KR100829891B1 - Inspection Method for Liquid Crystal Panel and Image Processing Apparatus - Google Patents

Abstract

This invention provides the inspection method which can distinguish the foreign material adhering to the polarizing plate or diffuser plate of a test | inspection apparatus, and the defect of a liquid crystal panel in the method of test | inspecting the liquid crystal panel without a polarizing plate. A first photographing step of photographing the exit surface of the polarizing plate facing the photographing means by the photographing means while maintaining the alignment of the liquid crystal of the liquid crystal panel so that light from the light source passes through the pair of polarizing plates; A second photographing step of removing the liquid crystal panel from the polarizing plate, maintaining the polarization directions of the polarizing plates at right angles to each other, and photographing the exit surface of the polarizing plate facing the photographing means; A third photographing step of photographing the exit surface of the diffusion plate facing the photographing means by the photographing means with the polarizing plate removed and the light source turned on, and based on the images obtained by the photographing, An extraction step of extracting the defect site.

Polarizing plate, diffuser plate, liquid crystal panel, photographing device, foreign object, defect, image, inspection device

Description

Inspection Method for Liquid Crystal Panel and Image Processing Apparatus

1 is a pro chart showing the inspection method according to the present invention.

2 is a configuration diagram schematically showing an inspection apparatus for implementing the inspection method according to the present invention.

3 is a block diagram schematically showing the configuration of the image processing apparatus of the inspection apparatus according to the present invention.

4 is an explanatory diagram schematically showing a photographing state in the first photographing step of the inspection method according to the present invention.

FIG. 5 is a view similar to FIG. 4 schematically showing a photographing state in a second photographing step of the inspection method according to the present invention. FIG.

FIG. 6 is a view similar to FIG. 4 schematically showing a photographing state in a third photographing step of the inspection method according to the present invention.

7 is a schematic diagram illustrating an example of a third image obtained by the third imaging step.

Description of the main symbols in the drawings

10: inspection device 12: liquid crystal panel

14: light source 16: CCD camera (shooting means)

18: one polarizer 20: the other polarizer

22: light diffusion plate 24: image processing apparatus

26: image read processing sections 28a to 28c: first to third comparison sections

30: extraction unit

Field of invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting the presence or absence of defects in a liquid crystal panel and an image processing apparatus used for the inspection, and more particularly, to an inspection method for a liquid crystal panel without a polarizing plate and an image processing apparatus for the same.

Background of the Invention

As one of the defect inspection methods of a liquid crystal panel, the method of following patent document 1 is known.

[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-170495

According to the inspection method of patent document 1, the light from a backlight light source is irradiated to the back surface of the liquid crystal panel in which the polarizing plate was woven on both surfaces. The back display screen of the liquid crystal panel is picked up by the photographing means arranged on the side opposite to the side where the backlight light source is arranged while the liquid crystal panel displays the so-called white display screen by the backlight light irradiation.

If foreign matter such as dust exists inside the liquid crystal panel and the same foreign material adheres to the surface of the photographing means side of the liquid crystal panel, these foreign substances cause scattering of backlight light, but are themselves lower than the white display screen serving as a background. It appears as a luminance point (black point) on the white display screen.

If foreign matter exists inside the liquid crystal panel, it is regarded as a defect of the liquid crystal panel similarly to the defect of the pixels themselves of the liquid crystal panel. However, since foreign matter adhering to the surface of the liquid crystal panel can be easily removed from the liquid crystal panel by cleaning, it is necessary to distinguish between black spots caused by foreign matter adhering to the surface and black spots caused by defects in the liquid crystal panel.

Thus, a polarizing filter is further inserted between the liquid crystal panel into which the pair of polarizing plates are incorporated and the photographing means. The polarization filter is disposed in a direction perpendicular to the polarization direction of the polarizing plate whose polarization direction is incorporated on the surface of the display panel. In this state, the display panel is displayed in white, and the display screen is photographed through the polarization filter.

