Method for judging MTF (Modulation Transfer Function) imaging characteristics

Abstract

The invention relates to an MTF imaging characteristic judgment method, and the method comprises the steps: shooting a screen body which displays a design pattern through employing a combination body of a to-be-tested camera and a lens, and obtaining a test pattern; calculating an MTF value of each position of the design pattern in the test pattern, and calculating an MTF average value of the design pattern based on the MTF value of each position of the design pattern; based on the MTF average value and the MTF maximum value and the MTF minimum value of the peripheral edge of the design pattern, the imaging symmetry is calculated; and the MTF imaging characteristics are judged according to the imaging symmetry. According to the method, the MTF value of each position of the design pattern in the test pattern is calculated, and the imaging symmetry of the whole test pattern can be calculated based on the MTF average value and the MTF maximum value and the MTF minimum value of the peripheral edge of the design pattern, so that the whole MTF imaging characteristics of the test pattern are judged; the problem that the method for drawing the MTF curve chart in the related technology can only represent the result of a certain area of the lens shooting picture and cannot reflect the integral imaging effect of the lens shooting picture is solved.

Description

Technical Field

[0001] The present application relates to the field of machine vision technology, and in particular to a method for determining MTF imaging characteristics. Background Art

[0002] At present, industrial cameras and industrial lenses in machine vision are used as high-precision imaging devices to detect defects in DUT (Device Under Test), so the MTF (Modulation transfer function) of visual imaging is very high. By analyzing the MTF imaging characteristics, we can infer whether the imaging quality of the camera and lens meets the standards through data support.

[0003] In the related technology, the current method for judging the MTF imaging characteristics is generally to calculate the MTF value of a certain area of ​​the lens shooting picture, and then draw an MTF curve chart. The horizontal axis of the MTF curve chart represents the distance from the center of the lens to the edge of the lens in millimeters, and the vertical axis represents the MTF value. The horizontal axis of the MTF curve chart is equivalent to the imaging circle radius, the left end of the horizontal axis is equivalent to the imaging center, and the right end is equivalent to the outer end of the imaging circle. By comparing the left and right parts of the MTF curve chart, it is easier to understand the imaging performance in all directions starting from the center of the lens. The slower the curve in the MTF curve chart decays from left to right, the better. The slower it decays, the smaller the imaging gap from the center to the edge of the lens.

[0004] However, the above method of drawing the MTF curve chart can only represent the result of a certain area of ​​the lens shooting picture, and cannot reflect the overall imaging effect of the lens shooting picture.

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

[0006] The present application provides a method for determining MTF imaging characteristics, which can solve the technical problem in the related art that the method of drawing MTF curve charts can only represent the result of a certain area of ​​the lens shooting picture, and cannot reflect the overall imaging effect of the lens shooting picture.

[0007] In a first aspect, an embodiment of the present application provides a method for determining MTF imaging characteristics, and the method for determining MTF imaging characteristics includes:

[0008] Use a combination of a camera and a lens to be tested to shoot a screen displaying a design pattern to obtain a test image;

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

[0010] Calculate the imaging symmetry based on the MTF average value and the maximum and minimum MTF values ​​around the edges of the design pattern;

[0011] The MTF imaging characteristics are determined based on the imaging symmetry.

[0012] In combination with the first aspect, in one implementation, the design pattern is a plurality of blade blocks displayed in the screen body, and the plurality of blade blocks are evenly arranged into a plurality of rows and a plurality of columns.

[0013] In combination with the first aspect, in one implementation, calculating the MTF value of each position of the design pattern in the test pattern, and calculating the MTF average value of the design pattern based on the MTF value of each position of the design pattern, includes:

[0014] Calculate the MTF value of each blade block in the test image;

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

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

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

[0018] Find the maximum MTF value among the four blade blocks at the four corners as the maximum MTF value of the edges around the design pattern;

[0019] From the MTF values ​​of the four blade blocks at the four corner positions, find the one with the smallest MTF value as the minimum MTF value of the edges around the design pattern.

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

[0021] The calculation formula of imaging symmetry is:

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

[0023] Among them, MTF maxValue is the maximum value of MTF; MTF minValue is the minimum value of MTF; MTF AverageValue is the MTF average value.

