CN115712202B - A method for compensating image quality degradation caused by temperature based on Zernike polynomials - Google Patents

Abstract

The present invention discloses a method for compensating for image quality degradation caused by temperature based on Zernike polynomials, comprising: an ideal imaging system simulation module, an image quality degradation analysis module caused by temperature, and a deconvolution image quality correction module. The ideal imaging system simulation module is used as an imaging module to perform simulation imaging; the image quality degradation analysis module caused by temperature uses multiple configuration modes in Zemax to analyze the corresponding Zernike polynomials at different temperatures and make a sequence list; the deconvolution image quality correction module uses an actual temperature sensor to measure the temperature corresponding to the ordered list and uses the corresponding Zernike polynomial to perform deconvolution to achieve the result of correcting the aberration change caused by temperature, which can achieve the effect of processing the image quality degradation caused by temperature, does not need to add an additional focusing component, simplifies the system, improves the system reliability, and reduces the system cost.

Description

A method for compensating image quality degradation caused by temperature based on Zernike polynomials

Technical Field

The present invention relates to the technical field of optical system imaging, and in particular to a method for compensating optical system aberrations based on Zernike polynomials, which mainly uses Zemax thermal analysis to obtain Zernike polynomials of optical systems at different temperatures to correct aberrations of actual systems.

Background Art

With the development of modern technology, the requirements for the observation and tracking capabilities of photoelectric tracking and measurement systems are getting higher and higher, so the design of optical systems is becoming more and more complex. The optical system has high detection accuracy and complex structure, especially the telephoto system, which has a long focal length and is easily affected by temperature. Therefore, temperature analysis and compensation of the optical system is conducive to improving imaging quality, compensating for temperature effects, and improving the temperature stability of the system.

The traditional method of temperature compensation for imaging systems is to design the system to athermalize. There are three main types of athermalization technologies currently used, namely mechanical passive, electromechanical active, and optical passive. The first two only compensate for image displacement but not focal length, and both methods will make the system more complex, increase volume and weight, and reduce system reliability. The principle of optical passive athermalization technology is that when the temperature changes, the defocus produced by the optical element and the change produced by the mechanical structure compensate each other, so that the defocus of the entire system is controlled within the allowable range to maintain the stability of the image plane. However, the optical lens materials are often difficult to process and the production batches are small, resulting in high system costs.

In view of the above problems, the present invention proposes a temperature compensation method based on Zernike polynomial deconvolution. Firstly, Zemax is used to obtain the corresponding Zernike polynomials at different temperatures and then deconvolute compensation, thereby avoiding excessively high requirements on optical materials at the beginning of the design. Secondly, after the sequence table is completed, real-time performance can be guaranteed when used in the actual system.

Summary of the invention

In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for obtaining Zernike polynomials corresponding to different temperatures based on Zemax analysis to perform deconvolution to compensate for image quality degradation caused by temperature.

The technical solution adopted by the present invention is: a method for compensating image quality degradation caused by temperature based on Zernike polynomials, the system used by the method includes: an ideal imaging system simulation module 1, a temperature-induced image quality degradation analysis module 2 and a deconvolution image quality correction module 3, and the method includes the following steps:

Step 1: Use the ideal imaging system simulation module 1 to obtain the imaging quality of the optical system under ideal conditions;

Step 2: Utilize the temperature-induced image quality degradation analysis module 2 to perform multiple configuration temperature analysis to obtain the image quality degradation at different temperatures, that is, the wave aberration reflected by the corresponding Zernike polynomial and the corresponding temperature to make a sequence table;

Step 3: Measure the temperature under the actual temperature sensor and obtain the corresponding image under the actual temperature;

Step 4: Use the deconvolution image quality correction module 3 to correspond the image obtained at the corresponding temperature to the Zernike polynomial temperature sequence table, substitute the Zernike coefficient into the pupil function phase for deconvolution to obtain the image after image quality restoration.

Furthermore, establishing an ideal imaging system simulation module 1 includes: establishing a complete ideal imaging system simulation model 1 according to actual needs, obtaining the actual target surface size and focal length according to the object distance, field of view size and resolution, establishing an optical system model in Zemax, obtaining the ideal imaging result at 20°C, and considering that the imaging quality meets the requirements when the modulation transfer function (MTF) is greater than 0.3 at the cutoff frequency, and using Zemax image simulation to obtain the ideal imaging result as the standard for image quality correction and as a reference image for the temperature correction image.