Since the polarization direction of the light passing through the polarizing plate incorporated on the surface of the display panel is perpendicular to the polarization direction of the polarization filter, the polarization component of the backlight light passing through the polarizing plate on the surface of the display panel passes through the polarization filter. I never do that. Therefore, the surface of the display panel photographed through the polarization filter newly inserted by the photographing means becomes a black display screen. However, if foreign matter adheres to the polarizing plate incorporated on the surface of the display panel, since the polarization component is scattered by the foreign matter, the scattered light passes through the polarization filter. On the other hand, the scattered light generated by the foreign matter inside the display panel is blocked by the polarizing plate and the polarizing filter which orthogonal to the polarization direction. Therefore, on the black display screen, the foreign material on the polarizing plate incorporated on the surface of the display panel is photographed with a point (white point) of luminance higher than that of the background.

Therefore, by comparing the two images, by removing the overlapping portion between the black spot and the white spot among the black spots on the white display screen as the foreign material image on the polarizing plate, the foreign material on the polarizing plate is a defect of the liquid crystal panel. Can be prevented.

However, when a light diffuser plate is generally inserted between the liquid crystal panel and the backlight light source to prevent luminance unevenness of the backlight light, and foreign matter adheres to the diffuser plate, the foreign material is observed as a black spot on the white display screen. do. In addition, the foreign matter adhering to the diffusion plate is not observed even in the black screen through the polarization filter. Therefore, in the said conventional method, when a diffusion plate is provided, the foreign material adhering to the said diffusion plate and the defect of the said liquid crystal panel cannot be distinguished.

In the inspection of the liquid crystal panel in which the polarizing plates are not incorporated on both surfaces of the liquid crystal panel, the white display screen as described above is photographed by the photographing means in a state where the polarizing plates are disposed on both surfaces of the liquid crystal panel, respectively. Of the above two polarizing plates, the foreign matter adhering to the back of the liquid crystal panel, that is, one polarizing plate disposed between the liquid crystal panel and the diffusion plate, is photographed as the same black spot as the defect on the white screen. In addition, since the foreign material is not photographed even on the black screen through the polarization filter inserted between the photographing means and the polarizing plate adjacent to the photographing means, the foreign material attached to the one polarizing plate and the defect of the liquid crystal panel cannot be identified.

In addition, it is preferable to perform defect inspection on the liquid crystal panel in a state in which these polarizing plates are not provided before attaching a pair of polarizing plates to the liquid crystal panel from the viewpoint of improvement of yield and resource saving.

SUMMARY OF THE INVENTION An object of the present invention is a method for inspecting a defect of a liquid crystal panel in which a polarizing plate is not provided, wherein the foreign matter attached to the polarizing plate or diffusion plate included in the inspection apparatus and the inspection method capable of identifying a defect of the liquid crystal panel and An image processing apparatus used for the inspection is provided.

The above and other objects of the present invention can be achieved by the present invention described below.

Summary of the Invention

In the inspection method according to the present invention, a pair of light sources and photographing means arranged at intervals to face each other, a pair that is arranged substantially parallel to each other between the light source and the photographing means and can maintain the polarization direction in a predetermined relationship A method for inspecting a defect of a liquid crystal panel in which a polarizing plate is not provided by using a tester equipped with a polarizing plate of the light source and a diffusion plate disposed between the light source and one of the polarizing plates arranged on the light source side, as described above. A first photographing step of photographing the exit surface of the other polarizing plate by the photographing means while maintaining the alignment of the liquid crystal of the liquid crystal panel disposed between the both polarizing plates so that light from the light source passes through the both polarizing plates; And the liquid crystal panel does not exist in the inspection apparatus, and the polarization directions of the polarizing plates are maintained at right angles to each other. A second photographing step of photographing the exit surface of the other polarizing plate with the light source turned on; and the light source being turned on without the liquid crystal panel and the other polarizing plate being present in the inspection apparatus; And a third photographing step of photographing the exit surface of the diffuser plate facing the photographing means by the photographing means, and an extraction step of extracting a defect portion of the liquid crystal panel based on the images obtained by the photographing steps. Characterized in that.

