product of the previous frame infrared image weight and the upper limit intermediate parameter of the previous frame infrared image.

[0076] Optionally, the lower grayscale threshold is the sum of the product of the current frame infrared image weight and the lower intermediate parameter of the current frame infrared image and the product of the previous frame infrared image weight and the lower intermediate parameter of the previous frame infrared image.

[0077] Optionally, the weight of the infrared image of the current frame is 0.01; the weight of the infrared image of the previous frame is 0.99.

[0078] Optionally, the mapping coefficient calculation module includes:

[0079] An intermediate mapping coefficient calculation unit, used to calculate and obtain the intermediate mapping coefficient based on the upper grayscale threshold, the lower grayscale threshold and the intermediate mapping coefficient calculation formula;

[0080] The mapping coefficient calculation unit is used to calculate the target mapping coefficient based on the upper grayscale threshold, the lower grayscale threshold and the intermediate mapping coefficient.

[0081] Based on this, the device calculates the upper and lower grayscale threshold parameters of each frame of infrared image according to the mean, standard deviation and grayscale cumulative distribution function of each frame of image, and thus constructs an exponential mapping function. Through this method, the high-dynamic infrared image with a quantization accuracy of 14 bits can be compressed and displayed as an 8-bit image, while the background occupying a large number of pixels and the highlighted target occupying a small number of pixels can be moderately suppressed, leaving room for target and detail enhancement, thereby overcoming the shortcoming of the traditional histogram equalization method in infrared image processing that over-enhances the background, and can achieve significant enhancement of the contrast of high-dynamic infrared images under different aerospace infrared backgrounds.

[0082] Example 3

[0083] Please refer to Figure 6, this embodiment provides an electronic device, which includes a processor, an internal bus, a network interface, a memory and a non-volatile memory, and of course may also include hardware required for other services. The processor reads the corresponding computer program from the non-volatile memory into the memory and then runs it, forming a high dynamic infrared image contrast enhancement method suitable for air and sky backgrounds at the logical level. Of course, in addition to software implementation methods, this specification does not exclude other implementation methods, such as logic devices or a combination of software and hardware, etc., that is, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0084] The network interface, processor and memory can be connected to each other through a bus system. The above bus can be divided into an address bus, a data bus, a control bus, etc.

[0085] The memory is used to store programs. Specifically, the program may include program code, and the program code includes computer operation instructions. The memory may include a read-only memory and a random access memory, and provides instructions and data to the processor.

[0086] The processor is used to execute the program stored in the above memory, and specifically perform:

[0087] Step 102, based on the mean, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image, construct an upper intermediate parameter and a lower intermediate parameter; the upper intermediate parameter is used to suppress the highlight target occupying a small number of pixels; the lower intermediate parameter is used to suppress the background occupying a large number of pixels;

[0088] Step 104, based on preset weights, converting the upper intermediate parameter and the lower intermediate parameter into an upper grayscale threshold and a lower grayscale threshold;

[0089] Step 106, calculating and obtaining a target mapping coefficient based on the upper grayscale threshold and the lower grayscale threshold;

[0090] Step 108, constructing a mapping function based on the target mapping coefficient and the lower grayscale threshold;

[0091] Step 110: obtaining a contrast-enhanced target infrared image based on the target infrared image and the mapping coefficients.

[0092] The processor may be an integrated circuit chip with signal processing capability. In the implementation process, each step of the above method may be completed by an integrated logic circuit of the processor hardware or by instructions in the form of software.

[0093] Based on the same invention, the embodiment of this specification also provides a computer-readable storage medium, which stores one or more programs. When the one or more programs are executed by an electronic device including multiple application programs, the electronic device executes Figure 1-Figure 4 The corresponding embodiment provides a high dynamic infrared image contrast enhancement method suitable for sky and space background.

[0094] Those skilled in the art will appreciate that the embodiments of this specification may be provided as methods, systems, or computer program products. Therefore, this specification may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this specification may take the form of a computer program product implemented on one or more computer-readable storage media containing computer-usable program code.

[0095] In addition, for the above-mentioned specific implementation of the system, since it is basically similar to the method implementation, the description is relatively simple, and the relevant parts can be referred to the partial description of the method implementation. Moreover, it should be noted that in each module of the system of the present application, the components therein are logically divided according to the functions to be implemented, but the present application is not limited thereto, and the components can be re-divided or combined as needed.

