CN117969024A - Resolution testing method and device for optical imaging system and readable storage medium - Google Patents

Abstract

The application provides a method and a device for testing resolution power suitable for an optical imaging system and a readable storage medium. The method for testing the resolution force comprises the following steps: determining a knife edge region of a test pattern based on a center of the test image, a contour line of the test pattern in the test image, and a center of a center zone of the test pattern; fitting the arc-shaped edge of the knife edge area to obtain an edge expansion function curve corresponding to the arc-shaped edge; and determining a resolution of the optical imaging system based on the edge spread function curve.

Description

Resolution testing method and device for optical imaging system and readable storage medium

Technical Field

The present application relates to the field of detection technologies of optical imaging systems, and in particular, to a method and apparatus for testing resolution of an optical imaging system, and a readable storage medium.

Background

At present, the detection method for representing the resolution of the optical imaging system can adopt various types of test targets, such as hyperbolic wedge-shaped graphs, linear sinusoidal gratings, inclined edges, dead leaf graphs, siemens star marks and the like. From the viewpoints of detection efficiency and wide acceptance, the inclined blade edge is used as a test target in many cases.

For example, when a rectangular color block is used as a target, a test pattern as shown in fig. 1 can be obtained, and a detection method in which a sloped edge in the test pattern is used as a test target can be roughly described as:

(1) A finer black-and-white curve (edge spread function, ESF) can be obtained by oversampling the graph of the oblique edge;

(2) Deriving the obtained curve to obtain the change rate (LSF) of the curve; and

(3) The resulting rate of change is subjected to FFT (DFT) conversion to obtain the value of MTF at each frequency.

However, the above detection method only can realize the transverse (Horizontal) and Vertical (Vertical) resolution test at each test point due to the limitation of the algorithm and the design of the test target on the inclination angle of the blade, etc., and the transverse and Vertical resolution test results have no correspondence with the radial (Sagittal) and Tangential (changing) resolution of the optical imaging system, and cannot truly reflect the characteristics of the optical imaging system itself.

Disclosure of Invention

The present application provides a method, apparatus, and readable storage medium for testing resolution suitable for an optical imaging system that at least partially solve the above-mentioned problems occurring in the related art.

The first aspect of the present application provides a method for testing resolution suitable for an optical imaging system, comprising: determining a knife edge region of a test pattern based on a center of the test image, a contour line of the test pattern in the test image, and a center of a center zone of the test pattern; fitting the arc-shaped edge of the knife edge area to obtain an edge expansion function curve corresponding to the arc-shaped edge; and determining a resolution of the optical imaging system based on the edge spread function curve.

In some embodiments, the method for testing a resolution further comprises: fitting the boundary of the test pattern by adopting an elliptic equation to determine the contour line of the test pattern; and determining the contour line of the central zone bit and taking the center of the area surrounded by the contour line of the central zone bit as the center of the central zone bit.

In some embodiments, the step of determining the knife edge region of the test pattern comprises: and determining a radial knife edge region and a tangential knife edge region of the test pattern based on two radial intersection points of a first straight line intersecting the contour line and two tangential intersection points of a second straight line intersecting the contour line, wherein the first straight line passes through the center of the test image and the center of the center zone bit, and the second straight line passes through the center of the center zone bit and is perpendicular to the first straight line. The knife edge regions include the radial knife edge region and the tangential knife edge region.

In some embodiments, the step of fitting the arcuate blade edge of the knife edge region to obtain an edge spread function curve corresponding to the arcuate blade edge comprises: fitting the arc-shaped edge of the knife edge region by using a polynomial equation to determine the contour line of the arc-shaped edge of the knife edge region; and determining the edge spread function curve based on the contour of the arcuate edge of the knife edge region.

In some embodiments, the step of fitting the arcuate edge of the knife edge region to determine a contour of the arcuate edge of the knife edge region using a polynomial equation comprises: performing first polynomial fitting on the arc-shaped edge of the knife edge region to obtain a first fitting curve; and performing a second degree polynomial fitting on the contour coordinates of the plurality of points on the first fitting curve to obtain a second fitting curve. The contour line of the arc-shaped blade edge comprises the second fitting curve.

In some embodiments, the method for testing a resolution further comprises: and determining the contour coordinates of each point of the plurality of points based on the tangent lines and the vertical lines at the plurality of points on the first fitting curve and processing the vertical lines at each point of the plurality of points by a region interpolation mode.

In some embodiments, the step of determining the edge spread function curve based on the contour of the arcuate edge of the knife edge region comprises: determining a first value based on a distance between a pixel point in the edge region and a tangent line of the contour line; taking the brightness of the pixel at the pixel point in the knife edge area as a second numerical value; forming a coordinate point by taking the first numerical value as an abscissa and the second numerical value as an ordinate; and determining the ESF curve based on the plurality of coordinate points determined by the plurality of pixel points in the knife edge area.

In some embodiments, the first fitted curve and/or the second fitted curve is a quadratic polynomial equation.

