KR20210105185A - Method for inspecting smudged defect - Google Patents

Abstract

A mura defect inspection method according to example embodiments acquires an inspection image including a mura region from an object to be inspected, calculates the difference between a representative RGB value of the mura region and a representative RGB value of a neighboring region of the mura region, and derives the mura intensity by dividing the difference between the representative RGB values by a representative brightness value of the inspection image. Therefore, the mura defect inspection method can effectively inspect the presence and intensity of mura defects.

Description

METHOD FOR INSPECTING SMUDGED DEFECT

The present invention relates to a stain defect inspection method.

A polarizing film used in various image display devices generally includes a polarizer and a polarizer protective film in which an iodine-based compound or a dichroic polarizing material is adsorbed and oriented on a polyvinyl alcohol (PVA) film.

Since such a polarizing plate is an optical element that converts unpolarized or randomly polarized natural light into linearly polarized light, if two polarizing plates are placed in an orthogonal state, light cannot pass through them during normal backlight light irradiation, resulting in a dark state.

However, in the case of some polarizing plates, even when two sheets are placed in an orthogonal state, 100% of the light is not blocked and a stripe-shaped stain is observed in the stretching direction. This is because the transmittance for each position of the polarizing plate is not uniform as a whole, and is due to uneven dyeing of dyes, poor adhesion, uneven stretching, and the like.

In the case where the unevenness is severe, it is difficult to implement an image of uniform luminance as a whole, resulting in defective final products. Therefore, there is a need for a method capable of accurately selecting the stain strength of a polarizing plate.

The conventional stain inspection of a polarizing plate is made by visual observation of an inspector.

For example, when two polarizing plates are placed in an orthogonal state and the backlight light is irradiated and observed, when both of the two polarizing plates are normal polarizing plates without non-uniformity, the backlight light does not pass through and the state is completely dark. Otherwise, when irradiated with light and observed, it is possible to confirm a stripe-shaped stain in the stretching direction.

Such an inspection method has a problem in that it is difficult to produce a product of uniform quality because the degree of product defect is determined according to the subjectivity of the inspector. In addition, when the proficiency of the inspector is low, inspection efficiency may decrease and a false inspection rate may increase.

For example, Korean Patent Laid-Open Publication No. 10-2015-0085398 discloses a stain inspection method of a polarizing plate that determines a stain when the difference between the luminance of transmitted light for each part and the reference luminance is a predetermined value or more. In some cases, there is a problem in that there is a difference between the visual inspection result and the result.

Korean Patent Publication No. 10-2015-0085398

One object of the present invention is to provide a stain defect inspection method having excellent inspection performance.

1. Acquiring an examination image including a speckle region from an examination object; calculating a difference between a representative RGB value of the speckle region and a representative RGB value of an adjacent region of the speckle region; and dividing the difference between the representative RGB values by the representative brightness value of the inspection image to derive the speckle intensity.

2. The method according to 1 above, wherein the representative RGB value of the speckle region includes the average RGB value of the speckle region, and the representative RGB value of the adjacent region includes the average RGB value of the neighboring region. .

3. The method according to 1 above, wherein the representative brightness value of the inspection image includes an average gray scale of the entire region of the inspection image.

4. The method according to 1 above, wherein the difference in the representative RGB values is a root sum square reflecting respective increasing/decreasing directions between the R values, G values, and B values of the blob region and the adjacent region. .

5. In the above 1, the difference between the representative RGB values satisfies the following Equation (1):

[Equation 1]

(In Equation 1, R ₁ , G _{1 ,} and B ₁ are representative RGB values of a speckle region, and R ₂ , G _{2 ,} and B ₂ are representative RGB values of an adjacent region).

6. The method of inspecting a spot defect according to the above 1, wherein the spot area and the adjacent area are alternately repeated in a width direction of the object to be inspected.

7. The method according to 1 above, further comprising the step of deriving a rate of change of the blob intensity by dividing the blob intensity by a distance between the blob area and the adjacent area.

