A method for determining MTF imaging characteristics

Abstract

This application relates to a method for determining MTF imaging characteristics. The method includes: using a combination of a camera and lens to capture images of a screen displaying a design pattern, obtaining a test image; calculating the MTF values ​​at various locations of the design pattern in the test image, and calculating the average MTF value of the design pattern based on these values; calculating the imaging symmetry based on the average MTF value and the maximum and minimum MTF values ​​at the edges of the design pattern; and determining the MTF imaging characteristics based on the imaging symmetry. This application, by calculating the MTF values ​​at various locations of the design pattern in the test image, and based on the average MTF value and the maximum and minimum MTF values ​​at the edges of the design pattern, can calculate the imaging symmetry of the entire test image, thereby determining the overall MTF imaging characteristics of the test image. This solves the problem in related technologies where methods for drawing MTF curves can only represent the results of a certain area of ​​the image captured by the lens, and cannot reflect the overall imaging effect of the image captured by the lens.

Description

Technical Field

[0001] This application relates to the field of machine vision technology, specifically to a method for determining MTF imaging characteristics. Background Technology

[0002] Currently, industrial cameras and lenses in machine vision serve as high-precision imaging devices for defect detection on DUTs (Device Under Test). Therefore, the requirements for the MTF (Modulation Transfer Function) of visual imaging are extremely high. By analyzing the MTF imaging characteristics, data can be used to infer whether the imaging quality of the camera and lens meets the standards.

[0003] In related technologies, the current method for judging MTF imaging characteristics generally involves calculating the MTF value of a certain area of ​​the image captured by the lens, and then plotting an MTF curve. The horizontal axis of the MTF curve represents the distance from the lens center to the lens edge in millimeters, and the vertical axis represents the MTF value. The horizontal axis of the MTF curve is equivalent to the radius of the image circle, with the left end corresponding to the image center and the right end to the outer edge of the image circle. Comparing the left and right parts of the MTF curve makes it easier to understand the imaging performance in various directions starting from the lens center. The slower the decay of the curve from left to right in the MTF curve, the better; a slower decay indicates a smaller imaging difference between the lens center and the edge.

[0004] However, the method of drawing MTF curves described above can only represent the results of a certain area of ​​the image captured by the lens, and cannot reflect the overall imaging effect of the image captured by the lens.

[0005] Therefore, it is necessary to design a new method for judging MTF imaging characteristics to overcome the above problems. Summary of the Invention

[0006] This application provides a method for judging MTF imaging characteristics, which can solve the technical problem in related technologies that the method of drawing MTF curve charts can only represent the results of a certain area of ​​the image captured by the lens, and cannot reflect the overall imaging effect of the image captured by the lens.

[0007] In a first aspect, embodiments of this application provide a method for determining MTF imaging characteristics, the method comprising:

[0008] The test image is obtained by photographing the screen displaying the designed pattern using the combination of the camera and lens under test;

[0009] Calculate the MTF value at each position of the design pattern in the test chart, and calculate the average MTF value of the design pattern based on the MTF value at each position of the design pattern.

[0010] The imaging symmetry is calculated based on the average MTF and the maximum and minimum MTF values ​​at the edges of the design pattern.

[0011] The imaging characteristics of MTF can be determined based on imaging symmetry.

[0012] In conjunction with the first aspect, in one embodiment, the design pattern is a plurality of blade blocks displayed in the screen body, the plurality of blade blocks being evenly arranged in multiple rows and columns.

[0013] In conjunction with the first aspect, in one embodiment, calculating the MTF value at each position of the design pattern in the test pattern, and calculating the average MTF of the design pattern based on the MTF values ​​at each position of the design pattern, includes:

[0014] Calculate the MTF value of each cutting edge block in the test diagram;

[0015] The average MTF of the design pattern is calculated based on the MTF values ​​of each blade block.

[0016] In conjunction with the first aspect, in one embodiment, before calculating the imaging symmetry based on the MTF average value and the maximum and minimum MTF values ​​around the edges of the design pattern, the method further includes:

[0017] Select the MTF values ​​of the four blade blocks located at the four corners of the test image;

[0018] Find the maximum MTF value among the four blade blocks at the four corners and take it as the maximum MTF value of the design pattern's four edges;

[0019] Find the minimum MTF value among the four blade blocks at the four corners and use it as the minimum MTF value for the four edges of the design pattern.

