TWI397683B - Optical inspection apparatus and optical inspection method - Google Patents

Description

Optical detecting device and optical detecting method

The present invention relates to optical inspection, and more particularly to an optical detection apparatus and an optical detection method for detecting a distribution of defects of a display panel.

In recent years, with the continuous development of technologies related to image display, various types of display devices different from conventional displays, such as liquid crystal displays and plasma displays, have appeared on the market. Among them, the popularity of products using liquid crystal display technology such as liquid crystal displays or liquid crystal televisions is the highest.

When the liquid crystal display produced by the factory is to be shipped, it is necessary to carry out product inspection by the inspectors. In general, most manufacturers have been improved by the traditional manual inspection method into automatic optical inspection (AOI) to detect the liquid crystal display panel. In order to detect all defects on the liquid crystal display panel, it is usually required to display a plurality of different screens in sequence by the liquid crystal display panel so that defects on the liquid crystal display panel can be revealed.

The automatic optical detection method currently used captures images of different screens by the liquid crystal display panel, and detects defects on the liquid crystal display panel by performing image processing on each of the captured images. However, in order to achieve a very accurate detection result to avoid the occurrence of certain defects not detected, it is necessary to perform a considerable number of image processing procedures. Since the number of images that need to be image processed is quite large, and the time taken by the automatic optical detection method to detect each liquid crystal display panel is lengthened, it will naturally have a negative impact on overall production efficiency and productivity.

Accordingly, it is a primary object of the present invention to provide an optical detecting device and an optical detecting method to solve the above problems.

A first embodiment according to the present invention is an optical detecting device. In fact, the optical detecting device is applied to the detection of the defect distribution of the display panel. In this embodiment, the optical detecting device includes an image capturing module and an image processing module. The image capture module is configured to capture a plurality of images displayed by the display panel at different times. The image processing module is coupled to the image capturing module, and is configured to generate a superimposed image according to the plurality of images and generate defect distribution information corresponding to the display panel according to the superimposed image.

A second embodiment of the present invention is an optical detection method. In this embodiment, the optical detection method is applied to the detection of the defect distribution of the display panel. The optical detection method comprises the steps of: (a) capturing a plurality of images displayed by the display panel at different times; (b) superimposing the plurality of images to generate a superimposed image; and (c) generating a superimposed image according to the superimposed image; The defect distribution information determines the defect distribution corresponding to the display panel based on the defect distribution information.

In summary, according to the optical detecting device and the optical detecting method of the present invention, since the image processing is performed by using the image superimposing method, it is possible to avoid the defect comparison of each of the images when the optical detecting panel is defective, and therefore, according to the present invention, The optical detecting device and the optical detecting method of the invention can greatly reduce the overall recognition time required for the optical detecting panel defect, and can also reduce the space for storing all captured images.

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

A first embodiment according to the present invention is an optical detecting device. In this embodiment, the optical detecting device is configured to detect the defect distribution of the display panel to ensure that the factory-displayed display panel can have excellent and reliable quality without defects such as bright spots. The display panel may be a liquid crystal display panel or other display device, but is not limited thereto. Please refer to FIG. 1 and FIG. 2 . FIG. 1 is a schematic diagram showing defect detection of the optical detection device for the display panel. FIG. 2 is a functional block diagram of the optical detection device.

As shown in FIG. 2 , the optical detecting device 1 includes an image capturing module 10 , an image processing module 12 , and a storage module 14 . The image processing module 12 is coupled to the image capturing module 10 and the storage module 14 is coupled to the image capturing module 10 and the image processing module 12 . Next, each module included in the optical detecting device 1 and its functions will be described in detail.

As shown in FIG. 1 , the image capturing module 10 of the optical detecting device 1 is configured to capture a plurality of images displayed by the display panel 2 at different times. In general, since optical inspection is performed on the display panel 2, it is necessary to cause the display panel 2 to display a plurality of different screens (i.e., display patterns), thereby judging whether the display panel 2 has defects and positions of defects. Therefore, each time the display panel 2 displays a different screen, the image capturing module 10 needs to capture the image when the display panel 2 displays the images, so as to facilitate subsequent steps of image processing and defect analysis.

In fact, the image capturing module 10 can be any device having an image capturing function, such as a camera or a camera. In addition, these different pictures (display styles) can be generated by randomly selecting from a picture (display style) database or by the user according to their habits or preferences, without limitation.

