CN218350145U - Four-focal-length phase coherent imaging optical measurement machine vision device - Google Patents

Abstract

The embodiment of the specification provides an optical measurement machine vision device for four-focal-length phase coherent imaging, which belongs to the technical field of image acquisition and comprises a detection light source assembly, a phase plate, a first Fourier transform lens, a semi-transparent semi-reflective lens and a second Fourier transform lens; the detection light source assembly, the phase plate, the first Fourier transform lens, the semi-transparent semi-reflecting mirror, the second Fourier transform lens and the image acquisition device are coaxially and sequentially arranged; the crystal to be detected is located on the focal plane where the first Fourier transform lens and the second Fourier transform lens are overlapped, and the method has the advantages that phase information of internal defects of the crystal is converted into gray information, and the crystal defects can be conveniently analyzed based on the crystal defect image.

Description

Four-focal-length phase coherent imaging optical measurement machine vision device

Technical Field

The specification relates to the field of image acquisition, in particular to an optical measurement machine vision device for four-focus phase coherent imaging.

Background

Vision is a sense produced by stimulating retina with an image of an object, and the work of human beings to perceive external environment is mainly borne by sense organs such as vision, touch, hearing and smell, wherein about 80% of information is acquired through the sense organs. The machine vision technology uses a photosensitive element and a computer technology to simulate the human vision function and replaces human eyes to finish part of detection work. This has made modern detection techniques more active and has also made machine vision detection a gradual replacement for traditional touch detection methods. The machine vision technology is utilized to detect the internal micro defects of the crystal, so that the contact with a sample in the actual production process can be avoided, and the method plays a very important role in ensuring the quality of the product.

Machine vision detection is to use a machine vision system to detect whether products on a production line have quality problems or not, and detect the attractiveness, comfort and usability of the products. The scanning electron microscope method combines optical microscopic observation and an electron microscope to detect parameters such as the appearance, defect state and the like of crystals with crystal defects, but the gold spraying operation needs to be carried out on samples. The crystal after the gold spraying treatment is difficult to be subjected to other treatments, and the detection efficiency is not suitable for large-batch crystal detection. In addition, the defect detection in the crystal can be realized by using a dynamic Taeman interferometer detection method and a laser focusing line scanning method, the detection relative error of the dynamic Taeman interferometer detection method is 2.4%, and the detection resolution of the laser focusing line scanning method reaches 40um. However, the detection accuracy and resolution of this type of method still need to be further improved. The machine vision improves the automation degree and the fault tolerance rate of the industry to a great extent, and is beneficial to improving the intelligent degree of precision machining in production. At present, a common machine vision detection system mainly aims at chips, shafts or other metal mechanical parts, most of the objects conform to the characteristics of solid, non-transparent and high imaging contrast, and few researches are made on the detection of crystal defects with high transparency and low imaging contrast.

Therefore, it is necessary to provide a four-focus phase coherent imaging optical measurement machine vision device for acquiring a crystal defect image, converting phase information of internal defects of a crystal into gray scale information, and facilitating subsequent analysis of the crystal defects based on the crystal defect image.

SUMMERY OF THE UTILITY MODEL

In order to solve the technical problem that crystal defect detection with high transparency and low imaging contrast ratio in the prior art does not have a mature scheme, one of the embodiments of the present specification provides an optical measurement machine vision device for four-focus phase coherent imaging, including a detection light source assembly, a phase plate, a first fourier transform lens, a half-mirror and a second fourier transform lens; the detection light source assembly, the phase plate, the first Fourier transform lens, the semi-transmitting and semi-reflecting mirror, the second Fourier transform lens and the image acquisition device are coaxially and sequentially arranged; and the crystal to be detected is positioned on a focal plane where the first Fourier transform lens and the second Fourier transform lens are superposed.

In some embodiments, the apparatus further includes a microscopic imaging component, and after the light passing through the crystal to be detected is split by the half-transmitting and half-reflecting mirror, a part of the light enters the microscopic imaging component, and the other part of the light enters the image acquisition device.

In some embodiments, the detection light source assembly comprises a semiconductor laser.

In some embodiments, the semiconductor laser emits detection light having a wavelength of 860 nanometers.

In some embodiments, the focal lengths of the first fourier transform lens and the second fourier transform lens are both 400 millimeters.

In some embodiments, the phase plate has a phase shift of 0.5 π.