[0024] In combination with the first aspect, in one implementation, after calculating the MTF value of each position of the design pattern in the test chart, the method further includes:

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

[0026] Calculate imaging uniformity based on the MTF mean and MTF standard deviation;

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

[0028] In combination with the first aspect, in one implementation, judging the MTF imaging characteristic according to the imaging uniformity includes:

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

[0030] If the value of imaging uniformity is greater than 0.9, it means that the imaging uniformity is good; if the value of imaging uniformity is between 0.8 and 0.9, it means that the imaging uniformity is average; if the value of imaging uniformity is less than 0.8, it means that the imaging uniformity is poor.

[0031] In combination with the first aspect, in one implementation, the determining the MTF imaging characteristic according to the 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 the 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 means that the lens has dark corners or the imaging light source is not uniform, or dust appears on the surface of the design pattern on the screen.

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

[0035] Adjust the fixture connected to the camera to keep the level between the fixture and the screen below the preset angle value.

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

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

[0038] The beneficial effects brought by the technical solution provided by the embodiments of the present application include:

[0039] 1. By calculating the MTF value of each position of the design pattern in the test chart, and based on the MTF average value and the maximum and minimum MTF values ​​around the edges of the design pattern, the imaging symmetry of the entire test chart can be calculated, and then the overall MTF imaging characteristics of the test chart can be judged, which can better illustrate the quality of the imaging effect of the camera and lens, and solves the technical problem that the method of drawing MTF curve charts in related technologies can only represent the results of a certain area of ​​the lens shooting picture, and cannot reflect the overall imaging effect of the lens shooting picture.

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

[0041] 3. The MTF value at each position in the design pattern can also be used to calculate the imaging uniformity, and the imaging effect of the overall test pattern can be judged, 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 pros and cons of the imaging effects of the camera and lens, and certain analytical conclusions can be obtained through the specific values ​​of imaging symmetry and imaging uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

[0044] Figure 2 A schematic diagram of the process of step S2 provided in an embodiment of the present application;

[0045] Figure 3 A schematic flow chart of another embodiment of a method for determining MTF imaging characteristics provided in an embodiment of the present application;

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

[0047] Figure 5 Selection test provided for the embodiment of the present application Figure 4 Schematic diagram of the angular position blade block. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0049] The embodiment of the present application provides a method for determining MTF imaging characteristics, which can solve the technical problem that the method of drawing an MTF curve chart can only represent the result of a certain area of ​​the lens shooting picture, and cannot reflect the overall imaging effect of the lens shooting picture.

[0050] See also Figure 1 As shown, a method for determining MTF imaging characteristics provided by an embodiment of the present application may include the following steps:

[0051] S1: Use a combination of a camera and a lens to be tested to shoot a screen displaying a design pattern to obtain a test image.

[0052] In this step, when shooting the test pattern, the shooting is carried out in a dark room. The lens is installed at the lower end of the camera to form a combination of the camera to be tested and the lens, and the lens and the camera are located directly above the screen. A specially made design pattern is displayed on the screen to test the MTF value, wherein the screen can be an iPad.

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

[0054] In this step, after the test pattern is captured, the design pattern will be displayed in the test pattern. 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 demarcated as a small area, and different positions will obtain multiple small areas evenly arranged in the design pattern. The MTF value of each small area is calculated separately, which is the MTF value of each position of the design pattern. The MTF average 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, the design pattern can also be directly designed as multiple independent small patterns, and multiple small patterns are evenly arranged on the screen to form a design pattern. After the test pattern 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 MTF average value is the sum of the MTF values ​​of all small patterns divided by the number of all small patterns.

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

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

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

[0058] In this embodiment, by calculating the MTF value of each position of the design pattern in the test chart, the MTF average value of the design pattern can be calculated based on the MTF values ​​of each position of the design pattern, and the imaging symmetry of the entire test chart can be calculated based on the MTF average value and the maximum and minimum MTF values ​​of the edges around the design pattern, and then the overall MTF imaging characteristics of the test chart are judged. Since the MTF value of each position of the test chart is calculated during the calculation process, and the imaging symmetry of the entire test chart is calculated using the MTF value of each position, the overall MTF imaging characteristics of the test chart are judged by a reasonable calculation method, which can better illustrate the quality of the imaging effects of the camera and the lens, and solves the technical problem in the related art that the method of drawing an MTF curve chart can only represent the result of a certain area of ​​the lens shooting picture, and cannot reflect the overall imaging effect of the lens shooting picture.