For example, when the optical detecting device 1 performs optical detection on the display panel 2, if the display panel 2 displays the first screen sequentially at the first time, the second time, the third time, the fourth time, and the fifth time, The image capturing module 10 of the optical detecting device 1 can respectively capture the display panel 2 to display the first time at the first time T1, five different screens, such as the second screen, the third screen, the fourth screen, and the fifth screen. The first image of the screen, the display panel 2 displays the second image of the second screen at the second time T2, the third image of the third screen is displayed by the display panel 2 at the third time T3, and the display panel 2 displays the fourth image at the fourth time T4. The fourth image of the four screens and the display panel 2 display the fifth image of the fifth screen at the fifth time T5.

In practical applications, since the display panel 2 includes a plurality of pixels, when the display panel 2 displays any one of the screens, each pixel of the display panel 2 corresponds to a gray-level value (gray-level value). ). In this embodiment, it is assumed that the display panel 2 includes six pixels arranged in a one-dimensional array, and the first pixel 21, the second pixel 22, the third pixel 23, the fourth pixel 24, and the fifth are respectively from left to right. The pixel 25 and the sixth pixel 26 are as shown in FIG. 3(A). In fact, the arrangement of the pixels of the display panel 2 can have various possibilities, and thus there is no limitation.

After the image capturing module 10 captures five images, such as the first image to the fifth image, the image processing module 12 generates a superimposed image according to the five images. Then, the image processing module 12 further generates defect distribution information corresponding to one of the display panels 2 according to the superimposed image. In fact, the defect distribution information is related to whether each pixel of the display panel 2 has a defect.

It is to be noted that, since the image processing module 12 of the optical detecting device 1 of the present invention performs image processing by means of image superimposition, it is possible to avoid defect defects of the conventional optical detecting display panel, and respectively perform defect ratios for each image. The time-consuming method can greatly reduce the overall recognition time required for optically detecting the defects of the display panel, and can also reduce the space for storing all captured images. Especially when the accuracy of the optical detection is strict, that is, the number of images that need to be processed by the image is large, the advantage of saving time and space of the invention is more obvious.

Next, the operation of the defect detection of the display panel 2 by the optical detecting device 1 will be described in detail through two different examples, so as to more clearly show how the image processing module 12 generates a superimposed image according to the captured image and performs subsequent steps. Image processing program.

First, in the first example, it is assumed that the display panel 2 is the first pixel 21, the second pixel 22, the third pixel 23, the fourth pixel 24, and the fifth pixel from left to right, as in FIG. 3(A). 25 and sixth pixel 26. Referring to FIG. 3(B), it is assumed that when the display panel 2 displays the first image to the fifth image, the grayscale values corresponding to the first pixel 21 to the sixth pixel 26 of the display panel 2 are as shown in FIG. 3(B). Show.

As shown in FIG. 3(B), in the first image captured by the image capturing module 10, the first pixel 21, the second pixel 22, the third pixel 23, the fourth pixel 24, and the fifth of the display panel 2 The gray scale values corresponding to the pixel 25 and the sixth pixel 26 are both 2. Similarly, in the third image, the gray scale values corresponding to the first pixel 21 to the sixth pixel 26 of the display panel 2 are all 7. In addition, in the fourth image, the gray scale values corresponding to the first pixel 21 to the sixth pixel 26 of the display panel 2 are all 4; in the fifth image, the first pixel 21 to the sixth pixel 26 of the display panel 2 The corresponding grayscale values are all 5.

The only difference is that in the second image, the grayscale values corresponding to the first pixel 21, the second pixel 22, the fourth pixel 24, the fifth pixel 25, and the sixth pixel 26 of the display panel 2 are all 3, but The grayscale value corresponding to the third pixel 23 is 6.

In this example, the image processing module 12 first adds the grayscale values corresponding to each pixel of the display panel 2 in different images in a summed manner to obtain the grayscale corresponding to each pixel respectively. Order value. In general, the superimposed grayscale values of each pixel have the same grayscale comparison value of most pixels, and the majority of the superimposed grayscale values can be regarded as normal, and different from the majority of the superimposed grayscale values. Pixel overlay grayscale values are considered abnormal. As shown in FIG. 3(B), the superimposed grayscale values of the first pixel 21, the second pixel 22, the fourth pixel 24, the fifth pixel 25, and the sixth pixel 26 are all 21; and the superimposed gray of the third pixel 23 The order value is 24, and the superimposed gray scale value of the other pixels is 21 below, and the superimposed gray scale value of the third pixel 23 is abnormal.

