JP2008171142A - Spot defect detection method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spot defect detection method for highly precisely detecting spot defect without causing erroneous detection. <P>SOLUTION: This spot defect detection method includes emphasizing spot defects surrounded by luminance comparison elements S1 to S32 on the basis of the mean value of luminance differences with respect to the object pixel O of two luminance comparison pixels made a set at point symmetric positions by using a spot defect emphasizing filter. Whether or not the luminance value of the two luminance comparison elements as the set is within a predetermined luminance range on processing is decided under the first to fourth conditions for each set of luminance comparison elements, and when one luminance comparison element is within the predetermined luminance range, the difference of the luminance value within the predetermined luminance range and the luminance value of an object pixel O is calculated as an emphasis calculation value for spot defect emphasis. The luminance range on the spot defect emphasis processing is set according to the luminance range of an inspection object range different according to the type of a display and the characteristics of the spot. Thus, it is possible to prevent erroneous detection by selectively and surely emphasizing spot defects out of the luminance range. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention automatically and accurately detects a spot defect in an inspection process of various products such as an inspection process in manufacturing various display devices such as liquid crystal panels, electrophoretic displays and organic EL displays and projectors which are applied products thereof. The present invention relates to a spot defect detection method and apparatus.

In the inspection of various display panels and the like, surface defects called spots and unevenness are difficult to detect automatically with an inspection apparatus because the shape is indefinite and the contrast is low. For this reason, the inspection is still carried out by the inspector's visual observation, and there is an urgent need to automate the inspection in order to reduce manufacturing costs.
Note that a spot or uneven defect is a state in which an area on a display screen has a difference in luminance from other areas, and in a certain range, there is a brighter or darker part than the surrounding area. Usually, a case where the defect area is relatively small is often called a spot defect, and a case where the defect area is relatively large is often called a mura defect. However, since there is no strict definition, in the present invention, surface system defects such as a spot defect and a mura defect are collectively referred to as a spot defect.

  Conventionally, as a method for automating the detection of a spot defect, a method for detecting a spot defect by performing an enhancement process using a secondary differential filter / secondary difference filter has already been proposed (see, for example, Patent Documents 1 to 4). ).

JP 2004-53477 A JP 2003-14580 A JP 2001-243473 A JP 2000-111492 A

In the above Patent Documents 2 to 4 and the like, a secondary difference filter is used as an enhancement process for detecting a spot.
Here, since the secondary differential filter and the secondary differential filter of Patent Documents 1 and 4 consider only the components in the vertical direction and the horizontal direction, and do not consider the components in the diagonal direction, the processing time is Although it can be shortened, there is a problem that the detection accuracy of the spot defect cannot be improved.
In this regard, in Patent Documents 1 to 3, not only the vertical direction and the horizontal direction but also the oblique direction is considered, but since the filter is set so as to react to a portion where the luminance change is large, Will also react and detect flaws and linear defects that are not spots. For this reason, there was a problem that the detection accuracy of the spot defect is lowered.
Further, in Patent Document 3, since the difference between the average brightness of the spot defect and the average brightness value of the outer periphery thereof is taken and the brightness difference is detected by comparison with the spot detection threshold value, the vicinity of the periphery of the spot-like unevenness is detected. A component in the direction opposite to the component of the spot defect to be detected is generated and may be erroneously detected (for example, in the case of a white spot defect, a black spot defect is detected). In addition, when a streak-like defect exists on the same screen, a streak-like defect may be detected at the same time as the spot defect, and there is a problem that the detection accuracy of the spot defect cannot be increased.
Further, in Patent Document 4, it is checked whether a luminance value of a filter application portion is convex or concave at the time of filter calculation by using a conditional expression, and a second derivative is calculated only when the condition is satisfied. It is possible to detect. However, although this method considers all four directions as conditions, there are actually spots that deviate from these conditions, so such spots cannot be detected.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a spot defect detection method and apparatus that can detect spot defects with high accuracy without erroneous detection.

  The spot defect detection method of the present invention includes a spot defect enhancement processing step for emphasizing a stain defect by applying a stain defect enhancement filter to each pixel of the captured image, and each pixel obtained in the stain defect enhancement processing step. A stain defect detecting step for detecting a stain defect based on a stain defect enhancement value, and the stain defect enhancement processing step is arranged at a predetermined distance from the target pixel selected in the captured image and around the target pixel. Each luminance comparison pixel is divided into sets of two luminance comparison pixels arranged at symmetrical positions across the target pixel, and for each set, the luminance value of one of the two luminance comparison pixels of the set is set to A minimum setting value in which a minimum luminance in a predetermined luminance range corresponding to the luminance of a predetermined inspection target area is set as the one luminance value and the other luminance value is determined as the second luminance value; Based on a comparison result between each of the maximum setting values at which the maximum luminance of the luminance range is set and the first luminance value, and a comparison result between the minimum setting value and each of the maximum setting values and the second luminance value. A first condition that is satisfied when both of the first luminance value and the second luminance value are within the predetermined luminance range, and the first luminance value is within the predetermined luminance range and the second luminance value. And a third condition that is satisfied when the first luminance value is outside the predetermined luminance range and the second luminance value is within the predetermined luminance range. When the first condition is satisfied, the difference between the luminance value of the target pixel and the average value of the first luminance value and the second luminance value is emphasized and calculated. Value, and if the second condition is satisfied, the target pixel The difference value between the luminance value and the first luminance value is set as the enhancement calculation value, and when the third condition is satisfied, the difference value between the luminance value of the target pixel and the second luminance value is set as the value. Emphasis calculation values are used to highlight a spot defect using a spot defect enhancement filter that uses a minimum value among the calculation values of each set as a defect defect enhancement value of the target pixel. The spot defect emphasis value is compared with a predetermined threshold value, and a spot defect candidate pixel is extracted to detect a spot defect.

  Further, the spot defect detection apparatus of the present invention includes a spot defect enhancement processing unit that emphasizes a spot defect by applying a stain defect enhancement filter to each pixel of the captured image, and each obtained by the stain defect enhancement processing unit. Spot defect detection means for detecting a spot defect based on a spot defect enhancement value of the pixel, and the spot defect enhancement processing means is separated from the target pixel selected in the captured image by a predetermined distance and around the target pixel. The arranged luminance comparison pixels are divided into sets of two luminance comparison pixels arranged at symmetrical positions with the target pixel in between, and for each set, one luminance value of the two luminance comparison pixels of the set. Is the first luminance value and the other luminance value is the second luminance value, respectively, and a minimum setting value in which the minimum luminance of the predetermined luminance range according to the luminance of the predetermined inspection target area is set, and A comparison result between each of the maximum setting values at which the maximum luminance of the predetermined luminance range is set and the first luminance value; a comparison result between the minimum setting value and each of the maximum setting values and the second luminance value; Based on the first condition that is satisfied when both the first luminance value and the second luminance value are within the predetermined luminance range, and the first luminance value is within the predetermined luminance range and the second luminance value. A second condition that is satisfied when the luminance value is outside the predetermined luminance range, and a second condition that is satisfied when the first luminance value is outside the predetermined luminance range and the second luminance value is within the predetermined luminance range. When a plurality of conditions including three conditions are set and the first condition is satisfied, the difference value between the luminance value of the target pixel and the average value of the first luminance value and the second luminance value is calculated. If the second calculated condition is satisfied, the The difference value between the luminance value of the pixel and the first luminance value is set as the enhancement calculation value, and when the third condition is satisfied, the difference value between the luminance value of the target pixel and the second luminance value Is used to highlight a spot defect using a spot defect enhancement filter that uses a minimum value among the calculated highlight values of each set as a spot defect enhancement value of the target pixel. A spot defect is detected by comparing a spot defect enhancement value of each pixel with a predetermined threshold to extract a spot defect candidate pixel.