In some embodiments, the optical measurement machine vision apparatus for four focal length phase coherent imaging further comprises a processor for: preprocessing the crystal defect characteristic image acquired by the image acquisition device to obtain a preprocessed gray level image; carrying out gray level analysis on the preprocessed gray level image to determine gray level information; determining a defect thickness based on the gray scale information.

In some embodiments, the processor is further configured to: repairing the crystal defect characteristic image to obtain a repaired gray level image; and determining a defect main information area and a defect secondary information area in the repaired gray-scale image.

In some embodiments, the processor is further configured to: respectively calculating a first average gray scale corresponding to the defect main information area and a second average gray scale corresponding to the defect secondary information area; calculating an average gray difference value corresponding to the first average gray and the second average gray; judging whether the average gray difference value is larger than a preset threshold value or not; and if the average gray difference value is larger than a preset threshold value, taking the first average gray as gray information.

In some embodiments, the processor is further configured to: and determining the defect thickness based on the average gray scale according to the corresponding relation between the gray scale and the thickness.

Drawings

The present description will be further explained by way of exemplary embodiments, which will be described in detail by way of the accompanying drawings. These embodiments are not intended to be limiting, and in these embodiments like numerals refer to like structures, wherein:

FIG. 1 is a schematic block diagram of an optical measurement machine vision apparatus for four focal length phase coherent imaging in accordance with some embodiments described herein;

FIG. 2 is a schematic illustration of a portion of pixels of a preprocessed gray scale image according to some embodiments of the present disclosure;

fig. 3 is a schematic diagram of a defect primary information area and a defect secondary information area of a preprocessed gray scale image according to some embodiments of the present description.

In the figure, 310, a detection light source assembly; 320. a phase plate; 330. a first Fourier transform lens; 340. detecting a crystal; 350. a semi-transparent semi-reflective mirror; 360. a second Fourier transform lens; 370. an image acquisition device; 380. a microscopic imaging assembly; 510. a defect main information area; 520. a defective secondary information area.

Detailed Description

In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings used in the description of the embodiments will be briefly described below. It is obvious that the drawings in the following description are only examples or embodiments of the present description, and that for a person skilled in the art, the present description can also be applied to other similar scenarios on the basis of these drawings without inventive effort. Unless otherwise apparent from the context, or otherwise indicated, like reference numbers in the figures refer to the same structure or operation.

It should be understood that "system", "apparatus", "unit" and/or "module" as used herein is a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, other words may be substituted by other expressions if they accomplish the same purpose.

As used in this specification and the appended claims, the terms "a," "an," "the," and/or "the" are not to be taken in a singular sense, but rather are to be construed to include a plural sense unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.

The crystal 340 to be detected may be a crystal with high transparency, for example, quartz glass or the like.

Fig. 1 is a schematic structural diagram of an optical measurement machine vision device for four-focus phase coherent imaging according to some embodiments of the present disclosure, and in some embodiments, the optical measurement machine vision device for four-focus phase coherent imaging includes a detection light source assembly 310, a phase plate 320, a first fourier transform lens 330, a half mirror 350, and a second fourier transform lens 360, as shown in fig. 1. The detection light source assembly 310, the phase plate 320, the first fourier transform lens 330, the half mirror 350, the second fourier transform lens 360, and the image capturing device 370 are coaxially and sequentially disposed. The crystal 340 to be detected is located in a focal plane where the first fourier transform lens 330 and the second fourier transform lens 360 coincide. In some embodiments, the optical measurement machine vision apparatus for four-focus phase coherent imaging further includes a microscopic imaging component 380, after the light passing through the crystal 340 to be detected is split by the half-mirror 350, a part of the light enters the microscopic imaging component 380, and an operator can determine the position of the crystal 340 to be detected according to the imaging of the microscopic imaging component 380, and another part of the light enters the image acquisition device 370. In some embodiments, detection light source assembly 310 may comprise a semiconductor laser having a wavelength of 860nm, image capture device 370 may be a CCD camera, and microscopic imaging assembly 380 may comprise a microscope CCD (microscope camera).

It can be understood that the detection light provided by the detection light source component 310 enters the first fourier transform lens 330 after being modulated by the phase plate 320, the sample to be detected is placed on the focal plane where the first fourier transform lens 330 and the second fourier transform lens 360 coincide, the light passing through the sample to be detected is split by the half-transmitting mirror 350, a part of the light enters the microscopic imaging component 380, and the other part of the light passing through the rear fourier transform lens is captured by the image acquisition device 370, so as to form a crystal defect characteristic image.