Then, the image processing module 12 will subtract the grayscale values of the adjacent pixels by subtracting the grayscale values of the adjacent pixels to generate grayscale comparison values corresponding to each pixel. As shown in FIG. 3(B), since the superimposed grayscale value 21 of the first pixel 21 minus the superimposed grayscale value 21 of the only adjacent second pixel 22 is exactly zero, it represents the gray corresponding to the first pixel 21. The order comparison value is zero.

For the second pixel 22, since the second pixel 22 has two adjacent pixels, respectively, the first pixel 21 and the third pixel 23, and the superimposed grayscale value 21 of the second pixel 22 is subtracted from the first pixel 21 The superimposed grayscale value 21 is just zero, and the superimposed grayscale value 21 of the second pixel 22 minus the superimposed grayscale value 24 of the third pixel 23 is -3, so the grayscale comparison value corresponding to the second pixel 22 is It is -3. Similarly, the grayscale comparison value corresponding to the third pixel 23 is 6; the grayscale comparison value corresponding to the fourth pixel 24 is -3; the grayscale comparison values corresponding to the fifth pixel 25 and the sixth pixel 26 are all zero.

Therefore, the image processing module 12 can determine whether each pixel has a defect according to whether the gray scale comparison value of the first pixel 21 to the sixth pixel 26 is abnormal, and generate defect distribution information according to the above judgment result for detection. Staff reference. In general, the grayscale comparison value of each pixel between the pixels has the same value of the grayscale comparison value of most pixels, and the majority of the grayscale comparison values can be regarded as normal, and different from the majority of the grayscale comparison values. Pixel grayscale comparison values are considered abnormal. In this example, the image processing module 12 can determine that the third pixel 23 is likely to have defects according to the grayscale comparison values of the second pixel 22, the third pixel 23, and the fourth pixel 24 that are abnormal. A further inspection procedure can be performed for the third pixel 23.

The above example describes a case where the same defect of the display panel 2 does not have bright or dark differences in different display images, that is, a pixel having defects and has an excessive abnormal gray scale value when displaying an image and It is shown that another image has an abnormally low grayscale value, but only an abnormally high grayscale value or only an abnormally low grayscale value.

In another example, the same defect of the display panel 2 has a difference in brightness and darkness in different display images, that is, the pixel having the defect has an excessive abnormal gray scale value when displaying an image and is displayed. Another image has a low abnormal grayscale value.

It is assumed that the display panel 2 is the first pixel 21, the second pixel 22, the third pixel 23, the fourth pixel 24, the fifth pixel 25, and the sixth pixel 26 from left to right as in the case of FIG. 3(A). Referring to FIG. 4(A), it is assumed that when the display panel 2 displays the first image to the fifth image, the grayscale values corresponding to the first pixel 21 to the sixth pixel 26 of the display panel 2 are as shown in FIG. 4(A). Show.

As shown in FIG. 4(A), in the first image captured by the image capturing module 10, the first pixel 21, the second pixel 22, the third pixel 23, the fourth pixel 24, and the fifth of the display panel 2 The gray scale values corresponding to the pixel 25 and the sixth pixel 26 are both 2. Similarly, in the fourth image, the first pixel 21 to the sixth pixel 26 of the display panel 2 have a grayscale value of 4; in the fifth image, the first pixel 21 to the sixth pixel of the display panel 2 The grayscale values corresponding to 26 are both 5.

It should be noted that, in the second image, the grayscale values corresponding to the first pixel 21, the second pixel 22, the fourth pixel 24, the fifth pixel 25, and the sixth pixel 26 of the display panel 2 are all 3, but The third pixel 23 corresponds to a grayscale value of 6; in the third image, the first pixel 21, the second pixel 22, the fourth pixel 24, the fifth pixel 25, and the sixth pixel 26 of the display panel 2 correspond to The grayscale values are all 7, but the grayscale value corresponding to the third pixel 23 is 4. That is to say, the grayscale value of the third pixel 23 has an abnormal grayscale value higher than that of the other pixels when the second image is displayed, but has an abnormal grayscale value lower than other pixels when the third image is displayed.