  In the present invention, in the spot defect enhancement process, a spot defect enhancement filter that emphasizes the spot defect based on the luminance value of the luminance comparison pixel arranged at a predetermined distance from the target pixel and around the target pixel is used. Therefore, for example, it is possible to reliably detect a stain spreading in a planar shape as compared with a case where the luminance comparison pixels are arranged only in the vertical and horizontal directions with respect to the target pixel.

The spot defect enhancement filter according to the present invention divides each luminance comparison pixel into a set of two luminance comparison pixels arranged at symmetrical positions with the target pixel in between, and when the first condition is satisfied, And the average value of the luminance values of the two luminance comparison pixels in the set are used as the enhancement calculation values for each set.
For this reason, for example, when a bright spot defect is generated in each of the luminance comparison pixels compared to the surroundings, the luminance value of the target pixel is larger than any of the luminance values of the two luminance comparison pixels of the set. Therefore, the calculated enhancement value is a large value. When this spot defect is contained in an area surrounded by each luminance comparison pixel, all of the enhancement calculation values of each set are large values.
On the other hand, when a streak defect passing through the target pixel and the two luminance comparison pixels set, the luminance values of these pixels are almost the same, so the enhancement calculation value in the set becomes a small value. . In addition, when a part of the bright spot defect including the target pixel reaches the brightness comparison pixel, the brightness value of the brightness comparison pixel at which the spot defect has reached becomes higher and approaches the brightness value of the target pixel. The value of the enhancement calculation value becomes small.
Of the calculated enhancement values of each set obtained in this way, the one with the smallest value is selected and used as the stain defect enhancement value of the target pixel. Is included in the defect, the spot defect enhancement value decreases, and the stain defect enhancement value increases only when the spot defect is within the area surrounded by the luminance comparison pixels. For this reason, if the spot defect emphasis value is compared with a predetermined threshold, only the spot defect can be detected with high accuracy.

  Here, with respect to the subtraction direction of the target pixel and the luminance comparison pixel, when emphasizing a white spot defect that is brighter than the surrounding area, the enhancement calculation value is obtained by subtracting the luminance value of the surrounding luminance comparison pixel from the luminance value of the target pixel. Find it. On the other hand, when emphasizing a black spot defect darker than the surrounding area, the enhancement calculation value may be obtained by subtracting the luminance value of the target pixel from the luminance value of the surrounding luminance comparison pixel. In this way, white spot defects and black spot defects are emphasized separately, the spot defect is cut out from the white spot defect enhancement result by the threshold for white spot defect detection, and the threshold for black spot defect detection from the black spot defect enhancement result. By cutting out the spot defect by the above, a defect such as the white spot and the black spot being reversed at the outer edge of the spot does not occur, and the accuracy of spot defect detection can be further improved.

Further, as one of the major features of the present invention, a luminance range (predetermined luminance range) corresponding to the luminance of the inspection target area is set in the spot enhancement process, and each of the two luminance comparison pixels in each set has this luminance. Whether it is within the range is determined by the first condition to the third condition. That is, since the predetermined luminance range can be arbitrarily set according to the display characteristics of each display image such as various displays, it is possible to cope with a wide variety of display image defect inspections.
Note that an arbitrary luminance range in processing for the inspection target region can be set as the predetermined luminance range. This predetermined luminance range is defined by a minimum value and a maximum value (minimum setting value and maximum setting value).

Here, if the luminance value of the target pixel is referred to, the luminance difference between the target pixel and each of the two luminance comparison pixels in the set is obtained, and the target pixel is determined based on the comparison between the luminance difference and a predetermined threshold value. And the two luminance comparison pixels are in the same region (inside or outside of the inspection target region depending on the position of the target pixel), the spot enhancement calculation value of the target pixel is derived. In this case, when the luminance value of the target pixel deviates more than expected from the luminance value of the luminance comparison pixel (when the threshold value is exceeded), the spot defect existing in the target pixel cannot be emphasized.
On the other hand, in the present invention, in the spot defect enhancement processing of the target pixel, it is not determined whether the luminance value of the target pixel is within the predetermined luminance range, but the luminance around the target pixel. Since it is determined whether the luminance value of the comparison pixel is within the predetermined luminance range, white that is out of the predetermined luminance range regardless of whether the luminance of the target pixel is inside or outside the predetermined luminance range. It is possible to reliably emphasize the target pixel in which a spot or a black spot exists.

In addition, when only one of the two luminance comparison pixels in the set is within the predetermined luminance range according to the second and third conditions, the luminance difference between the one luminance comparison pixel and the target pixel within the predetermined luminance range is determined. Since the brightness value of the other brightness comparison pixel is not taken into account for spot defect enhancement as an enhancement calculation value, if one brightness comparison pixel is within the specified brightness range and the other brightness comparison pixel is outside the specified brightness range, the target Even though the pixel has no spot defect, it is possible to prevent the target pixel from being subjected to the spot defect enhancement process. On the other hand, the actual spot defect can be surely emphasized and detected.
As described above, each condition of the first condition to the third condition, and by referring to the brightness of the brightness comparison pixel instead of the target pixel in these conditions, even if the filter straddles the inside and outside of the inspection target area, no erroneous detection is performed. Inspection can be fully automated, and remarkable bright spots and spots that deviate from the predetermined luminance range in the inspection target area can be emphasized and detected without omission.

  When the first condition is satisfied, the average value of the luminance values of two luminance comparison pixels arranged at symmetrical positions with respect to the target pixel is obtained, so that the influence of shading of the background can be reduced, and the spot defect is further reduced. It can be detected with high accuracy. That is, due to the influence of background shading, one of the two luminance comparison pixels arranged at symmetrical positions across the target pixel often has a high luminance value and the other becomes small. Therefore, the influence of shading can be smoothed by obtaining the average luminance value of these two luminance comparison pixels, and as a result, the enhancement calculation value becomes a small value. Thereby, a spot defect can be detected with higher accuracy.

As the inspection target area, for example, a display screen by various image display devices such as a liquid crystal panel, a DMD (direct mirror device) panel, a plasma display, an organic EL display, an electrophoretic display, a front projector, and a rear projector is imaged. An image display area such as a rectangular shape in the image can be given.
According to the present invention described above, by setting the brightness range in the spot defect enhancement process according to the brightness range of the inspection target area and the characteristics of the spot that differ depending on the type of display, etc., the spot defect deviates from this brightness range. Can be selectively and reliably emphasized, so that erroneous detection can be prevented and spot defect detection can be performed appropriately.

  In each conditioning of the first to third conditions, when the first and second luminance values are not less than the minimum set value and not more than the maximum set value, it may be determined that they are within the predetermined luminance range. When the first and second luminance values are both greater than the minimum set value and less than the maximum set value, it may be determined that they are within a predetermined luminance range. In short, it is only necessary that these minimum set value and maximum set value become the threshold values at both ends of the predetermined luminance range to perform each conditioning.

  In the spot defect detection method of the present invention, the fourth condition includes the fourth condition that is satisfied when both the first luminance value and the second luminance value are outside the predetermined luminance range in the plurality of conditions. In the case of being established, it is preferable that a predetermined invalid value that can be distinguished from a value that can be taken by a luminance difference between the target pixel and each luminance comparison pixel is used as the enhancement calculation value.

According to the present invention, when the fourth condition is satisfied, the invalid value that is not confused with the emphasized calculated value calculated based on the first and second luminance values in the first to third conditions is emphasized. Therefore, it does not affect the spot defect emphasis value obtained as the minimum value among the emphasis calculated values calculated in each set.
Here, it is normal that the luminance range is different between the inside and the outside of the inspection target region. Therefore, if the predetermined luminance range is set according to the luminance range assumed in the inspection target region, When the target pixel and each luminance comparison pixel in the set are outside the inspection target area (that is, the background area) and there is a luminance difference between the target pixel and the luminance comparison pixel (that is, there is a luminance change in the background area) ) Can be prevented from being erroneously detected as a defect.