8. The method of 1 above, wherein the acquiring of the inspection image comprises disposing an upper polarizing plate and a lower polarizing plate on the upper and lower portions of the inspection object, respectively, and irradiating light to pass through the upper polarizing plate, the inspection object, and the lower polarizing plate A method for inspecting stain defects, comprising:

9. The method of 8 above, wherein the inspection object, the upper polarizing plate, and the lower polarizing plate are arranged in parallel.

10. The method according to 9 above, wherein the inspection image is obtained by a light source and a photographing device disposed perpendicular to the inspection object, the upper polarizing plate, and the lower polarizing plate.

11. The method of 1 above, wherein the inspection object includes a polarizing film.

According to exemplary embodiments of the present invention, the blob intensity may be derived by dividing the difference between the representative RGB values of the blob region and the adjacent region by the representative brightness value of the inspection image. In this case, the inspection result through the inspection device may be synchronized with the visual inspection result. Therefore, it is possible to automate the speckle defect inspection and improve the speckle defect detection performance.

1 is a schematic flowchart illustrating a method for inspecting spot defects according to exemplary embodiments of the present invention.
2 is a schematic side view illustrating an apparatus for inspecting spot defects according to exemplary embodiments.
3 is an examination image including a speckle area and an adjacent area obtained according to example embodiments.

Exemplary embodiments of the present invention provide a smear defect inspection method for deriving a speckle intensity by dividing a difference between representative RGB values of a speckle region and an adjacent region of an inspection image by a representative brightness value of the inspection image. The presence and intensity of stain defects can be effectively inspected.

Hereinafter, embodiments of the present invention will be described in detail. However, this is merely exemplary and the present invention is not limited to the specific embodiments described by way of example.

1 is a schematic flowchart illustrating a method for inspecting spot defects according to exemplary embodiments of the present invention.

Referring to FIG. 1 , an examination image including a speckle region may be obtained from an examination object (eg, step S10 ).

The test object may be a film that transmits a predetermined amount of light. For example, the test object may be a polarizing film.

The test object may have, for example, a speckle defect. The spot defect may include a portion in which a color such as brightness is observed non-uniformly when the inspection object is observed. For example, when the object to be inspected is a polarizing plate, non-uniformity applied to a manufacturing process such as stretching and dyeing may cause the stain defect.

For example, the inspection image may be acquired by the speckle defect inspection apparatus illustrated in FIG. 2 .

2 is a schematic side view illustrating an apparatus for inspecting spot defects according to exemplary embodiments.

Referring to FIG. 2 , the speckle defect inspection apparatus 10 may include a light source 100 , a lower polarizing plate 110 , an upper polarizing plate 130 , an imaging unit 140 , and a processing unit 150 . The object 120 may be disposed between the lower polarizing plate 110 and the upper polarizing plate 130 .

The light source 100 may irradiate light to the lower polarizing plate 110 . The light may pass through the lower polarizing plate 110 , the inspection object 120 , and the upper polarizing plate 130 to be obtained by the imaging unit 140 .

The light source 100 may include a metal halide lamp, an LED lamp, and the like. The light source 100 may have a bar shape. The bar shape may have a length greater than or equal to the width of the test object 120 .

The lower polarizing plate 110 and the upper polarizing plate 130 may be disposed parallel to each other. The test object 120 may be disposed parallel to the lower polarizing plate 110 and the upper polarizing plate 130 .

For example, the polarization axis of the lower polarizing plate 110 and the polarization axis of the upper polarizing plate 130 may be parallel to each other. The inspection may be performed by disposing the polarization axes of the object 120 to be orthogonal to each other between the upper and lower polarizing plates 110 and 130 having polarization axes parallel to each other.

In some embodiments, the polarization axis of the lower polarizing plate 110 and the polarization axis of the upper polarizing plate 130 may form an angle of about 1 to 5 degrees in parallel. In this case, the amount of light of the inspection image may increase. The polarization axis of the object 120 may be disposed orthogonal to one of the polarization axis of the lower polarizing plate 110 and the polarization axis of the upper polarizing plate 130 .