In some embodiments, the method for testing a resolution further comprises: receiving an initial image obtained by shooting a target pattern by the optical imaging system; binarizing the initial image to obtain a binarized image; and identifying contours of patterns in the binarized map to obtain the test image.

A second aspect of the present application provides a resolution testing apparatus adapted for use in an optical imaging system, comprising: the target comprises a circular pattern with a central marker bit; a light source that provides illumination light to the target; the test board faces the standard board and is used for installing an optical imaging system; and an electronic device connected to the optical imaging system. An electronic device includes: a processor; and a memory communicatively connected to the processor, wherein the memory stores a program executable by the processor, and the processor is capable of executing the method for testing resolution according to the above when the program is executed by the processor.

A third aspect of the present application provides a readable storage medium having stored thereon a computer program which, when executed by a processor, implements a method for testing resolution according to the above.

According to the resolution test method suitable for the optical imaging system, provided by at least one embodiment of the application, after the knife edge area of the test pattern is determined based on the center of the test image, the central zone bit and the contour line of the test pattern, the ESF curve of the arc-shaped knife edge of the knife edge area is fitted, so that the resolution calculation is carried out on the ESF curve to determine the radial (Sagittal) and/or Tangential (ranging) resolution of the optical imaging system.

Drawings

Other features, objects and advantages of the present application will become more apparent upon reading of the detailed description of non-limiting embodiments, made with reference to the following drawings. Wherein:

FIG. 1 is a schematic diagram of a test pattern employed in a method for testing resolution of an optical imaging system according to the related art;

FIG. 2 is a schematic diagram of a resolution testing apparatus of an optical imaging system according to an exemplary embodiment of the present application;

FIG. 3 is a schematic illustration of a target in an exemplary embodiment according to the present application;

FIG. 4 is a flow chart of a method for testing resolution of an optical imaging system according to an exemplary embodiment of the application;

FIG. 5 is a flow chart of acquiring a test image according to an exemplary embodiment of the present application;

FIG. 6 is a gray scale pictorial view of an initial image in accordance with an exemplary embodiment of the present application;

FIG. 7 is a binarized pictorial view of an initial image in accordance with an exemplary embodiment of the application;

FIG. 8 is a schematic diagram of a test image in an exemplary embodiment in accordance with the application;

FIG. 9 is a flow chart of acquiring the contour line of a test pattern and the center of a center bit of the test pattern in an exemplary embodiment according to the present application;

FIG. 10 is a schematic outline of a test image in an exemplary embodiment according to the application;

Fig. 11 is a flowchart illustrating step S410 in an exemplary embodiment according to the present application;

FIG. 12 is a schematic illustration of radial and tangential intersection points on the contour lines of a test image in accordance with an exemplary embodiment of the present application;

FIG. 13 is a schematic view of a knife edge region in an exemplary embodiment in accordance with the application;

Fig. 14 is a flowchart illustrating step S420 in an exemplary embodiment of the present application;

fig. 15 is a flowchart illustrating step S421 in an exemplary embodiment of the present application;

FIG. 16 is a schematic diagram of determining contour coordinates of contour points in accordance with an exemplary embodiment of the present application;

fig. 17 is a luminance weight graph in an exemplary embodiment according to the present application;

fig. 18 is a flowchart illustrating step S422 in an exemplary embodiment according to the present application;

FIG. 19 is a schematic diagram of determining coordinate points constituting an ESF curve in accordance with an exemplary embodiment of the present application; and

Fig. 20 is a schematic structural view of an electronic device according to an exemplary embodiment of the present application.

Detailed Description

For a better understanding of the application, various aspects of the application will be described in more detail with reference to the accompanying drawings. It should be understood that the detailed description is merely illustrative of exemplary embodiments of the application and is not intended to limit the scope of the application in any way. Like reference numerals refer to like elements throughout the specification. The expression "and/or" includes any and all combinations of one or more of the associated listed items.

It should be noted that in this specification, the expressions first, second, third, etc. are used only to separate one feature from another feature region, and do not denote any limitation of features, particularly do not denote any order of precedence. Thus, a first portion discussed in this disclosure may also be referred to as a second portion, and vice versa, without departing from the teachings of the present disclosure.

In the drawings, the thickness, size, and shape of the components have been slightly adjusted for convenience of description. The figures are merely examples and are not drawn to scale. As used herein, the terms "about," "approximately," and the like are used as terms of a table approximation, not as terms of a table degree, and are intended to account for inherent deviations in measured or calculated values that will be recognized by one of ordinary skill in the art.

It will be further understood that terms such as "comprises," "comprising," "includes," "including," "having," "containing," "includes" and/or "including" are open-ended, rather than closed-ended, terms that specify the presence of the stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, elements, components, and/or groups thereof. Furthermore, when a statement such as "at least one of the following" appears after a list of features listed, it modifies the entire list of features rather than just modifying the individual elements in the list. Furthermore, when describing embodiments of the application, use of "may" means "one or more embodiments of the application. Also, the term "exemplary" is intended to refer to an example or illustration.

Unless otherwise defined, all terms (including engineering and technical terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The application will be described in detail below with reference to the drawings in connection with embodiments.