[0020] In conjunction with the first aspect, in one implementation, calculating the imaging symmetry based on the average MTF and the maximum and minimum MTF values ​​around the edges of the design pattern includes:

[0021] The formula for calculating imaging symmetry is:

[0022] Symmetry = 1 - (MTF) maxValue -MTF minValue ) / (2*MTF AverageValue );

[0023] Among them, MTF maxValue MTF is the maximum value; MTF minValue Minimum MTF; MTF AverageValue This represents the average MTF value.

[0024] In conjunction with the first aspect, in one embodiment, after calculating the MTF values ​​at various locations of the design pattern in the test chart, the method further includes:

[0025] Calculate the standard deviation of the MTF of the design pattern based on the MTF values ​​at each position of the design pattern;

[0026] Imaging uniformity is calculated based on the MTF mean and MTF standard deviation;

[0027] The imaging characteristics of MTF are determined based on the imaging uniformity.

[0028] In conjunction with the first aspect, in one embodiment, determining the MTF imaging characteristics based on imaging uniformity includes:

[0029] Determine whether the image uniformity value is between 0.8 and 0.9;

[0030] If the image uniformity value is greater than 0.9, it indicates good image uniformity; if the image uniformity value is between 0.8 and 0.9, it indicates average image uniformity; if the image uniformity value is less than 0.8, it indicates poor image uniformity.

[0031] In conjunction with the first aspect, in one embodiment, determining the MTF imaging characteristics based on imaging symmetry includes:

[0032] Determine whether the difference between the maximum MTF value and the average MTF value, and the difference between the minimum MTF value and the average MTF value, are greater than a set difference.

[0033] If the difference between the maximum MTF value and the average MTF value and / or the difference between the minimum MTF value and the average MTF value is greater than the set difference, it indicates that the lens has vignetting or poor uniformity of the imaging light source, or that there is dust on the surface of the design pattern on the screen.

[0034] In conjunction with the first aspect, in one embodiment, before photographing the screen displaying the design pattern using the combination of the camera and lens under test to obtain the test image, the method further includes:

[0035] Adjust the fixture connected to the camera so that the horizontal angle between the fixture and the screen is below the preset value.

[0036] In conjunction with the first aspect, in one embodiment, before photographing the screen displaying the design pattern using the combination of the camera and lens under test to obtain the test image, the method further includes:

[0037] The camera and lens combination to be tested is focused. When the image is magnified and shows a preset number of transition pixels, the focus is successful.

[0038] The beneficial effects of the technical solutions provided in this application include:

[0039] 1. By calculating the MTF values ​​at various locations of the design pattern in the test image, and based on the average MTF value and the maximum and minimum MTF values ​​at the edges of the design pattern, the imaging symmetry of the entire test image can be calculated, thereby judging the overall MTF imaging characteristics of the test image. This can better illustrate the quality of the camera and lens imaging effect, and solves the technical problem in related technologies that the method of drawing MTF curve charts can only represent the results of a certain area of ​​the lens-captured image and cannot reflect the overall imaging effect of the lens-captured image.

[0040] 2. In this embodiment, when calculating the maximum and minimum MTF values ​​of the four edges of the design pattern, the blade blocks at the four corners of the design pattern are selected, which better reflects the MTF characteristics of the image at the edge of the lens's field of view and is more representative.

[0041] 3. Furthermore, the MTF values ​​at various positions in the design pattern can be used to calculate the imaging uniformity, which can be used to evaluate the overall imaging effect of the test image. That is, not only the imaging symmetry but also the imaging uniformity can be calculated. These two values ​​can be used to better illustrate the quality of the imaging effect of the camera and lens. Moreover, certain analytical conclusions can be obtained through the specific values ​​of imaging symmetry and imaging uniformity. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A flowchart illustrating a method for determining MTF imaging characteristics provided in an embodiment of this application;

[0044] Figure 2 A flowchart illustrating step S2 provided in an embodiment of this application;

[0045] Figure 3 A flowchart illustrating another embodiment of the method for determining MTF imaging characteristics provided in this application.

[0046] Figure 4 A schematic diagram of a test pattern provided in an embodiment of this application;

[0047] Figure 5 Selection test provided for embodiments of this application Figure 4 A schematic diagram of the blade block at the corner position. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present application.

