KR20210105174A - Method of inspecting intensity of smudge - Google Patents

Abstract

A smear intensity inspection method according to exemplary embodiments generates an inspection graph including brightness data along a first direction from an inspection image obtained from an inspection object. A brightness reference line reflecting the color change tendency of the inspection object itself is set on the inspection graph. The inspection graph is divided into an upper region and a lower region based on the brightness reference line. The smear intensity is determined by comparing the adjacent upper and lower regions of the inspection graph. The intensity of the smear defect can be inspected with an automated device.

Description

METHOD OF INSPECTING INTENSITY OF SMUDGE

The present invention relates to a stain strength test method. More particularly, it relates to a stain intensity inspection method using an image processing technique.

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 strength inspection method having excellent inspection performance.

1. Generating an examination graph including brightness data in a first direction from an examination image obtained from an examination object; setting a brightness baseline reflecting a color change tendency of the test object itself on the test graph; dividing the inspection graph into an upper region and a lower region based on the brightness reference line; and determining a spot intensity by comparing the adjacent upper region and the lower region of the inspection graph.

2. The method according to 1 above, wherein in the color change tendency, brightness and saturation decrease from a central portion of the object to an outer portion in the first direction.

3. The method of 1 above, wherein generating the inspection graph comprises compressing the brightness data of the inspection image in a second direction perpendicular to the first direction.

4. The method according to 1 above, wherein the generating of the inspection graph includes expanding a lightness range of the lightness data.

5. The method of 1 above, wherein the upper region and the lower region each include a plurality of unit upper regions and unit lower regions, and the step of dividing the upper region and the lower region into the unit upper regions or the unit lower regions and merging adjacent ones of the regions.

6. The stain strength inspection method according to 1 above, wherein the stain strength is determined based on the area of the upper region and the area of the lower region.

7. The method according to 1 above, wherein the stain strength is determined by comparing the highest point of the upper region and the lowest point of the lower region based on the brightness reference line.

8. The method according to 1 above, further comprising converting the inspection graph into a standardized inspection graph by standardizing the inspection graph based on the lightness baseline before dividing the region into the upper region and the lower region.

9. The method of 1 above, wherein the object to be inspected includes spot defects extending in a second direction perpendicular to the first direction and repeatedly arranged along the first direction.

10. 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 testing stain strength, comprising:

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

According to exemplary embodiments of the present disclosure, the intensity of the stain may be determined by setting a brightness reference line reflecting the color change tendency of the examination object itself on the examination graph and comparing the upper area and the lower area based on the brightness reference line. Therefore, it is possible to examine the intensity of the stain due to the defect except for the effect of the stain on the test object itself.

Also, it is possible to effectively inspect the presence and intensity of spots by compressing the brightness data of the inspection image in the second direction or by expanding the brightness range of the brightness data.

1 is a schematic flowchart illustrating a stain strength inspection method according to exemplary embodiments of the present invention.
2 is a schematic side view illustrating an apparatus for inspecting stain strength according to exemplary embodiments.
3 is an examination image obtained according to example embodiments.
4 is an examination graph in which a brightness baseline is set, according to example embodiments.
5 is a schematic flowchart illustrating a stain strength inspection method according to example embodiments.
6 is a standardized examination graph according to exemplary embodiments.

Exemplary embodiments of the present disclosure include generating an examination graph including brightness data along a first direction from an examination image, setting a brightness reference line reflecting the color change tendency of the examination object itself, and setting the examination graph as the brightness reference line There is provided a stain strength inspection method, comprising: dividing an upper region and a lower region based on The intensity of the speckle defect can be inspected with an automated device.

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.

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 graph including brightness data along a first direction may be generated from an examination image 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.

For example, the first direction may mean a direction perpendicular to the polarization axis of the polarizing film. For example, in the manufacturing process of the polarizing film, a traverse direction (TD) direction may be defined as the first direction. A machine direction (MD) perpendicular to the first direction and parallel to the polarization axis may be defined as a second direction.

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 determining 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 determination unit 150 may perform image processing, which will be described later, based on the examination image obtained by the imaging unit 140 . The determination unit 150 may determine the presence and intensity of a speckle defect of the test object based on the image 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 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 spot area SA may extend in the second direction, for example. In example embodiments, the stain area SA may be repeatedly formed in the first direction of the object 120 .

In example embodiments, the smear area SA and the adjacent area AA may be alternately repeated with respect to the first direction of the object 120 .

An examination graph may be generated by graphing a brightness value according to a position in the first direction from a specific point on the y-axis (the second direction) of the examination image.

In example embodiments, the brightness value of each point (eg, pixel) of the examination image may be compressed along the second direction. The compression may include simply accumulating the brightness values or deriving an average of the brightness values. In this case, it is possible to obtain a compressed brightness value for the position in the first direction. Accordingly, it is possible to increase the contrast of the brightness values in the first direction. The inspection graph may be generated using the compressed brightness value.

In example embodiments, the brightness range of the brightness data may be extended. For example, the extension of the brightness range may be performed by histogram equalization.

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

For example, when the original lightness range of the lightness data is grayscale, and the lower limit is greater than 0 and the upper limit is less than 255, the original lightness range may be changed to a more extended range within 0 to 255 grayscale. In this case, the brightness value of the original brightness data may be changed according to ratios of the upper and lower limits of the original brightness data and the upper and lower limits of the extended brightness data. In this case, it is possible to additionally increase the contrast of the brightness values, and the stain can be easily inspected.

A brightness reference line reflecting the color change tendency of the test object itself may be set on the test graph (eg, step S20 ).

