Simple optical system design method based on optical transfer function consistency constraint

Abstract

The invention belongs to the technical field of optical imaging calculation, and discloses a simple optical system design method based on optical transfer function consistency constraint, which comprises the following steps of: firstly, designing an initial structure of a simple lens, specifically, calculating the aperture of a sub-aperture of the lens, calculating the position of the sub-aperture of the lens, and setting a multi-structure of the sub-aperture of the lens; setting an evaluation function for optimization; and secondly, controlling the consistency of the optical transfer function of the simple lens, specifically, keeping the evaluation function, calculating an average optical transfer function, calculating the consistency of the optical transfer function, and adding the evaluation function for optimization. By the adoption of the simple optical system design method based on the optical transfer function consistency constraint, optimization design of a single-chip calculation infrared system based on calculation optics is achieved, the consistency of the optical transfer function is effectively controlled, and the method has important guiding significance for real-time imaging of the single-chip calculation infrared system.

Description

Technical Field

[0001] The present invention relates to the technical field of computational optical imaging, and in particular to a simple optical system design method based on optical transfer function consistency constraints. Background Art

[0002] In recent years, with the rapid development of space remote sensing, autonomous driving, infrared guidance and other fields, the demand for optical imaging systems with high imaging quality and light weight and miniaturization has been increasing. In order to achieve high-quality imaging effects, traditional optical imaging systems often rely on complex lens groups to correct optical aberrations, which not only makes the system bulky and heavy, but also increases the complexity of design and manufacturing. Computational imaging technology uses image processing algorithms as a virtual aberration correction method to effectively achieve high-quality imaging without increasing or even reducing the number of optical components, thus becoming an ideal solution that takes into account both high imaging quality and light weight and miniaturization. Based on this, single-lens computational imaging systems have received widespread attention and research.

[0003] However, single-lens computational imaging systems face a significant challenge in practical applications: the complexity of image processing algorithms often makes it difficult to meet the demand for real-time video-level output of reconstructed images in practical applications. The huge computing requirements make it difficult for existing algorithms to achieve real-time video-level output of reconstructed images on the neural network chip side, further limiting the practical application potential of single-lens computational imaging systems.

[0004] In single-lens computational imaging systems, there is a close connection between optical design and the selection and complexity of image processing algorithms. A single-lens design method based on subaperture optimization successfully realizes a single-lens system with a spatially invariant point spread function. This design allows the algorithm in the subsequent image processing stage to select a lighter Unet neural network, thereby significantly reducing the computational complexity of the algorithm while maintaining high-performance imaging. Therefore, a lightweight Res-Unet neural network algorithm can be selected in the image processing stage to achieve high-performance imaging. Nevertheless, this method still has limitations in reducing the computational complexity of the algorithm. Such high computing requirements still far exceed the real-time processing capabilities of the neural network chip, limiting the real-time video-level output of the reconstructed image. Therefore, how to further optimize the optical design method and develop a single-lens optical design method that can significantly reduce the complexity of image processing has become a key issue that needs to be solved urgently. The solution to this problem will not only promote the implementation of single-lens computational imaging technology in more practical application scenarios, but will also provide important reference and reference for the design of other high-performance computational imaging systems. Summary of the invention

[0005] The purpose of the present invention is to provide a simple optical system design method based on optical transfer function consistency constraints to solve the problems of high complexity and poor real-time performance of image processing algorithms in the prior art. This method can significantly reduce the complexity of image processing algorithms by controlling the consistency of the optical transfer function (OTF) of a single lens system within the entire field of view, thereby achieving efficient and real-time imaging effects.

[0006] To achieve the above object, the present invention provides a simple optical system design method based on optical transfer function consistency constraint, comprising the following steps: Step S1, designing a simple lens initial structure; Step S2: controlling the consistency of the optical transfer function of the simple lens.

[0007] Preferably, in step S1, a simple lens initial structure is designed, and the specific process is as follows: Step S11, calculating the lens sub-aperture diameter; Step S12, calculating the lens sub-aperture position; Step S13, setting a lens sub-aperture multiple structure; Step S14: setting an evaluation function for optimization.

[0008] Preferably, in step S2, the consistency of the optical transfer function of the simple lens is controlled, and the specific process is as follows: Step S21, maintaining the evaluation function of step S1; Step S22, calculating the average optical transfer function; Step S23, calculating the consistency of the optical transfer function; Step S24: adding an evaluation function for optimization.

