Device and method for distinguishing dot-shaped dust and bubble defects by utilizing stripe grating plate

Abstract

The invention relates to the technical field of automobile glass detection, in particular to a device and method for distinguishing dot-shaped dust and bubble defects through a stripe grating plate. The device comprises a first conveying line, a second conveying line, a camera, a light source and an image processing unit. Detection glass passes through the first conveying line and the second conveying line, the camera is arranged above the detection glass, the light source is arranged below the detection glass, a stripe grating plate is arranged on an installation frame of the light source, grid lines parallel to each other are arranged on the stripe grating plate, and light beams penetrate through the stripe grating plate and are emitted to the detection glass. And the image processing unit is arranged in the computer or the mobile phone and is used for analyzing, processing and identifying the image acquired by photographing so as to distinguish bubble defects and dotted dust. Based on the unique optical modulation principle of the stripe grid plate, the fine difference of bubble defects and dotted dust on stripe patterns can be accurately captured, so that high-accuracy distinguishing is achieved, the possibility of misjudgment is greatly reduced, and the precision of automobile glass quality detection is improved.

Description

Technical Field

[0001] The present application relates to the technical field of automobile glass detection, and in particular to a device and method for distinguishing point-shaped dust and bubble defects by using a striped grating plate. Background Art

[0002] During the glass production process, various defects may appear on the surface or inside of the glass, among which bubble defects and point dust are two of the more common types. Bubbles are usually generated during the glass manufacturing process due to impure raw materials, improper process parameters, etc. These defects will seriously affect the quality and performance of the glass, reduce its optical transmittance, mechanical strength, etc., and are not allowed to exist in high-end glass applications or must be strictly controlled in number and size. Point dust is mainly impurity particles attached to the surface of the glass during glass processing, transportation or storage.

[0003] Traditional glass defect detection methods often have difficulty accurately distinguishing between bubble defects and point-like dust, because they may present similar appearance characteristics under some conventional detection methods such as visual inspection and simple optical imaging inspection, which can easily lead to misjudgment. For example, dust particles on the glass surface may block light, forming dark shadows similar to bubble defects, and some tiny bubble defects may also look similar to dust when imaged due to resolution limitations or other factors. This misjudgment can cause huge economic losses to glass manufacturers. On the one hand, glass with serious bubble defects may be misjudged as qualified products and put on the market, affecting product reputation and corporate image; on the other hand, glass with only dust attached may be misjudged as waste and unnecessary processing may be carried out, increasing production costs.

[0004] Therefore, developing a method that can accurately distinguish bubble defects and dust in glass defect detection has extremely important practical significance and industrial application value. Summary of the invention

[0005] The purpose of the present application is to provide a device and method for distinguishing point-shaped dust and bubble defects using a striped grating plate, so as to solve the problems existing in the prior art.

[0006] In order to solve the above technical problems, the present application provides the following technical solutions: a device for distinguishing point-like dust and bubble defects by using a striped grating plate, comprising a conveyor line one, a conveyor line two, a camera and a light source, wherein the conveyor line one and the conveyor line two are for inspection glass to pass through, the camera is arranged above the inspection glass, the light source is arranged below the inspection glass, a striped grating plate is also arranged on a mounting frame of the light source, a plurality of mutually parallel grating lines are arranged on the striped grating plate, and a light beam of the light source is emitted toward the inspection glass through the striped grating plate.

[0007] Through the above technical solution, the light beam of the light source passes through the striped grating plate and hits the detection glass. The camera then takes a picture of the detection glass to obtain the image of the light beam acting on the grating lines of the striped grating plate and the striped pattern formed on the detection glass, so as to distinguish between bubble defects and point-like dust, thus overcoming the problem of misjudgment in the past.

[0008] Furthermore, the grating line width of the striped grating plate ranges from 0.1 to 0.2 mm, and the grating line spacing ranges from 0.1 to 0.2 mm.