[1. Overall Configuration of Spot Defect Detection Device]
FIG. 1 is a block diagram showing the configuration of a spot defect detection apparatus according to the first embodiment of the present invention.
In FIG. 1, 1 is a display panel, 2 is a projector which is an image projector, and the display panel 1 can be set from the outside. Reference numeral 3 denotes a pattern generator that is a pattern generation device that outputs various patterns to the display panel 1, reference numeral 4 denotes a screen, and reference numeral 5 denotes a CCD (charge-coupled device) camera that is an imaging unit that captures an image projected on the screen 4. A CCD having a resolution higher than that of the display panel 1 is mounted. A computer device 6 is an image processing means for controlling the pattern generator 3 and the CCD camera 5 to detect a spot defect in the display panel 1, and a display device 7 is connected to the computer device 6.

  The computer device 6 includes an image input means 60, a background image difference processing means 61, a reduced image creation means 63, a spot defect enhancement processing means 64, a noise removal means 65, a spot defect extraction processing means 66, and a blob process. It comprises means 67 and defect rank classification processing means 68.

Image data of the captured image captured by the CCD camera 5 is input to the image input means 60 of the computer device 6. The captured image is stored in a storage means (not shown). Accordingly, an imaging process (image input process) is performed in which the inspection target is imaged using the CCD camera 5 by the image input means 60.
The display panel 1 is various display devices such as a TFT (Thin Film Transistor) liquid crystal panel and a DMD (direct mirror device) panel, and an inspection target area (inspection target) on which an image is displayed on the display panel. In order to image the entire (region), the image is captured in a state including some regions around the inspection target region.

  The background image difference processing means 61 carries out a background image difference processing step for obtaining a background difference image in which a difference between an input image and a background image created in advance is removed and defective luminance changes caused by things other than the inspection target are removed. To do. In this embodiment, this background difference image is used as an inspection image (captured image).

  The reduced image creating means 63 performs a reduced image creating process for creating a reduced image from the inspection image obtained by the background image difference processing means 61. For example, the reduced image creating means 63 performs a process of reducing the inspection image to ¼ size in order to detect a relatively large spot defect in the inspection image (captured image). As will be described later, the size of the stain that can be emphasized is determined to some extent in the stain defect enhancement filter used in the stain defect enhancement processing means 64. For this reason, even if the same spot defect emphasis filter is used, a relatively large spot defect is detected by reducing the size of the spot defect by reducing the size of the image itself as compared with the case where the image is not reduced. be able to. Note that when a small spot defect is detected, the reduced image creating step by the reduced image creating means 63 may not be performed. In addition, a process of reducing the size to 1/2 size or 1/8 size, which is another reduction rate, may be performed.

  The spot defect enhancement processing unit 64 performs a spot defect enhancement process step of enhancing and detecting a spot defect by applying a spot defect enhancement filter (stain defect detection filter) to the image.

  The noise removing unit 65 performs a noise removing process step of removing noise by applying a median filter to the result processed by the spot defect enhancement processing unit 64.

  The spot defect extraction processing unit 66 extracts a spot defect candidate by comparing the result processed by the noise removing unit 65 with a predetermined threshold. Note that the spot defect includes a white spot defect having a high luminance value with respect to other pixel portions and a black spot defect having a low luminance value. For this reason, the white spot defect threshold value and the black spot defect threshold value are set as the threshold values, and the white spot defect candidate is extracted by comparing with the white spot defect threshold value, and the black spot defect threshold value is compared with the black spot defect threshold value. A defect candidate is extracted.

The blob processing means 67 performs a blob processing step for obtaining the area of the region extracted as the defect candidate and the average luminance.
The defect rank classification processing unit 68 evaluates the rank of the spot defect based on the area and average brightness obtained by the blob processing unit 67, and classifies which defect rank the current inspection object corresponds to. carry out.
Therefore, in the present embodiment, the spot defect detection processing unit 66, the blob processing unit 67, and the defect rank classification processing unit 68 constitute a spot defect detection unit.

[2. Operation of spot defect detection device]
Next, the operation of the spot defect detection device according to the present embodiment will be described.
FIG. 2 is a flowchart for explaining the operation of the spot defect detection apparatus of the present embodiment. The operation shown in FIG. 2 is realized by a program executed on the computer device 6.
First, the display panel 1 to be inspected is set on the projector 2, the pattern generator 3 is controlled by the computer device 6 to display a specific brightness pattern on the display panel 1, and this is projected onto the screen 4 by the projector 2. To do. Then, the image projected on the screen 4 is photographed by the CCD camera 5, the image of the photographed data is output to the computer device 6, and a spot defect detection process is performed by the computer device 6 to detect a spot defect in the display panel 1. The result is displayed on the display device 7.

Here, the operation of spot defect detection by the computer device 6 will be described based on the flowchart of FIG.
First, an image projected on the screen 4 is photographed by the CCD camera 5, and an image of the photographed data is taken into the image input means 60 of the computer device 6, and an image input process (imaging process) is performed (step S1). . At this time, the photographing data is taken into the computer device 6 as 4096 gradation (12 bits) digital data by an A / D converter (not shown).
Next, the background image difference processing means 61 performs a background image difference processing step for removing defective luminance changes caused by things other than the liquid crystal panel such as illumination and lenses from the captured image data (step) S2).

  In this background image difference processing step, the background image shown in FIG. 3C is created by subtracting the background image shown in FIG. 3B from the input image (projected image) shown in FIG. The background image is an image of luminance change of the optical system excluding the display panel 1. Since the luminance change on the defect due to the projection lamp and the projection lens occurs in both the input image and the background image, if the background image is subtracted from the input image, the background difference image is not a liquid crystal panel such as a projection lamp or a projection lens. The luminance change component on the defect caused by the object is removed.

Next, the reduced image creating means 63 performs a reduced image creating process for reducing the inspection image subjected to the background image difference process (step S3).
In the reduced image creating step, an image reduced from the inspection image to a predetermined size, for example, 1/4 size is created. Specifically, in the case of creating a 1/4 size reduced image, a 1/2 size reduced image is created by setting the average value of the 4 pixels of the inspection image to 1 pixel. By reducing the average value of the four pixels of the reduced image to one pixel, a 1/4 size reduced image is created.

Therefore, if the original image is 1.3 million pixels of 1300 × 1000, the reduced image of ½ has 325,000 pixels of 650 × 500, and the reduced image of ¼ has 81,250 pixels of 325 × 250. become.
In this way, a reduced image of a predetermined size is created because a stain defect enhancement filter, which will be described later, is designed to emphasize a spot defect of a predetermined size, and by reducing the image size, This is to make it possible to emphasize a relatively large spot that cannot be emphasized by a spot defect enhancement filter, which will be described later, by reducing the image size.

Next, the spot defect emphasis processing means 64 performs a spot defect emphasis process step for emphasizing a spot defect on the created reduced image (step S4). This spot defect enhancement processing step emphasizes only a spot defect in an image because it is difficult to detect a minute level of white spot defect / black spot defect as it is.
In addition, when detecting only a spot defect of a predetermined size, it suffices to apply one kind of spot defect enhancement filter to the created reduced image, but when detecting a spot defect having a different size, A plurality of types of spot defect enhancement filters having different sizes of spot defects to be detected may be applied to detect a spot defect of a predetermined size.

[3. Structure and action of a spot defect enhancement filter]
As shown in FIG. 4, the spot defect enhancement filter sets the central pixel of the inspection area sequentially set when scanning the reduced image obtained by the reduced image creating unit 63 as the target pixel O, and around the target pixel O. Luminance comparison pixels (S1 to S32) are provided that are arranged in a substantially circular shape and are separated from the target pixel O by a predetermined length.
The luminance comparison pixels S1 to S32 are divided into 16 sets, with two arranged in a point-symmetric position with the target pixel O in between as one set. For example, S1 and S17, S2 and S18, and S3 S19... S15 and S31, and S16 and S32 are each set. The spot defect enhancement filter exists within the range surrounded by the luminance comparison pixels S1 to S32 by using the luminance difference (16 values in this embodiment) from the target pixel O obtained for each set. The spots to be emphasized are emphasized in the vertical, horizontal, and diagonal directions of the inspection image. The size of the stain that can be enhanced by the stain defect enhancement filter depends on the distance from the target pixel O to the luminance comparison pixels S1 to S32.

