KR101549310B1 - Apparatus and method phase shifting stripe patterns projection for detecting defect of transparent object - Google Patents

Abstract

The present invention provides a phase shift projection apparatus and method for detecting a defect in a transparent body and includes a projection unit that emits light of a grid image to a measurement unit to generate a dark field of the measurement object, (300); A measurement unit 200 for allowing the light emitted from the projection unit 300 to pass through the transparent object 210; The measurement unit 200 receives the light that has passed through the measurement object 210 by the light receiving optical system 120 and acquires an image from the camera 110. The Z map which is darkness darkness information extracted from the acquired image And an image acquiring unit (100) for performing defect detection of the measurement object (210) by using the projection optical system (200), thereby realizing a phase shift of repeated grating patterns and adjusting a projection magnification, So that all the light rays passing through the LCD can be incident along the optical axis of the light receiving unit to effectively inspect the light.

Description

[0001] The present invention relates to a phase shift projection apparatus for detecting defects in a transparent body, and a phase shift projection apparatus for detecting defects of a transparent body,

The present invention relates to the detection of defects in a transparent body, and in particular, in generating a dark field and extracting defects using only a projection grating, it is possible to perfectly implement a repeated phase pattern of the grating pattern and adjust the projection magnification A phase shift projection apparatus and method for detecting defects of a transparent body that are suitable for effectively inspecting light by allowing all light rays passing through the LCD to be incident along an optical axis of a light receiving unit .

In general, the word Moire is what the French referred to as the wave pattern on silk imported from ancient China. Moire phenomenon is an interference fringe caused by the overlapping of two or more periodic wave patterns. That is, the moire phenomenon refers to an interference pattern generated between objects having a constant gap, in which a beat phenomenon occurs visually.

The moire pattern is defined as a type of interference pattern that has a relatively low frequency compared to the reference pattern, which occurs when two or more periodic patterns are overlapped. This unique low-frequency moire pattern, which is described as a beat phenomenon, has a wide range of applications ranging from 2D to 3D shape measurement throughout engineering. The moire method is divided into a shadow moire method and a projection moire method according to a method of forming a moire pattern. If the object has many properties of the mirror surface, it is possible to measure the 3D shape using a reflection moire.

(2008), Reflective fringe pattern technique for subsurface crack detection, NDTE International 41: 602-610) and a method of using a lattice using an LCD (A Machine Vision for Automated Headlamp Lens Inspection: Edited by Francisco Gallegos-Funes, ISBN 978-953-307-098-8, 196 pages, Publisher: Sciyo, Chapters published August 12, 2010).

In the projection type moire method, three or more patterns are moved at regular intervals at regular intervals in order to obtain a projected image, and then the photographed image is stored in a memory. The moiré pattern can be interpreted in three dimensions by calculating the phase using the bucket algorithm and obtaining the difference between the reference phase and the object phase by unwrapping each of the three or more images thus obtained, It is possible.

However, the above method has a problem in that it is difficult to measure when the height of the measurement object is higher than the period, depending on the period of the moire pattern. Therefore, in the prior art, there are problems such as relative height measurement, shadow generation, and deterioration of measurement accuracy, and in the case of reducing the measurement error, there is a limit that absolute three-dimensional coordinates in space can not be obtained.

FIG. 1 is a block diagram of an apparatus for detecting a defect of a transparent body by a grid pattern projection using a conventional LCD, and FIG. 2 is a diagram showing a modified stripe pattern obtained by FIG. The operation principle of the projection type moire device using only the projection grating shown in FIG. 1 is as follows.

First, when all the light beams of the BLU 11 are projected on the measurement object 13 through the LCD lattice pattern panel 12, the LCD lattice pattern panel 12 appears in a striped pattern passing through the transparent measurement object 13. [ Then, the stripe pattern passes through the imaging lens 14 and is formed on a sensing surface of a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) camera 15, as shown in FIG.

In order to obtain three or more images as described above, a grid pattern is moved at regular intervals and then photographed and stored in a memory. The normalized background value of the transparent object is calculated using the dark field algorithm on each of the three or more images obtained as described above, and then the background value or more can be determined as a defect.