[0049] This application provides a method for judging MTF imaging characteristics, which can solve the technical problem that the method of drawing MTF curve charts can only represent the results of a certain area of ​​the lens-captured image and cannot reflect the overall imaging effect of the lens-captured image.

[0050] See Figure 1 The image shows a method for determining MTF imaging characteristics according to an embodiment of this application. The method for determining MTF imaging characteristics may include the following steps:

[0051] S1: Use the combination of the camera and lens under test to photograph the screen displaying the design pattern to obtain the test image.

[0052] In this step, the test images are taken in a darkroom. A lens is mounted at the bottom of the camera to form a combined camera and lens assembly, with the lens and camera positioned directly above the screen. The screen displays a specially designed pattern used to test the MTF value; the screen can be an iPad.

[0053] S2: Calculate the MTF value at each position of the design pattern in the test diagram, and calculate the average MTF value of the design pattern based on the MTF value at each position of the design pattern.

[0054] In this step, after the test image is captured, the design pattern will be displayed on the test image. When calculating the MTF value of each position of the design pattern, if the design pattern is a whole, each position in the design pattern can be defined as a small area. Multiple small areas will be evenly arranged in the design pattern at different positions. The MTF value of each small area is calculated separately, which is the MTF value of each position of the design pattern. The average MTF value is the sum of the MTF values ​​of all small areas divided by the number of all small areas. Of course, when designing the design pattern, it can also be designed as multiple independent small patterns. Multiple small patterns are evenly arranged on the screen to form the design pattern. After the test image is captured, the MTF value corresponding to each small pattern is directly calculated, which is the MTF value of each position of the design pattern. The average MTF value is the sum of the MTF values ​​of all small patterns divided by the number of all small patterns.

[0055] S3: Calculate imaging symmetry based on the average MTF and the maximum and minimum MTF values ​​at the edges of the design pattern.

[0056] In this step, the maximum MTF value is the largest MTF value among different positions around the edges of the design pattern, and the minimum MTF value is the smallest MTF value among different positions around the edges of the design pattern. The imaging symmetry can be obtained by using the maximum, minimum, and average MTF values, and then the MTF imaging characteristics can be determined.

[0057] S4: Determine the MTF imaging characteristics based on imaging symmetry.

[0058] In this embodiment, by calculating the MTF values ​​at various positions of the design pattern in the test image, the average MTF of the design pattern can be calculated based on these values. Furthermore, based on the average MTF and the maximum and minimum MTF values ​​at the edges of the design pattern, the imaging symmetry of the entire test image can be calculated, thereby determining the overall MTF imaging characteristics of the test image. Since the MTF values ​​at various positions of the test image are calculated during the calculation process, and the imaging symmetry of the entire test image is calculated using these MTF values, the overall MTF imaging characteristics of the test image can be evaluated through a reasonable calculation method. This better illustrates the quality of the camera and lens imaging, solving the technical problem in related technologies where the method of drawing MTF curve charts can only represent the results of a certain area of ​​the image captured by the lens and cannot reflect the overall imaging effect of the image captured by the lens.

[0059] Further, preferably, in this embodiment, the design pattern is a plurality of blade blocks displayed on the screen (e.g., ...). Figure 4 The square block shown has multiple blade blocks evenly arranged in multiple rows and columns. See also... Figure 4 As shown, 9 rows and 11 columns of blade blocks are designed in the screen, resulting in a total of 9*11 (99) blade blocks. Each blade block is designed with a specific tilt angle. The multi-row, multi-column blade blocks displayed in the screen will be shown in the test image after the test image is captured. In this embodiment, the design pattern is designed as mutually independent blade blocks arranged in multiple rows and columns. The MTF values ​​corresponding to each blade block are also neatly arranged in rows and columns. This setting makes it easier to calculate the MTF value at each position in the design pattern, and then calculate the average MTF of the design pattern based on the MTF values ​​at each position.

[0060] In other embodiments, the design pattern may be designed in other styles, which are not limited here.

[0061] Based on the above technical solutions, see [link to relevant documentation]. Figure 2As shown, in one embodiment, calculating the MTF value at each position of the design pattern in the test pattern, and calculating the average MTF value of the design pattern based on the MTF values ​​at each position of the design pattern, may include:

[0062] S21: Calculate the MTF value of each blade block in the test diagram.

[0063] S22: Calculate the average MTF of the design pattern based on the MTF values ​​of each blade block.