[Brightness range set in the filter]
In such a spot defect emphasis filter, in the spot emphasis process for emphasizing a spot defect in the target pixel O according to the brightness difference between the two brightness comparison pixels in the set and the target pixel O, a processing brightness range is set. Yes. This luminance range is defined by the minimum setting value MinLevel and the maximum setting value MaxLevel.
Here, MinLevel and MaxLevel are set, but these MinLevel and MaxLevel are not the minimum luminance and the maximum luminance in the inspection target area of the display panel 1, respectively, but according to the luminance of the inspection target area and according to the processing. Can be set arbitrarily. For example, the luminance data in the inspection target area of the display panel 1 may be investigated in advance and manually set, or the luminance average value (avr) and standard deviation (σ) in the inspection target area are obtained, and the following calculation formula It may be set with.

MinLevel = avr − a × σ (Formula 1)
MaxLevel = avr + a × σ (Formula 2)

[Conditions 1 to 4]
Based on the comparison result when the MinLevel and MaxLevel set in this way and the luminance values of the luminance comparison pixels S1 to S32 are compared for each set, conditions 1 to 4 as the first to fourth conditions (below) Set.
That is, the luminance values of two luminance comparison pixels in the same set are obtained as a first luminance value and a second luminance value, and each of the first luminance value and the second luminance value is within a luminance range defined by MinLevel and MaxLevel. The following conditions 1 to 4 can be conditioned depending on whether or not there is.
These conditions 1 to 4 are mutually exclusive, and an enhancement calculation value for calculating a spot defect enhancement value of the target pixel O is obtained by the following equations 3 to 6 corresponding to each condition. F1 shown below is an enhancement calculation value of the set of S1 and S17.

Condition 1
(MinLevel <= S1 <= MaxLevel) ∧ (MinLevel <= S17 <= MaxLevel)
F1 = O − (S1 + S17) / 2 (Equation 3)
Condition 2
(MinLevel <= S1 <= MaxLevel) ∧ (S17 <MinLevel ∨ S17> MaxLevel)
F1 = O − S1 (Formula 4)
Condition 3
(S1 <MinLevel ∨ S1> MaxLevel) ∧ (MinLevel <= S17 <= MaxLevel)
F1 = O − S17 (Formula 5)
Condition 4
(S1 <MinLevel ∨ S1> MaxLevel) ∧ (S17 <MInLevel ∨ S17> MaxLevel)
F1 = InvalidData (Formula 6)

That is, Condition 1 indicates that both of the luminance values (first luminance value and second luminance value) of the luminance comparison pixels S1 and S17 are within the luminance range defined by MinLevel and MaxLevel. In this case, S1 , The difference between the average value of the luminance values in S17 and the luminance value of the target pixel O is defined as F1 (Formula 3).
Condition 2 and condition 3 indicate that one of the luminance comparison pixels S1 and S17 is within the luminance range defined by MinLevel and MaxLevel, and the other is outside the luminance range. In this case, each luminance of S1 and S17 Among the values, the difference between the luminance value within the luminance range and the luminance value of the target pixel O is F1. In other words, when the luminance value of S1 is within the luminance range (condition 2), the luminance difference between S1 and the target pixel O is used as the enhancement calculation value (Equation 4), and conversely, the luminance value of S17 is within the luminance range. In some cases (condition 3), the luminance difference between S17 and the target pixel O is set as an enhancement calculation value (Formula 5).
In this embodiment, white spot defects that are brighter than the surrounding areas and black spot defects that are darker than the surrounding areas are individually emphasized to create a white spot defect enhanced image and a black spot defect enhanced image. When emphasizing a white spot defect brighter than the surrounding area, the luminance value of the surrounding luminance comparison pixel is subtracted from the luminance value of the target pixel O as in the above Expressions 3 to 5. The reverse case of black spot defect enhancement will be described later.

  Condition 4 indicates that both of the luminance comparison pixels S1 and S17 are outside the luminance range defined by MinLevel and MaxLevel. In this case, an invalid value InvalidData is set in F1 (Equation 6). This invalid value InvalidData is a value that is much larger or smaller than the luminance difference that can occur in the inspection target region, and can be determined as F1 when the first to third conditions are satisfied. For this reason, when F1 is an invalid value InvalidData in the process described later, it is possible to invalidate F1 which is the invalid value without using it for the spot defect enhancement process of the target pixel O.

  By performing the same processing as in the above conditions 1 to 4 and equations 1 to 6 for other sets other than S1 and S17, 16 emphasized calculation values are obtained as secondary differences from the target pixel O for each set. F1 to F16 are obtained.

After performing the above calculation, the stain defect enhancement filter selects the minimum value among the values of F1 to F16, and sets the value as the stain defect enhancement value of the target pixel O.
Here, FIG. 4 and FIG. 5 to FIG. 10 respectively show examples in which the above-described conditions 1 to 4 are satisfied in acquiring the emphasis calculation value of each set.

[When Condition 1 is met]
Condition 1 is satisfied when the luminance values of the two luminance comparison pixels in the set are both within the luminance range defined by MinLevel and MaxLevel in the luminance comparison pixels S1 to S32 as described above. 4 and 5 show examples in which the condition 1 is satisfied in all sets.
As shown in FIG. 4, when there is no defect in the area surrounded by the luminance comparison pixels S1 to S32, there is almost no difference between the luminance value of the target pixel O and the luminance values of the luminance comparison pixels S1 to S32. become. Therefore, according to Expression 3 in the case of Condition 1, the above F1 to F16, which are the average luminance values of the two luminance comparison pixels in the set, are all small values.

On the other hand, FIG. 5 shows a state in which a white spot defect 70 brighter than other parts is present in the area surrounded by the luminance comparison pixels S1 to S32 and the target pixel O is a part of the white spot defect 70. Indicates. In FIG. 5, since the luminance values of the luminance comparison pixels S1 to S32 are lower than those of the target pixel O, all of F1 to F16 are larger than those in the case where there is no spot defect.
That is, when the spot defect 70 exists in the area surrounded by the luminance comparison pixels S1 to S32 as shown in FIG. 5, the above F1 to F16 all have relatively large values. On the other hand, in the case of FIG. 4 where there is no spot defect, F1 to F16 are small values.

  FIG. 6 shows a state where the streak-like defect 71 exists. For example, the average brightness value of the set luminance comparison pixels S2 and S18 is the same as the brightness value of the target pixel O included in the streak-like defect 71. Since they are almost the same, the difference from the target pixel O is small with respect to the set of S2 and S18. That is, at least one of F1 to F16 has a small value.

[When Condition 2 or Condition 3 is met]
In the above, a case has been described in which each of the luminance comparison pixels S1 to S32 is within the luminance range, and the condition 1 is satisfied when acquiring the enhancement calculation values of all the sets. Subsequently, the above condition 2 or condition 3 is satisfied. An example of this is shown in FIGS.