Furthermore, establishing a temperature-induced image quality degradation analysis module 2 includes: based on the ideal imaging result at 20°C, establishing a configuration at intervals of 1°C from -30°C to 60°C, and inputting the thermal expansion coefficients of the corresponding shell and spacer materials for temperature analysis to obtain the corresponding relationship between temperature and imaging quality, using 1-37 order Zernike polynomials as the evaluation criteria, and obtaining a sequence table of different Zernike polynomials corresponding to different temperatures.

Furthermore, the temperature is measured by an actual temperature sensor and a corresponding image at the actual temperature is obtained, and deconvolution is performed according to the obtained Zernike polynomial sequence table to compensate for image quality degradation caused by the temperature.

The principle of the present invention is that: from the analysis of the optical system, the optical system is greatly affected by temperature. The greater the deviation from the normal temperature within the temperature range of -30°C to 60°C, the more the optical performance of the system changes. Therefore, a new temperature compensation idea is proposed. During the optical design, the Zernike polynomial change trend of the optical system under ambient temperature conditions is quantitatively analyzed and made into a sequence table. When used, the table is looked up according to the ambient temperature to obtain the pupil function phase for image deconvolution, and the real-time image is corrected and compensated, which can improve the imaging quality. In this way, the complex focusing mechanism in the system can be removed, the system can be simplified, and the system reliability can be improved. Specifically, a method for compensating for image quality degradation caused by temperature based on Zernike polynomials includes the following steps: Step 1: Establishing a corresponding imaging system in Zemax and obtaining the imaging quality of the optical system under ideal conditions; Step 2: Establishing multiple configurations and performing thermal analysis to obtain the image quality degradation of the imaging system at different temperatures, and listing a temperature sequence table corresponding to the Zernike polynomials; Step 3: Using a temperature sensor to measure the actual ambient temperature and obtain a corresponding image; Step 4: Substituting the Zernike polynomial obtained in step 2 into the phase of the pupil function and deconvolving the actually measured temperature image to achieve correction of the aberration caused by temperature.

Compared with the existing method, the present invention has the following advantages:

(1) Compared with the traditional mechanical passive and electromechanical active temperature aberration compensation methods, the system is simplified and the system reliability is improved.

(2) Compared with the temperature aberration compensation method of optical athermalization, the system tolerance is improved and the processing cost is reduced.

(3) The invention has a simple structure and is easy to implement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a method for compensating for image quality degradation caused by temperature based on Zernike polynomials according to the present invention; in FIG1 , 1 is an ideal imaging system simulation module; 2 is an image quality degradation analysis module caused by temperature; and 3 is a deconvolution image quality correction module.

FIG. 2 is a flow chart of a method for compensating for image quality degradation caused by temperature based on Zernike polynomials according to the present invention.

FIG. 3 is an image at -30° C. and an image after deconvolution correction according to the present invention.

DETAILED DESCRIPTION

The specific implementation of the present invention is described in detail below with reference to the accompanying drawings:

As shown in FIG1 , the method for compensating for image quality degradation caused by temperature based on Zernike polynomials uses a system comprising: an ideal imaging system simulation module 1 , a temperature-induced image quality degradation analysis module 2 , and a deconvolution image quality correction module 3 .

First, an ideal imaging system is established based on existing parameters such as field of view, resolution, and camera target surface. The system imaging at 20°C is used as the ideal imaging standard. When the modulation transfer function (MTF) is greater than 0.3 at the spatial cutoff frequency, the system imaging quality is considered to meet the requirements, and the Zemax image simulation function is used to obtain the image at 20°C through the system as a control image, see the ideal imaging system simulation module 1 in Figure 1. Then, multiple configurations are established using Zemax, and a configuration is established every 1°C from -30°C to 60°C. By inputting the thermal expansion coefficients of the optical system housing and the spacer material for thermal analysis, the first 37-order Zernike polynomial sequence table 1 corresponding to different temperatures is obtained.

Table 1

Among them: T ₁ ~ T ₁₀₁ corresponds to -30℃ ~ 60℃, Corresponding to the coefficients of the first 37th order Zernike polynomials at temperature T _i , ρ and θ are two continuous orthogonal variables inside the unit circle, ρ*cos(θ), ρ*sin(θ),…,924ρ ¹² -2772ρ ¹⁰ +3150ρ ⁸ -1680ρ ⁶ +420ρ ⁴ -42ρ ² +1 are the 1st, 2nd,…, 37th order Zernike polynomials respectively.