[0009] Through the above technical solution, the grid lines of the striped grating plate can be printed by a laser inkjet printer after the thickness is set according to the program. If the grid line width of the striped grating plate exceeds or is equal to 0.2mm, then smaller bubble defects may be missed, and there may be a phenomenon that the distortion effect cannot appear just between the grid lines; if the grid lines are too thin, less than 0.1mm, then the sensitivity to some subtle interference will increase and over-detection will occur. The range of the grid line spacing is selected with the consideration of the grid line width. The grid lines and the grid line spacing make the striped grating plate form spaced black and white stripes.

[0010] Furthermore, the grating line width of the striped grating plate is 0.1 mm and the grating line spacing is 0.1 mm.

[0011] Through the above technical solution, the most suitable grid line width and grid line spacing make the imaging of the stripe pattern more obvious and easier to distinguish bubble defects and point-like dust. Considering the above factors and test results, 0.1mm is the best choice for this application.

[0012] Furthermore, the striped grating plate on the light source is parallel to the detection glass, and the distance between the upper surface of the striped grating plate and the lower surface of the detection glass is in the range of 200 to 300 mm; the striped grating plate is made of acrylic plate.

[0013] Through the above technical solution, the striped grating plate is parallel to the detection glass, which can reduce the refraction during the light beam transmission process and make the imaging of the striped pattern more accurate. The distance range between the striped grating plate and the detection glass needs to consider the curvature of the car surface. Too large or too small will affect the imaging of the striped pattern. If the curvature of the upper surface of the car glass is large, the distance between the striped grating plate and the detection glass is slightly larger, which can be between 250 and 300 mm; if the curvature of the upper surface of the car glass is small or flat, the distance between the striped grating plate and the detection glass is slightly smaller, controlled at 200 to 250 mm. Acrylic plate has good optical transmittance and diffraction and interference characteristics of light beams.

[0014] Furthermore, the camera is connected to an image processing unit, which is arranged in a computer or a mobile phone. The image processing unit is suitable for performing data analysis, result display and data storage on the stripe image obtained by taking pictures with the camera.

[0015] Through the above technical solution, although the stripe pattern can be seen by the naked eye, the efficiency is low; after inputting the judgment criteria, the image processing unit can quickly identify bubble defects and point-like dust, intuitively display the results, and store the data to form a database for reuse.

[0016] Based on the above technical problems, the present application provides a second technical solution: a method for distinguishing point dust and bubble defects by using a striped grating plate, using the above-mentioned device, specifically including the following actions: preparing and cleaning the detection glass, and then putting it into conveyor line one or conveyor line two, turning on the light source, irradiating the light beam onto the detection glass, and the light beam passing through the striped grating plate undergoes diffraction and interference effects, irradiating the detection glass to form a striped pattern, the camera takes a picture to obtain an image of the detection glass modulated by the striped grating plate, the image processing unit processes and analyzes the image, and outputs and displays the detection results.

[0017] Through the above technical solution, the modulation effect of the stripe grating plate on the light beam and the different optical characteristics and spatial distribution characteristics of bubble defects and point-shaped dust inside or on the surface of the glass can project different stripe patterns, based on which the image processing unit can identify bubble defects and point-shaped dust. This identification method is accurate, efficient and labor-saving.

[0018] Further, the light source is turned on, the light beam is irradiated onto the detection glass, the light beam passing through the striped grating plate undergoes diffraction and interference effects, and is irradiated onto the detection glass to form a stripe pattern. The specific process is as follows: for the detection glass with bubble defects, the light beam is projected onto the corresponding position of the bubble defect after passing through the striped grating plate, and the stripe pattern formed is that the stripes are distorted, deformed, or the intensity changes; for the detection glass with point-shaped dust, the light beam is projected onto the corresponding position of the bubble defect after passing through the striped grating plate, and the stripe pattern formed is that a local dark spot or a blurred area appears at the point-shaped dust position, and the degree of distortion is smaller than that of the stripe pattern of the bubble defect.

[0019] Through the above technical solution, the difference between the stripe pattern of bubble defects and the stripe pattern of point-shaped dust is provided. It is summarized from past test experience. After the difference of the stripe pattern is input into the image processing unit, the image processing unit can quickly identify it.

[0020] Furthermore, the camera takes pictures, and the specific process is as follows: the camera takes a picture once under light source exposure to obtain an image modulated by the striped grating plate and containing point-shaped dust and / or bubble defects.