[0064] In this embodiment, since the design pattern consists of multiple evenly arranged blade blocks, the MTF value of each blade block can be directly calculated when calculating the MTF value at each position of the design pattern. This embodiment uses a total of 99 blade blocks, and the formula for calculating the average MTF is: MTF... AverageValue = (MTF1 + MTF2 + ... + MTF) 99 ) / 99, where MTF1 is the MTF value of the first cutting edge block; MTF2 is the MTF value of the second cutting edge block; MTF 99 This is the MTF value of the 99th blade block.

[0065] Furthermore, in some optional embodiments, before calculating the imaging symmetry based on the MTF average value and the maximum and minimum MTF values ​​around the edges of the design pattern, the following may be included:

[0066] Step a: Select the MTF values ​​of the four blade blocks located at the four corners of the test image (see...). Figure 5 (As shown).

[0067] Step b: Find the MTF value with the largest value among the four blade blocks at the four corners and use it as the maximum MTF value of the four edges of the design pattern.

[0068] Step c: Find the minimum MTF value among the four blade blocks at the four corners and use it as the minimum MTF value for the four edges of the design pattern.

[0069] In this embodiment, the 99 cutting edge blocks are arranged in a 9x11 grid to form a rectangle. The MTF values ​​of the four cutting edge blocks at the four vertices of this rectangle are selected as MTF_TopLeft, MTF_TopRight, MTF_BottomLeft, and MTF_BottomRight, respectively. Then, the maximum value MTF is selected from these four MTF values. maxValue =max(MTF_TopLeft, MTF_TopRight, MTF_BottomLeft, MTF_BottomRight), selects the minimum MTF value from these four MTF values. minValue=min(MTF_TopLeft, MTF_TopRight, MTF_BottomLeft, MTF_BottomRight). In this embodiment, when calculating the maximum and minimum MTF values ​​of the four edges of the design pattern, the blade blocks at the four corners of the design pattern are selected, which better reflects the MTF characteristics of the image at the edge of the lens's field of view and is more representative.

[0070] In other embodiments, other locations can also be selected, such as around the entire perimeter of the design pattern (i.e., Figure 4 The maximum and minimum values ​​of the blade blocks in the top row, bottom row, left row, and right row.

[0071] Further, in one embodiment, calculating the imaging symmetry based on the average MTF and the maximum and minimum MTF values ​​around the edges of the design pattern may include:

[0072] The formula for calculating imaging symmetry is:

[0073] Symmetry = 1 - (MTF) maxValue -MTF minValue ) / (2*MTF AverageValue );

[0074] Where Symmetry represents imaging symmetry; MTF maxValue MTF is the maximum value; MTF minValue Minimum MTF; MTF AverageValue The MTF average value is used. In this embodiment, the calculation of imaging symmetry utilizes the maximum and minimum values ​​and the average value of the 99 blade blocks. The symmetry result is obtained by dividing the difference between the maximum and minimum values ​​by twice the average value. This calculation method can be used to obtain the uniformity of the image.

[0075] Furthermore, in some alternative embodiments, see Figure 3 As shown, after calculating the MTF values ​​at various positions of the pattern in the test chart, the following steps may also be included:

[0076] S5: Calculate the MTF standard deviation of the design pattern based on the MTF values ​​at each position of the design pattern.

[0077] S6: Calculate imaging uniformity based on the MTF mean and MTF standard deviation.

[0078] S7: Determine the MTF imaging characteristics based on imaging uniformity.

[0079] In this embodiment, when the design pattern consists of 99 blade blocks, after calculating the MTF value of each blade block, the MTF standard deviation of these 99 blade blocks can be further calculated. The imaging uniformity is calculated as 1 - Std / Mean, where Std is the MTF standard deviation and Mean is the MTF average (i.e., the aforementioned MTF). AverageValue The formula for calculating the standard deviation is: Where Σ represents summation; x i Here, is the MTF value of each blade block, where i represents the i-th blade block, i = 1, 2, 3, ..., 99; μ is the average MTF (arithmetic mean) of all blade blocks; and N is the total number of blade blocks, which is N = 99 in this embodiment. This calculation method provides a standardized metric, comparing the values ​​of each blade block to measure the dispersion of the overall data. The closer STD / Mean is to 1, the more uneven the data distribution, indicating poorer lens imaging characteristics and greater dispersion. A larger value for the Uniformity calculation, closer to 1, indicates better image consistency. Furthermore, by calculating the Uniformity using the MTF values ​​at various positions in the design pattern, the overall imaging effect of the test image can be evaluated. This means that not only imaging symmetry but also imaging uniformity are calculated. These two values ​​better illustrate the quality of camera and lens imaging, and specific analytical conclusions can be drawn from the specific values ​​of imaging symmetry and uniformity.