In the inspection method of the present invention, since the orientation of the liquid crystal of the liquid crystal panel is maintained so that light from the light source passes through the both polarizing plates, the first image obtained by the first photographing step is a so-called background having high luminance. It becomes the back screen. If foreign matter exists inside the liquid crystal panel, and foreign matter adheres to the one polarizing plate and the diffusion plate arranged on the light source side, the shadow by these foreign matters is lower than the luminance of the background on the white screen (black spot). Respectively).

In addition, since the liquid crystal panel is removed on the second image obtained by the second photographing step, information about the liquid crystal panel is not included, and on the surface facing the liquid crystal panel of the one polarizing plate disposed on the light source side. The adhered foreign matter is observed by the scattered light at a luminance point (white point) higher than the luminance of the background through the other polarizing plate. In addition, even if foreign matter adheres to the diffusion plate, since the shadow is observed through both polarizing plates, the shadow is indistinguishable from the background. Therefore, even if a foreign material existed on the said diffusion plate, for example, the shadow cannot be caught clearly. Therefore, on the 2nd image, if a foreign material adheres on the said one polarizing plate, only the white point by this foreign material will be observed in a low luminance background.

In addition, since the one polarizing plate is removed in addition to the liquid crystal panel, the third image obtained by the third imaging step is a so-called white screen having the same background as that of the first image. Therefore, in the third photographing step, since the light from the light source is photographed by the photographing means through the diffusion plate and the one polarizing plate, the foreign material attached to the diffusion plate or between the diffusion plate and the one polarizing plate. The shadows of the foreign objects present are observed as dark spots, each of which is lower than the luminance of the background.

Therefore, by removing the black spot at the position overlapping with the black spot on the second image and the black spot on the third image among the black spots on the first image, the remaining black spots are determined as defects in the liquid crystal panel itself, thereby deforming the defects of the liquid crystal panel and the one polarizing plate or diffusion. Foreign matter attached to the plate can be identified.

The extracting step includes a portion exceeding a predetermined brightness specified from a second image obtained by the second photographing step, and a portion not exceeding a predetermined brightness from the first image obtained by the first photographing step; It may include extracting a portion that does not overlap with a portion that does not exceed a specified brightness from the third image obtained by the third imaging step. It may be determined that the extraction region extracted in the extraction step is a defect of the liquid crystal panel.

When the liquid crystal panel is, for example, a TN type, in the first imaging step, for example, the deflection axes of the two polarizing plates are kept at right angles to each other, and the liquid crystal panel is in the state of giving a 90 degree twist to the alignment of the liquid crystal. It is arranged between the pair of polarizing plates. Thereby, in the state in which the deflection axes of the both polarizing plates are kept at right angles to each other, the both polarizing plates and the liquid crystal panel are combined so as to perform a so-called normally white operation. Therefore, in the first photographing step performed in this combination, an electric field is not applied to the liquid crystal of the liquid crystal panel, which is equivalent to a white display screen in a normally white display panel in which a pair of polarizing plates are incorporated. The first image is obtained.

In the first imaging step, the both polarizing plates and the liquid crystals can be combined so that they show a normally black type. In the normally black type, a white display screen is obtained in a state in which an electric field is applied to the liquid crystal of the liquid crystal panel. Therefore, in the combination of the normally black type | mold, the white screen in a 1st imaging | photography process is obtained in the state which provided the electric field to the liquid crystal of a liquid crystal panel.

An image processing apparatus according to the present invention includes a first comparison unit for comparing luminance information of each portion of the first image with a first threshold, and luminance information of each portion of the second image with a second threshold value. A second comparator for comparison, a third comparator for comparing luminance information of each part of the third image with a third threshold value, and positional information corresponding to output information from the first to third comparators; And a positional information which does not overlap with the positional information corresponding to the output information from the second and third comparison units from the positional information corresponding to the output information from the first comparing unit and the positional information for storing as a defective part. Characterized in that the determination unit.