[0021] Through the above technical solution, the camera only needs to take a picture of the inspection glass once to complete the inspection process, which is very fast.

[0022] Furthermore, the image processing unit processes and analyzes the image, and the specific process is as follows: after the image processing unit of the computer system receives the image data, it first pre-processes each frame of the image; uses a median filtering algorithm to remove noise interference in the image, and then uses a grayscale stretching algorithm to enhance the contrast of the image to make the stripe pattern obvious; uses an edge detection algorithm to extract edge information of the stripe pattern, and then calculates the period and amplitude parameters of the stripes; for areas suspected of defects, by analyzing the phase changes and distortion characteristics of the surrounding stripes, classification and judgment are performed according to pre-set judgment criteria.

[0023] Through the above technical solution, the image quality is first enhanced and then the result analysis is performed, which can further improve the recognition accuracy, reduce the number of suspected stripe patterns, and reduce the occurrence of misjudgment.

[0024] Furthermore, the classification and judgment are performed according to a pre-set judgment standard, and the judgment method is as follows: if the periodic change rate of the stripe pattern in the area of ​​the suspected defect exceeds the periodic change rate threshold, and the phase change amount is greater than the phase change threshold, and the stripe pattern distortion amplitude reaches the distortion amplitude threshold, then the defect is judged to be a bubble defect; if the suspected defect only appears as a dark spot with a low grayscale value, the periodic change rate of the stripe pattern does not exceed the periodic change rate threshold, and the phase change amount is less than the phase change threshold, and the stripe pattern distortion amplitude is lower than the distortion amplitude threshold, then it is judged to be point dust.

[0025] Through the above technical solution, for ambiguous imaging, reasonable data analysis can be performed to analyze and identify the results, thereby improving the stability and accuracy of recognition.

[0026] Compared with the prior art, the beneficial effects achieved by this application are: (1) High accuracy: Based on the unique optical modulation principle of the stripe grid, the present invention can accurately capture the subtle differences between bubble defects and point-shaped dust on the stripe pattern, thereby achieving high-accuracy distinction, greatly reducing the possibility of misjudgment, and effectively improving the accuracy of automotive glass quality inspection; (2) Non-contact testing: The entire testing process of this application does not require direct contact with the test glass, thus avoiding scratches or other damage to the surface of the test glass. It is particularly suitable for the testing of high-end automotive glass products with extremely high surface quality requirements; (3) High efficiency: The structure of the entire device of the present application is relatively simple, the detection steps are clear and easy to operate, and the image processing algorithm has high computational efficiency. It can complete the comprehensive detection of glass samples in a short time, meeting the online detection needs in large-scale industrial production; (4) Strong adaptability: The method of the present application has good adaptability to different types, thicknesses, and sizes of detection glass. It only needs to adjust some parameters of the device according to the specific parameters of the detection glass, such as adjusting the intensity of the light source, the distance between the stripe grating plate and the detection glass, etc., and make appropriate adjustments. It has a wide range of application prospects. (5) In summary, the method of using the striped grating plate of the present application to distinguish between bubble defects and point-like dust in glass defect detection has important technical innovation value and broad market application prospects, and will have a positive and far-reaching impact on the development of the glass industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings: Figure 1 It is a schematic diagram of the overall structure of the device; Figure 2 Schematic diagram of the installation position of the striped grating plate; Figure 3 is a schematic diagram of the upper surface of the striped grating plate; Figure 4 This is a schematic diagram of a bubble defect; Figure 5 This is a schematic diagram of the imaging of point-shaped dust; Figure 6 This is a schematic diagram of the second imaging of point-shaped dust; Figure 7 It is a schematic diagram of suspected defects obtained by detection.

[0028] Among them, 1. Conveyor line 1; 2. Conveyor line 2; 3. Camera; 4. Light source; 5. Stripe grating plate; 6. Image processing unit; 7. Detection glass. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions 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.