When there is no speckle defect in the inspection object 120 , the imaging unit 140 may acquire a dark image. When a speckle defect exists in the inspection object 120 , an inspection image including a speckle region corresponding to the speckle defect may be acquired by the imaging unit 140 by scattering, diffraction, or the like of light.

As shown in FIG. 2 , the object 120 may be disposed between the lower polarizing plate 110 and the upper polarizing plate 130 .

The imaging unit 140 may acquire an inspection image by obtaining light that has passed through the lower polarizing plate 110 , the inspection object 120 , and the upper polarizing plate 130 . The imaging unit 140 may include a line scan camera. Preferably, the imaging unit 140 may include a color line scan camera. In this case, the contrast between the spot area and the adjacent area may be emphasized.

The processing unit 150 may perform arithmetic processing, which will be described later, based on the inspection image obtained by the imaging unit 140 . The processing unit 150 may determine the presence and/or strength of a spot defect of the object to be inspected based on the calculation processing.

In example embodiments, the light source 100 and the imaging unit 140 may be disposed to face each other with the lower polarizing plate 110 and the upper polarizing plate 130 interposed therebetween. For example, the light source 100 and the imaging unit 140 may be disposed on a vertical extension line of the lower polarizing plate 110 and the upper polarizing plate 130 .

3 is an examination image including a speckle area and an adjacent area obtained according to example embodiments.

Referring to FIG. 3 , the inspection image may include a speckle area SA and an adjacent area AA.

The spot area SA may be an area corresponding to the spot defect of the object 120 . An area adjacent to the speckle area SA in the inspection image may be defined as an adjacent area AA.

The speckle area SA may have a higher or lower brightness than the background of the inspection image. For example, in FIG. 3 , the brightness of the speckle area SA is lower than that of the background (eg, the adjacent area AA).

The stain area SA may extend, for example, in the longitudinal direction of the object 120 . In example embodiments, the stain area SA may be repeatedly formed in the width direction of the object 120 .

In example embodiments, the stain area SA and the adjacent area AA may be alternately repeated in the width direction of the object 120 .

A difference between the representative RGB value of the spot region and the representative RGB value of the adjacent region may be calculated (eg, step S20 ).

The representative RGB value of the speckle region may include an average RGB value of the speckle region. The representative RGB value of the adjacent area may include an average RGB value of the adjacent area.

In example embodiments, the difference between the representative RGB values may be calculated as a root sum square that reflects the increasing/decreasing directions of the R values, G values, and B values of the blob region and the adjacent region, respectively.

For example, the representative RGB value difference may be calculated through Equation 1 below.

[Equation 1]

In Equation 1, R ₁ , G _{1 ,} and B ₁ may be representative RGB values of the speckle region, and R ₂ , G _{2 ,} and B ₂ may be representative RGB values of the adjacent region.

In Equation 1, Equation 2 below may reflect the increase/decrease trend of the R value of the speckle region and the R value of the adjacent region.

[Equation 2]

For example, by reflecting the increase/decrease tendency of each of the R value, G value, and B value in the root of the sum of squares, the calculated RGB value difference can be made similar to the difference at the time of visual inspection.

The speckle intensity may be derived by dividing the difference between the representative RGB values by the representative brightness value of the inspection image (eg, step S30 ).

The brightness value may be expressed in grayscale. The gray scale may include, for example, a brightness value expressed as a number from 0 to 255.

The representative brightness value of the examination object may be represented as an average gray scale of each point (eg, pixels) of the entire area of the examination image. When the difference in the representative RGB values is divided by the representative brightness value, a color difference between the speckle region and the adjacent region can be derived based on the overall brightness of the inspection image. The color difference is provided as the intensity of the speckle defect can be

In general, due to optical illusions during visual observation, even a speckle defect having the same intensity may be observed to have different intensity depending on ambient brightness. In addition, when the surrounding is bright, even a spot defect of strong intensity is observed with a weak intensity.