The test object may have a tendency to change color by itself. For example, brightness and chroma of the object to be examined may decrease from a central portion toward an outer portion in the first direction. For example, when the test object is a polarizing plate, the color change tendency may inevitably occur in the stretching process. The color change tendency alone may not substantially affect the performance of the test subject.

However, when the color change tendency of the test object overlaps with the spot defect, the intensity of the spot defect may be numerically determined to be greater than the actual intensity. Therefore, a product that is normal during a visual inspection may be determined to be defective.

In example embodiments, the defect determination rate may be reduced by introducing the own color change tendency as the brightness reference line in the inspection method.

4 is an examination graph in which a brightness baseline is set, according to example embodiments.

Referring to FIG. 4 , the inspection graph may include a brightness reference line 200 .

In the inspection graph, an area above the brightness reference line 200 may be divided into an upper area 210 , and an area below the brightness reference line 200 may be divided into a lower area 220 (eg, step S30).

The brightness reference line 200 may indicate a tendency of a color change of an object to be examined in which there is substantially no speckle defect. The speckle defect may be detected by comparing the brightness values for positions in the first direction with respect to the brightness reference line 200 .

The stain intensity may be determined by comparing the adjacent upper region 210 and the lower region 220 of the inspection graph (eg, step S40 ).

In example embodiments, the speckle intensity may be determined based on the area of the upper region 210 and the area of the lower region 220 . For example, as the sum of the area (absolute value) of the adjacent upper region 210 and the area (absolute value) of the lower region 220 increases, the stain intensity may increase.

In example embodiments, the blob intensity may be determined by comparing the highest point of the upper region 210 and the lowest point of the lower region 220 . For example, the greater the difference in elevation between the highest point and the lowest point, the greater the stain strength may be.

For example, when the sum of the area of the upper region 210 and the area of the lower region 220 or the elevation difference is equal to or greater than a target value, the inspection region and the inspection object may be determined as defective. In addition, when the sum of the area of the upper region 210 and the area of the lower region 220 or the elevation difference is less than the target value and is not substantially visually observed, the inspection region and the inspection object may be determined as normal.

In some embodiments, the blob intensity may be determined based on a slope between the highest point and the lowest point. For example, the greater the slope, the stronger the stain strength may be. Also, when the first upper region, the lower region, and the second upper region are sequentially positioned, two slopes may be calculated between the two highest points and one lowest point. As the difference between the slopes increases, the test object may have a strong stain intensity.

5 is a schematic flowchart illustrating a stain strength inspection method according to example embodiments.

Referring to FIG. 5 , the test graph may be standardized based on the brightness reference line and converted into a standardized test graph (eg, step S25 ).

6 is a standardized examination graph according to exemplary embodiments.

The standardization may include converting the curvature and inclination of the brightness reference line 200 into a flat straight line, and adjusting the brightness data of the inspection graph according to a brightness value conversion ratio of the brightness reference line. The standardized brightness reference line 205 may extend in the first direction.

In this case, the upper region 210 and the lower region 220 may be intuitively compared based on the standardized brightness reference line 205 . In addition, the area of the upper region 210 and the lower region 220 may easily calculate the slope between the highest point of the upper region 210 and the lowest point of the lower region 220 .

In example embodiments, the upper region 210 and the lower region 220 may include a plurality of unit upper regions and unit lower regions, respectively. For example, the upper region 210 of FIG. 6 may include a first unit upper region 212 and a second unit upper region 214 .

For example, as shown in FIG. 6 , when the first unit upper region 212 and the second unit upper region 214 are adjacent to each other, the first unit upper region 212 and the second unit upper region 214 are adjacent to each other. may be merged to form one upper region 210 .

When the adjacent unit upper regions 212 and 124 and the adjacent unit lower regions are merged into the upper region 210 and the lower region 220, respectively, it may be easy to determine the brightness change tendency. For example, a speckle defect observed with the naked eye may be due to a difference in general brightness between the adjacent upper region 210 and the lower region 220 . After merging the small area unit upper area or unit lower area with the surrounding unit area to make a large area area, the actual stain strength can be inspected with a standard similar to visual inspection by comparing it with the adjacent area.

The stain strength inspection method according to the exemplary embodiments may automate the stain 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: judgment unit

Claims (11)

generating an examination graph including brightness data in a first direction from the examination image obtained from the examination object;
setting a brightness baseline reflecting a color change tendency of the test object itself on the test graph;
dividing the inspection graph into an upper region and a lower region based on the brightness reference line; and
and determining a spot intensity by comparing the adjacent upper region and the lower region of the inspection graph.
The method of claim 1 , wherein the color change tendency decreases brightness and saturation from a central portion of the object to an outer portion in the first direction.
The method of claim 1 , wherein generating the inspection graph comprises compressing brightness data of the inspection image in a second direction perpendicular to the first direction.
The method according to claim 1 , wherein the generating of the inspection graph comprises expanding a lightness range of the lightness data.
The method according to claim 1, wherein the upper region and the lower region include a plurality of unit upper regions and unit lower regions, respectively,
The dividing into the upper region and the lower region includes merging adjacent regions of the unit upper regions or the unit lower regions.
The method of claim 1 , wherein the stain strength is determined based on an area of the upper region and an area of the lower region.
The method according to claim 1, wherein the stain intensity is determined by comparing the highest point of the upper region and the lowest point of the lower region based on the brightness reference line.
The method according to claim 1, further comprising the step of converting the inspection graph into a standardized inspection graph by standardizing the inspection graph based on the brightness baseline before dividing the region into the upper region and the lower region.
The method of claim 1 , wherein the inspection object includes spot defects that extend in a second direction perpendicular to the first direction and are repeatedly arranged along the first direction.
The method according to claim 1, 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 How to check stain strength.
The method according to claim 1, wherein the test object comprises a polarizing film.

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