According to the image processing apparatus according to the present invention, the inspection method according to the present invention can be efficiently performed. Each comparator and information processor of the image processing apparatus can be realized by program processing of a CPU of a computer.

Detailed description of the invention

1 shows a procedure of an inspection method according to the present invention, and FIGS. 2 and 3 show an inspection apparatus suitable for carrying out the inspection method of the present invention. Prior to the description of FIG. 1, the inspection apparatus 10 according to the present invention will be described with reference to FIGS.

The inspection apparatus 10 according to the present invention is used to inspect the presence or absence of a defect in the liquid crystal panel 12, as shown in FIG. Although the liquid crystal panel 12 is not shown in the prior art, as is well known, a liquid crystal is enclosed between a pair of glass plates in which, for example, a pair of glass plates face each other, for example, an alignment surface orthogonal to each alignment axis is formed. It is a liquid crystal panel body. The polarizing plate is not attached to both surfaces of the said liquid crystal panel main body. The liquid crystal panel 12 is, for example, a TN type liquid crystal panel. In the TN liquid crystal panel, as is well known in the art, the arrangement of liquid crystal molecules between a pair of alignment films in a state in which no voltage is applied between the pair of glass plates, and thus an electric field is not applied between the pair of alignment films. Is given a twist of 90 degrees. When the electric field is provided between the pair of alignment surfaces, the twist of the liquid crystal is eliminated.

The inspection apparatus 10 for inspecting the liquid crystal panel 12 in which the polarizing plate is not provided includes a light source 14 and a photographing means 16, a light source 14, and a photographing means 16 arranged at intervals from each other. A light diffuser plate 22 disposed between a pair of polarizing plates 18 and 20 disposed substantially parallel to each other with a mutual gap therebetween, and a light source 14 and one polarizing plate 18 disposed adjacent to the light source. )

The photographing means 16 is, for example, a CCD (charge coupled device) camera, and the photographing lens surface 16a is disposed to face the light emitting surface 14a of the light source 14. The CCD camera 16 is connected to an image processing device 24 for processing a captured image. The light source 14 is a conventionally well-known backlight light source for liquid crystals.

The pair of polarizing plates 18 and 20 are arranged with the polarization axes perpendicular to each other, whereby the combination of the pair of polarizing plates 18 and 20 with the liquid crystal panel 12 disposed therebetween is normal. ) As a liquid crystal panel assembly of a white type. The light diffusion plate 22 disposed between the one polarizing plate 18 and the light source 14 prevents luminance unevenness of the light source 14, as is well known in the art, and enables uniform backlight light irradiation.

As shown in Fig. 3, the image processing apparatus 24 scans an image received from the CCD camera 16, thereby generating the position data and the luminance data for each cell coordinate (x, y) of the scanning portion of the image. An image read processing section 26, first to third comparison sections 28a to 28c, an extraction section 30 for processing positional information based on output data from the comparison section, and a storage section 32 ) And a control unit 34 for controlling the operation of each unit.

In the storage unit 32, the data generated by the image read processing unit 26 is stored under the control of the control unit 34. In each of the first to third comparison units 28a to 28c, first to third threshold values for luminance are respectively set. The first to third comparison units 28a to 28c compare the luminance data obtained by the image read processing unit 26 with the respective first to third threshold values under the control of the control unit 34.

Under the control of the control unit 34, the first comparison unit 28a outputs the position data corresponding to the comparison data to the storage unit 32 when the luminance data to be compared does not exceed the first threshold. In addition, under the control of the control unit 34, the second comparison unit 28b outputs the position data corresponding to the comparison data to the storage unit 32 when the luminance data to be compared exceeds the second threshold. In addition, under the control of the control unit 34, the third comparison unit 28c outputs the position data corresponding to the comparison data to the storage unit 32 when the luminance data to be compared does not exceed the third threshold.

The extraction part 30 arithmetic-processes the said positional information obtained from the output information of each of the 1st-3rd comparison parts 28a-28c under the control of the control part 34. FIG. As a result of the arithmetic processing, the extraction unit 30 removes the positional information obtained by the second comparing unit 28b and the third comparing unit 28c from the positional information obtained by the first comparing unit 28a. , And outputs the remaining position information as the operation result.