Hereinafter, specific examples of the present scheme will be described in more detail with reference to the accompanying drawings.

Fig. 2 shows a schematic diagram of a resolution testing apparatus 200 suitable for use in the optical imaging system 100 according to an exemplary embodiment of the present application. As shown in fig. 2, the resolution testing apparatus 200 includes a target 210, a light source 220, a test stand 230, and an electronic device 240.

The target 210 may be specifically shown in fig. 3, and is a central symmetrical structure, for example, a rectangular structure with symmetry between the upper and lower sides and the left and right sides. The reticle 210 includes a plurality of circular patterns having a center marker for photographing by the optical imaging system 100 mounted on the test stand 230 to analyze the resolution of the optical imaging system 100. These circular patterns appear, for example, as circular black blocks with the center left white as the center bit. As an example, the shape of the center bit may be implemented as a circle, square, triangle, or other feature shape. The outer edge of the round black block is a white color block. In some embodiments, the white color block is provided with a black mark point in four directions of up, down, left and right of the round black block. That is, the black mark points in the circular black blocks alternate with the black mark points in the white blocks.

In the transverse direction and the longitudinal direction, the white bottom plate of the target 210 is distributed with round black blocks and black identification points with white left in the center, which are distributed according to a certain interval, and the radius of the round black blocks and the interval between the round black blocks and the black identification points are matched with the test distance and the performance of the optical imaging system 100 to be tested. Reticle 210 is placed within the field of view of optical imaging system 100 to ensure that the image captured by optical imaging system 100 is clear.

As shown in fig. 2, the light source 220 is disposed on a side of the target 210 remote from the optical imaging system 100, but it should be noted that the position of the light source 220 is not absolute, as long as the light source 220 provides sufficient brightness when the optical imaging system 100 captures an image of the target 210. That is, reticle 210 and light source 220 may be disposed on a side of reticle 210 away from optical imaging system 100, or on a side of reticle 210 facing optical imaging system 100.

The test stand 230 functions to mount the optical imaging system 100. The test stand 230 may be configured to mount only one optical imaging system 100, or may be configured to mount a plurality of optical imaging systems 100. The electronic device 240 is connected to the optical imaging system 100, wherein the electronic device 240 may be implemented, for example, as a computer comprising a processor and a memory. The memory is communicatively connected to the processor, and the memory stores a program executable by the processor, and when the program is executed by the processor, the processor is capable of executing the method for testing the resolution of the optical imaging system 100 provided according to the exemplary embodiment of the present application.

As shown in fig. 4, an exemplary embodiment of the present application provides a resolution testing method 400 suitable for use with an optical imaging system 100. As shown in fig. 4, the method 400 for testing the resolution of the optical imaging system 100 includes the following steps:

S410, determining a knife edge region of the test pattern based on the center of the test image, the contour line of the test pattern in the test image and the center of the central zone bit of the test pattern;

S420, fitting the arc-shaped edge of the knife edge area to obtain an edge expansion function curve corresponding to the arc-shaped edge; and

S430, determining the resolution of the optical imaging system based on the edge expansion function curve.

It should be understood that the steps shown in the method 400 of testing a resolution suitable for use in the optical imaging system 100 are not exclusive and that other steps may be performed before, after, or between any of the steps shown. Further, some of the above steps may be performed simultaneously or may be performed in an order different from that shown in fig. 4.

In order to facilitate understanding of the technical solution of the present application, a method for obtaining a test image, a contour line of the test pattern in the test image, and a center of a center bit of the test pattern will be described before describing steps S410 to S430.

In some embodiments, the test image may be acquired using steps S401 to S403 as shown in fig. 5. It should be noted that, steps S401 to S403 may be performed before the implementation of the method 400, or may be included in the steps of the method 400, which is not limited to this aspect of the application.

The steps S401 to S403 may specifically include:

s401, receiving an initial image obtained by shooting a target pattern by an optical imaging system;

s402, binarizing the initial image to obtain a binarization map;

s403, identifying the outline of the pattern in the binarization map to obtain a test image.

As an example, the optical imaging system 100 mounted on the test stand 230 photographs the reticle 210 to obtain an initial image, which is imported into the electronic device 240 in real time to cause the processor of the electronic device 240 to receive the initial image obtained by photographing the reticle pattern by the optical imaging system in step S401.

Alternatively, an initial image obtained by photographing the target 210 by the optical imaging system 100 may be stored in the memory in advance, and the processor of the electronic device 240 reads the initial image stored in the memory to cause the processor of the electronic device 240 to receive the initial image obtained by photographing the target pattern by the optical imaging system in step S401.

After receiving the initial image obtained by photographing the target 210 in step S401, the initial image is binarized in step S402. In some embodiments, the initial image is first converted to a gray scale map 211 as shown in fig. 6, the initial image is scanned and the scanned gray scale values are sorted from small to large, the first derivative of the gray scale values is calculated, the maximum point is found, and the corresponding gray scale value is found. The initial image is binarized using the gray value corresponding to the maximum point of the first derivative as the threshold for image binarization, resulting in a binarization map 212 as shown in fig. 7. As can be seen from fig. 6 and 7, the image obtained by photographing the target 210 by the optical imaging system 100 is distorted, and the circular black block, the central marker and the black marker on the target 210 are deformed more or less. Specifically, the round black block is distorted to an oval black block, the round center zone is distorted to an oval center zone, and the round black mark point is distorted to an oval black mark point.

