A method for quickly extracting geometric parameters of a screen printing master gray scale image

Abstract

The application discloses a method for quickly extracting geometric parameters of a silk screen printing master gray scale image, which comprises the following steps: S1, obtaining a silk screen printing master gray scale image by scanning; the silk screen printing master gray scale image comprises black grid lines, white rectangular blocks and gray rectangular blocks distributed in the black grid lines; S2, performing two-dimensional Fourier transform on the silk screen printing master gray scale image to obtain a two-dimensional Fourier transform image; S3, taking a midpoint of the two-dimensional Fourier transform image as an origin to establish a plane rectangular coordinate system, and obtaining an amplitude peak point of the two-dimensional Fourier transform image in a first quadrant; S4, obtaining a rotation angle of the silk screen printing master gray scale image according to a coordinate of the amplitude peak point; and S5, obtaining a period of the silk screen printing master gray scale image according to the coordinate of the amplitude peak point and a width and a height of the silk screen printing master gray scale image.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of machine vision automatic optical inspection, and particularly relates to a method for rapidly extracting geometric parameters of a screen printing master gray scale image. BACKGROUND

[0002] Machine vision is widely used in the technical field of automatic optical inspection (AOI). Screen printing is widely used in various pattern drawing occasions in the national economy. Machine vision has been gradually popularized in the screen printing industry and is used to replace manual quality inspection of printing masters, thereby improving the automation level.

[0003] AOI of a screen printing master, that is, using computer software (fusing image analysis algorithms) to analyze a printing master image and detecting various defects of the printing master. There are many image analysis algorithms, and the implementation methods are different, mainly considering speed, accuracy and stability. When designing an image analysis algorithm, first, pre-processing is performed to extract various key geometric parameters (such as rotation angle, main period length, etc.) of the image as the basis for further processing. The current method such as Hough transform method has problems such as large amount of calculation, large deviation and low accuracy when extracting these geometric parameters. SUMMARY

[0004] The present application aims to provide a method for rapidly extracting geometric parameters of a screen printing master gray scale image, so as to realize rapid, stable and reliable acquisition of geometric parameters in the screen printing master gray scale image.

[0005] To solve the above technical problems, the present application provides a technical solution: a method for rapidly extracting geometric parameters of a screen printing master gray scale image, characterized by comprising the following steps,

[0006] S1, acquiring a screen printing master gray scale image by scanning; the screen printing master gray scale image comprises black grid lines and white and gray rectangular blocks distributed in the black grid lines;

[0007] S2, performing two-dimensional Fourier transform on the screen printing master gray scale image to obtain a two-dimensional Fourier transform image;

[0008] S3, establishing a plane rectangular coordinate system with the midpoint of the two-dimensional Fourier transform image as the origin, and obtaining an amplitude peak point P1(u, v) of the two-dimensional Fourier transform image in the first quadrant;

[0009] S4, obtaining a rotation angle a of the screen printing master gray scale image according to the coordinates of the amplitude peak point P1,

[0010]

[0011] S5, obtaining a period l of the screen printing master gray scale image according to the coordinate of the amplitude peak point P1 and the width M and the height N of the screen printing master gray scale image, the period l being the distribution period length of the rectangular block in the black grid line in the length and width directions of itself;

[0012]

[0013] According to the above scheme, the two-dimensional Fourier transform adopts a fast Fourier transform.

[0014] A computer device comprises a memory, a processor, and a computer program stored on the memory and executable on the processor, and the processor implements the steps of the above-mentioned method for quickly extracting geometric parameters of a screen printing master gray scale image when executing the computer program.

[0015] A computer readable storage medium has a computer program stored thereon, and the computer program implements the steps of the above-mentioned method for quickly extracting geometric parameters of a screen printing master gray scale image when executed by a processor.

[0016] A method for correcting the rotation of a screen printing master gray scale image according to the above-mentioned method for quickly extracting geometric parameters of a screen printing master gray scale image, and the screen printing master gray scale image is corrected in rotation according to a rotation angle a of the screen printing master gray scale image.

[0017] The present application has the beneficial effect that the overall data of the screen printing master gray scale image is processed by Fourier transform, the original gray scale image data is naturally averaged, the interference of noise in the original gray scale image is reduced, and the inaccuracy of the parameter extraction result caused by the possible large noise in the local gray scale image data is overcome, so that the reliability of the geometric parameters obtained by the method is high.

[0018] Further, the original gray scale image is processed by using a fast Fourier transform, and the speed of the parameter extraction operation process is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a global image of the screen printing master gray scale image;

[0020] Figure 2 is a local enlarged image of the screen printing master gray scale image;

[0021] Figure 3 is a mathematical model diagram of the screen printing master gray scale image;

[0022] Figure 4 is a parameter diagram of the two-dimensional Fourier transform;

[0023] Figure 5is a schematic diagram of geometric parameters of a screen printing master gray scale image;

[0024] Figure 6 is a schematic diagram of amplitude peak point distribution of a two-dimensional Fourier transform image;

[0025] Figure 7 is a global image of a screen printing master gray scale image after rotation correction;

[0026] Figure 8 is a local enlarged image of a screen printing master gray scale image after rotation correction. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without any inventive effort fall within the protection scope of the present disclosure.