[0059] Further, preferably, in this embodiment, the design pattern is a plurality of blade blocks (such as Figure 4 The plurality of blade blocks are evenly arranged in multiple rows and columns. Figure 4 As shown, 9 rows and 11 columns of blade blocks are designed in the screen body, and a total of 9*11 (that is, 99) blade blocks are obtained, and each blade block is designed with a specific tilt angle. The multiple rows and columns of blade blocks displayed in the screen body will be displayed in the test image after the test image is shot. The design pattern in this embodiment is designed to be independent of each other and arranged in multiple rows and columns of blade blocks. The MTF values ​​corresponding to each blade block are also neatly arranged in rows and columns. With this arrangement, it is easier to calculate the MTF values ​​of each position in the design pattern, and then calculate the MTF average value of the design pattern based on the MTF values ​​of each position.

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

[0061] Based on the above technical solution, see Figure 2As shown, in one embodiment, the calculating of the MTF value of each position of the design pattern in the test pattern and the calculating of the MTF average value of the design pattern based on the MTF value of each position of the design pattern may include:

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

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

[0064] In this embodiment, since the design pattern is a plurality of evenly arranged blade blocks, when calculating the MTF value of each position of the design pattern, the MTF value of each blade block can be directly calculated; in this embodiment, a total of 99 blade blocks are set, and the calculation formula of the MTF average value is: MTF AverageValue =(MTF 1 +MTF 2 +…+MTF 99 ) / 99, where MTF 1 is the MTF value of the first blade block; MTF 2 is the MTF value of the second blade block; MTF 99 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 MTF maximum value and the MTF minimum value of the edges around the design pattern, the following may also 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 shown).

[0067] Step b: Find the maximum MTF value among the MTF values ​​of the four blade blocks at the four corner positions as the maximum MTF value of the edges around the design pattern.

[0068] Step c: Find the minimum MTF value among the MTF values ​​of the four blade blocks at the four corner positions as the minimum MTF value of the edges around the design pattern.

[0069] In this embodiment, 99 blade blocks are arranged in 9 rows and 11 columns to form a rectangle. The MTF values ​​of the four blade blocks at the four vertices of the rectangle are selected, namely MTF_TopLeft, MTF_TopRight, MTF_BottomLeft and MTF_BottomRight, and then the maximum value MTF is selected from these four MTF values. maxValue=max(MTF_TopLeft, MTF_TopRight, MTF_BottomLeft, MTF_BottomRight), select the minimum MTF 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 edges around the design pattern, the blade blocks at the four corners of the design pattern are selected, which can better reflect the MTF characteristics of the edge imaging of the lens field of view and is more representative.

[0070] In other embodiments, other positions may be selected, such as a circle around the entire design pattern (i.e. Figure 4 The maximum and minimum values ​​in the blade blocks of the top row, bottom row, leftmost row, and rightmost row.

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

[0072] The calculation formula of imaging symmetry is:

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

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

[0075] Further, in some optional embodiments, see Figure 3 As shown, after calculating the MTF value of each position of the design 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 average and MTF standard deviation.

[0078] S7: Determine the MTF imaging characteristics according to the imaging uniformity.