[0096] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other. Each embodiment focuses on the differences between it and other embodiments.

[0097] The above is a description of a specific embodiment of the present specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the specific order or sequential order shown in the process depicted in the drawings is not necessarily required to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0098] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A high dynamic infrared image contrast enhancement method suitable for sky and space background, characterized in that: include: Based on the mean value, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image, an upper intermediate parameter and a lower intermediate parameter are constructed; The upper limit intermediate parameter is used to suppress the highlight target that occupies a small number of pixels; the lower limit intermediate parameter is used to suppress the background that occupies a large number of pixels; Based on a preset weight, the upper limit intermediate parameter and the lower limit intermediate parameter are converted into an upper limit grayscale threshold and a lower limit grayscale threshold; Based on the upper grayscale threshold and the lower grayscale threshold, the target mapping coefficient is calculated; Based on the target mapping coefficient and the lower grayscale threshold, a mapping function is constructed; Based on the target infrared image and the mapping coefficients, a contrast-enhanced target infrared image is obtained.

2. The method according to claim 1, characterized in that The construction of the upper limit intermediate parameter and the lower limit intermediate parameter based on the mean value, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image includes: Based on the mean and standard deviation of the infrared image of the current frame, the lower limit intermediate parameter is obtained; The grayscale corresponding to when the cumulative distribution function of the current frame infrared image is equal to the preset threshold is used as the upper limit intermediate parameter.

3. The method according to claim 2, characterized in that The preset threshold is 0.

95.

4. The method according to claim 1, characterized in that: The preset weight includes the weight of the infrared image of the current frame and the weight of the infrared image of the previous frame, and the sum of the weight of the infrared image of the current frame and the weight of the infrared image of the previous frame is equal to 1.

5. The method according to claim 4, characterized in that The upper grayscale threshold is the sum of the product of the current frame infrared image weight and the upper limit intermediate parameter of the current frame infrared image and the product of the previous frame infrared image weight and the upper limit intermediate parameter of the previous frame infrared image.

6. The method according to claim 5, characterized in that The lower grayscale threshold is the sum of the product of the current frame infrared image weight and the lower intermediate parameter of the current frame infrared image and the product of the previous frame infrared image weight and the lower intermediate parameter of the previous frame infrared image.

7. The method according to claim 6, characterized in that The weight of the infrared image of the current frame is 0.01; the weight of the infrared image of the previous frame is 0.

99.

8. The method according to claim 1, characterized in that The calculating and obtaining the target mapping coefficient based on the upper grayscale threshold and the lower grayscale threshold comprises: Based on the upper grayscale threshold, the lower grayscale threshold and the intermediate mapping coefficient calculation formula, the intermediate mapping coefficient is calculated and obtained; Based on the upper grayscale threshold, the lower grayscale threshold and the intermediate mapping coefficient, the target mapping coefficient is calculated.

9. A high dynamic infrared image contrast enhancement device suitable for air and sky background, characterized in that: include: An intermediate parameter construction module is used to construct an upper intermediate parameter and a lower intermediate parameter based on the mean value, standard deviation and cumulative distribution function of the grayscale probability distribution function of each frame of infrared image; the upper intermediate parameter is used to suppress a highlight target that occupies a small number of pixels; the lower intermediate parameter is used to suppress a background that occupies a large number of pixels; A grayscale threshold obtaining module, used for converting the upper limit intermediate parameter and the lower limit intermediate parameter into an upper limit grayscale threshold and a lower limit grayscale threshold based on a preset weight; A mapping coefficient calculation module, used to calculate and obtain a target mapping coefficient based on an upper grayscale threshold and a lower grayscale threshold; A mapping function building module, used to build a mapping function based on a target mapping coefficient and a lower grayscale threshold; The contrast enhancement module is used to obtain a contrast-enhanced target infrared image based on the target infrared image and the mapping coefficient.

10. An electronic device, characterized in that: include: processor; and a memory arranged to store computer executable instructions which, when executed, cause the processor to perform the steps of the method as claimed in any one of claims 1 to 8.

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