부터

구간인 선(line)에 투영되어 형성된 암시야(dark field)를 얻기 위해서는 스크래치나 얼룩과 같이 투과 및 반사할 수 있어야 하며, 상기 투과 및 반사하는 광선이 매핑되어질 선의 방향은 결함의 주축각과 같아야 한다. 그렇지 않을 경우 결함을 검출할 수 없다. 그래서 종래기술에서는 진폭의 크기를 극대화함과 동시에 요구되는 검출력의 조절과 정확한 격자의 이동량을 카메라의 픽셀 분해능에 맞출 수 없어 투과의 형태지만 얼룩과 같이 희미한 결함의 경우 구형파와 정현파의 차이로 발생되는 만큼은 검출할 수 없는 한계도 있었다.
However, such a method has a problem in that when the projected grid pattern is a sine wave rather than a complete square wave, information of fine defects is lost in the process of being normalized to an average value. Light refracted and diffracted at the boundary between a space through which light is transmitted and a line that is reflected or absorbed is converted into a sinusoidal wave

from

In order to obtain a dark field formed by projecting on a line that is a section, it must be able to transmit and reflect like a scratch or a speckle, and the direction of the line to which the transmitted and reflected light should be mapped should be the same as the principal axis angle of the defect . Otherwise, the defect can not be detected. Therefore, in the prior art, the size of the amplitude is maximized, and the required detection power is adjusted and the moving amount of the correct grating can not be adjusted to the pixel resolution of the camera, which is a form of transmission, but in the case of faint defects such as stains, There was also a limit that could not be detected.

It is therefore an object of the present invention to provide a method and apparatus for generating a dark field using only a projection grating, A phase shift for detecting defects of a transparent body which can effectively inspect light by allowing all light rays passing through the LCD to be incident along the optical axis of the light receiving unit, A projection apparatus and a method thereof.

3 is a configuration diagram of an LCD phase shift projection apparatus for detecting defects of a transparent body according to an embodiment of the present invention.

A projection unit 300 for emitting light of a grid image to the measurement unit 200 to generate a dark field of the measurement object 210; A measurement unit 200 for allowing the light emitted from the projection unit 300 to pass through the transparent object 210; The measurement unit 200 receives the light that has passed through the measurement object 210 by the light receiving optical system 120 and acquires an image from the camera 110. The Z map which is darkness darkness information extracted from the acquired image And an image obtaining unit (100) for detecting defects of the measurement object (210) by using the image data.

The projection unit 300 includes a BLU 330 for emitting light; An LCD panel 320 for generating a grid image using light of the BLU 330; And a projection optical system 310 for irradiating the measurement unit 200 with the lattice image generated by the LCD panel 320.

The projection unit 300 includes an OLED or a PDP, and emits light of a grid image to the measurement unit 200.

The measurement unit 200 includes a transfer table 220 on which a measurement object 210 is installed; And driving means (230) of a transfer table for driving the transfer table (220) to transfer the measurement object (210).

FIG. 4 is a block diagram illustrating an example in which the control module unit and the central control unit are combined in FIG.

As shown in the figure, the phase shift projection apparatus for detecting defects of the transparent body includes a control module unit 400 for controlling operations of the projection unit 300 and the image acquisition unit 100; A central control unit 500 for controlling the control module unit 400 and extracting defects of the measurement object 210 as a transparent chain using the Z map which is darkness darkness information generated by the image acquisition unit 100 ). ≪ / RTI >

The control module 400 includes a motor driver 410 for driving the driving unit 230 of the transfer table in the measuring unit 200; And an LCD driver (420) for controlling the operation of the projection unit (300).

The central control unit 500 includes a motor control board 510 for controlling the operation of the motor driver 410 in the control module unit 400; An LCD control board 520 for controlling the operation of the LCD driving driver 420 in the control module 400 so as to realize a small displacement of a grid image to be diverged; And an image board 530 for processing the image obtained from the camera 110 in the image acquiring unit 100. As shown in FIG.

5 is a configuration diagram of an LCD phase shift projection apparatus for detecting a defect of a transparent body according to another embodiment of the present invention.