[0030] Example 1

[0031] like Figure 1 As shown, a device for distinguishing point-shaped dust and bubble defects by using a striped grating plate includes a conveyor line 1, a conveyor line 2, a camera 3 and a light source 4. The conveyor line 1 and the conveyor line 2 are for the detection glass 7 to pass through, the camera 3 is arranged above the detection glass, and the light source 4 is arranged below the detection glass. The camera 3 can be set vertically or tilted to take pictures according to different setting positions of the detected automobile glass. The data obtained by taking pictures can be transmitted to the image processing unit 6. The image processing unit 6 can be set in a computer or a mobile phone.

[0032] like Figure 2 As shown, a stripe grating plate 5 is inserted into the mounting frame where the light source 4 is located, and the light beam of the light source 4 is projected toward the detection glass through the stripe grating plate 5. The core principle of this structure is that different stripe patterns can be projected based on the special modulation effect of the stripe grating plate on the light beam and the different optical properties and spatial distribution characteristics of bubble defects and point-shaped dust inside or on the surface of the glass.

[0033] Based on the above, if Figure 3 As shown, a plurality of black grid lines are sprayed on the striped grating plate 5 by CNC laser spraying, the grid line width ranges from 0.1 to 0.2 mm, and the grid line spacing ranges from 0.1 to 0.2 mm. If the grid line width of the striped grating plate exceeds or is equal to 0.2 mm, then smaller bubble defects may be missed, and there may be a phenomenon that the distortion effect cannot appear just between the grid lines; if the grid lines are too thin, less than 0.1 mm, then the sensitivity to some subtle interferences will be increased, resulting in over-detection. The range of grid line spacing is selected in the same consideration as the grid line width. The grid lines and the grid line spacing enable the striped grating plate to form spaced black and white stripes. The range of grid line spacing is selected in the same consideration as the grid line width. After testing, the preferred grid line width of this embodiment is 0.1 mm and the grid line spacing is 0.1 mm. The placement of the striped grating plate 5 needs to consider the spatial geometric relationship between the detection glass and the camera. When installing, the striped grating plate 5 is recommended to be parallel to the detection glass. The distance between the upper surface of the striped grating plate 5 and the lower surface of the detection glass is in the range of 200 to 300 mm, preferably 200 mm. The material of the striped grating plate 5 is preferably an acrylic plate, which has good optical transmittance and diffraction and interference properties of light beams.

[0034] Based on the above, the light source 4 uses a high-brightness light source with a wavelength of 600 to 700 nanometers, which can provide stable and uniform illumination, ensuring that the light beam can effectively penetrate the striped grating plate, detect the glass, and interact with the striped grating plate and glass defects.

[0035] Based on the above, the camera 3 uses a high-resolution camera and an optical lens purchased from the market, which can capture the glass defect image modulated by the striped grid, and convert the optical signal into a digital signal and transmit it to the image processing unit.

[0036] Based on the above, the image processing unit 6 analyzes, processes and identifies the collected images to distinguish between bubble defects and point-shaped dust.

[0037] The detection method using the above device specifically includes the following steps: Step 1: Prepare and clean the test glass, and then put it into conveyor line 1 or conveyor line 2.

[0038] Specifically, the test glass is placed at a specific position of the device, such as a hollow tray on conveyor line 1 or conveyor line 2, to ensure that the surface of the test glass is clean and free of obvious stains or other interferences to avoid affecting the test results.

[0039] Step 2: Turn on the light source, and the light beam is irradiated onto the detection glass. The light beam passing through the stripe grating plate undergoes diffraction and interference effects, and is irradiated onto the detection glass to form a stripe pattern.

[0040] Specifically, after the light source is turned on, a special stripe pattern will be imaged on the upper surface of the test glass due to the diffraction and interference effects of the stripe grating plate. For test glass with bubble defects inside, since the refractive index of the bubble is different from that of the glass matrix, it will scatter and refract the light, thereby changing the propagation path of the light beam passing through the vicinity, and further affecting the local morphology of the stripe pattern, causing the stripes to be distorted, deformed, or have intensity changes at the position corresponding to the bubble defect, such as Figure 4 As shown. For the detection glass with dotted dust on the surface, the dust on the surface mainly affects the light beam by blocking and scattering, so the stripe pattern shows different characteristics from the bubble defect. For example, local dark spots or blurred areas will appear at the dust position, and the degree of distortion of the stripes is relatively small, such as Figure 5 and Figure 6 shown.