FIG. 7 shows a state in which some of the luminance comparison pixels S21 to S29 are included in the peripheral region of the inspection target region outside the panel. For example, the luminance value of one luminance comparison pixel S21 in the set of S5 and S21 Is out of the predetermined luminance range, the calculation of the emphasis calculation value (F5) in the set of S5 and S21 is performed under Condition 2 among Conditions 1 to 4 above. In this case, according to the above equation 4, the difference (O−S5) between the luminance value of the luminance comparison pixel S5 and the luminance value of the target pixel O within the predetermined luminance range is set as the enhancement calculation value in the set.
FIG. 8 also shows a state in which some of the luminance comparison pixels S5 to S13 are included in the peripheral area of the inspection target area outside the panel. For example, the other luminance comparison pixel in the set of S5 and S21. Since the brightness value of S5 is out of the predetermined brightness range, when calculating the emphasis calculation value (F5) in the set of S5 and S21, the condition 3 is performed among the conditions 1 to 4. In this case, according to the above formula 5, the difference (O−S21) between the luminance value of the luminance comparison pixel S21 and the luminance value of the target pixel O within the predetermined luminance range is set as the enhancement calculation value in the set.

Here, in the state of FIG. 7, the luminance comparison pixels S1 to S20 in the inspection target area are used without using the luminance comparison pixels S21 to S29 included in the surrounding area of the inspection target area and outside the predetermined luminance range. Using S30 and S31, the enhancement calculation value of the position of the target pixel O is obtained. Similarly, in the state of FIG. 8, the luminance comparison pixel included in the area around the inspection target area and outside the predetermined luminance range. The enhancement calculation value of the position of the target pixel O is obtained using S1 to S4 and S14 to S32 that are the luminance comparison pixels in the inspection target area without using S5 to S13.
That is, when calculating the enhancement calculation value, it is possible to obtain the enhancement calculation value without being affected by the luminance value of the area around the inspection target area, so that a spot defect can be detected without any problem even in the states of FIGS. I can do it.

[When condition 4 is met]
FIG. 9 is an example in which the above condition 2 or 3 and 4 are satisfied. A state in which some of the luminance comparison pixels S1 to S5 and S21 to S32 are included in the peripheral region of the inspection target region outside the panel is shown. For example, in the set of S1 and S17, the inspection target region which is a panel image region Since one luminance comparison pixel S17 exists in the above-described conditions, the calculation of the enhancement calculation value (F1) in the set of S1 and S17 is performed under Condition 3 among Conditions 1 to 4 above. In this case, the difference (O−S17) between the luminance value of the luminance comparison pixel S17 and the luminance value of the target pixel O within the predetermined luminance range is set as the enhancement calculation value in the set according to the above formula 4.
Similarly, in FIG. 9, in the set of S6 and S22, since the luminance value of one luminance comparison pixel S22 is out of the predetermined luminance range, the enhancement calculation value (F6) in the set of S6 and S22 is calculated. In this case, it is performed under condition 2 out of the above conditions 1 to 4. In this case, the difference (O−S6) between the luminance value of the luminance comparison pixel S6 and the luminance value of the target pixel O within the predetermined luminance range is set as the enhancement calculation value in the set according to the above formula 4.
Furthermore, in FIG. 9, in the set of S5 and S21, since each luminance value of these luminance comparison pixels is out of the predetermined luminance range, when calculating the enhancement calculation value in the set of S5 and S21. Is performed under condition 4. In this case, the invalid value InvalidData is set as the enhancement calculation value in the set according to the above equation 6.
As described above, since the enhancement calculation value can be obtained without being affected by the luminance value of the area around the inspection target area with respect to the evaluation at the position of the target pixel O, the spot defect is detected without any problem even in the state of FIG. I can do it.

Further, FIG. 10 shows a state in which a filter is applied outside the inspection target area such as a background area around the image display area of the display panel 1. The luminance range in the background area of the display panel 1 of the present embodiment is out of the luminance range defined by the above MinLevel and MaxLevel. That is, the luminance values of the luminance comparison pixels S1 to S32 are all outside the luminance range defined by MinLevel and MaxLevel, and Condition 4 is satisfied in all sets.
Here, a spot defect 70 is present in the center of the filter surrounded by the luminance comparison pixels S1 to S32, but this is outside the inspection target region. F1 etc.) is set, and in the state of FIG. 10, the enhancement calculation values of all sets are InvalidData. For this reason, a spot defect outside the inspection target area is not detected.

[Calculation of spot defect enhancement value for target pixel]
In each example of FIGS. 5 to 10 described above, the spot defect enhancement value of the target pixel O calculated from the enhancement calculation value of each set is as follows.
That is, when the spot defect 70 exists in the area surrounded by the luminance comparison pixels S1 to S32 as shown in FIG. 5, the above F1 to F16 all have relatively large values. On the other hand, in the case of FIG. 4 where no spot defect exists or when the streak-like defect 71 exists as shown in FIG. 6, at least one of the above F1 to F16 becomes a small value, so the minimum value from F1 to F16 The spot defect emphasis value is reduced and no defect is detected.
Further, even in the case of FIGS. 7 and 8 where some of the luminance comparison pixels are in the peripheral region of the inspection target region, the use of Condition 2 or Condition 3 is affected by the luminance value of the peripheral region of the inspection target region. Therefore, the emphasis calculation value of the target pixel O can be obtained. Therefore, if the spot defect 70 exists, all of F1 to F16 are relatively large values.
Further, even in the case of FIG. 9 where the partial condition 4 is satisfied, the InvalidData is excluded from consideration when the calculated calculated value is selected, and the minimum value is selected from the calculated calculated values obtained under the conditions 2 and 3 Then, since it is possible to detect whether or not the spot defect 70 exists, it is only necessary to store the minimum value as the spot defect enhancement value of each target pixel O from among the respective enhancement calculation values from which InvalidData is removed.
To summarize the above, if an emphasized calculation value that is not InvalidData with the values of F1 to F16 is selected and the minimum value is selected from among them, the target pixel O is included and surrounded by the luminance comparison pixels S1 to S32. Since it is possible to detect whether or not there is a spot defect 70 that fits in the specified area, this minimum value may be stored as a spot defect enhancement value for each target pixel.

  On the other hand, in the case as shown in FIG. 10, the spot defect enhancement process for the target pixel O can be invalidated. That is, if at least one set is not InvalidData, a value smaller than InvalidData other than InvalidData becomes the emphasis calculation value, but there is no problem. However, as shown in FIG. 10, the emphasis calculation values of all sets are InvalidData, If the minimum value in the set enhancement calculation value is also InvalidData, the stain defect enhancement processing for the target pixel O being processed may be invalidated.

  Incidentally, in the spot defect enhancement filter of this embodiment shown in FIG. 4, the distance from the target pixel to the upper and lower, left and right luminance comparison pixels is six pixels, and the distance between the target pixel and the other luminance comparison pixels is also the same. Approximately 6 pixels. The spot defect enhancement filter of the present embodiment is suitable for extracting a spot defect having an area that is slightly smaller than the area surrounded by the luminance comparison pixels. That is, when the area of the measurement target stain is larger than the area within the area surrounded by each luminance comparison pixel, the stain defect enhancement filter emphasizes only the outline portion and cannot emphasize the entire stain portion. . Accordingly, the size of the spot defect that can be detected differs depending on the distance between the target pixel and the luminance comparison pixel. For this reason, in the following description, in each spot defect emphasis filter, a pixel having a distance between the target pixel and the luminance comparison pixel of n is referred to as a distance n pixel filter. For example, the spot defect enhancement filter shown in FIG. 4 is a 6-pixel distance filter.

In the filter with a distance of 6 pixels, the secondary difference processing is performed with 16 sets, but this number changes as the filter distance n changes.
By applying this process to the entire screen, it is possible to obtain an image in which a spot defect is emphasized. However, as described above, it is not possible to deal with various defect sizes with only one type of filter having a distance between the target pixel and the luminance comparison pixel. For example, the 6-distance filter shown in FIG. 4 can detect only a spot defect having a size up to 11 in diameter. For this reason, in the present embodiment, processing is performed by changing the distance between the target pixel and the luminance comparison pixel in several stages, and enhanced images corresponding to spot defects of various sizes are obtained.
Specifically, the spot defect emphasis process is performed using three filters of distance 3, distance 6, and distance 12 pixels. In other words, if a 12-pixel filter is used, it is possible to detect a spot defect having a diameter of 23. However, if the defect is sufficiently small compared to the filter, the distance from the pixel being compared with the target is long and an accurate result is obtained. Does not come out. For this reason, the distance 3 and 6 pixel filters are used in combination to improve the spot defect detection accuracy.
Since three stain-enhanced images can be obtained by this processing, the brightness of the processing result pixels at the same point in each image is finally compared, and the value having the maximum absolute value is used as the stain defect enhancement result. The image is synthesized as a single spot-enhanced image.