[0080] Based on the above technical solution, in one embodiment, determining the MTF imaging characteristics based on imaging uniformity may include:

[0081] S71: Determine whether the image uniformity value is between 0.8 and 0.9.

[0082] S72: If the image uniformity value is greater than 0.9, it indicates that the image uniformity is good; if the image uniformity value is between 0.8 and 0.9, it indicates that the image uniformity is average; if the image uniformity value is less than 0.8, it indicates that the image uniformity is poor.

[0083] In this embodiment, after calculating the image uniformity value, it can be compared with a pre-set value to determine the quality of the image uniformity. This embodiment uses 0.8 and 0.9 as the dividing points. An image uniformity above 0.9 indicates good image uniformity; an image uniformity between 0.8 and 0.9 indicates average image uniformity, possibly due to optical axis misalignment, lens eccentricity, or slight sensor misalignment; an image uniformity below 0.8 indicates poor image uniformity, possibly due to poor lens assembly or severe sensor misalignment. In other embodiments, the dividing point can be set to other values ​​according to actual needs; this is not limited here.

[0084] Further, preferably, the step of determining the MTF imaging characteristics based on imaging symmetry may include:

[0085] S41: Determine whether the value of the imaging symmetry is between 0.8 and 0.9.

[0086] S42: If the image symmetry value is greater than 0.9, it indicates that the image symmetry is good; if the image symmetry value is between 0.8 and 0.9, it indicates that the image symmetry is average; if the image symmetry value is less than 0.8, it indicates that the image symmetry is poor.

[0087] In this embodiment, after calculating the numerical value of imaging symmetry, it can be compared with a pre-set value to determine the quality of imaging symmetry. This embodiment also uses 0.8 and 0.9 as the dividing point. An imaging symmetry value above 0.9 indicates good imaging symmetry; an imaging symmetry value between 0.8 and 0.9 indicates average imaging symmetry; and an imaging symmetry value less than 0.8 indicates poor imaging symmetry. In other embodiments, the dividing point can be set to other values ​​according to actual needs; no restrictions are imposed here.

[0088] Furthermore, it may also include:

[0089] S43: Determine whether the difference between the maximum MTF value and the average MTF value, and the difference between the minimum MTF value and the average MTF value, are greater than a set difference.

[0090] S44: If the difference between the maximum MTF value and the average MTF value and / or the difference between the minimum MTF value and the average MTF value is greater than the set difference, it indicates that the lens has vignetting or poor uniformity of the imaging light source, or that dust appears on the surface of the design pattern on the screen.

[0091] In this embodiment, the set difference is set to 0.5. If the difference between the maximum or minimum MTF value and the average MTF value is large, for example, greater than 0.5, it may be that the lens has vignetting or the imaging light source has poor symmetry (used to reverse-engineer and troubleshoot abnormal phenomena in the experimental process), or dust appears on the surface of the design pattern on the screen, causing abnormal MTF values.

[0092] Furthermore, in one embodiment, before using the combination of the camera and lens to photograph the screen displaying the design pattern to obtain the test image, the method further includes: adjusting the fixture connected to the camera to keep the level of the fixture and the screen below a preset angle value. In this embodiment, a multi-axis adjustment platform can be used to mount the camera, lens, and screen. The multi-axis adjustment platform has a fixture with a mounting plane. The lens is mounted on the camera, and the camera is mounted on the mounting plane. When comparing the level of the fixture and the screen, a level is directly used to measure the level of the mounting plane and the screen surface, keeping the level below 0.02° (as close to 0° as possible). In this embodiment, since the fixture and screen have been adjusted to be sufficiently level before photographing the test image, the test image obtained by photographing the screen in this state will be more accurate.