As shown in the figure, a BLU 330 for emitting light, a lithography 321 for generating a lattice image using the light of the BLU 330, a piezoelectric actuator 340 for miniaturizing the lithography 321, And a projection optical system 310 for irradiating the measurement unit 200 with the grid image generated by the lithography unit 321. The projection optical system 310 emits light of the grid image to the measurement unit 200, A projection unit (300) for generating a projection image; A measurement unit 200 for allowing the light emitted from the projection unit 300 to pass through the transparent object 210; The measurement unit 200 receives the light that has passed through the measurement object 210 by the light receiving optical system 120 and acquires an image from the camera 110. The Z map which is darkness darkness information extracted from the acquired image An image obtaining unit (100) for detecting a defect of the measurement object (210) using the image data; A motor driver 410 for driving the driving unit 230 of the transfer table in the measuring unit 200 and a piezoelectric actuator driving driver 421 for controlling the operation of the piezoelectric actuator 340 in the projection unit 300 A control module 400 for controlling operations of the projection unit 300 and the image acquisition unit 100; A motor control board 510 for controlling the operation of the motor driver 410 and a piezoelectric actuator control board for controlling the operation of the piezoelectric actuator driving driver 421 so as to realize a minute displacement of a lattice image, And an image board 530 for processing the image obtained from the camera 110. The Z coordinate of the Z coordinate is calculated using the Z map which is darkness darkness information generated by the image obtaining unit 100, And a central control unit (500) for extracting defects of the object (210).

6 is a flowchart illustrating a phase shift projection method for defect detection of a transparent body according to an embodiment of the present invention.

A first step (ST1) of causing the projection unit (300) to irradiate the measurement object (210) in the measurement unit (200) with the projection grating, A second step ST2 of acquiring an image from the camera 110 in the image acquisition unit 100 when the grating is transferred from the projection unit 300 to the measurement object 210 while finely moving the projection grating, Wow; A third step (ST3) of receiving the moving image of the projection grating input to the camera 110 and receiving the moving image from the central control unit 500 and applying it to the dark field algorithm; The central control unit 500 further includes a fourth step (ST4) of extracting a Z map from the image to which the ambiguity algorithm is applied in the third step; The central control unit 500 includes a fifth step of detecting a defect of the measurement object 210 using the extracted Z map (ST5).

The phase shift projection apparatus and method for detecting defects of a transparent body according to the present invention can be applied to a system and method for generating a dark field and extracting defects using only a projection grating, It is possible to detect defects of a minute object and all the light rays passing through the LCD are incident along the optical axis of the light receiving unit, thereby effectively inspecting the light.

The present invention also provides an apparatus for projecting a pixel unit square wave of an LCD at a reduction or enlargement ratio of 1: 1 to 1: n using a projection optical system, It is possible to improve the detection performance through the dark field and the Z map, thereby improving the accuracy and reliability.

FIG. 1 is a block diagram of an apparatus for detecting a defect of a transparent body by a lattice pattern projection using a conventional LCD.
Fig. 2 is a view showing a modified stripe shape obtained by Fig. 1. Fig.
3 is a configuration diagram of a phase-shift projection apparatus for detecting a defect in a transparent body according to an embodiment of the present invention.
FIG. 4 is a block diagram illustrating an example in which the control module unit and the central control unit are combined in FIG.
5 is a configuration diagram of an LCD phase shift projection apparatus for detecting a defect of a transparent body according to another embodiment of the present invention.
6 is a flowchart illustrating a phase shift projection method for defect detection of a transparent body according to an embodiment of the present invention.
FIG. 7 is a diagram showing a result of inspecting a measurement object with a program actually implemented by the present invention. FIG.

A phase shift projection apparatus and method for detecting a defect of a transparent body according to the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. It is to be understood that the following terms are defined in consideration of the functions of the present invention, and may be changed according to the intention of the user, the operator, or the precedent, and the meaning of each term should be interpreted based on the contents will be.

First, in the present invention, when generating a dark field using only a projection lattice and extracting defects, it is possible to complete the phase shift implementation of repeated lattice patterns and to adjust the projection magnification, thereby detecting defects of a minute object In addition, all of the rays passing through the LCD are incident along the optical axis of the light receiving part, thereby effectively testing the light.

Here, in the present invention, the measurement object 210 to be measured is a transparent body. In general, a translucent body has a transmittance of about 50 to 70%. If the transparent body has a transmittance of 70% or more, All can be found.

4 is a plan view of a phase-shift projection apparatus configured to acquire a phase-shifted image using only a grid pattern and to project an image with a minute displacement through an LCD controller using an LCD panel. I will explain in detail.