For this phenomenon, the image processing module 12 first squares the grayscale values corresponding to each pixel of the display panel 2 when displaying different images by squares, so as to obtain each pixel when displaying different images. The square value of the corresponding grayscale value is shown in Figure 4(B).

Then, the image processing module 12 adds the square values of the grayscale values corresponding to each pixel when displaying different images to obtain the superimposed grayscale value of each pixel. As shown in FIG. 4(B), the superimposed grayscale values of the first pixel 21, the second pixel 22, the fourth pixel 24, the fifth pixel 25, and the sixth pixel 26 are all 103; the superimposed grayscale of the third pixel 23 The value is 97.

Then, the image processing module 12 generates grayscale comparison values respectively corresponding to each pixel by subtracting the superimposed grayscale values of the adjacent pixels from the superimposed grayscale values of each pixel and then summing them. As shown in FIG. 4(B), since the superimposed grayscale value 103 of the first pixel 21 minus the superimposed grayscale value 103 of the only adjacent second pixel 22 is exactly zero, it represents the gray corresponding to the first pixel 21. The order comparison value is zero.

For the second pixel 22, since the second pixel 22 shares two adjacent pixels, respectively, the first pixel 21 and the third pixel 23, and the superimposed grayscale value 103 of the second pixel 22 is subtracted from the first pixel 21 The superimposed grayscale value 103 is just zero, and the superimposed grayscale value 103 of the second pixel 22 minus the superimposed grayscale value 97 of the third pixel 23 is 6, so the grayscale comparison value corresponding to the second pixel 22 is 6. Similarly, the grayscale comparison value corresponding to the third pixel 23 is -12; the grayscale comparison value corresponding to the fourth pixel 24 is 6; and the grayscale comparison value corresponding to the fifth pixel 25 and the sixth pixel 26 is obtained. Both are zero.

Therefore, the image processing module 12 can determine whether each pixel has a defect according to whether the gray scale comparison value of the first pixel 21 to the sixth pixel 26 is abnormal, and generate defect distribution information according to the above judgment result for detection. Staff reference. In this example, the image processing module 12 can determine that the third pixel 23 is likely to have defects according to the grayscale comparison values of the second pixel 22, the third pixel 23, and the fourth pixel 24 that are abnormal. Other inspection procedures can be further performed for the third pixel 23.

The storage module 14 is used to store all the images captured by the image capturing module 10, and is used to provide the image processing module 12 to read the images for subsequent image processing. In fact, the storage module 14 can be a memory, a hard disk or other storage device, without limitation.

A second embodiment in accordance with the present invention is an optical detection method. In this embodiment, the optical detection method is applied to the detection of the defect distribution of the display panel. In fact, the display panel may be a liquid crystal display panel, but is not limited thereto. Please refer to FIG. 5 , which is a flow chart showing the optical detection method.

As shown in FIG. 5, first, step S10 is executed to capture a plurality of images displayed by the display panel at different times. In general, in order to effectively detect all defects on the liquid crystal display panel, the method must display the display panel at different times to display a plurality of different screens (display styles) and capture the display panel display. The images of these pictures are used as the main basis for the defect judgment and analysis of the method.

In fact, these pictures (display styles) can be different and can be generated in a random manner or arbitrarily set by the user without limitation.

Then, step S12 is performed to superimpose the plurality of images captured in step S10 to generate a superimposed image. Then, step S14 is executed to generate defect distribution information corresponding to one of the display panels according to the superimposed image obtained in step S12, and determine a defect distribution corresponding to the display panel according to the defect distribution information. Through the steps S12 and S14, the method does not need to perform the image processing procedure for each image separately as in the conventional optical detection method, and the defect distribution information corresponding to the display panel can be smoothly generated, so that the method can effectively Reduce the overall image processing time and image storage space.

In an actual application, since the display panel includes a plurality of pixels, when the display panel displays one of the plurality of images, each of the plurality of pixels respectively corresponds to a grayscale value. The defect distribution information is related to whether each of the plurality of pixels has a defect.

In fact, the defect distribution information described above is generated by comparing a plurality of superimposed gray scale values corresponding to the plurality of pixels. As for the manner in which the method generates the plurality of superimposed grayscale values, there may be the following two types: In the first method, the method respectively respectively displays a plurality of grayscale values corresponding to each pixel in displaying the plurality of images. Adding the plurality of superimposed gray scale values. This method is more suitable for the same defect of the display panel when there is no difference between light and dark when displaying different display images, that is, the pixel with defects does not have excessive abnormal gray scale when displaying a certain image. The value (as compared to other grayscale values of the same image) and has too low anomalous grayscale values when displaying another image (compared to other grayscale values of the same image).