The operation of each of the first to third comparison units 28a to 28c and the extraction unit 30 will be described according to the flow chart of Fig. 1 showing the procedure of the method of the present invention.

In the first photographing step S1 of the method of the present invention, as shown in FIG. 4, the light source 14 is turned on with the liquid crystal panel 12 held between the pair of polarizing plates 18 and 20. In the liquid crystal panel combinations 12, 18, and 20 which are irradiated with irradiated light whose luminance is uniform through the light diffusion plate 22 from the light source 14, a pair of polarizing plates 18 and 20 are perpendicular to their polarization axes. Since it is arrange | positioned so that it may become, it operates as a normally white type | mold. Therefore, when the liquid crystal panel 12 is observed through the other polarizing plate 20 located on the CCD camera 16 side without giving an electric field to the liquid crystal panel 12, the whole is observed as a white display with high luminance. Therefore, if the CCD camera 16 captures the emission surface 20a of the other polarizing plate 20, that is, the surface 20a that is close to the CCD camera 16 of the polarizing plate 20, the screen is displayed with a white display screen. do.

At this time, if foreign matter A such as dust exists in the liquid crystal panel 12, the scattered light is generated by the foreign matter, but the scattered light is extremely low compared to the luminance of the white display screen. Therefore, the foreign material A is observed as a shadow (black spot) lower than the luminance of the background on the background of the white display screen. In addition to the foreign material A, if the foreign material B adheres on the one surface 18a facing the liquid crystal panel 12 of the one polarizing plate 18, the foreign material B causes scattered light, but the brightness of the white display screen Since it is extremely low in comparison, like the foreign material A, the foreign material B is observed as the shadow (black spot). In addition, when the same foreign material C adheres to the one surface 22a facing the polarizing plate 18, for example, the light diffusion plate 22, the shadow of the said foreign material C is similarly observed as a black spot.

As a result, black spots of these foreign materials A to C appear on the white display screen picked up by the CCD camera 16 in the first photographing step S1. The brightness of the white display screen including these black spots is converted into data by the image read processing unit 26 together with the positional information. The luminance of the image data is compared with the first threshold value appropriately set by the first comparison unit 28a, whereby the positional information corresponding to the foreign materials A to C is extracted and stored in the storage unit 32.

In the second imaging step S2, the liquid crystal panel 12 is removed between the pair of polarizing plates 18 and 20, as shown in FIG. As a result, the irradiation light which passed through the light diffuser plate 22 from the light source 14 through the pair of polarizing plates 18 and 20 without the liquid crystal panel 12 between the pair of polarizing plates 18 and 20. This is captured by the CCD camera 16. Here, since the pair of polarizing plates 18 and 20 are arrange | positioned orthogonally to the deflection axis mutually, as mentioned above, the polarized light which permeate | transmitted one polarizing plate 18 does not transmit the other polarizing plate 20. As shown in FIG. Therefore, the image of the emission surface 20a of the other polarizing plate 20 picked up by the CCD camera 16 becomes a black display screen whose luminance is remarkably low throughout.

At this time, when the polarized light transmitted through the one polarizing plate 18 touches the foreign material B attached to the one side 18a, the polarized light is scattered, and thus the polarized light along the deflection axis of the other polarizing plate 20 of the scattered light is The polarization component passes through the other polarizing plate 20. This transmitted light shows a high luminance compared with the luminance of the black display screen, that is, the luminance of the background. Therefore, the foreign material B appears on the black display screen as a bright point (white point) having a higher luminance than the background. On the other hand, even in the foreign material C on the light diffuser plate 22, scattered light is generated, but the scattered light is polarized by passing through one polarizing plate 18, and since the polarized light is shielded by the other polarizing plate 20, the foreign material It is not observed as a bright spot like B, and is almost integrated with the background of the black display screen.