[0041] Step three: the camera takes a picture to obtain an image of the detection glass modulated by the striped grating plate.

[0042] Specifically, the camera collects images after the light source is exposed for 1 to 2 seconds. Only one photo is needed to obtain an image modulated by the striped grid and containing glass defect information.

[0043] Step 4: The image processing unit processes and analyzes the image.

[0044] Specifically, after receiving the image data, the image processing unit first preprocesses each frame of the image. The median filter algorithm is used to remove noise interference in the image, and then the grayscale stretching algorithm is used to enhance the contrast of the image, making the features of the stripe pattern and bubble defects or point-shaped dust more obvious. The edge detection algorithm is used to extract the edge information of the stripe pattern, and then calculate the characteristic parameters such as the periodic change rate and distortion amplitude of the stripes. For suspected defect areas, by analyzing the periodic change rate, phase change, and distortion amplitude value of the surrounding stripes, classification and judgment are performed according to the pre-set judgment criteria.

[0045] The discrimination criteria have three indicators, namely, period change threshold, phase change threshold and distortion amplitude threshold.

[0046] Periodicity change threshold: The applicant uses appropriate algorithms or analysis tools to observe the collected data and graphics, and try to find possible periodic patterns. For example, by drawing a waveform graph of the data, you can visually check whether there are repeated similar parts in the waveform to infer the period and obtain the periodicity change threshold. Compare the periodicity-related indicators obtained by analysis with the set periodicity change threshold.

[0047] Distortion amplitude threshold: Based on the basic theories of geometric optics, wave optics, etc., analyze the possible distortion of light when it propagates in different media and different optical structures. Construct a suitable mathematical model for specific optical application scenarios. The parameters of the lens can be changed, such as different focal length settings, different lens combinations, etc. At the same time, a target is placed on the image plane. By shooting the target image and analyzing the deviation of the image point position relative to the ideal imaging position in the image, the distortion amplitude of the light during the imaging process is determined, and the distortion amplitude data under different lens parameters is also recorded. The large amount of data collected on the distortion amplitude is sorted out, and finally the distortion amplitude threshold is determined based on the specific optical application requirements.

[0048] Phase change threshold: In the field of optics, when using the interference and diffraction phenomena of light for detection, two beams of coherent light are superimposed to produce interference fringes. The threshold judgment standard corresponding to the phase difference change is related to the physical quantity to be detected. Through basic optical formulas and principles, we can theoretically analyze the approximate range of possible phase differences under different optical structures, different media and other conditions, and provide a basic theoretical reference for subsequent threshold setting. Change the relevant variables to conduct multiple experiments and collect data. Sort out the many phase difference data collected, calculate the mean, standard deviation, maximum value, minimum value and other statistics, and obtain the phase change threshold.

[0049] The specific judgment method is as follows: if the fringe period change rate at the suspected defect area exceeds the period change rate threshold, and the phase change is greater than the phase change threshold, and the fringe distortion amplitude reaches the distortion amplitude threshold, then the defect is judged to be a bubble defect, such as Figure 7 As shown; if the stripes in the suspected defect area only appear as dark spots with low grayscale values, and the periodic change rate of the stripe pattern does not exceed the periodic change rate threshold, and the phase change is less than the phase change threshold, and the distortion amplitude of the stripe pattern is lower than the distortion amplitude threshold, then it is judged as point dust.

[0050] Step 5: Output and display the detection results.

[0051] Specifically, the test results are displayed in an intuitive manner on a computer or mobile phone display screen, such as defect type, location, quantity, etc., or a test report is generated and output to an operator or production control system for subsequent quality assessment and processing decisions of the tested glass.

[0052] It is obvious to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above, and that the present application can be implemented in other specific forms without departing from the spirit or essential features of the present application. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present application. Any mark in a claim should not be regarded as limiting the claim involved.