In some embodiments, the optical measurement machine vision apparatus for four focal length phase coherent imaging may further comprise a processor, the processor may be configured to:

preprocessing a crystal defect characteristic image acquired by an image acquisition device to obtain a preprocessed gray level image;

carrying out gray level analysis on the preprocessed gray level image to determine gray level information;

based on the gray scale information, a defect thickness is determined.

Preprocessing refers to an operation performed on the crystal defect feature image to reduce interference information. In some embodiments, the pre-processing may include image denoising, image enhancement, and the like.

In some embodiments, image denoising refers to removing interference information in the crystal defect feature image. The interference information in the crystal defect feature image may degrade the quality of the crystal defect feature image. In some embodiments, the processor implements image denoising via a median filter, a machine learning model, or the like.

Image enhancement refers to increasing missing information in the crystal defect feature image. Missing information in the crystal defect feature image can cause image blur. In some embodiments, the processor implements image enhancement through a smoothing filter, a median filter, or the like.

In some embodiments, the preprocessing the crystal defect feature image by the processor may include:

repairing the crystal defect characteristic image to obtain a repaired gray level image;

the defect main information area 510 and the defect sub information area 520 in the repaired gray scale image are determined.

It can be understood that, in the actual detection process, when the detection light provided by the detection light source component 310 causes phase information to be lost due to dark spots, dark marks and the like appearing in the crystal defect characteristic image due to external factors such as lens dust, potential scratches of the lens and the like, the processor may repair the crystal defect characteristic image to reduce the loss of the phase information. In some embodiments, the processor may repair the defect region grayscale image by a laplacian filter algorithm.

In some embodiments, the processor may repair the gray image of the defect region by using a laplacian filtering algorithm, which may specifically include the following steps:

extracting a gray level change area in the crystal defect characteristic image;

and repairing the gray scale change area.

In some embodiments, the preprocessing module may determine the gray-level change region according to the degree of the sudden change of the adjacent gray levels in the crystal defect feature image using a laplacian filtering algorithm.

Repairing the gray image of the defect area by using the laplacian filter algorithm may specifically include: the calculation result of the laplacian operator of one point is the gray levels of the upper, the lower, the left and the right and the gray level minus 4 times of the gray level of the point, which is the four adjacent laplacian operators, the operator is rotated by 45 degrees and then added with the original operator, and the eight-neighborhood operator is changed, namely the difference between 8 circles of the sum of 8 pixels around one pixel and 8 times of the middle pixel. For example, for a pixel point in the gray scale change region, the gray values of 8 surrounding pixels are all high, but the gray value corresponding to the pixel point is low, a larger value can be obtained by calculating the result of subtracting 8 times of the gray value corresponding to the pixel point from the sum of 8 surrounding pixels, and the larger value is multiplied by a certain coefficient and then added to the original gray value of the pixel point, so that the gray value corresponding to the pixel point is improved, and finally, the pixel point is repaired.

The gray value corresponding to the pixel point after repair can be expressed as:

wherein g (x, y) is the gray value corresponding to the pixel point (x, y) after the repair, f (x, y) is the gray value corresponding to the pixel point (x, y) before the repair,

the method is a result of calculating the sum of 8 pixels around the pixel point (x, y) and subtracting 8 times of the gray value corresponding to the pixel point (x, y), and k is a coefficient and is used for adjusting the influence of the Laplace filter algorithm on the image before restoration. In some embodiments, the stability of the system caused by external uncontrollable factors can be effectively reduced by repairing the crystal defect characteristic imageThe detection result is more credible due to the influence of the detection result.

In some embodiments, the determining the defect primary information area 510 and the defect secondary information area 520 in the repaired gray scale image by the processor may include:

determining the gradient module value and the gradient direction of each pixel point in the repaired gray level image;

determining a separation contour based on the gradient module value and the gradient direction of each pixel point;

the defect main information area 510 and the defect sub information area 520 in the repaired gray image are determined based on the separation contour.

In some embodiments, by determining the defect primary information area 510 and the defect secondary information area 520 in the repaired gray-scale image, the data to be processed for subsequently determining the defect thickness can be effectively reduced, and the detection efficiency can be improved.