As a result, a white spot of only the foreign material B appears on the black display screen picked up by the CCD camera 16 in the second photographing step S2. The brightness of the black display screen including the white point is converted into data by the image read processing unit 26 together with the positional information. The luminance of the image data is compared with the second threshold value appropriately set by the second comparison unit 28b, whereby the positional information corresponding to the foreign material B is extracted and stored in the storage unit 32.

In the third imaging step S3, as shown in Fig. 6, in addition to the liquid crystal panel 12, the other polarizing plate 20 is also removed. As a result, the CCD camera 16 captures the light passing through the light diffusion plate 22 and the remaining polarizing plate 18 from the light source 14. At this time, the light passing through the remaining polarizing plate 18 becomes polarized light along the flat axis of the polarizing plate, and the polarized light is transmitted through the polarizing plate 18. Therefore, the emission surface 18a of the polarizing plate 18 picked up by the CCD camera 16 becomes a white display screen. In addition, since the scattered light of the foreign material B on one side 18a of the polarizing plate 18 is caught by the CCD camera 16 without passing through the other polarizing plate 20 that has been removed, it appears on the white display screen as a bright spot. Almost one.

On the other hand, the scattered light in the foreign material C on one surface on the light diffuser plate 22 is displayed as a shadow in the background of the white display screen because its luminance is reduced by passing through the remaining polarizing plate 18. As a result, in the third imaging step S3, only the shadow of the foreign material C appears as black spots on the white display screen captured by the CCD camera 16 as shown in FIG. The luminance of the white display screen including the black spot is dataized by the image read processing unit 26 together with its positional information. The luminance of the image data is compared with the third threshold value appropriately set by the third comparison unit 28c, whereby the positional information corresponding to the foreign material C is extracted and stored in the storage unit 32.

The deviation of the respective positional information due to the difference between the distance between the CCD camera 16 and the photographing surface in the first and second photographing steps S1 and S2 and the distance in the third photographing step S3 For example, it can correct programmatically by arithmetic processing.

In the fourth extraction step S4, the positions of the respective portions specified by the first to third images obtained in each of the first to third imaging steps S1 to S3, that is, the respective images of the white display screen and the black display screen. From the information, the extraction part 30 extracts the site | part by the defect A of the liquid crystal panel 12. FIG. For the extraction, the extraction unit 30 is under the control of the control unit 34, the portion specified by the position information for the foreign substance B among the portions specified by the position information about the foreign substance A stored in the storage unit 32 and The control unit 34 outputs the positional information of the portion that does not overlap with the portion specified as the positional information on the foreign material C. The control part 34 displays the extraction result of the extraction part 30 as a coordinate or an image on the display part like a display panel which is not shown in figure.

In the display result, only the defect A of the liquid crystal panel 12 which is the test object appears, and the foreign materials B and C of the polarizing plate 18 and the light diffuser plate 22 constituting a part of the inspection apparatus 10. Since the shadow of is removed, the real defect A of the liquid crystal panel 12 can be identified.

In the above description, the foreign material C was attached to one surface 22a on the light diffusion plate 22, but the other surface of the one polarizing plate 18, as indicated by the dotted line in FIG. Since foreign matter existing between the light emitting surface 14a of the light source 14 and 18b can be handled in the same manner as the foreign material C, the defect A of the liquid crystal panel 12 is the other side of the polarizing plate 18. It can identify from the foreign material which exists between the surface 18b and the light emitting surface 14a of the light source 14. As shown in FIG.

Moreover, in the 1st imaging | photography stage S1, the example which has arrange | positioned a pair of polarizing plates 18 and 20 so that the polarization axis may orthogonal to each other was shown. Instead, the pair of polarizing plates 18 and 20 can be arranged so that their polarization axes are parallel to each other. In this case, the pair of polarizing plates 18 and 20 arranged in parallel with each other and the liquid crystal panel 12 arranged therebetween function as a so-called normally black liquid crystal. Therefore, in the first photographing step S1, the emission surface 20a of the polarizing plate 20 is photographed by the CCD camera 16 while the electric field is applied to the liquid crystal panel 12. The same first image is obtained.