In the present embodiment, the white spot defect enhanced image and the black spot defect enhanced image are individually created. As described above, as indicated by the subtraction directions in the above formulas 3 to 5, the target pixel O is surrounded. A brighter white spot defect-enhanced image can be obtained.
Here, in black spot defect enhancement processing in the spot defect enhancement filter of the present embodiment, the above conditions 1 to 4 are determined in the same manner, and the subtraction direction in each expression when each condition is satisfied is the above expressions 3 to 6. The following formulas 3 ′ to 6 ′ are applied in the opposite direction. The black spot defect enhancement process is performed in the same manner as the above-described white spot defect enhancement process only by the difference in this equation.

Condition 1
(MinLevel <= S1 <= MaxLevel) ∧ (MinLevel <= S17 <= MaxLevel)
F1 = (S1 + S17) / 2 − O (Formula 3 ′)
Condition 2
(MinLevel <= S1 <= MaxLevel) ∧ (S17 <MinLevel ∨ S17> MaxLevel)
F1 = S1 − O (Formula 4´)
Condition 3
(S1 <MinLevel ∨ S1> MaxLevel) ∧ (MinLevel <= S17 <= MaxLevel)
F1 = S17 − O (Formula 5 ′)
Condition 4
(S1 <MinLevel ∨ S1> MaxLevel) ∧ (S17 <MInLevel ∨ S17> MaxLevel)
F1 = InvalidData (Formula 6´)

[4. Processing in the spot defect enhancement processing step]
Here, the process of the spot defect emphasis process step S4 of the present embodiment and the subsequent processes will be described. In this embodiment, three types of spot defect enhancement filters are applied to an image reduced to ¼. Specifically, each spot defect emphasis filter of distance 3, 6, 12 pixel filter is applied. Then, the result of synthesis processing is obtained by synthesizing the application result of the spot defect enhancement filter of the distance 3, 6, 12 pixel filter.
Here, the plurality of spot defect emphasis filters having different distances are used for detecting spot defects of various sizes as described above. That is, if only the stain defect enhancement filter whose distance from the processing target pixel is 6 pixels is used, the size of the stain defect that can be detected is limited (only a stain defect in the vicinity of about 12 pixel size can be detected).
Therefore, in the present embodiment, in order to deal with spot defects of various sizes existing in the screen, the enhancement processing is performed by changing the distance in three steps, that is, three pixels, six pixels, and twelve pixels. Emphasizes spot defects.

  The reason why the enhancement results are combined is to improve detection accuracy. That is, when spot defects are extracted from each enhancement result and evaluated individually, one spot defect may be detected by being divided into enhancement results of 3 pixels and 6 pixels. May not match. Therefore, by combining a plurality of enhancement results to match the results, the separated spot defects are combined into one to improve detection accuracy.

The result of applying the spot defect enhancement filter of the present embodiment to the pseudo spot defect image shown in FIG. 11 is shown in FIGS.
The pseudo spot defect shown in FIG. 11 is a white spot defect and a black spot defect that are created in a pseudo manner. Then, the image shown in FIG. 11 was reduced to ¼ size, and the following spot defect enhancement filters were applied to the reduced image.

The configuration of each spot defect emphasis filter is as described above. In this embodiment, white spot defect enhancement and black spot defect enhancement are individually performed. Here, white spot defect enhancement processing is shown in FIGS.
FIG. 12 shows an enhancement result when a stain defect enhancement filter (distance 3 pixel filter) having a distance of 3 pixels between the target pixel and the luminance comparison pixel is applied.
FIG. 13 shows an enhancement result when a stain defect enhancement filter (distance 6 pixel filter) having a distance of 6 pixels between the target pixel and the luminance comparison pixel is applied.
FIG. 14 shows an enhancement result when a stain defect enhancement filter (distance 12 pixel filter) having a distance of 12 pixels between the target pixel and the luminance comparison pixel is applied.
As shown in FIGS. 12 to 14, the spot defect corresponding to each size is most emphasized by the filter of each distance. However, as shown in FIGS. 13 and 14, the spot defect emphasis filter of the present embodiment can emphasize the spot defect even if the spot defect is somewhat smaller than the distance between the filters.

FIG. 15 shows the result of synthesizing the enhancement results of the filters of distances 3, 6, and 12 shown in FIGS. FIG. 16 shows the result of combining the enhancement results of the filters with distances of 3, 6, and 12 pixels for the black spot defect as in the case of the white spot defect. As described above, since the subtraction directions of Formulas 3 to 5 and Formulas 3 ′ to 5 ′ are opposite to each other, the white color and the black color in FIGS.
In the synthesis process, the spot defect enhancement values of the pixels at the same position are compared in the enhancement result of each filter, and the value having the maximum absolute value among them is used as the synthesis result.
When the distance of the spot defect emphasis filter is very large compared to the size of the spot defect, if the brightness comparison pixel is located in another spot area, the spot cannot be correctly detected due to the spot defect. For this reason, it is preferable to use a stain defect enhancement filter having a size slightly larger than the size of the stain defect to be detected, for example, a size of about 1 to 3 pixels.
Therefore, if the enhancement results of the filters of the distances 3, 6, and 12 pixels are synthesized, the spot defect corresponding to each size of the distances 3, 6, and 12 can be enhanced and detected.

  Next, the noise removing means 65 applies a median filter to the result of the spot defect enhancement processing step S4 to connect and smooth the defect components separated by the noise, and removes noise other than the spot defect. A noise removal process is performed (S5). As the median filter, for example, a median filter may be used in which the median value (median value) of each luminance value of 9 pixels of 3 × 3 is used as the luminance value of the target pixel located at the center of 3 × 3.

Next, the spot defect extraction processing unit 66 sets a threshold value for cutting out a white spot defect and a threshold value for cutting out a black spot defect with respect to the result of the noise removal processing step S5, and sets a spot for extracting each spot defect candidate area. A defect extraction step is performed (S6). Here, each threshold value may be set to an optimum value according to the situation of the image. For example, the average value of the spot emphasis value (luminance value) and the standard deviation of the spot defect emphasis image (composite image) are obtained, and the threshold value is set by the following equations 9 and 10.
White spot defect threshold wslevel = avr + α1 · σ + β1 (Formula 9)
Black spot defect threshold bslevel = avr + α2 · σ + β2 (Formula 10)
Here, avr is an average value of the composite image, σ is a standard deviation of the composite image, α1, α2, β1, and β2 are arbitrarily determined depending on the situation of the image to be inspected.

  Here, FIG. 17 shows the result of binarizing the composite image of FIG. 15 with the white spot defect threshold value calculated by setting α1 to 3 and β1 to 0. FIG. 17 shows white spot defect candidates cut out with the white spot defect threshold. The area displayed in white in FIG. 17 is the area of the spot defect candidate cut out. Similarly, FIG. 18 shows the result of binarizing the composite image of FIG. 16 with the black spot defect threshold value calculated by setting α2 to 3 and β2 to 0. FIG. 18 shows black spot defect candidates cut out with the black spot defect threshold. The area displayed in white in FIG. 18 is the area of the spot defect candidate cut out.