Claims

1. A device for distinguishing point-shaped dust and bubble defects by using a stripe grating plate, comprising a conveyor line 1, a conveyor line 2, a camera and a light source, wherein the conveyor line 1 and the conveyor line 2 are for the detection glass to pass through, the camera is arranged above the detection glass, and the light source is arranged below the detection glass, characterized in that: A striped grating plate is also arranged on the mounting frame of the light source. A plurality of parallel grating lines are arranged on the striped grating plate. The light beam of the light source is projected toward the detection glass through the striped grating plate.

2. The device for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 1, characterized in that: The grating line width of the striped grating plate ranges from 0.1 to 0.2 mm, and the grating line spacing ranges from 0.1 to 0.2 mm.

3. The method for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 2, characterized in that: The grating line width of the striped grating plate is 0.1 mm and the grating line spacing is 0.1 mm.

4. The device for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 1, characterized in that: The striped grating plate on the light source is parallel to the detection glass, and the distance between the upper surface of the striped grating plate and the lower surface of the detection glass is in the range of 200 to 300 mm; the striped grating plate is made of acrylic plate.

5. The device for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 1, characterized in that: The camera is connected to an image processing unit, which is arranged in a computer or a mobile phone. The image processing unit is suitable for performing data analysis, result display and data storage on the stripe image obtained by the camera.

6. A method for distinguishing point-like dust and bubble defects using a striped grating plate, characterized in that: The device as described in any one of claims 1 to 5 specifically includes the following actions: preparing and cleaning the detection glass, then putting it into conveyor line one or conveyor line two, turning on the light source, irradiating the light beam onto the detection glass, and the light beam passing through the striped grating plate undergoes diffraction and interference effects and irradiates the detection glass to form a striped pattern, the camera takes a picture to obtain an image of the detection glass modulated by the striped grating plate, and the image processing unit processes and analyzes the image, and outputs and displays the detection result.

7. The method for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 6, characterized in that: The light source is turned on, and the light beam is irradiated onto the detection glass. The light beam passing through the striped grating plate undergoes diffraction and interference effects, and is irradiated onto the detection glass to form a stripe pattern. The specific process is as follows: for the detection glass with bubble defects, the light beam is projected onto the corresponding position of the bubble defect after passing through the striped grating plate, and the stripe pattern formed is that the stripes are distorted, deformed, or have intensity changes; for the detection glass with dotted dust, the light beam is projected onto the corresponding position of the bubble defect after passing through the striped grating plate, and the stripe pattern formed is that a local dark spot or a blurred area appears at the dotted dust position, and the degree of distortion is smaller than that of the stripe pattern of the bubble defect.

8. The method for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 6, characterized in that: The camera takes pictures, and the specific process is as follows: the camera takes a picture once under the light source exposure to obtain an image modulated by the striped grating plate and containing point-shaped dust and / or bubble defects.

9. The method for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 6, characterized in that: The image processing unit processes and analyzes the image, and the specific process is as follows: after receiving the image data, the image processing unit of the computer system first pre-processes each frame of the image; uses a median filtering algorithm to remove noise interference in the image, and then uses a grayscale stretching algorithm to enhance the contrast of the image to make the stripe pattern obvious; uses an edge detection algorithm to extract edge information of the stripe pattern, and then calculates the period and amplitude parameters of the stripes; for areas suspected of defects, by analyzing the phase changes and distortion characteristics of the surrounding stripes, classification and judgment are performed according to pre-set judgment criteria.

10. The method for distinguishing point-shaped dust and bubble defects by using a striped grating plate according to claim 9, characterized in that: The classification and judgment are performed according to a pre-set judgment standard, and the judgment method is as follows: if the periodic change rate of the stripe pattern in the suspected defect area exceeds the periodic change rate threshold, and the phase change amount is greater than the phase change threshold, and the stripe pattern distortion amplitude reaches the distortion amplitude threshold, then the defect is judged to be a bubble defect; if the suspected defect only appears as a dark spot with a low grayscale value, the periodic change rate of the stripe pattern does not exceed the periodic change rate threshold, and the phase change amount is less than the phase change threshold, and the stripe pattern distortion amplitude is lower than the distortion amplitude threshold, then it is judged to be point dust.

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