The second method is that if one of the plurality of pixels has an abnormally high grayscale value when displaying the first image in the plurality of images and has a low abnormal gray when displaying the second image The step value, the method will respectively square each of the plurality of grayscale values corresponding to each pixel when displaying the plurality of images, and then add the plurality of grayscale values to obtain the plurality of superimposed grayscale values. This method is more suitable for the same defect of the display panel. When displaying different display screens, there will be a difference between light and dark, that is, the defective pixel has an excessive abnormal gray scale value when displaying an image and is displayed. Another image has an abnormally low grayscale value.

As shown in FIG. 6 , after the method generates the superimposed grayscale value of each pixel, step S20 is performed, and the superimposed grayscale value corresponding to each pixel is respectively subtracted from the superimposed grayscale value corresponding to the adjacent pixel, and then added. In total, a plurality of grayscale comparison values corresponding to the plurality of pixels are generated. Next, step S22 is performed to compare the plurality of gray scale comparison values to generate the defect distribution information for reference by the detecting personnel. In general, the grayscale comparison value of each pixel between the pixels has the same value of the grayscale comparison value of most pixels, and the majority of the grayscale comparison values can be regarded as normal, and different from the majority of the grayscale comparison values. Pixel grayscale comparison values are considered abnormal. Therefore, in practical applications, step S22 may determine whether each of the plurality of pixels has a defect by comparing whether each of the plurality of gray scale comparison values is abnormal.

In summary, according to the optical detecting device and the optical detecting method of the present invention, since image processing is performed by using image superimposition, it is possible to avoid the defect comparison of each of the images when the optical detecting panel is defective, thereby greatly reducing the situation. The overall recognition time required for optical inspection panel defects also reduces the space for storing all images. Especially when the accuracy of the optical detection is strict, that is, the number of images that need to be processed by the image is large, the advantage of saving time and space of the invention is more obvious.

The features and spirit of the present invention will be more apparent from the detailed description of the preferred embodiments. On the contrary, the intention is to cover various modifications and equivalents within the scope of the invention as claimed.

S10~S22. . . Process step

1. . . Optical detection device

2. . . Display panel

10. . . Image capture module

12. . . Image processing module

14. . . Storage module

twenty one. . . First pixel

twenty two. . . Second pixel

twenty three. . . Third pixel

twenty four. . . Fourth pixel

25. . . Fifth pixel

26. . . Sixth pixel

1 is a schematic view showing the detection of a display panel by an optical detecting device according to a first embodiment of the present invention.

Figure 2 is a functional block diagram showing an optical detecting apparatus according to a first embodiment of the present invention.

Figure 3 (A) shows the pixels included in the display panel.

Figure 3 (B) shows an example of the defect distribution information generated by the image processing module.

FIG. 4(A) and FIG. 4(B) illustrate another example of the defect distribution information generated by the image processing module.

Figure 5 is a flow chart showing an optical detecting method according to a second embodiment of the present invention.

FIG. 6 is a detailed flow chart showing the defect detection information generated by the optical detection method according to the superimposed gray scale value of each pixel.

1. . . Optical detection device

10. . . Image capture module

12. . . Image processing module

14. . . Storage module

Claims (13)