The present invention may include at least one of a projection unit 300, a measurement unit 200, an image acquisition unit 100, a control module unit 400, and a central control unit 500.

Thus, in the projection unit 300, the BLU 330 is installed below the transfer table 220 and emits light.

The LCD control board 520 in the central control unit 500 controls the LCD driver 420 so that the lattice pattern of the LCD panel 320 can be slightly deformed.

The projection optical system 310 includes an optical system through which a lattice image generated in the LCD panel 320 is transmitted to assist in extracting defects of an object. The projection optical system 310 is located in the vertical direction of the measurement object 210 and is positioned within the same angle range as the optical axis.

The projection unit 300 may include the BLU 330, the LCD panel 320, and the projection optical system 310, but may be replaced with other display means capable of projecting a grid image such as an OLED or a PDP Do.

In addition, the transfer table 220 in the measurement unit 200 allows the measurement object 210 to be placed.

The driving unit 230 of the transfer table in the measuring unit 200 is driven by the motor driver 410 of the control module unit 400 under the control of the motor control board 510 of the central control unit 500, (220).

The image acquisition unit 100 is installed in the vertical direction of the projection unit 300.

The light receiving optical system 120 and the camera 110 in the image obtaining unit 100 receive the grid image from the measurement object 210 and transmit the grid image to the image board 530 of the central control unit 500.

The control module unit 400 controls the operation of the lattice pattern projection unit 300 and the image acquisition unit 100.

The motor driver 410 drives the driving means 230 of the transfer table in the measuring unit 200 under the control of the motor control board 510 of the central control unit 500 in the control module unit 400.

The LCD driver 420 in the control module 400 controls the operation of the LCD panel 320 of the projection unit 300 by interfacing with the LCD control board 520 of the central control unit 500.

Then, the central control unit 500 controls the control module unit 400, obtains the bias magnitude of the object using the Z map of the dark field for the image acquired by the image acquisition unit 100, And the height of the unwrapped object is calculated using the correction surface phase of the projection unit 300. [ Here, the correction plane is for estimating a measurement position spaced vertically from the grid image.

In the central control unit 500, the motor control board 510 controls the operation of the motor driver 410 in the control module unit 400.

In the central control unit 500, the image board 530 processes the image obtained from the camera 110 in the image acquisition unit 100. [

A process of acquiring a moire pattern using such a device will be described below.

The measurement object 210 is placed and a grid pattern is projected through the LCD panel 320 of the projection unit 300 (ST1) and the deformed grid pattern is projected to acquire an image (ST2). (ST3), which is a light-receiving unit equipped with a camera 110 for receiving a grid transmitted through the measurement object 210, calculates a Z map using the dark field algorithm, (ST4). Then, the defect of the object is detected from the Z map of the dark field obtained (ST5).

A process of generating the dark field and extracting the Z map and a polynomial solution used to extract defects of the object are well known to those skilled in the art, and thus a detailed description thereof will be omitted. However, in the case of the Z map, a general Z map means a height information map of the object. In the present invention, the Z map, which is a height information map of the object, is used as a darkness information map for the transparent object to extract defect information of the transparent object.

The algorithm for obtaining the dark field information is similar to the method for calculating the phase of the moiré, so that a Z map for all points of the image can be constructed in the same way as the moire's 3 buckets, 4 buckets or 5 buckets. Among them, the 5-bucket algorithm is expressed as follows.

라 하고,The amount of phase shift

However,

라 할 때,The light intensity of the image observed by the CCD camera

In other words,

The image obtained through the phase shift is expressed by the following equations (1) and (2).

의 대푯값으로 5개의 광강도 가운데 가장 작은 값을 갖는 경우는 정현파의 최저점 또는 결함으로 인해 위상이 변형된 경우로 볼 수 있으며, 다음의 수학식 3으로 표현된다.Any one point

Is the smallest value among the five light intensities, it can be regarded as a case where the phase is deformed due to the lowest point or defect of the sine wave, and is represented by the following equation (3).