[0009] Preferably, in step S11, the lens sub-aperture diameter is calculated, and the specific process is as follows: The diffraction-limited MTF corresponding to the subaperture at the Nyquist frequency is The value is between 0.1 and 0.2 as the guideline to determine the subaperture diameter The range is as follows: ; in, is the central wavelength, is the focal length of the system.

[0010] Preferably, in step S12, the lens sub-aperture position is calculated, and the specific process is as follows: Assuming that the projection of each subaperture related to the field of view on the real aperture is uniformly distributed, calculate the coordinate of the projected aperture in the y direction , as shown below: ; in, is the i-th field of view, is the total field of view, is the diameter of the true aperture; According to the trigonometric relationship, the distance between the sub-aperture and the real aperture is calculated. , as shown below: .

[0011] Preferably, in step S13, the parameters of each aperture in the optical design software are set as a multi-structure to form a multi-structure optimization system.

[0012] Preferably, in step S14, the lens parameters of the simple optical system and the distance parameters of the sub-aperture from the real aperture are set as variables, and an evaluation function is set in the optical design software, with minimization of the diffuse spot radius as the evaluation index, and the focal length of the system is constrained at the same time.

[0013] Preferably, in step S22, the average optical transfer function is calculated, and the optical transfer functions of all fields of view are averaged to obtain the average optical transfer function , as shown below: ; in, is the optical transfer function of the ith field of view, N is the number of fields of view, are simple optical system parameters.

[0014] Preferably, in step S23, the consistency of the optical transfer function is calculated, and the sum of the absolute values ​​of the differences between the optical transfer function of each field of view and the average optical transfer function is defined as the consistency of the optical transfer function. , as shown below: .

[0015] Preferably, in step S24, an evaluation function for optimization is added, and based on step S1, two operands are added to the evaluation function: One is to control the consistency of the optical transfer function , making it close to 0; the second is to control the minimum value of the optical transfer function.

[0016] Therefore, the present invention adopts the above-mentioned simple optical system design method based on the consistency constraint of optical transfer function, which is applicable to the design of simple lens group optical system, simple reflector group optical system, single lens optical system and single reflector optical system. The present invention reduces the complexity of the image processing algorithm by controlling the consistency of the optical transfer function of the optical system. This design strategy enables the image reconstruction of the simple computational imaging system on the neural network chip to achieve real-time video output, greatly improving the efficiency and response speed of the imaging system.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of a simple optical system design method based on optical transfer function consistency constraint of the present invention; Figure 2 It is a light path diagram of a single-lens computational infrared optical system in an implementation case of the present invention; Figure 3 is a schematic diagram of the position of the subaperture in an embodiment of the present invention; Figure 4 It is an OTF diagram of a single-lens computational infrared optical system designed by a traditional design method in an implementation case of the present invention; Figure 5 It is the OTF diagram of the single-lens computational infrared optical system designed by the design method proposed by us in the implementation case of the present invention; Figure 6 The present invention is a comparison diagram of the imaging performance (peak signal-to-noise ratio) of a single-lens infrared optical system in an implementation case; Figure 7 is a comparison diagram of imaging performance (structural similarity) of a single-lens computational infrared optical system in an implementation case of the present invention; Figure 8 It is a comparison chart of the imaging performance (simulated image) of a single-lens computational infrared optical system in an implementation case of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0020] like Figure 1 As shown, a simple optical system design method based on optical transfer function consistency constraint includes the following steps: Step S1: designing a simple lens initial structure. The specific process is as follows: Step S11, calculating the lens sub-aperture diameter; Step S12, calculating the lens sub-aperture position; Step S13, setting a lens sub-aperture multiple structure; Step S14: setting an evaluation function for optimization.

[0021] Step S2: Control the consistency of the optical transfer function of the simple lens. The specific process is as follows: Step S21, maintaining the evaluation function of step S1; Step S22, calculating the average optical transfer function; Step S23, calculating the consistency of the optical transfer function; Step S24: adding an evaluation function for optimization.

[0022] Example 1 The embodiment of the present invention is a single-lens computational infrared imaging system, which has a focal length of 70 mm, an F number of 1, a field of view of 6.4°×4.8°, a detection spectrum range of 8 μm~12 μm, and uses an uncooled detector with 12 μm pixel. The detector array size is 640×480. The optical path diagram of the optical system is as follows: Figure 2 shown.

[0023] Step S1, designing a simple lens initial structure.