An optical inspection apparatus for detecting a defect distribution of a display panel, the optical detecting apparatus comprising: an image capturing module for capturing the display panel a plurality of images displayed at different times; and an image processing module coupled to the image capturing module, the image processing module generating a superimposed image according to the plurality of images and generating corresponding to the superimposed image according to the superimposed image a defect distribution information of the display panel; wherein the display panel includes a plurality of pixels, and when the display panel displays one of the plurality of images, each of the plurality of pixels respectively corresponds to one a gray-level value, the image processing module respectively adds a plurality of grayscale values corresponding to each pixel in displaying the plurality of images to obtain a plurality of superimposed grayscales of the superimposed image. a value, and then subtracting the superimposed grayscale value corresponding to each pixel from the superimposed grayscale value of the adjacent pixel, respectively, to generate corresponding to the plurality of pixels a plurality of gray scale comparison values of the pixels, and comparing the plurality of gray scale comparison values to generate the defect distribution information, and a plurality of the plurality of superimposed gray scale values have an identical value. An optical detecting device is applied to the detection of a defect distribution of a display panel, the optical detecting device comprising: an image capturing module for capturing a plurality of images displayed by the display panel at different times; and an image The processing module is coupled to the image capturing module, and the image processing module Generating a superimposed image according to the plurality of images and generating defect distribution information corresponding to the display panel according to the superimposed image; wherein the display panel includes a plurality of pixels, when the display panel displays one of the plurality of images Each of the plurality of pixels corresponds to a grayscale value, and the image processing module respectively adds a square of the plurality of grayscale values corresponding to each pixel when displaying the plurality of images, After the plurality of squares of the superimposed image are obtained, the grayscale values are superimposed, and then the squared superimposed grayscale values of each pixel are respectively subtracted from the squares of the adjacent pixels and the grayscale values are superimposed to generate corresponding numbers. a plurality of gray scale comparison values of the pixels, and then comparing the plurality of gray scale comparison values to generate the defect distribution information, and a plurality of the plurality of squared superimposed gray scale values have an identical value. The optical detecting device of claim 1 or 2, wherein the plurality of images are generated according to a plurality of display patterns displayed on the display panel. The optical detecting device of claim 3, wherein all of the display patterns of the plurality of display patterns are different. The optical detecting device of claim 3, wherein the plurality of display patterns are generated in a random manner or are set by a user. The optical detection device of claim 1 or 2, further comprising: a storage module coupled to the image capture module and the image processing module for storing the image capture module Capture the multiple images and provide The image processing module reads. An optical inspection method for detecting a defect distribution of a display panel, the display panel includes a plurality of pixels, and when the display panel displays one of the plurality of images, the plurality of pixels Each of the pixels corresponds to a grayscale value, and the optical detection method includes the following steps: capturing a plurality of images displayed by the display panel at different times; respectively, respectively, corresponding to each pixel when displaying the plurality of images The plurality of grayscale values are squared and added to obtain a plurality of squared superimposed grayscale values of the superimposed image; respectively, the squared superimposed grayscale values of each pixel are respectively subtracted from the square of the adjacent pixels and then superimposed with grayscale And generating a plurality of grayscale comparison values corresponding to the plurality of pixels; and comparing the plurality of grayscale comparison values to generate the defect distribution information. The optical detection method of claim 7, wherein the squared superimposed grayscale value of each pixel is respectively subtracted from the square of the adjacent pixel and the grayscale value is superimposed, and correspondingly generated corresponding to the plurality of pixels The plurality of grayscale comparison values of the pixels include: adding the difference between the squared post-gradation grayscale value of each pixel not located at the boundary and the squared value of the adjacent two pixels, and adding the grayscale values, and A plurality of gray scale comparison values corresponding to the plurality of pixels are generated. An optical detection method is applied to the detection of a defect distribution of a display panel, the display panel includes a plurality of pixels, and when the display panel displays one of the plurality of images, each of the plurality of pixels is respectively Corresponding to a gray scale value, when the plurality of images are superimposed, a plurality of superimposed gray scale values are generated to correspond to the plurality of pixels, and the optical detecting method comprises the following steps: capturing a plurality of the display panels displayed at different times An image; superimposing the plurality of images to generate a superimposed image; respectively subtracting a superimposed grayscale value of each pixel from a superimposed grayscale value of the adjacent pixel, and generating a plurality of grayscales corresponding to the plurality of pixels accordingly Comparing the values; and comparing the plurality of grayscale comparison values to generate the defect distribution information. The optical detection method of claim 7 or 9, further comprising the display panel displaying a plurality of patterns to generate the plurality of images. The optical detection method of claim 10, wherein all of the plurality of patterns are different. The optical detection method of claim 10, further comprising generating the plurality of patterns in a random manner or by a user setting. The optical detecting method according to claim 9, wherein the superimposed grayscale value of each pixel is respectively subtracted from the superimposed grayscale value of the adjacent pixel, and Generating a plurality of grayscale comparison values corresponding to the plurality of pixels includes: adding the difference between the superimposed grayscale values of each pixel not located at the boundary and the superimposed grayscale values of the two adjacent pixels respectively And generating a plurality of grayscale comparison values corresponding to the plurality of pixels.