In the first imaging step S1, when a pair of polarizing plates 18, 20 having polarization axes arranged in parallel with each other is used, in the second imaging step S2, both polarizing plates 18, 20 have their polarization axes. It is arranged to face at right angles to each other.

In addition, in the first photographing step S1, when the first image of the back display screen is obtained while functioning as a normally black liquid crystal and applying an electric field to the liquid crystal panel 12, the back display screen includes a liquid crystal panel. In addition to the defects caused by the foreign material A in (12), since black defects due to malfunction of the cell itself of the liquid crystal panel are detected as black spots in the first image, the black defects also serve as defects of the liquid crystal panel 12 itself. Can be detected.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit thereof. For example, as long as the first to third imaging steps S1 to S3 are performed before the extraction step S4, there is no problem even if the mutual order between the steps S1 to S3 is before and after.

According to the inspection method of the present invention, it is possible to identify defects in the liquid crystal panel and foreign matters attached to one of the polarizing plates or diffusion plates of the inspection apparatus from the images obtained by each photographing step, and to misjudge these foreign objects as defects. It can certainly be prevented.

Moreover, according to the said apparatus of this invention, the said inspection method of this invention can be implemented efficiently.

Simple modifications and variations of the present invention can be readily used by those skilled in the art, and all such variations or modifications can be considered to be included within the scope of the present invention.

Claims (5)

Light sources and photographing means disposed at intervals to face each other; A pair of polarizing plates arranged substantially parallel to each other between the light source and the photographing means and capable of maintaining a polarization direction in a specific relationship; In the method of inspecting the defect for the liquid crystal panel in which the polarizing plate is not provided using the inspection apparatus provided with the said light source and the diffuser plate arrange | positioned between the said one polarizing plate arrange | positioned at the light source side, First photographing for photographing the exit surface of the other polarizing plate by the photographing means while maintaining the alignment of the liquid crystal of the liquid crystal panel disposed between the both polarizing plates so that light from the light source passes through the both polarizing plates. step; A second photographing step of photographing the exit surface of the other polarizing plate in a state in which the liquid crystal panel is not present in the inspection apparatus, and maintaining the polarization directions of the two polarizing plates at right angles to each other and lighting the light source; ; A third photographing step of photographing the exit surface of the diffuser plate facing the photographing means by the photographing means while the liquid crystal panel and the other polarizing plate are not present in the inspection apparatus and the light source is turned on; And An extraction step of extracting a defective portion of the liquid crystal panel based on the images obtained by the respective imaging steps; Inspection method of the liquid crystal panel comprising a. The predetermined step according to claim 1, wherein the extracting step includes a predetermined part specified from the second image obtained by the second photographing step among the portions not exceeding a predetermined brightness specified from the first image obtained by the first photographing step. Extracting a portion which does not overlap with a portion not exceeding the specified predetermined brightness from the portion exceeding the luminance and the third image obtained by the third photographing step, and determining that the extraction portion is a defect. Inspection method of liquid crystal panel. The liquid crystal panel of claim 1, wherein in the first photographing step, the liquid crystal panel is combined with the pair of polarizing plates in a normally white type, and the pair of liquid crystal panels is not provided with an electric field. Inspection method of a liquid crystal panel, characterized in that disposed between the polarizing plate. The pair of polarizing plates of claim 1, wherein in the first photographing step, the liquid crystal panel is combined with the pair of polarizing plates in a normally black type, and an electric field is applied to the liquid crystal of the liquid crystal panel. Inspection method of a liquid crystal panel, characterized in that disposed between. An image processing apparatus for use in the method of claim 1, comprising: a first comparison section for comparing luminance information of each portion of the first image with a first threshold value; A second comparing unit which compares luminance information of each part of the second image with a second threshold value; A third comparing unit which compares luminance information of each part of the third image with a third threshold value; A storage unit for storing positional information corresponding to output information from the first to third comparison units; And an extraction unit for outputting, as a defective portion, position information corresponding to output information from the second and third comparison units from position information corresponding to the output information from the first comparing unit. An image processing apparatus.

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