[0079] In this embodiment, when the design pattern is 99 blade blocks, after calculating the MTF value of each blade block, the MTF standard deviation of the 99 blade blocks can be further calculated, and the imaging uniformity Uniformity = 1-Std / Mean, where Std is the MTF standard deviation and Mean is the MTF average value (that is, the above-mentioned MTF AverageValue ), the formula for calculating the standard deviation is Among them, Σ represents summation; x i is the MTF value of each blade block, i represents the i-th blade block, i=1,2,3,…,99; μ is the MTF average value (arithmetic mean) of all blade blocks; N is the total number of blade blocks, and in this embodiment, N=99. The calculation method adopted in this embodiment provides a standardized measurement, which compares the values ​​of each blade block to measure the discreteness of the overall data. The closer STD / Mean is to 1, the more uneven the data distribution is, that is, the worse the imaging characteristics of the lens are, and the greater the discreteness is; the larger the value of the calculation result of imaging uniformity, that is, the closer it is to 1, the better the picture consistency is; and the imaging uniformity is calculated using the MTF values ​​of each position in the design pattern, which can judge the imaging effect of the overall test image, that is, not only the imaging symmetry but also the imaging uniformity is calculated, and these two values ​​are used to better illustrate the advantages and disadvantages of the imaging effects of the camera and the lens, and certain analytical conclusions can be obtained through the specific values ​​of imaging symmetry and imaging uniformity.

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

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

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

[0083] In this embodiment, after calculating the value of imaging uniformity, it can be compared with a pre-set value to determine the quality of imaging uniformity. In this embodiment, 0.8 and 0.9 are used as the dividing points. If the calculated imaging uniformity is above 0.9, it means that the imaging uniformity is good; if the calculated imaging uniformity is between 0.8 and 0.9, it means that the imaging uniformity is general, and there may be an offset in the optical axis, an eccentric lens, or a slight offset in the sensor installation; if the calculated imaging uniformity is less than 0.8, it means that the imaging uniformity is poor, and there are problems such as poor lens assembly process or serious sensor offset. In other embodiments, the dividing point here can also be set to other values ​​according to actual needs, and there is no limitation here.

[0084] Further, preferably, judging the MTF imaging characteristic according to the 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 value of imaging symmetry is greater than 0.9, it means that the imaging symmetry is good; if the value of imaging symmetry is between 0.8 and 0.9, it means that the imaging symmetry is average; if the value of imaging symmetry is less than 0.8, it means that the imaging symmetry is poor.

[0087] In this embodiment, after the imaging symmetry value is calculated, it can be compared with a pre-set value to determine the quality of the imaging symmetry. In this embodiment, 0.8 and 0.9 are used as the dividing points. If the calculated imaging symmetry is above 0.9, it means that the imaging symmetry is good; if the calculated imaging symmetry is between 0.8 and 0.9, it means that the imaging symmetry is average; if the calculated imaging symmetry is less than 0.8, it means that the imaging symmetry is poor. In other embodiments, the dividing point here can also be set to other values ​​according to actual needs, and there is no limitation 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 means that the lens has dark corners or the imaging light source is not uniform, or 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 MTF value or the minimum MTF value and the MTF average value is large, for example, greater than 0.5, it may be that the lens has dark corners or the imaging light source is not symmetrical (used to reversely troubleshoot abnormal phenomena during the experiment), or dust appears on the surface of the designed pattern on the screen, causing the MTF value to be abnormal.

[0092] Furthermore, in one embodiment, before the combination of the camera to be tested and the lens is used to shoot the screen displaying the design pattern and obtain the test pattern, it also includes: adjusting the jig connected to the camera so that the level of the jig and the screen is maintained below a preset angle value. In this embodiment, a multi-axis adjustment platform can be used to install the camera, the lens and the screen. The multi-axis adjustment platform is equipped with a jig, the jig has 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 jig and the screen, the level meter is directly used to measure the level of the mounting plane and the surface of the screen so that the level is maintained below 0.02° (as close to 0° as possible). In this embodiment, since the jig and the screen have been adjusted to be sufficiently level before shooting the test pattern, the test pattern obtained by shooting the screen in this state will be more accurate.

[0093] Furthermore, in some optional embodiments, before the combination of the camera to be tested and the lens is used to shoot the screen displaying the design pattern and obtain the test pattern, it may also include: focusing the combination of the camera to be tested and the lens, and when the image is enlarged and a preset number of transition pixels are present, the focus is successful. In this embodiment, before shooting the test pattern and calculating the MTF, the focus is first performed, and the image is enlarged to see the transition pixels, and the focus is successful when about 1 to 2 transition pixels are seen. In this embodiment, focusing first and then measuring and calculating the MTF can ensure that the test pattern shot after focusing is as clear as possible, and the calculated MTF value is also more accurate.