[0093] Furthermore, in some optional embodiments, before photographing the screen displaying the designed pattern using the combination of the camera and lens under test to obtain the test image, the process may further include: focusing the combination of the camera and lens under test; when the image is magnified and a preset number of transition pixels are visible, the focus is considered successful. In this embodiment, before photographing the test image and calculating the MTF, focusing is performed first, and the image is magnified to observe the transition pixels; approximately 1-2 transition pixels are visible, indicating successful focusing. This embodiment, by focusing first and then measuring and calculating the MTF, ensures that the test image taken after focusing is as clear as possible, and the calculated MTF value is more accurate.

[0094] The method for judging MTF imaging characteristics provided in this application can be used to judge the quality of lens imaging and to judge the quality of lens imaging through specific values.

[0095] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0096] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0097] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for determining MTF imaging characteristics, characterized in that, The methods for determining the MTF imaging characteristics include: The test image is obtained by photographing the screen displaying the designed pattern using the combination of the camera and lens under test; Calculate the MTF value at each position of the design pattern in the test chart, and calculate the average MTF value of the design pattern based on the MTF value at each position of the design pattern. The imaging symmetry is calculated based on the average MTF and the maximum and minimum MTF values ​​at the edges of the design pattern. Determine MTF imaging characteristics based on imaging symmetry; The calculation of imaging symmetry based on the average MTF and the maximum and minimum MTF values ​​at the edges of the designed pattern includes: The formula for calculating imaging symmetry is: ； in, This represents the maximum MTF value. Minimum MTF value; This represents the average MTF value.

2. The method for determining MTF imaging characteristics as described in claim 1, characterized in that, The design pattern consists of multiple blade blocks displayed on the screen, which are evenly arranged in multiple rows and columns.

3. The method for determining MTF imaging characteristics as described in claim 2, characterized in that, The calculation of the MTF value at each position of the design pattern in the test chart, and the calculation of the average MTF value of the design pattern based on the MTF values ​​at each position, includes: Calculate the MTF value of each cutting edge block in the test diagram; The average MTF of the design pattern is calculated based on the MTF values ​​of each blade block.

4. The method for determining MTF imaging characteristics as described in claim 2, characterized in that, Before calculating the imaging symmetry based on the average MTF and the maximum and minimum MTF values ​​around the edges of the design pattern, the following steps are also included: Select the MTF values ​​of the four blade blocks located at the four corners of the test image; Find the maximum MTF value among the four blade blocks at the four corners and take it as the maximum MTF value of the design pattern's four edges; Find the minimum MTF value among the four blade blocks at the four corners and use it as the minimum MTF value for the four edges of the design pattern.

5. The method for determining MTF imaging characteristics as described in claim 1, characterized in that, After calculating the MTF values ​​at various locations of the pattern in the test chart, the method further includes: Calculate the standard deviation of the MTF of the design pattern based on the MTF values ​​at each position of the design pattern; Imaging uniformity is calculated based on the MTF mean and MTF standard deviation; The imaging characteristics of MTF are determined based on the imaging uniformity.

6. The method for determining MTF imaging characteristics as described in claim 5, characterized in that, The method of determining MTF imaging characteristics based on imaging uniformity includes: Determine whether the image uniformity value is between 0.8 and 0.9; If the image uniformity value is greater than 0.9, it indicates good image uniformity; if the image uniformity value is between 0.8 and 0.9, it indicates average image uniformity; if the image uniformity value is less than 0.8, it indicates poor image uniformity.

7. The method for determining MTF imaging characteristics as described in claim 1, characterized in that, The method of determining MTF imaging characteristics based on imaging symmetry further includes: Determine whether the difference between the maximum MTF value and the average MTF value, and the difference between the minimum MTF value and the average MTF value, are greater than a set difference. If the difference between the maximum MTF value and the average MTF value and / or the difference between the minimum MTF value and the average MTF value is greater than the set difference, it indicates that the lens has vignetting or poor uniformity of the imaging light source, or that there is dust on the surface of the design pattern on the screen.

8. The method for determining MTF imaging characteristics as described in claim 1, characterized in that, Before obtaining the test image by photographing the screen displaying the design pattern using the combination of the camera and lens under test, the process also includes: Adjust the fixture connected to the camera so that the horizontal angle between the fixture and the screen is below the preset value.

9. The method for determining MTF imaging characteristics as described in claim 1, characterized in that, Before obtaining the test image by photographing the screen displaying the design pattern using the combination of the camera and lens under test, the process also includes: The camera and lens combination to be tested is focused. When the image is magnified and shows a preset number of transition pixels, the focus is successful.

Images