After the binarized map 212 of the initial image is acquired in step S402, the pattern in the binarized map 212 is subjected to contour detection in step S403, resulting in a test image 213 as shown in fig. 8. As can be seen in fig. 8, the test image 213 includes a plurality of larger elliptical contours and a plurality of smaller elliptical contours. It can be understood that the larger elliptical contour is a contour distorted by a circular black block, the smaller elliptical contour located inside the larger elliptical contour is a contour distorted by a central marker, and the smaller elliptical contour located outside the larger elliptical contour is a contour distorted by a black mark point.

In some embodiments, the number of larger and smaller elliptical contours may also be counted in step S403 to ensure that the number of larger and smaller elliptical contours matches the number of circular black blocks, center marker bits, and black marker points on target 210. If it is determined in step S403 that the number of larger and smaller elliptical contours does not match the number of circular black blocks, center marks, and black mark points on the target 210, the initial image should be received again for processing accordingly, thereby ensuring accuracy in testing the resolution of the optical imaging system 100.

The larger elliptical profile and the smaller elliptical profile located inside the larger elliptical profile constitute a test pattern (larger elliptical profile) with a center marker bit (smaller elliptical profile) described in the present application.

In some embodiments, the contour line of the test pattern and the center of the center bit of the test pattern may be acquired using steps S404 to S405 as shown in fig. 9. It should be noted that, steps S404 to S405 may be performed before the implementation of the method 400, or may be included in the steps of the method 400, which is not limited in this regard.

The steps S404 to S405 may specifically include:

s404, fitting the boundary of the test pattern by adopting an elliptic equation to determine the contour line of the test pattern; and

S405, determining the contour line of the central zone bit and taking the center of the area surrounded by the contour line of the central zone bit as the center of the central zone bit.

As described above, the image of the target 210 photographed by the optical imaging system 100 is distorted from circular to elliptical, and based on this, the boundary of the test pattern is fitted using an elliptical equation to determine the contour line C of the test pattern as shown in fig. 10 in step S404.

In other words, the contour line C of each test pattern as shown in fig. 10 can be expressed as an elliptic equation.

The shape of the center bit may be implemented as a circle, a square, a triangle, or other characteristic shapes, and based on this, the center bit contour line may be determined in step S405. Alternatively, the center flag bit is circular as shown in fig. 3, and thus, the distorted circular center flag bit is converted into an elliptical center flag bit. In step S405, an elliptic equation may be used to fit the contour line of the central zone bit, so that the center of the area surrounded by the contour line of the central zone bit may be determined, and thus the determined center may be used as the center O of the central zone bit, referring to fig. 10.

Steps S410 to S430 described above are further described below in conjunction with fig. 2 to 19.

S410

In some embodiments, the step of determining the knife edge region of the test pattern in step S410 includes: and determining a radial knife edge region and a tangential knife edge region of the test pattern based on two radial intersection points where the first straight line intersects the contour line and two tangential intersection points where the second straight line intersects the contour line. The first straight line passes through the center of the test image and the center of the center zone bit, and the second straight line passes through the center of the center zone bit and is perpendicular to the first straight line. The above-mentioned knife edge regions of the present application include the radial knife edge regions and the tangential knife edge regions determined in step S410.

In some embodiments, the above steps may be employed to determine the knife edge region of each test pattern in the test image 213. A method of determining the knife edge region of a test pattern is described below by taking one of the test patterns as an example.

In a possible embodiment, as shown in fig. 11, step S410 includes:

s411, acquiring a first straight line passing through the center of the test image and the center of the center marker bit, and determining two radial intersection points of the first straight line and the contour line;

S412, obtaining a second straight line which passes through the center of the center marker bit and is perpendicular to the first straight line, and determining two tangential intersection points of the second straight line and the contour line; and

S413, determining a radial knife edge region of the test pattern by taking the two radial intersection points as the center, and determining a tangential knife edge region of the test pattern by taking the two tangential intersection points as the center.

Specifically, since the target 210 has a center-symmetrical structure as described above, the center of the test image 213 can be specified in the test image 213 obtained by photographing the target 210. After the center of the center bit of the test pattern and the contour line of the test pattern are obtained, in step S411, a first straight line passing through two points, i.e., the center of the test image 213 and the center O of the center bit of the test pattern, is obtained, and two points, i.e., the first straight line and the contour line of the test pattern intersect, are defined as radial intersection points S1 and S2 (see fig. 12).

Then, in step S412, a second straight line passing through the center O of the center flag bit of the test pattern and perpendicular to the first straight line is acquired, and two points at which the second straight line intersects with the contour line of the test pattern are taken as tangential intersection points T1, T2 (refer to fig. 12).