The RGB value difference that does not reflect the overall brightness of the inspection image does not reflect the intensity observed during the above-described visual inspection. However, when the difference between the representative RGB values is divided by the representative brightness values of the inspection image, the blob intensity calculated and determined by the processing unit 150 and the blob intensity observed with the naked eye may be substantially similar. Accordingly, the speckle defect can be inspected substantially accurately by the automated inspection method.

For example, when the spot intensity is equal to or greater than a target value, the inspection object including the spot defect corresponding to the spot area may be determined to be defective. In addition, when the stain intensity is less than the target value and is not substantially visually recognized when observed with the naked eye, the inspection object including the stain defect corresponding to the stain area may be determined as normal.

In example embodiments, the blob intensity change rate may be derived by dividing the speckle intensity by a distance between the speckle area and the adjacent area (eg, in step S40 ).

Accordingly, the speckle intensity change rate may be defined as the speckle intensity change amount per unit distance. From the amount of change in stain intensity per unit distance, it is possible to determine the stain intensity for each area of the object 120 and the area in which the stain is concentrated.

For example, when the spot intensity change rate is equal to or greater than a target value, an inspection object including a spot defect corresponding to the spot area may be determined to be defective. In addition, when the stain intensity change rate is less than the target value and is not substantially visually observed, the inspection object including the stain defect corresponding to the stain area may be determined as normal.

The smear defect inspection method according to the exemplary embodiments may automate the smear defect inspection of the polarizing plate, which has traditionally relied on visual observation, through an inspection apparatus. Accordingly, it is possible to improve the inspection quality deviation according to the inspector, the inspection consistency, and the inspection efficiency. In addition, the performance of automated blob inspection can be improved to a level similar to that of visual inspection.

10: stain strength test device
100: light source 110: lower polarizing plate
120: test object 130: upper polarizing plate
140: imaging unit 150: processing unit

Claims (11)

obtaining an examination image including a speckle area from the examination object;
calculating a difference between a representative RGB value of the speckle region and a representative RGB value of an adjacent region of the speckle region; and
and deriving a stain intensity by dividing a difference between the representative RGB values by a representative brightness value of the inspection image.
The method according to claim 1, wherein the representative RGB value of the speckle region includes an average RGB value of the speckle region, and the representative RGB value of the adjacent region includes the average RGB value of the neighboring region.
The method of claim 1 , wherein the representative brightness value of the inspection image includes an average grayscale of an entire area of the inspection image.
The method according to claim 1, wherein the difference in the representative RGB values is a root sum square reflecting respective increasing/decreasing directions between R values, G values, and B values of the blob region and the adjacent region.
The method according to claim 1, wherein the representative RGB value difference satisfies Equation 1 below:
[Equation 1]

(In Equation 1, R ₁ , G _{1 ,} and B ₁ are representative RGB values of a speckle region, and R ₂ , G _{2 ,} and B ₂ are representative RGB values of an adjacent region).
The method of claim 1 , wherein the spot region and the adjacent region are alternately repeated in a width direction of the object to be inspected.
The method according to claim 1, further comprising the step of dividing the blob intensity by a distance between the blob area and the adjacent area to derive a rate of change of the blob intensity.
The method according to claim 1, wherein the obtaining of the inspection image comprises disposing an upper polarizing plate and a lower polarizing plate on the upper and lower portions of the inspection object, respectively, and irradiating light to pass through the upper polarizing plate, the inspection object, and the lower polarizing plate How to check for stain defects.
The method of claim 8 , wherein the inspection object, the upper polarizing plate, and the lower polarizing plate are disposed in parallel.
The method of claim 9 , wherein the inspection image is acquired by a light source and a photographing device disposed perpendicular to the inspection object, the upper polarizing plate, and the lower polarizing plate.
The method according to claim 1, wherein the inspection object comprises a polarizing film.

Images