[0024] Step S11, calculate the lens sub-aperture diameter: the diffraction-limited optical transfer function (OTF) corresponding to the sub-aperture at the Nyquist frequency The value is between 0.1 and 0.2 as the guideline to determine the subaperture diameter The range is as follows: ; in, is the central wavelength, is the focal length of the system.

[0025] Here, the diffraction-limited OTF corresponding to the subaperture is taken at the Nyquist frequency The value is about 0.1, and the subaperture diameter is about 36mm.

[0026] Step S12, calculate the position of the lens sub-aperture: Assuming that the projection of each sub-aperture related to the field of view on the real aperture is uniformly distributed, calculate the coordinate of the projected aperture in the y direction , as shown below: ; in, is the i-th field of view, is the total field of view, is the diameter of the actual aperture; its schematic diagram is as follows Figure 3 shown.

[0027] According to the trigonometric relationship, the distance between the sub-aperture and the real aperture is , as shown below: ; Here, five uniformly distributed fields of view are selected, namely 0°, 1°, 2°, 3° and 4°, and the corresponding sub-aperture position coordinates ( , ) are (0, 0), (4.25, 243.48), (5.8, 243.41), (12.75, 243.28) and (17, 243.11) respectively.

[0028] Step S13, setting the lens sub-aperture multiple structures: setting the parameters of each aperture as a multiple structure in the optical design software to form a multiple structure optimization system.

[0029] Step S14, setting an evaluation function for optimization: setting parameters such as lens parameters of the simple optical system and the distance between the sub-aperture and the real aperture as variables, setting an evaluation function in the optical design software, taking minimization of the diffuse spot radius as the evaluation index, and at the same time constraining the focal length of the system to 70 mm.

[0030] After multiple rounds of optimization iterations, a single lens design parameter is obtained, and its full-field OTF consistency is poor, such as Figure 4 shown.

[0031] Step S2, controlling the consistency of the optical transfer function of the simple lens, and further controlling the consistency of the optical transfer function of the entire field of view of the system.

[0032] Step S21, maintaining the evaluation function of step S1: based on the evaluation function set in step S1, a new multi-structure is created and the evaluation function is set to control the consistency of the full-field OTF under the real aperture.

[0033] Step S22, calculate the average optical transfer function (OTF): average the optical transfer functions of all fields of view to obtain the average optical transfer function , as shown below: ; in, is the ith field of view OTF, N is the number of fields of view, are simple optical system parameters.

[0034] Step S23, calculate the consistency of the optical transfer function: the sum of the absolute values ​​of the difference between the OTF of each field of view and the average OTF is defined as the OTF consistency , as shown below: ; Step S24, adding an evaluation function for optimization: Based on step S1, two operands are added to the evaluation function: one is to control the consistency of the optical transfer function , making it as close to 0 as possible; the second is to control the minimum value of the optical transfer function to make it as large as possible.

[0035] After multiple rounds of iterative optimization, the optimal design parameters of the single lens are obtained, and the consistency of its full-field OTF is effectively controlled, with good consistency. Figure 5 shown.

[0036] Example 2 In order to verify the superiority of the simple optical system design method based on optical transfer function consistency constraint proposed by the present invention in reducing the complexity of image processing algorithms, a simulation comparison experiment was carried out in this embodiment.

[0037] Firstly, a single lens was designed using the traditional design method and the method proposed in the present invention respectively.

[0038] Next, using the classic Res-Unet as the basic network, we adjust the number of channels to implement image processing algorithms of different complexities.

[0039] On this basis, three new algorithms were further developed: SS-Res-Unet (the number of channels is only one-fourth of Res-Unet), S-Res-Unet (the number of channels is only one-half of Res-Unet) and L-Res-Unet (the number of channels is twice that of Res-Unet). When processing degraded images with a resolution of 640×480, the FLOPs of these algorithms are 4.79G (SS-Res-Unet), 19.2G (S-Res-Unet), 76.62G (Res-Unet) and 306.12G (L-Res-Unet).

[0040] Finally, the parameters of the two single-lens systems mentioned above were trained and optimized under four different algorithms, and the quality and performance of the restored images were compared and analyzed.

[0041] 30 untrained infrared images were selected as the validation set, and the average peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) before and after the restoration of the image were calculated, as shown in Figure 6 and Figure 7 As shown. Under the same algorithm complexity, compared with the traditional design method, the single lens designed by the design method proposed in the present invention has higher PSNR and SSIM. Specifically, the average PSNR is improved by 0.97dB to 1.80dB, and the average SSIM is improved by 0.0085 to 0.0116.