Then, in step S413, two partial areas on the test pattern are cut out as two radial edge areas QS1, QS2 according to the preset edge size with the two radial intersection points S1, S2 as the edge center points in the radial direction, and two partial areas on the test pattern are cut out as two tangential edge areas QT1, QT2 according to the preset edge size with the two tangential intersection points T1, T2 as the edge center points in the tangential direction (see fig. 13).

The radial edge regions QS1 and QS2 and the tangential edge regions QT1 and QT2 determined in step S413 form edge regions of the test pattern. In practical application, the size of the preset knife edge can be determined according to the test requirement, so that the sizes of the radial knife edge area and the tangential knife edge area can be determined.

S420

After the knife edge region is determined in step S410, the determined arc-shaped edge of the knife edge region is fitted in step S420 to obtain an Edge Spread Function (ESF) curve corresponding to the arc-shaped edge of the knife edge region, so that the resolution of the optical imaging system 100 is determined based on the obtained edge spread Function curve in a subsequent step.

In some embodiments, as shown in fig. 14, step S420 includes:

S421, fitting the arc-shaped edge of the knife edge area by using a polynomial equation to determine the contour line of the arc-shaped edge of the knife edge area; and

S422, determining an edge expansion function curve based on the contour line of the arc-shaped edge of the edge region.

Specifically, since the shapes of the plurality of test patterns in the test image 213 are substantially elliptical, the outline of the arc-shaped edge can be determined by fitting the polynomial equation to the arc-shaped edge of the edge region, and then the ESF curve can be determined based on the determined outline of the arc-shaped edge, so that the outline of the arc-shaped edge obtained by fitting can more accurately represent the outline of the test pattern, and further the accuracy of the resolution test of the optical imaging system 100 can be improved.

In some embodiments, as shown in fig. 15, step S421 includes:

S4211, performing first polynomial fitting on the arc-shaped edge of the edge region to obtain a first fitting curve;

s4212, performing second polynomial fitting on the contour coordinates of the plurality of points on the first fitting curve to obtain a second fitting curve.

Specifically, in step S4211, a first polynomial fit may be performed on the arc-shaped edge of the knife edge region using a quadratic polynomial equation to obtain a first fitted curve. Optionally, the data obtained during the first polynomial fit is pixel level data.

It should be noted that, in step S4211, the process of performing the first polynomial fitting on the arc edge of the knife edge region may be performed using a already trained fitting model. The training process and the fitting process of the fitting model may be performed by techniques well known in the art, and the present application is not described herein.

In step S4212, the first fitting curve may be obtained by fitting the first fitting curve to the tangent line and the perpendicular line at the plurality of points; and processing the vertical line at each of the plurality of points by means of area interpolation to determine the contour coordinates of each of the plurality of points.

It is understood that the first fitted curve obtained in step S4211 is composed of a plurality of points. Optionally, n profile points are selected on the first fitted curve, and then there are n tangent lines at the n profile points, and n perpendicular lines at the n profile points are determined.

The first fitted curve may be represented by, for example, formula (1), the tangent line at the kth contour point of the n contour points on the first fitted curve may be represented by, for example, formula (2), and the perpendicular line at the kth contour point of the n contour points on the first fitted curve may be represented by, for example, formula (3).

y＝a₁x²+b₁x+c₁ (1)

y_k＝v_kx_k+r_k,k＝1........n (2)

y_k＝m_kx_k+b_k,k＝1........n (3)

Wherein a ₁、b₁ and c ₁ in formula (1) are coefficients of the first fitted curve, v _k、r_k in formula (2) is coefficients of a tangent line at the kth contour point, and m _k、b_k in formula (3) is coefficients of a perpendicular line at the kth contour point.

The vertical line at each of the n profile points selected is processed by the area interpolation method to obtain the profile coordinates of each of the n profile points.

For example, with reference to equation (3) and fig. 16, the contour coordinates of the kth contour point are obtained by processing equation (3) by the method of area interpolation and luminance weight with respect to the perpendicular line Lk at the kth contour point of the n contour points. The value Outline _X in the x-direction and the value Outline _Y in the y-direction of the contour coordinates can be obtained by equation (4) and equation (5), respectively.

Outline_Y＝m_kOutline_X+b_k (5)

Wherein y_value _i in the formula (4) is obtained by the formula (6), i is a lateral coordinate of an index luminance weight map, and the luminance weight map is shown with reference to fig. 17. The value Outline _X of the contour coordinate in the x direction is a newly generated pixel when the vertical line at the kth contour point is subjected to region interpolation, and the newly generated pixel is obtained by weighting the pixels around the newly generated pixel, as shown with reference to fig. 16. The ratio_pixel _p in the formula (6) represents the specific gravity of one of the peripheral pixels in the newly generated Pixel, the y_pixel _p represents the luminance of one of the peripheral pixels, and P represents the weight of the newly generated Pixel in each region obtained by weighting the P peripheral pixels around the Pixel in the region interpolation.

The contour coordinates of each of the n contour points can be obtained by performing the processing of the above-described formulas (4) to (6) on each of the n contour points.