[0094] The method for determining the MTF imaging characteristic provided in the embodiment of the present application can be used to determine the quality of lens imaging, and the quality of lens imaging can be determined by specific numerical values.

[0095] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present 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 only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0097] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for determining MTF imaging characteristics, characterized in that: The method for determining the MTF imaging characteristic includes: Use a combination of a camera and a lens to be tested to shoot a screen displaying a design pattern to obtain a test image; Calculate the MTF value of each position of the design pattern in the test pattern, and calculate the MTF average value of the design pattern based on the MTF value of each position of the design pattern; Calculate the imaging symmetry based on the MTF average value and the maximum and minimum MTF values ​​around the edges of the design pattern; The MTF imaging characteristics are determined based on the imaging symmetry.

2. The method for determining the MTF imaging characteristic according to claim 1, wherein: The design pattern is a plurality of blade blocks displayed in the screen body, and the plurality of blade blocks are evenly arranged in a plurality of rows and columns.

3. The method for determining the MTF imaging characteristic according to claim 2, wherein: The step of calculating the MTF value of each position of the design pattern in the test pattern, and calculating the MTF average value of the design pattern based on the MTF value of each position of the design pattern, comprises: Calculate the MTF value of each blade block in the test image; The MTF average of the design pattern is calculated based on the MTF values ​​of each blade block.

4. The method for determining the MTF imaging characteristic according to claim 2, wherein: Before calculating the imaging symmetry based on the MTF average value and the MTF maximum value and the MTF minimum value of the edges around the design pattern, the method further includes: Select the MTF values ​​of the four blade blocks located at the four corners in the test image; Find the maximum MTF value among the four blade blocks at the four corners as the maximum MTF value of the edges around the design pattern; From the MTF values ​​of the four blade blocks at the four corner positions, find the one with the smallest MTF value as the minimum MTF value of the edges around the design pattern.

5. The method for determining the MTF imaging characteristic according to claim 1, wherein: The imaging symmetry is calculated based on the MTF average value and the MTF maximum value and the MTF minimum value of the edges around the design pattern, including: The calculation formula of imaging symmetry is: Symmetry=1-(MTF maxValue -MTF minValue ) / (2*MTF AverageValue ); Among them, MTF maxValue is the maximum value of MTF; MTF minValue is the minimum value of MTF; MTF AverageValue is the MTF average value.

6. The method for determining the MTF imaging characteristic according to claim 1, wherein: After calculating the MTF value of each position of the design pattern in the test chart, the method further includes: Calculate the MTF standard deviation of the design pattern based on the MTF values ​​at each position of the design pattern; Calculate imaging uniformity based on the MTF mean and MTF standard deviation; The MTF imaging characteristics are determined based on the imaging uniformity.

7. The method for determining the MTF imaging characteristic according to claim 6, wherein: The determining of the MTF imaging characteristics according to the imaging uniformity includes: Determine whether the value of imaging uniformity is between 0.8 and 0.9; If the value of imaging uniformity is greater than 0.9, it means that the imaging uniformity is good; if the value of imaging uniformity is between 0.8 and 0.9, it means that the imaging uniformity is average; if the value of imaging uniformity is less than 0.8, it means that the imaging uniformity is poor.

8. The method for determining the MTF imaging characteristic according to claim 1, wherein: The determining of the MTF imaging characteristics according to the imaging symmetry 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 the 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 means that the lens has dark corners or the imaging light source is not uniform, or dust appears on the surface of the design pattern on the screen.

9. The method for determining the MTF imaging characteristic according to claim 1, wherein: Before using the combination of the camera to be tested and the lens to photograph the screen displaying the design pattern to obtain the test image, the method further includes: Adjust the fixture connected to the camera to keep the level between the fixture and the screen below the preset angle value.

10. The method for determining the MTF imaging characteristic according to claim 1, wherein: Before using the combination of the camera to be tested and the lens to photograph the screen displaying the design pattern to obtain the test image, the method further includes: Focus the combination of the camera and lens to be tested. When the image is magnified and a preset number of transition pixels appear, the focus is successful.

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