의 크기를 갖는 서피스

는 대상물체의 투과하는 공간(space)과 반사내지 흡수되는 선(line)의 경계에서 굴절 및 회절되어진 빛이 정현파의

부터

구간인 선(line)에 투영되어 형성된 암시야(dark field)를 수학식 4와 같이 정의할 수 있다.If the width is w and the height is h,

Surface of the size

The light that is refracted and diffracted at the boundary between the space through which the object is transmitted and the line that is reflected or absorbed is converted into a sinusoidal wave

from

A dark field formed by projecting on a line that is a section can be defined as shown in Equation (4).

The actual measurement process will be described with reference to FIGS. 4 and 6.

First, the present invention is divided into a method of obtaining the dark field of the measurement object and a method of acquiring the defect information of the measurement object.

First, the steps of using the projection unit 300 and obtaining the dark field of the object corresponding to the measurement object 210 will be described.

The measurement object 210 is placed on the transfer table 220 and the light of the BLU 330 is projected onto the measurement object 210 through the projection optical system 310. The image of the grid pattern of the LCD panel 320 is projected onto the measurement object 210 at regular intervals using the LCD control board 520 so that one of the three buckets, the four buckets, and the five buckets can be applied, Through the video board 110 and the video board 530. The Z map of the measurement object 210 is obtained by applying the dark field algorithm of Equation (3) to the acquired grid pattern image.

Then, defect information of the object is obtained from the Z map. The black stuff, which is not calculated due to the darkness, is obtained by replacing defects by using an LCD image as a backlight.

On the other hand, FIG. 5 shows an example in which the configuration of the projection unit 300 is configured by using the piezoelectric actuator 340 in the configuration of FIG.

That is, the projection unit 300 includes a BLU 330 for emitting light, a lithography 321 for generating a lattice image using the light of the BLU 330, a piezoelectric actuator 340 for minutely displacing the lithography 321, And a projection optical system 310 for irradiating the measurement unit 200 with the grid image generated by the projection optical system 321.

The control module 400 includes a motor driver 410 for driving the driving unit 230 of the transfer table in the measuring unit 200, a piezoelectric actuator driving driver 421 for controlling the operation of the piezoelectric actuator in the projection unit 300, .

The central control unit 500 includes a motor control board 510 for controlling the operation of the motor driver 410 and a piezoelectric actuator driving driver 421 for controlling the operation of the piezoelectric actuator driving driver 421, An etcher control board 521, and an image board 530 for processing images obtained from the camera 110. [

Fig. 7 is a result of showing the actual implemented system as a program. And to prove the usefulness of the present invention by detecting defects and showing their shapes.

Therefore, the measurement data 531 in FIG. 7 is the raw data measured by the present invention. By processing the original data, the defect check image 532 in the measurement data can be extracted. When the defect confirmation image is processed, a processing screen 533 is secured. The processing screen 533 is an example of measuring the window glass of a smartphone. The data coordinate value 534 indicates the position coordinate value of the data on the processing screen 533. [

As described above, in the present invention, it is possible to detect defects of fine objects by making it possible to perfectly adjust the projection magnification of the repeated grating pattern in generating dark field using only the projection grating and extracting defects, In addition, all the light rays passing through the LCD are incident along the optical axis of the light receiving unit, thereby effectively examining the light.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not to be limited to the details thereof, and various changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but are intended to illustrate and not limit the scope of the technical spirit of the present invention. The scope of protection of the present invention should be construed according to the claims, and all technical ideas which are within the scope of the same should be interpreted as being included in the scope of the present invention.

100:
110: camera
120: receiving optical system
210: object to be measured
220: Feed table
230: Driving means of the transfer table
300: Consular Section
310:
320: LCD panel
321: Lithography
330: BLU (backlight unit)
341: Piezoelectric actuator
400: Control module section
410: Motor Driver
420: LCD driver
421: Piezoelectric actuator driver
500:
510: Motor control board
520: LCD control board
521: Piezoelectric actuator control board
530: Video board

Claims (9)