Then, in step S4212, a second polynomial fitting is performed on the contour coordinates of the plurality of contour points to obtain a second fitted curve. Optionally, a second polynomial equation is used to perform a second polynomial fit on the profile coordinates of the plurality of profile points, so as to obtain a second fitted curve. The data obtained during the second polynomial fit is at the sub-pixel level.

It should be noted that, in step S4212, the second polynomial fitting of the contour coordinates of the plurality of contour points may also be performed by using a trained fitting model, which is not described herein. The second fitted curve obtained by fitting can be expressed as formula (7), for example.

y＝a₂x²+b₂x+c₂ (7)

Wherein a ₂、b₂ and c ₂ in formula (1) are coefficients of the second fitted curve.

The second fitted curve obtained in step S4212 forms the contour of the arc-shaped edge of the knife edge region. In the process, the contour line of the arc-shaped edge obtained by fitting can more accurately embody the contour of the test pattern through primary pixel level fitting and primary sub-pixel level fitting.

In some embodiments, as shown in fig. 18, step S422 includes:

s4221, determining a first numerical value based on the distance between the pixel point in the edge region and the tangent line of the contour line;

S4222, taking the brightness of the pixel at the pixel point in the knife edge area as a second numerical value;

s4223, forming a coordinate point by taking the first numerical value as an abscissa and taking the second numerical value as an ordinate; and

S4224, determining an edge expansion function curve based on the plurality of coordinate points determined by the plurality of pixel points in the edge region.

It should be noted that the edge of the knife edge region in the present application is an arc edge, and thus, the characteristic of each pixel point in the knife edge region contributes to the edge spread function curve.

Step S422 is described below with reference to a radial blade area QS 1. In addition, the rectangular radial blade area QS1 may be rotated to a horizontal and vertical direction in order to describe step S422.

As fig. 19 shows the radial blade area QS1 after rotation, it can be seen that the contour of the arcuate edge of the radial blade area QS1 is arcuate in shape. The contour line of the arc-shaped blade edge comprises a plurality of contour points, and the radial blade edge area QS1 comprises a plurality of pixel points.

As an example, a plurality of contour points on the contour line of the arc-shaped blade edge may be determined according to the number of pixels of the blade height of the radial blade region QS 1. For example, if the number of pixels of the knife edge height of the radial knife edge region QS1 is H, a rectangular coordinate system is established with the center of the bottom of the radial knife edge region as the origin of coordinates, the horizontal direction as the x direction and the vertical direction as the y direction, and H horizontal lines are sequentially taken in the y direction according to the rules of y=0.5, 1.5 … … H-1.5 and H-0.5. The H horizontal lines and the contour lines of the arc-shaped edges are provided with H intersecting points, and the H intersecting points form H contour points on the contour lines. In addition, each of the H horizontal lines includes a plurality of pixel points thereon.

Steps S4221 to S4223 are described below with reference to one of the contour points a in the contour line of the arc-shaped edge.

Referring to fig. 19, in step S4221, a tangent LA of the contour line at the contour point a is obtained, the pixels P1 and P2 in the radial blade area QS1 are located on a horizontal line SA passing through the contour point a, a distance D1 (first numerical value) between the pixel P1 and the tangent LA is determined, and a distance D2 (first numerical value) between the pixel P2 and the tangent LA is determined. In step S4222, it is determined that the pixel luminance at the pixel point P1 is B1 (the second value), and the pixel luminance at the pixel point P2 is B2 (the second value). In step S4223, at the pixel point P1, a coordinate point (D1, B1) at the pixel point P1 is formed with D1 as the abscissa and B1 as the ordinate, and similarly, a coordinate point (D2, B2) at the pixel point P2 is formed with D2 as the abscissa and B3 as the ordinate.

Steps S4221 to S4223 are described below with reference to one of the contour points B in the contour line of the arc-shaped edge.

Referring to fig. 19, in step S4221, a tangent line LB of the contour line at a contour point B is obtained, the pixels P3 and P4 in the radial blade area QS1 are located on a horizontal line SB passing through the contour point B, a distance D3 (first numerical value) between the pixel P3 and the tangent line LB is determined, and a distance D4 (first numerical value) between the pixel P4 and the tangent line LB is determined. In step S4222, it is determined that the pixel luminance at the pixel point P3 is B3 (the second value), and the pixel luminance at the pixel point P4 is B4 (the second value). In step S4223, at the pixel point P3, a coordinate point (D3, B3) at the pixel point P3 is formed with D3 as the abscissa and B3 as the ordinate, and similarly, a coordinate point (D4, B4) at the pixel point P4 is formed with D4 as the abscissa and B4 as the ordinate.

It will be appreciated that, according to the steps S4221 to S4223 described above, a plurality of coordinate points of a plurality of pixel points in the knife edge region may be determined.

Subsequently, in step S4224, an edge spread function curve of the radial blade area QS1 is formed from the determined plurality of coordinate points.

According to the same concept, the edge spread function curve of the other radial blade area QS2 and the edge spread function curves of the two tangential blade areas QT1, QT2 can be determined.