Fig. 2 is a schematic diagram of a part of pixel points of a preprocessed gray-scale image according to some embodiments of the present disclosure, as shown in fig. 2, for a pixel point M5, it is required to read gray scales G1, G2, G3, G4, G6, M7, M8, and G9 of peripheral pixel points M1, M2, M3, M4, M6, M7, M8, and M9 of the pixel point M5, and calculate a gradient modulus and a gradient direction of the pixel point M5 based on the following formulas:

wherein, T _x5 Is the transverse gradient modulus, T, of pixel point M5 _y5 Is the longitudinal gradient modulus, gr, of pixel point M5 _M5 Is the gradient modulus, θ, of pixel point M5 _M5 Is the gradient angle of pixel point M5.

It can be understood that after traversing the complete restored gray image, each pixel point has a corresponding gradient mode and gradient direction, and one of the pixel points with the largest gradient mode value in the region with the same gradient direction is screened, and the pixel points are extracted to form a separation outline. The screening condition is determined by the detection environment and the defect main information area 510, so as to achieve better extraction effect. In some embodiments, the screening condition may include a dual threshold, which may include a gray maximum threshold and a gray minimum threshold, which may be determined based on the detection target. For example only, when the brightness of the acquired image is high and the gray-level value of the defect main information area 510 is low, the separation of the contours may be selected to be achieved by using a low dual threshold. In some embodiments, in addition to setting the dual threshold, the pre-processing module may determine the defect primary information area 510 and the defect secondary information area 520 by setting the area and/or the roundness of the area. For example only, the defect main information area 510 may be screened out by setting the area to (lower limit: 1741 pixels, upper limit: 2167 pixels); the defect main information region 510 can be screened by setting the region circularity to (upper limit: 0.62, lower limit: 0.67).

Fig. 3 is a schematic diagram of a defect primary information area 510 and a defect secondary information area 520 of a preprocessed gray-scale image according to some embodiments of the present disclosure, where, as shown in fig. 3, on the preprocessed gray-scale image, a circle with a larger radius determines the overall range of the crystal 340 to be detected, a circle with a smaller radius in the middle marks the defect primary information area 510, a cross in the middle of the circle marks the position of the center of the circle, and an area inside the large circle and outside the small circle is the defect secondary information area 520.

The gray analysis may refer to an operation of extracting gray of a defect region in the preprocessed gray image, and the gray information may represent gray of the defect region.

In some embodiments, the processor performs gray scale analysis on the preprocessed gray scale image to determine gray scale information, which may include:

calculating a first average gray corresponding to the defect primary information area 510 and a second average gray corresponding to the defect secondary information area 520, respectively;

calculating an average gray difference value corresponding to the first average gray and the second average gray;

judging whether the average gray difference value is larger than a preset threshold value or not;

if the average gray difference value is larger than a preset threshold value, taking the first average gray as gray information;

if the average gray difference is smaller than the preset threshold, it is determined that there is no defect on the crystal 340 to be detected.

In some embodiments, whether the average gray difference is smaller than the preset threshold value or not can be judged in advance to judge whether the crystal 340 to be detected has defects or not, and only when the average gray difference is larger than the preset threshold value, the first average gray is used as gray information for determining the thickness of the defects, so that invalid defect thickness calculation is avoided when the average gray difference is smaller than the preset threshold value (that is, the crystal 340 to be detected has no defects), and the detection efficiency is improved.

The defect thickness may be used to characterize the depth of the defect on the crystal 340 to be inspected.

In some embodiments, the processor determines the defect thickness based on the gray scale information, which may include:

and determining the thickness of the defect based on the average gray scale according to the corresponding relation between the gray scale and the thickness.

It will be appreciated that the gray scale to thickness correspondence may be predetermined. In some embodiments, the gray scale to thickness correspondence may be expressed by the following equation:

where l' (x, y) is the defect thickness of (x, y) at a location of the crystal 340 to be inspected, k _g As a gray scale response parameter of the image acquisition means 370, b _g As correction amount, P ₀ The real amplitude of the incident light, λ is the wavelength of the incident light, r is the refractive index of the crystal to be measured, and G (x, y) is the gray scale information determined in step 240. In some embodiments, the maximum light intensity and the minimum light intensity collected by the image collection device 370 and their corresponding gray levels may be measured to determine k _g And b _g . Specifically, a light source component with adjustable brightness is used for replacing a detection light source component, a crystal to be detected is not placed, and the ambient light in the surrounding environment of the system is keptAnd (5) stabilizing, wherein the image acquired by the image acquisition device is an image without gray level change. Adjusting the light emitted by the light source component with adjustable brightness to the darkest, and recording the image P acquired by the image acquisition device at the moment ₁ Average gray value C of ₁ And the light intensity I of the light source ₁ (ii) a Then, the light emitted by the light source component with adjustable brightness is brightest, and the image P acquired by the image acquisition device at the moment is recorded ₂ Average gray value C of ₂ And the light intensity I at that time ₂ It is worth to say that the image P ₁ Gray value of (2) and image P ₂ The gray values of (a) are all located in the acquisition range of the image acquisition device. According to the measurement principle, the light intensity and the gray value satisfy the following linear relation:

I＝k _g C+b _g

image P ₁ Average gray value C of ₁ And the light intensity I of the light source ₁ And image P ₂ Average gray value C of ₂ And the light intensity I at that time ₂ Substituting the linear relation to obtain k _g And b _g 。

By way of example only, a semiconductor laser with a wavelength of 860nm is used as a detection beam, and a sample to be detected is 2mm quartz glass with central plating thickness of 60nm and radius of 0.5mm of SiO ₂ Film for simulating defects inside the crystal, focal length f of front and rear lenses of a four-focal-length phase-coherent system ₁ ＝f ₂ =400mm, magnification G =1, phase plate 320 phase shift phi =0.5 pi. The pixels of the image capturing device 370 are 1280 × 1024, each pixel has 1023 kinds of gray levels, and the pixel size is 5.2um × 5.2um. Ten measurements were made on the sample to be tested, five measurements were made on the sample to be tested in each measurement, and the measurement results are shown in table 1,

TABLE 1

As shown in Table 1, the average of the results of the ten experiments is 58.84nm, the variance σ ^2 is 0.72, and the standard deviation S is 0.85. The defect thickness is known to be 60nm, the mean absolute error of the system is-1.16 nm, and the mean relative error is 1.93%. The smaller the variance and standard deviation value is, the stronger the representative stability is, and the smaller the variance and standard deviation value of the current result is; the smaller the absolute error and the relative error, the higher the representation accuracy.

The dynamic Thyman interferometer and the laser focal line scanning method can also finish the detection of the internal defects of the crystal, as a comparison, the dynamic Thyman interferometer is also applied to the defect detection of the sample to be detected, according to the experimental result, the average absolute error of the dynamic Thyman interferometer is-2.55 nm, the average relative error is 2.40%, the crystal defect detection method based on the four-focus phase coherent machine vision provided by the specification finally achieves the average relative error of 1.93% and the average absolute error of-1.16 nm, and compared with the dynamic Thyman interferometer, the precision is higher.

In some embodiments, the crystal defect detection method based on the four-focus phase coherent machine vision provided by the present specification is used for detecting a micro defect inside a crystal, and converts phase information of the defect inside the crystal into gray scale information through a four-focus phase coherent optical path, so as to form a crystal defect characteristic image of the crystal 340 to be detected, optimize and repair the crystal defect characteristic image of the crystal 340 to be detected, and reduce the influence of a phase information loss point on a final detection result. And finally, processing and analyzing the defect characteristic image by utilizing a characteristic extraction and gray level analysis algorithm, and calculating to obtain the information of the internal defect of the crystal. Compared with the prior art, the method is superior to a dynamic Taeman interferometer in detection error and superior to a laser focal line scanning method in detection resolution. Finally, the relative error is 1.93%, and the detection resolution reaches the nanometer level. Furthermore, the method can efficiently process the crystal defect characteristic image of the crystal 340 to be detected, the average time for processing the crystal defect characteristic image of one crystal 340 to be detected is 132ms, certain guarantee is provided on efficiency, and other errors caused by manual operation are reduced.

It should be noted that the above description of a crystal defect detection method based on four-focus phase coherent machine vision is only for illustration and description, and does not limit the application scope of the present specification. It will be apparent to those skilled in the art from this disclosure that various modifications and variations can be made in a crystal defect detection method based on four-focus phase coherent machine vision. However, such modifications and variations are intended to be within the scope of the present description.

Having thus described the basic concept, it will be apparent to those skilled in the art that the foregoing detailed disclosure is to be regarded as illustrative only and not as limiting the present specification. Various modifications, improvements and adaptations to the present description may occur to those skilled in the art, although not explicitly described herein. Such modifications, improvements and adaptations are proposed in the present specification and thus fall within the spirit and scope of the exemplary embodiments of the present specification.