[0042] Finally, S-Res-Unet was selected as the image processing algorithm of the embodiment of the present invention. The reason for the selection is that when the algorithm complexity is further improved, the average PSNR and SSIM increase very little, while reducing the algorithm complexity will cause the average PSNR and SSIM to decrease significantly. Therefore, S-Res-Unet has achieved an ideal balance between algorithm complexity and performance.

[0043] In addition, the image reconstruction performance of the embodiment of the present invention is better than that of the traditional design method. Specifically, the average PSNR of the reconstructed image using the S-Res-Unet image processing algorithm is 34.17dB, while the average PSNR of the reconstructed image using the traditional design method is only 33.70dB even if the more complex L-Res-Unet image processing algorithm is used. This advantage is Figure 8 As shown, the embodiment of the present invention shows better performance in reconstructing image details. Especially in a low temperature environment of -40°C, the traditional design method cannot effectively restore the image details even if the S-Res-Unet neural network image processing algorithm is used.

[0044] Although the L-Res-Unet neural network image processing algorithm can improve the detail resolution ability of the restored image, the degree of improvement is limited. In contrast, the restored image details of the S-Res-Unet neural network image processing algorithm used in the embodiment of the present invention are clearly visible, and its algorithm complexity is 16 times lower than that of L-Res-Unet, and it can achieve real-time video-level output of the reconstructed image on the neural network chip side.

[0045] Therefore, the present invention adopts the above-mentioned simple optical system design method based on the consistency constraint of optical transfer function, which is applicable to the design of simple lens group optical system, simple reflector group optical system, single lens optical system and single reflector optical system. The present invention reduces the complexity of the image processing algorithm by controlling the consistency of the optical transfer function of the optical system. This design strategy enables the image reconstruction of the simple computational imaging system on the neural network chip to achieve real-time video output, greatly improving the efficiency and response speed of the imaging system.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A simple optical system design method based on consistency constraints of optical transfer functions, characterized in that: The following steps are involved: Step S1, designing a simple lens initial structure; Step S2: controlling the consistency of the optical transfer function of the simple lens.

2. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S1, the initial structure of a simple lens is designed. The specific process is as follows: Step S11, calculating the lens sub-aperture diameter; Step S12, calculating the lens sub-aperture position; Step S13, setting a lens sub-aperture multiple structure; Step S14: setting an evaluation function for optimization.

3. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S2, the consistency of the optical transfer function of the simple lens is controlled, and the specific process is as follows: Step S21, maintaining the evaluation function of step S1; Step S22, calculating the average optical transfer function; Step S23, calculating the consistency of the optical transfer function; Step S24: adding an evaluation function for optimization.

4. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S11, the lens sub-aperture diameter is calculated, and the specific process is as follows: The diffraction-limited MTF corresponding to the subaperture at the Nyquist frequency is The value is between 0.1 and 0.2 as the guideline to determine the subaperture diameter The range is as follows: ； in, is the central wavelength, is the focal length of the system.

5. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S12, the lens sub-aperture position is calculated, and the specific process is as follows: Assuming that the projection of each subaperture related to the field of view on the real aperture is uniformly distributed, calculate the coordinate of the projected aperture in the y direction , as shown below: ； in, is the i-th field of view, is the total field of view, is the diameter of the true aperture; According to the trigonometric relationship, the distance between the sub-aperture and the real aperture is calculated. , as shown below: 。 6. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S13, the parameters of each aperture in the optical design software are set as a multi-structure to form a multi-structure optimization system.

7. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S14, the lens parameters of the simple optical system and the distance parameters of the sub-aperture from the real aperture are set as variables, and an evaluation function is set in the optical design software, with minimization of the diffuse spot radius as the evaluation index, while constraining the focal length of the system.

8. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S22, the average optical transfer function is calculated, and the optical transfer functions of all fields of view are averaged to obtain the average optical transfer function , as shown below: ； in, is the optical transfer function of the ith field of view, N is the number of fields of view, are simple optical system parameters.

9. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S23, the consistency of the optical transfer function is calculated, and the sum of the absolute values ​​of the differences between the optical transfer function of each field of view and the average optical transfer function is defined as the consistency of the optical transfer function , as shown below: 。 10. The simple optical system design method based on optical transfer function consistency constraint according to claim 1, characterized in that: In step S24, an evaluation function for optimization is added. Based on step S1, two operands are added to the evaluation function: One is to control the consistency of the optical transfer function , making it close to 0; the second is to control the minimum value of the optical transfer function.

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