Next, the blob processing means 67 performs a blob processing step for obtaining the area and the average luminance of the area cut out as the defect candidate for the white spot defect candidate image and the black spot defect candidate image (S7).
Next, the defect rank classification processing unit 68 performs a defect rank classification step of classifying the rank of the spot defect in the image based on the calculated area and average luminance of the defect candidate area (S8).
The defect rank obtained by the defect rank classification processing unit 68 is displayed on the display device 7, and the inspector can easily grasp the defect rank of the display panel 1 to be inspected.
Therefore, in the present embodiment, the stain defect detection step S5, the stain defect extraction step S6, the blob processing step S7, and the defect rank classification step S8 constitute a stain defect detection step.

[5. Effects of this embodiment]
According to this embodiment, there are the following effects.
(1) The spot defect enhancement processing unit 64 emphasizes the spot defect based on the luminance values of the luminance comparison pixels S1 to S32 that are separated from the target pixel O by a predetermined distance and are arranged around the target pixel O. Since the emphasis filter is used, for example, compared to the case where the luminance comparison pixels S <b> 1 to S <b> 32 are arranged only in the vertical and horizontal directions with respect to the target pixel O, it is possible to reliably detect a spot spreading in a planar shape.
In addition, the spot defect enhancement filter divides each luminance comparison pixel S1 to S32 into a set of two pixels arranged at point-symmetric positions with the target pixel O in between, and when the condition 1 is satisfied, the luminance value of the target pixel O The difference value (enhancement calculation value) between the average luminance value of the two luminance comparison pixels of each set is obtained, and the smallest value among the difference values of each set is selected as the stain defect enhancement value. For this reason, when there is a streak-like defect or when a part of the brightness comparison pixel is included in the defect, the spot defect enhancement value becomes small and the spot defect is contained in the area surrounded by the brightness comparison pixel. The spot defect enhancement value is increased only when the defect is detected, and by comparing the stain defect enhancement value with a predetermined threshold value, it is possible to eliminate streak defects and the like, so that only the stain defect can be detected with high accuracy.

(2) In particular, a luminance range (predetermined luminance range) in the inspection target region is set based on MinLevel and MaxLevel in the spot enhancement process, and each of the two luminance comparison pixels S1 to S32 in each set has this luminance. Whether or not it is within the range is determined by the first condition to the fourth condition. That is, since the predetermined luminance range can be arbitrarily set according to the display characteristics of each display image of the various display panels 1, it is possible to deal with a wide variety of display image defect inspections.

  Here, in the spot defect enhancement processing for the target pixel O, it is not determined whether the luminance value of the target pixel O is within the predetermined luminance range, but the luminance comparison pixels S1 around the target pixel O. Since it is determined whether or not the luminance values of .about.S32 are within the predetermined luminance range, it is possible to reliably emphasize the target pixel O in which white spots and black spots outside the predetermined luminance range exist.

  In addition, when only one of the two luminance comparison pixels S1 to S32 in the set is within the predetermined luminance range due to the second and third conditions, the luminance comparison pixels S1 to S32 within the predetermined luminance range and the target Since the luminance value of the other luminance comparison pixels S1 to S32 is not taken into account when enhancing the spot defect using the luminance difference from the pixel O as an enhancement calculation value, one luminance comparison pixel S1 to S32 is included in the inspection target region and the other luminance. When the comparison pixels S1 to S32 are outside the inspection target region, it is possible to prevent the target pixel O from being subjected to the spot defect enhancement process even though the target pixel O has no spot defect.

(3) Furthermore, condition 4 is provided as an invalid condition for spot defect enhancement, and when this condition 4 is satisfied, the enhancement calculation value is the invalid value InvalidData (Equation 6). Does not affect the required spot defect enhancement value.

(4) A white spot defect-enhanced image (FIG. 15) and a black spot defect-enhanced image (FIG. 16) are created, and the threshold values (Equation 9 and Eq. 10), spot defects are cut out. As a result, a defect such as a white stain and a black stain being reversed at the outer edge of the stain does not occur, and the accuracy of spot defect detection can be further improved.

(5) In this embodiment, since the average value of the luminance values of two luminance comparison pixels arranged at point-symmetric positions with respect to the target pixel O is obtained, the influence of background shading can be reduced, and a spot defect Can be detected with higher accuracy. That is, one of the two luminance comparison pixels arranged at a point-symmetrical position across the target pixel O often has a high luminance value due to the influence of background shading, and the other is often small. Therefore, the influence of shading can be smoothed by obtaining the average luminance value of these two luminance comparison pixels, and a spot defect can be detected with higher accuracy.

(6) Furthermore, since the spot defect enhancement filter can be set appropriately according to the distance between the target pixel and the luminance comparison pixel, the size of the spot defect that can be detected by the filter can be set. Can be easily detected.
Moreover, even when a plurality of spot defect emphasis filters corresponding to the size of each spot defect are applied, it is possible to easily detect a spot defect of each size by evaluating only the synthesis result of the enhancement results.

(7) In the present embodiment, the spot defect enhancement value is calculated from the luminance value of the target pixel and the average luminance value of the luminance comparison pixel, and the luminance value of the pixel between the target pixel and the luminance comparison pixel is used. Absent. For this reason, as long as the spot defect is smaller than the area surrounded by the luminance comparison pixels and includes the target pixel, even if the spot defect size changes to some extent, it is the same as the conventional visual inspection of the inspector. Spot defects can be detected. For this reason, it is not necessary to set the filter distance size very finely, and accordingly, the number of filters can be reduced and the inspection time can be shortened.

[Modification of the present invention]
The present invention is not limited to the above embodiment.
For example, in the embodiment, when the first condition is satisfied, the difference between the average luminance value of each luminance comparison pixel in the set and the luminance value of the target pixel O is used as the enhancement calculation value of the set. Not limited to this, the smaller one of the first difference and the second difference may be used as the enhancement calculation value of the set. As described above, the smaller value of the first and second differences is used as the enhancement calculation value, and the minimum value (or the absolute minimum value) of the enhancement calculation value of each set is used as the spot defect enhancement value. Spot defects that fit in the designated area can be emphasized without problems.

In the embodiment, in order to cope with various spot defect sizes, a plurality of kinds of spot defect enhancement filters having different distances between the target pixel and the luminance comparison pixel are used. The resulting image may be reduced in a plurality of stages, and a predetermined spot defect emphasis filter may be applied to each image having a different reduction size to detect spot defects of various sizes.
Further, depending on the size of the spot defect to be detected, the image reduction process or the filter size change may not be performed, and the process may be performed using only one type of filter.

  In the above embodiment, the threshold values for white spot defect and black spot defect are set so that both the white spot defect and the black spot defect can be detected. However, only one defect may be detected. For example, when only white spot defects need to be detected, processing may be performed without performing comparison processing with the black spot defect threshold.

Furthermore, in the present invention, the background image difference processing step S2 is performed before the stain defect enhancement processing step S4 by the stain defect enhancement processing means 64. However, this processing may not be performed depending on the state of the photographed image. Also good. Similarly, the reduced image creating step S3 by the reduced image creating means 63 may not be performed depending on the size of the spot to be detected. Further, the noise removal processing step S5 by the noise removing means 65 may not be performed if the image state is good.
In the above embodiment, the inspection target area or the like is not cut out from the surrounding area or the like, or the process of correcting the shape of the distorted inspection target area is not performed. However, such a process is appropriately performed as necessary. It doesn't matter. As such processing, for example, the coordinates of the four corners of the captured image are detected by pattern matching processing, and affine transformation is performed so that the positional relationship of the coordinates of the four corners becomes a rectangle.

  In the above embodiment, the noise removal processing step S5, the stain defect extraction processing step S6, the blob processing step S7, and the defect rank classification step S8 are performed as the stain defect detection step. A defect may be detected. In short, the spot defect detection process may be any process that can determine whether or not it corresponds to a spot defect based on the spot defect emphasized in the spot defect enhancement processing step S4.

  In the above embodiment, when a plurality of spot defect emphasis filters are applied, the results of the filters are combined and determined. However, it is determined separately for each filter result whether there is a spot defect. May be. However, it is possible to detect a spot defect more efficiently by judging based on the synthesis result.