[0028] Firstly, the relationship between Fourier parameters and image parameters is established according to the characteristics of the screen printing image:

[0029] a. Geometric meaning of two-dimensional Fourier transform parameters

[0030] The two-dimensional Fourier transform can obtain the amplitude and phase (corresponding to the direction of the plane wave) of each plane wave basis function (corresponding to different spatial frequencies). That is, the two-dimensional Fourier transform can obtain two important parameters of the spatial frequency and direction of each plane wave.

[0031] The two-dimensional Fourier transform of the image f(x, y) is

[0032]

[0033] e -j2π(ξx+ηy) is a two-dimensional plane wave basis function, and ξ and η are the spatial frequencies in the horizontal and vertical directions, respectively. The direction of the plane wave is The direction angle of is β = atan(η / ξ). The geometric meanings of the parameters are shown in Figure 4 .

[0034] b. Characteristics of the master image

[0035] In the printing master image (with a width x height of M x N, in units of pixels), the direction and spatial frequency of the plane wave with the peak amplitude correspond to the main direction p and the main period l of the image.

[0036] The direction angle and the main period parameters of the master image are shown in Figure 5The period of the master image is l and the direction is p. The two-dimensional plane wave of this frequency and direction shows a peak in the two-dimensional Fourier result.

[0037] c. After two-dimensional Fourier transform of the image, the plane wave with the peak value corresponds to the parameter of the periodic function of the master image. Thus the relationship between the key parameters of the image and the parameters after Fourier transform is established, and the former can be quickly obtained through the latter.

[0038] (3) Figure 6 The peak point distribution diagram of the frequency space after Fourier transform of the master image. Each quadrant of the frequency space has a peak point, which is p1, p2, p3 and p4 respectively. p1 and p2 are symmetrical,

[0039] p3 and p4 are symmetrical, p1 and p3 are perpendicular, and p2 and p4 are perpendicular.

[0040] After Fourier transform, find the peak point in the first quadrant. Let the peak point coordinate be (u, v), and the main direction angle of the image is

[0041]

[0042] atan is the inverse tangent function.

[0043] The main period l is calculated as follows:

[0044]

[0045] Δx = Δy = 1, so

[0046]

[0047] (4) After the angle is extracted, the image can be corrected to be horizontal, and the next step of detection work can be carried out.

[0048] Figure 7 The gray scale image of the screen printing master selected in this embodiment is 2560x2560 pixels. After two-dimensional Fourier transform of the gray scale image, four peak points are obtained, among which the peak frequency (u, v) in the first quadrant is (106, 236);

[0049] According to Calculation: α = 65.81°;

[0050] According to Calculation:

[0051]

[0052] Then, according to the obtained α, rotation correction is carried out, and the corrected image is shown in Figure 7 , Figure 8 .

[0053] The above merely illustrates the embodiments of the present application, and is not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process conversion, or direct or indirect application in other related technical fields, which is made according to the content of the present application, shall be included in the patent protection scope of the present application.

Claims

1. A method for fast extraction of geometric parameters of a screen printing master gray scale image, characterized in that: The method comprises the following steps of: S1, obtaining a screen printing master gray image by scanning; The screen printing master gray image comprises black grid lines, white rectangular blocks and gray rectangular blocks distributed in the black grid lines; S2, performing two-dimensional Fourier transform on the screen printing master gray image to obtain a two-dimensional Fourier transform image; S3, establishing a plane rectangular coordinate system with the midpoint of the two-dimensional Fourier transform image as the origin, and obtaining an amplitude peak point P1(u, v) in the first quadrant of the two-dimensional Fourier transform image; S4, obtaining a rotation angle a of the screen printing master gray image according to the coordinates of the amplitude peak point P1, S5, obtaining a period l of the screen printing master gray image according to the coordinates of the amplitude peak point P1 and the width M and the height N of the screen printing master gray image, wherein the period l is the length of the distribution period of the rectangular blocks in the black grid lines in the length and width directions of the rectangular blocks.

2. The method for quickly extracting geometric parameters of a screen printing master gray scale image according to claim 1, characterized in that: The two-dimensional Fourier transform is fast Fourier transform.

3. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that: The processor executes the computer program to realize the steps of the method for quickly extracting the geometric parameters of the screen printing master gray image according to any one of claims 1-2.

4. A computer readable storage medium having stored thereon a computer program, characterized in that: The computer program is executed by the processor to realize the steps of the method for quickly extracting the geometric parameters of the screen printing master gray image according to any one of claims 1-2.

5. A method for correcting the rotation of a screen printing master gray scale image according to the method for quickly extracting the geometric parameters of a screen printing master gray scale image according to any one of claims 1-2, characterized in that: The screen printing master gray image is rotated and corrected according to the rotation angle a of the screen printing master gray image.

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