A projection unit 300 for emitting light of a grid image to the measurement unit 200 to generate a dark field of the measurement object 210;
A measurement unit 200 for allowing the light emitted from the projection unit 300 to pass through the transparent object 210;
The measurement unit 200 receives the light that has passed through the measurement object 210 by the light receiving optical system 120 and acquires an image from the camera 110. The Z map which is darkness darkness information extracted from the acquired image An image obtaining unit (100) for detecting a defect of the measurement object (210) using the image data;
And a phase shift projection device for detecting a defect in the transparent body.
The method according to claim 1,
The projection unit 300,
A BLU 330 for emitting light;
An LCD panel 320 for generating a grid image using light of the BLU 330;
A projection optical system 310 for irradiating the measurement unit 200 with the grid image generated by the LCD panel 320;
And a phase shift projection device for detecting a defect in the transparent body.
The method according to claim 1,
The projection unit 300,
OLED or PDP and emits light of a grid image to the measuring unit 200. The phase shift projection apparatus for detecting defects of a transparent body according to claim 1,
The method according to claim 1,
The measuring unit 200 may measure,
A transfer table 220 on which the measurement object 210 is installed; Driving means (230) of a transfer table for driving the transfer table (220) to transfer the measurement object (210);
Wherein the phase shift projection device is configured to detect a defect in the transparent body.
The method according to claim 1,
A phase shift projection apparatus for detecting a defect in a transparent body,
A control module 400 for controlling operations of the projection unit 300 and the image acquisition unit 100;
A central control unit 500 for controlling the control module unit 400 and extracting defects of the measurement object 210 as a transparent chain using the Z map which is darkness darkness information generated by the image acquisition unit 100 );
And a phase shift projection device for detecting a defect in the transparent body.
The method of claim 5,
The control module 400,
A motor driver 410 for driving the driving unit 230 of the transfer table in the measuring unit 200;
An LCD driving driver 420 for controlling the operation of the projection unit 300;
And a phase shift projection device for detecting a defect in the transparent body.
The method of claim 5,
The central control unit (500)
A motor control board 510 for controlling the operation of the motor driver 410 in the control module unit 400;
An LCD control board 520 for controlling the operation of the LCD driving driver 420 in the control module unit 400 to realize a minute displacement of a diverging grid image;
An image board 530 for processing the image obtained from the camera 110 in the image acquiring unit 100;
And a phase shift projection device for detecting a defect in the transparent body.
A lithography 321 for producing a lattice image using the light of the BLU 330; a piezoelectric actuator 340 for micro-displacing the lithography 321; And a projection optical system 310 for allowing the generated grating image to be irradiated to the measurement unit 200. The grating image is emitted to the measurement unit 200 to generate a dark field of the measurement object 210 A projection unit 300 for projecting the image;
A measurement unit 200 for allowing the light emitted from the projection unit 300 to pass through the transparent object 210;
The measurement unit 200 receives the light that has passed through the measurement object 210 by the light receiving optical system 120 and acquires an image from the camera 110. The Z map which is darkness darkness information extracted from the acquired image An image obtaining unit (100) for detecting a defect of the measurement object (210) using the image data;
A motor driver 410 for driving the driving unit 230 of the transfer table in the measuring unit 200 and a piezoelectric actuator driving driver 421 for controlling the operation of the piezoelectric actuator 340 in the projection unit 300 A control module 400 for controlling operations of the projection unit 300 and the image acquisition unit 100;
A motor control board 510 for controlling the operation of the motor driver 410 and a piezoelectric actuator control board for controlling the operation of the piezoelectric actuator driving driver 421 so as to realize a minute displacement of a lattice image, And an image board 530 for processing the image obtained from the camera 110. The Z coordinate of the Z coordinate is calculated using the Z map which is darkness darkness information generated by the image obtaining unit 100, A central control unit 500 for extracting defects of the object 210;
And a phase shift projection device for detecting a defect in the transparent body.
A first step (ST1) for causing the projection unit (300) to irradiate the measurement object (210) in the measurement unit (200) with a projection grating;
A second step ST2 of acquiring an image from the camera 110 in the image acquisition unit 100 when the grating is transferred from the projection unit 300 to the measurement object 210 while finely moving the projection grating, Wow;
A third step (ST3) of receiving the moving image of the projection grating input to the camera 110 and receiving the moving image from the central control unit 500 and applying it to the dark field algorithm;
The central control unit 500 further includes a fourth step (ST4) of extracting a Z map from the image to which the ambiguity algorithm is applied in the third step;
A fifth step (ST5) of detecting a defect of the measurement object 210 using the extracted Z map;
And performing a phase shift projection operation for detecting a defect in the transparent body.

Images