Spots for detecting spot defects are not limited to liquid crystal light valves using TFT elements, but include liquid crystal panels using other diode elements, plasma displays, organic EL displays, DMD (direct mirror device), etc. Needless to say, the present invention can be used for inspection of display body parts and display devices / products using them, and even when used for these, they are not excluded from the scope of the present invention.
Furthermore, the present invention is not limited to the inspection of various display devices. For example, when there are spot-like scratches on a printed matter, a case of a household electrical appliance, a car body, or the like, an image with a spot-like defect is picked up. If it is obtained, the stain can be detected, so that it can also be applied to stain inspection of various products such as surface coating and printed matter.
In short, the present invention can be used to detect a brightness spot defect or a color spot defect because it can detect any spot having a brightness difference from the surroundings.

Although the best configuration, method and the like for carrying out the present invention have been disclosed in the above description, the present invention is not limited to this. That is, the invention has been illustrated and described primarily with respect to particular embodiments, but may be configured for the above-described embodiments without departing from the scope and spirit of the invention. Various modifications can be made by those skilled in the art in terms of materials, quantity, and other detailed configurations.
Therefore, the description limited to the shape, material, etc. disclosed above is an example for easy understanding of the present invention, and does not limit the present invention. The description by the name of the member which remove | excluded the limitation of one part or all of such restrictions is included in this invention.

1 is a block configuration diagram of a screen spot defect detection device according to a first embodiment of the present invention. FIG. The flowchart for demonstrating operation | movement of the said spot defect detection apparatus. Explanatory drawing which shows the background image difference process of the same spot defect detection apparatus. The figure which shows the example of a spot defect emphasis filter. The figure which shows the example of the spot defect detected by the spot defect emphasis filter when the condition 1 is satisfied. The figure which shows the example of the stripe-shaped defect which is not detected with a spot defect emphasis filter. The figure which shows the example of the spot defect detected by the spot defect emphasis filter when the condition 2 is satisfied. The figure which shows the example of the spot defect detected by the spot defect emphasis filter when the condition 3 is satisfied. The figure which shows the example of the spot defect detected by the spot defect emphasis filter when the condition 2, the condition 3 or the condition 4 is established. The figure which shows the example of the spot-like defect which is not detected by the spot defect emphasis filter when the condition 4 is satisfied. The figure which shows the image which provided the pseudo white spot defect and the black spot defect. The figure which shows the result of applying a distance 3 pixel filter (white spot defect emphasis process). The figure which shows the result of applying a distance 6 pixel filter (white spot defect emphasis process). The figure which shows the result of applying a distance 12 pixel filter (white spot defect emphasis process). The figure which shows the state which synthesize | combined the application result of the distance 3, 6, and 12 pixel filter (white spot defect emphasis process). The figure which shows the state which synthesize | combined the application result of the distance 3, 6, and 12 pixel filter (black spot defect emphasis process). The figure which shows the white spot result candidate which cut out the synthetic | combination result with the white spot defect threshold value. The figure which shows the black spot result candidate which cut out the synthetic | combination result with the black spot defect threshold value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Display panel, 2 ... Projector, 3 ... Pattern generator, 4 ... Screen, 5 ... CCD camera, 6 ... Computer apparatus, 7 ... Display apparatus, 60 ... Image input means, 61 ... background image difference processing means, 63 ... reduced image creation means, 64 ... stain defect enhancement processing means, 65 ... noise removal means, 66 ... stain defect extraction processing Means, 67... Blob processing means, 68... Defect rank classification processing means, 70... Spot defect, O... Target pixel, S1 to S32.

Claims (3)

A stain defect enhancement processing step of emphasizing a stain defect by applying a stain defect enhancement filter to each pixel of the captured image;
A stain defect detection step of detecting a stain defect based on a stain defect enhancement value of each pixel obtained in the stain defect enhancement processing step;
The spot defect emphasis processing step includes
Divide each luminance comparison pixel arranged at a predetermined distance from the selected target pixel in the captured image and around the target pixel into a set of two luminance comparison pixels arranged at symmetrical positions with the target pixel in between. ,
For each set, obtain one luminance value of the two luminance comparison pixels of the set as the first luminance value and the other luminance value as the second luminance value, respectively.
Comparison result between each of the first setting and the minimum setting value for setting the minimum luminance in the predetermined luminance range according to the luminance of the predetermined inspection target area and the maximum setting value for setting the maximum luminance in the predetermined luminance range. , And a comparison result between each of the minimum setting value and the maximum setting value and the second luminance value,
A first condition that is established when both the first luminance value and the second luminance value are within the predetermined luminance range; and the first luminance value is within the predetermined luminance range and the second luminance value is A second condition that is satisfied when the luminance value is outside the predetermined luminance range; and a third condition that is satisfied when the first luminance value is outside the predetermined luminance range and the second luminance value is within the predetermined luminance range. Set multiple conditions including
When the first condition is satisfied, a difference value between the luminance value of the target pixel and the average value of the first luminance value and the second luminance value is set as an enhancement calculation value,
When the second condition is satisfied, a difference value between the luminance value of the target pixel and the first luminance value is set as the enhancement calculation value,
When the third condition is satisfied, a difference value between the luminance value of the target pixel and the second luminance value is set as the enhancement calculation value,
Emphasizes a spot defect using a spot defect enhancement filter that uses the minimum value of the enhancement calculation values of each set as a spot defect enhancement value of the target pixel,
The spot defect detection step is characterized by detecting a spot defect by extracting a spot defect candidate pixel by comparing the spot defect enhancement value of each pixel with a predetermined threshold value. In the spot defect detection method according to claim 1,
The plurality of conditions include a fourth condition that is established when both the first luminance value and the second luminance value are outside the predetermined luminance range,
When the fourth condition is satisfied, a predetermined invalid value that can be distinguished from a value that can be taken by a luminance difference between the target pixel and each luminance comparison pixel is used as the enhancement calculation value. Detection method. A stain defect enhancement processing means for emphasizing a stain defect by applying a stain defect enhancement filter to each pixel of the captured image;
Spot defect detection means for detecting a spot defect based on the spot defect enhancement value of each pixel obtained by the spot defect enhancement processing means;
The spot defect emphasis processing means is
Divide each luminance comparison pixel arranged at a predetermined distance from the selected target pixel in the captured image and around the target pixel into a set of two luminance comparison pixels arranged at symmetrical positions with the target pixel in between. ,
For each set, obtain one luminance value of the two luminance comparison pixels of the set as the first luminance value and the other luminance value as the second luminance value, respectively.
Comparison result between each of the first setting and the minimum setting value for setting the minimum luminance in the predetermined luminance range according to the luminance of the predetermined inspection target area and the maximum setting value for setting the maximum luminance in the predetermined luminance range. , And a comparison result between each of the minimum setting value and the maximum setting value and the second luminance value,
A first condition that is established when both the first luminance value and the second luminance value are within the predetermined luminance range; and the first luminance value is within the predetermined luminance range and the second luminance value is A second condition that is satisfied when the luminance value is outside the predetermined luminance range; and a third condition that is satisfied when the first luminance value is outside the predetermined luminance range and the second luminance value is within the predetermined luminance range. Set multiple conditions including
When the first condition is satisfied, a difference value between the luminance value of the target pixel and the average value of the first luminance value and the second luminance value is set as an enhancement calculation value,
When the second condition is satisfied, a difference value between the luminance value of the target pixel and the first luminance value is set as the enhancement calculation value,
When the third condition is satisfied, a difference value between the luminance value of the target pixel and the second luminance value is set as the enhancement calculation value,
Emphasizes a spot defect using a spot defect enhancement filter that uses the minimum value of the enhancement calculation values of each set as a spot defect enhancement value of the target pixel,
The spot defect detection device detects a spot defect by extracting a spot defect candidate pixel by comparing the spot defect enhancement value of each pixel with a predetermined threshold value.