S430

After the edge spread function curve of the radial blade area and the edge spread function curve of the tangential blade area are obtained in step S420, the resolution forces of the optical imaging system 100 in the radial direction and the tangential direction are determined based on the edge spread function curves in step S430.

As an example, a line spread Function (LINE SPREAD Function, LSF) of the boundary of the test pattern in the knife edge region is determined based on the obtained edge spread Function curve; and determining a resolution of the optical imaging system 100 based on the line spread function of the test pattern.

Specifically, deriving the determined edge spread function curve may result in a line spread function. The derivative operation may be performed by a discrete data difference method. Finally, the line spread function is fourier transformed to obtain modulation transfer function (Modulation Transfer Function, MTF) values at each spatial frequency. In this process, the normalization operation may be performed with the modulation transfer function value of the zero frequency as a reference, and the modulation transfer function value at a certain spatial frequency may be obtained by an interpolation fitting method. The resolution of the optical imaging system 100 is determined from the modulation transfer function values.

Fig. 20 shows a schematic structural diagram of an electronic device 240 according to an exemplary embodiment of the present application.

As shown in fig. 20, the electronic device 240 includes a processor 241 that can perform various suitable steps and processes in accordance with computer program instructions stored in a Read Only Memory (ROM) 242 or loaded from a memory 248 into a Random Access Memory (RAM) 243. In the RAM 243, various programs and data required for the operation of the electronic device 240 may also be stored. The processor 241, the ROM 242, and the RAM 243 are connected to each other by a bus 244. An input/output (I/O) interface 245 is also connected to bus 244.

The electronic device 240 is intended to represent various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, and other appropriate computers. Electronic device 240 may also represent various forms of servers. The components shown herein, their connections and relationships, and their functions, are meant to be exemplary only, and are not meant to limit implementations of the applications described and/or claimed herein.

Various components in electronic device 240 are connected to I/O interface 245, including: an input unit 246 such as a keyboard, a stylus, etc.; an output unit 247 such as various types of displays, speakers, and the like; memory 248, such as a magnetic disk, external hard disk, etc.; and a communication unit 249 such as a network card, modem, wireless communication transceiver, and the like. The communication unit 249 allows the electronic device 240 to exchange information/data with other devices via a computer network, such as the internet, and/or various telecommunications networks.

Processor 241 may be a variety of general-purpose and/or special-purpose processing components having processing and computing capabilities. Some examples of processor 241 include, but are not limited to, a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), various specialized Artificial Intelligence (AI) computing chips, various processors running machine learning model algorithms, digital Signal Processors (DSPs), and any suitable processor, controller, microcontroller, etc. Processor 241 may perform the various methods and processes described above, such as performing method 400. For example, in some embodiments, the method 400 may be implemented as a computer software program stored on a machine-readable medium, such as the memory 248. In some implementations, part or all of the computer program may be loaded and/or installed onto the electronic device 240 via the ROM 242 and/or the communication unit 249. When the computer program is loaded into RAM 243 and executed by processor 241, one or more steps of method 400 described above may be performed. Alternatively, in other embodiments, processor 241 may be configured to perform one or more steps of method 400 in any other suitable manner (e.g., by means of firmware).

It is further noted that the present application may include methods, apparatus, systems, and/or computer program products. The computer program product may include a computer readable storage medium having computer readable program instructions embodied thereon for performing various aspects of the present application.

The computer readable storage medium may be a tangible device that can hold and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium would include the following: portable computer disks, hard disks, random Access Memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static Random Access Memory (SRAM), portable compact disk read-only memory (CD-ROM), digital Versatile Disks (DVD), memory sticks, floppy disks, mechanical coding devices, punch cards or in-groove structures such as punch cards or grooves having instructions stored thereon, and any suitable combination of the foregoing. Computer-readable storage media, as used herein, are not to be construed as transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., optical pulses through fiber optic cables), or electrical signals transmitted through wires.

The computer readable program instructions described herein may be downloaded from a computer readable storage medium to a respective computing/processing device or to an external computer or external storage device over a network, such as the internet, a local area network, a wide area network, and/or a wireless network. The network may include copper transmission cables, fiber optic transmissions, wireless transmissions, routers, firewalls, switches, gateway computers and/or edge servers. The network interface card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium in the respective computing/processing device.

Computer program instructions for carrying out operations of the present application may be assembly instructions, instruction Set Architecture (ISA) instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source or object code written in any combination of one or more programming languages, including an object oriented programming language such as SMALLTALK, C ++ or the like and conventional procedural programming languages, such as the C-language or similar programming languages. The computer readable program instructions may be executed entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computer (for example, through the Internet using an Internet service provider). In some embodiments, aspects of the present application are implemented by personalizing electronic circuitry, such as programmable logic circuitry, field Programmable Gate Arrays (FPGAs), or Programmable Logic Arrays (PLAs), with state information for computer readable program instructions, which can execute the computer readable program instructions.

Various aspects of the present application are described herein with reference to flowchart illustrations and/or timing diagrams of methods, apparatus (systems) and computer program products according to exemplary embodiments of the application. It will be understood that each step of the flowchart and/or timing diagram, and combinations of steps in the flowchart and/or timing diagram, can be implemented by computer readable program instructions.