Also, the description uses specific words to describe embodiments of the description. Reference throughout this specification to "one embodiment," "an embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic described in connection with at least one embodiment of the specification is included. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, certain features, structures, or characteristics may be combined as suitable in one or more embodiments of the specification.

It should be noted that in the foregoing description of embodiments of the present specification, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the embodiments. This method of disclosure, however, is not intended to imply that more features than are expressly recited in a claim. Indeed, the embodiments may be characterized as having less than all of the features of a single embodiment disclosed above.

For each patent, patent application publication, and other material, such as articles, books, specifications, publications, documents, etc., cited in this specification, the entire contents of each are hereby incorporated by reference into this specification. Except where the application history document is inconsistent or contrary to the present specification, and except where the application history document is inconsistent or contrary to the present specification, the application history document is not inconsistent or contrary to the present specification, but is to be read in the broadest scope of the present claims (either currently or hereafter added to the present specification). It is to be understood that the descriptions, definitions and/or uses of terms in the accompanying materials of this specification shall control if they are inconsistent or contrary to the descriptions and/or uses of terms in this specification.

Finally, it should be understood that the embodiments described herein are merely illustrative of the principles of the embodiments of the present disclosure. Other variations are also possible within the scope of the present description. Thus, by way of example, and not limitation, alternative configurations of the embodiments of the specification can be considered consistent with the teachings of the specification. Accordingly, the embodiments of the present description are not limited to only those embodiments explicitly described and depicted herein.

Claims (10)

1. The optical measurement machine vision device for the four-focal-length phase coherent imaging is characterized by comprising a detection light source assembly, a phase plate, a first Fourier transform lens, a semi-transmitting and semi-reflecting mirror, a second Fourier transform lens and an image acquisition device;

the detection light source assembly, the phase plate, the first Fourier transform lens, the semi-transmitting and semi-reflecting mirror, the second Fourier transform lens and the image acquisition device are coaxially and sequentially arranged;

and the crystal to be detected is positioned on a focal plane where the first Fourier transform lens and the second Fourier transform lens are superposed.

2. The optical measurement machine vision device for four-focus phase coherent imaging according to claim 1, further comprising a microscopic imaging assembly, wherein after the light passing through the crystal to be detected is split by the half-mirror, one part of the light enters the microscopic imaging assembly, and the other part of the light enters the image acquisition device.

3. The optical measurement machine vision device for four focal length phase coherent imaging of claim 1, wherein said detecting light source assembly comprises a semiconductor laser.

4. The optical measurement machine vision device for four focal length phase coherent imaging of claim 3, wherein said semiconductor laser emits detection light at a wavelength of 860 nm.

5. The optical measurement machine vision device for four focal length phase coherent imaging of claim 1, wherein said first fourier transform lens and said second fourier transform lens each have a focal length of 400 millimeters.

6. The optical measurement machine vision device for four focal length phase coherent imaging of claim 1, wherein the phase plate phase shift is 0.5 pi.

7. The optical measurement machine vision device for four focal length phase coherent imaging of any one of claims 1 to 5, further comprising a processor for:

preprocessing the crystal defect characteristic image acquired by the image acquisition device to obtain a preprocessed gray level image;

carrying out gray level analysis on the preprocessed gray level image to determine gray level information;

determining a defect thickness based on the gray scale information.

8. The optical measurement machine vision apparatus for four focal length phase coherent imaging of claim 7, wherein said processor is further configured to:

repairing the crystal defect characteristic image to obtain a repaired gray level image;

and determining a defect main information area and a defect secondary information area in the repaired gray-scale image.

9. The optical measurement machine vision device for four focal length phase coherent imaging of claim 8, wherein said processor is further configured to:

respectively calculating a first average gray scale corresponding to the defect main information area and a second average gray scale corresponding to the defect secondary information area;

calculating an average gray difference value corresponding to the first average gray and the second average gray;

judging whether the average gray difference value is larger than a preset threshold value or not;

and if the average gray difference value is larger than a preset threshold value, taking the first average gray as gray information.

10. The optical measurement machine vision device for four focal length phase coherent imaging of claim 9, wherein said processor is further configured to:

and determining the defect thickness based on the average gray scale according to the corresponding relation between the gray scale and the thickness.

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