Then, according to the imaging principle of the optical system: the image plane intensity distribution is equal to the convolution of the object plane intensity distribution and the system point spread function, i(x,y) = o(x,y)*h(x,y), where (x,y) represents the point on the image plane, i(x,y) represents the image plane intensity distribution that can be obtained through the CCD, o(x,y) represents the unknown object plane intensity information, and h(x,y) represents the point spread function of the system. The specific formula is:

Where A(u,v) represents the aperture function, The wave aberration is usually represented by Zernike polynomials:

Where μ _i is the polynomial coefficient of each term of the Zernike polynomial, and _Zi (u, v) is the wavefront mode of different terms decomposed.

Through Zemax, the coefficients of the 1-37th order Zernike polynomials at different temperatures can be obtained, and the phase factor of the pupil function can be further obtained. The point spread function can be calculated, and the image after image quality restoration can be obtained by deconvolving the measured blurred image, as shown in the deconvolution image quality correction module 3 in Figure 1.

As shown in Figure 2, the specific process of the method for compensating image quality degradation caused by temperature based on Zernike polynomials is to establish an ideal imaging system model and obtain the system imaging situation under ideal conditions as a control. In Zemax, a variety of configuration modes are used to perform thermal analysis on the system to obtain a Zernike polynomial sequence table at different temperatures. The system is imaged at the actual ambient temperature to obtain the actual image quality degradation results at different temperatures. Finally, the aberration is corrected by deconvolution by comparing the existing Zernike sequence table.

As shown in Figure 3, (a) is the Zemax simulation image at -30°C and (b) is the image after deconvolution correction.

The present invention discloses a method for compensating for image quality degradation caused by temperature based on Zernike polynomials. There are many methods and approaches to implement the technical solution. The above is only a preferred implementation of the present invention. All components not specified in this embodiment can be implemented using existing technologies.

Claims (2)

1. A method for compensating for image quality degradation caused by temperature based on Zernike polynomials, characterized in that: the system used in the method comprises: an ideal imaging system simulation module (1), a temperature-induced image quality degradation analysis module (2) and a deconvolution correction module (3), and the method comprises the following steps: Step 1: Use the ideal imaging system simulation module (1) to obtain the imaging quality of the optical system under ideal conditions; Step 2: Use the temperature-induced image quality degradation analysis module (2) to perform multiple configuration temperature analysis to obtain the image quality degradation at different temperatures, that is, the wave aberration reflected by the corresponding Zernike polynomial and the corresponding temperature to make a sequence table; Step 3: Measure the temperature under the actual temperature sensor and obtain the corresponding image under the actual temperature; Step 4: Use the deconvolution image quality correction module (3) to correspond the image obtained at the corresponding temperature to the Zernike polynomial temperature sequence table, substitute the Zernike coefficient into the pupil function phase for deconvolution to obtain the image after image quality restoration; The establishment of an ideal imaging system simulation module (1) includes: establishing a complete ideal imaging system simulation model (1) according to actual needs, obtaining the actual target surface size and focal length according to the object distance, field of view size and resolution, establishing an optical system model in Zemax, obtaining an ideal imaging result at 20°C, and considering that the imaging quality meets the requirements when the modulation transfer function (MTF) is greater than 0.3 at the cutoff frequency, and using Zemax image simulation to obtain an ideal imaging result, using this result as a standard for image quality correction and as a reference image for the temperature correction image; Establishing a temperature-induced image quality degradation analysis module (2) includes: according to an ideal imaging result at 20°C, establishing a configuration at intervals of 1°C from -30°C to 60°C, and inputting the thermal expansion coefficients of the corresponding shell and spacer materials for temperature analysis, obtaining a corresponding relationship between temperature and imaging quality, using 1-37 Zernike polynomials as a criterion, and obtaining a temperature sequence table of different Zernike polynomials corresponding to different temperatures. 2. The method for compensating for image quality degradation caused by temperature based on Zernike polynomials according to claim 1 is characterized in that the temperature is measured by an actual temperature sensor and a corresponding image at the actual temperature is obtained, and deconvolution is performed according to the obtained Zernike polynomial sequence table to compensate for image quality degradation caused by temperature.