These computer readable program instructions may be provided to a processor in an electronic device, a processing unit of a general purpose computer, a special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, when executed by the processing unit of the computer or other programmable data processing apparatus, create means for implementing the functions/steps specified in the flowchart and/or sequence diagram block or blocks. These computer-readable program instructions may also be stored in a computer-readable storage medium that can direct a computer, programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer-readable medium having the instructions stored therein includes an article of manufacture including instructions which implement the function/act specified in the flowchart and/or sequence diagram block or blocks.

The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer, other programmable apparatus or other devices implement the functions/steps specified in the flowchart and/or sequence diagram block or blocks.

The flowcharts and time diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of devices, methods and computer program products according to various embodiments of the present application. In this regard, each step in the flowchart or timing diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the steps may occur out of the order noted in the figures. For example, two consecutive steps may in fact be performed substantially in parallel, they may sometimes also be performed in the opposite order, depending on the function involved. It will also be noted that each step of the timing diagrams and/or flowchart illustration, and combinations of steps in the timing diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

The above description is only illustrative of the embodiments of the application and of the technical principles applied. It will be appreciated by those skilled in the art that the scope of the application is not limited to the specific combination of the above technical features, but also encompasses other technical solutions which may be formed by any combination of the above technical features or their equivalents without departing from the technical concept. Such as the above-mentioned features and the technical features disclosed in the present application (but not limited to) having similar functions are replaced with each other.

Claims (10)

1. A method for testing the resolution of an optical imaging system, the method comprising:

Determining a knife edge region of a test pattern based on a center of the test image, a contour line of the test pattern in the test image, and a center of a center zone of the test pattern;

Fitting the arc-shaped edge of the knife edge area to obtain an edge expansion function curve corresponding to the arc-shaped edge; and

And determining the resolution of the optical imaging system based on the edge extension function curve.

2. The method of claim 1, further comprising:

Fitting the boundary of the test pattern by adopting an elliptic equation to determine the contour line of the test pattern; and

And determining the contour line of the central zone bit and taking the center of an area surrounded by the contour line of the central zone bit as the center of the central zone bit.

3. The method of claim 1, wherein the step of determining a knife edge region of the test pattern comprises:

Determining a radial knife edge region and a tangential knife edge region of the test pattern based on two radial intersection points of a first straight line intersecting the contour line and two tangential intersection points of a second straight line intersecting the contour line, wherein the first straight line passes through the center of the test image and the center of the center zone bit, and the second straight line passes through the center of the center zone bit and is perpendicular to the first straight line;

wherein the knife edge region comprises the radial knife edge region and the tangential knife edge region.

4. A method of testing a resolution as claimed in any one of claims 1 to 3, wherein the step of fitting an arcuate edge of the knife edge region to obtain an edge spread function curve corresponding to the arcuate edge comprises:

Fitting the arc-shaped edge of the knife edge region by using a polynomial equation to determine the contour line of the arc-shaped edge of the knife edge region; and

And determining the edge expansion function curve based on the contour line of the arc-shaped edge of the knife edge region.

5. The method of claim 4, wherein the step of fitting the arcuate edge of the knife edge region to determine the contour of the arcuate edge of the knife edge region using a polynomial equation comprises:

Performing first polynomial fitting on the arc-shaped edge of the knife edge region to obtain a first fitting curve; and

Performing a second polynomial fit on the profile coordinates of the plurality of points on the first fitted curve to obtain a second fitted curve;

Wherein the contour line of the arc-shaped edge comprises the second fitting curve.

6. The method of claim 5, further comprising:

And determining the contour coordinates of each point of the plurality of points based on the tangent lines and the vertical lines at the plurality of points on the first fitting curve and processing the vertical lines at each point of the plurality of points by a region interpolation mode.

7. The method of claim 4, wherein determining the edge spread function curve based on the contour of the arcuate edge of the knife edge region comprises:

determining a first value based on a distance between a pixel point in the edge region and a tangent line of the contour line;

taking the brightness of the pixel at the pixel point in the knife edge area as a second numerical value;

Forming a coordinate point by taking the first numerical value as an abscissa and the second numerical value as an ordinate; and

And determining the edge expansion function curve based on the plurality of coordinate points determined by the plurality of pixel points in the knife edge area.

8. The method of claim 5, wherein,

The first fitted curve and/or the second fitted curve is a quadratic polynomial equation.

9. A resolution testing apparatus adapted for use in an optical imaging system, the resolution testing apparatus comprising:

a target comprising a circular pattern having a central marker bit;

A light source that provides illumination light to the target;

a test bed facing the target and for mounting the optical imaging system; and

An electronic device connected to the optical imaging system, the electronic device comprising:

A processor; and

A memory communicatively coupled to the processor, wherein the memory stores a program executable by the processor, the processor being capable of performing the resolution testing method of any one of claims 1 to 8 when the program is executed by the processor.

10. A readable storage medium, characterized in that the readable storage medium has stored thereon a computer program which, when executed by a processor, implements the resolution testing method according to any one of claims 1 to 8.