JP6114559B2 - Automatic unevenness detector for flat panel display - Google Patents

Description

The present invention relates to an automatic unevenness detection device for a flat panel display for automatically detecting luminance and color non-uniformity (unevenness) generated in a flat panel display manufacturing process by performing arithmetic processing based on image data.

  In recent years, various types of flat panel displays have been developed and commercialized. One of the defects that degrade the image quality of such flat panel displays is luminance and color non-uniformity (unevenness).

  Conventionally, inspection of unevenness at a production site has been visually performed by an inspector. However, since much time, inspection personnel, and cost are required, automation of inspection is desired, and some automation is progressing.

  As an example of such an automation method, a technique for photographing an emitted flat panel with a camera and detecting unevenness by image processing has been developed and is used in an inspection process (for example, non-patented). Reference 1).

Tetsuya Otani et al., “Image quality inspection algorithm for flat panel displays”, Yokogawa technique, vol. 47 No. 3 (2003)

However, the prior art has the following problems.
Such automatic inspection is still insufficient in performance and cannot cope with various defects other than specific point defects and line defects.

FIG. 9 is a flowchart relating to a series of unevenness detection processing performed by a conventional flat panel display automatic unevenness detection apparatus. The flow shown in FIG. 9 is roughly divided into the following three parts.
(1) Pre-processing unit (noise removal by filters, background image estimation, etc.)
(2) Defect candidate extraction unit (candidates are extracted by binarization and labeling)
(3) Judgment unit (extracts feature quantities related to defects, identifies and displays defective parts with judgment rules based on experience)

  That is, in the unevenness inspection, the estimation accuracy of the background image has a great influence on the subsequent processing, which is very important. However, conventionally, the estimation accuracy of the background image is not always sufficient. For this reason, there is a problem that false detection eventually occurs such as detecting false unevenness at a place other than unevenness (overdetection) or not detecting the unevenness to be detected (undetected).

  As a method for estimating the background image, a two-dimensional low-pass filter process having a large filter size is usually performed on the unevenness inspection target image. However, if unevenness (a part of) is included in the filter range, the output value of the filter is affected by the influence, and the estimation accuracy of the background image is lowered. For example, in the case of bright unevenness, the background of the uneven portion becomes slightly brighter than in the case where there is no unevenness, and on the contrary, it becomes slightly darker around the unevenness.

  In addition, when the filter range extends beyond the end of the frame, the image data inside the frame is usually folded outward and the portion is filled in for filtering. At this time, if the brightness of the flat panel display is as low as the edge of the frame, or if the brightness is low near the edge of the frame because the peripheral brightness is low when shooting with the camera, the protruding filter part is filled. Since the pixel value is different from the desired pixel value, erroneous detection occurs near the frame end.

The present invention has been made to solve the above-described problems, and is a flat that can achieve high accuracy when automatically detecting non-uniformity (unevenness) areas by image processing in an inspection process. An object is to obtain an automatic unevenness detection device for a panel display.

  An automatic unevenness detection apparatus for a flat panel display according to the present invention takes a two-dimensional image of a light emission state of a flat panel display imaged by a camera as an unevenness inspection target image, and generates a background image without unevenness based on the unevenness inspection target image. A pre-processing unit that generates a difference image between the unevenness inspection target image and the background image, a defect candidate extraction unit that performs a non-uniformity candidate region extraction process on the difference image generated by the pre-processing unit, and defect candidate extraction An automatic unevenness detection device for a flat panel display that determines the presence or absence of a uneven region by performing image processing with a determination unit that performs authenticity determination of the unevenness candidate region extracted by the image processing unit. Equipped with multiple filters to calculate the estimated background pixel value of the pixel of interest from pixel values at multiple pixel positions near the pixel The plurality of filters are configured as a one-dimensional or two-dimensional array that defines a plurality of pixel positions in the vicinity of the target pixel, and the interval between the plurality of pixels constituting the array and the direction of the array differ depending on each filter. Using each of the plurality of filters for the unevenness inspection target image, the respective background pixel estimation values for the target pixel are calculated based on the pixel values at the plurality of pixel positions specified by the respective filters. By performing statistical processing on each of the background pixel estimated values, a background image is generated by selecting one background pixel estimated value suitable for the background pixel for each pixel of interest.

According to the present invention, in the estimation of the background image in the preprocessing, the estimation accuracy is improved by adaptively selecting an appropriate filter from a plurality of filters according to the pixel position and performing the filter processing. Thus, it is possible to obtain an automatic unevenness detection device for a flat panel display capable of realizing high accuracy when automatically detecting a non-uniformity (unevenness) region by image processing in an inspection process.

1 is an overall configuration diagram of an automatic unevenness detection apparatus for a flat panel display according to Embodiment 1 of the present invention. It is explanatory drawing regarding the conventional background image estimation process. It is explanatory drawing regarding the background image estimation process of the automatic nonuniformity detection apparatus of the flat panel display in Embodiment 1 of this invention. It is explanatory drawing regarding the some filter used by the background image estimation process in Embodiment 1 of this invention. It is a figure which shows the 1st Example in the pre-processing part of the automatic nonuniformity detection apparatus of the flat panel display of this invention. It is a figure which shows the 2nd Example in the pre-processing part of the automatic nonuniformity detection apparatus of the flat panel display of this invention. It is a figure which shows the 3rd Example in the pre-processing part of the automatic nonuniformity detection apparatus of the flat panel display of this invention. It is explanatory drawing of the clustering process in Embodiment 1 of this invention. It is a flowchart regarding a series of nonuniformity detection processing by the automatic nonuniformity detection apparatus of the conventional flat panel display.

Hereinafter, preferred embodiments of an automatic unevenness detection apparatus and automatic unevenness detection method for a flat panel display according to the present invention will be described with reference to the drawings.
It should be noted that the present invention is based on preprocessing for accurately detecting irregular irregularities in a technique for capturing irregularities automatically by image processing by taking a camera-captured image of a flat panel display that emits light in an arbitrary pattern into a computer. This relates to background image estimation.

More specifically, the present invention, when estimating a non-uniform background image based on the non-uniformity detection target image,
(1) In order to estimate the background pixel value at the position of the target pixel, a plurality of filters having different tap shapes and arrangements are used.
(2) Perform candidate selection and determination of appropriate filters and estimated pixel values based on statistical methods,
(3) The technical feature is to improve the accuracy of the background image, which is the difference between the background image and the unevenness inspection target image, and the background image. As a result, the accuracy of detecting unevenness can be improved. .

Embodiment 1 FIG.
FIG. 1 is an overall configuration diagram of an automatic unevenness detection apparatus for a flat panel display according to Embodiment 1 of the present invention. The automatic unevenness detection apparatus for a flat panel display according to the first embodiment shown in FIG. 1 includes a camera 10, an image processing unit 20, and a display unit 30, and is a flat panel display (hereinafter referred to as “inspection target”). Automatic unevenness detection of “inspection panel 1” is performed.

  The image processing unit 20 performs image processing on the light emission state of the inspection panel 1 captured by the camera 10, thereby specifying a region where unevenness has occurred and causing the display unit 30 to display the specified location. Can do. The image processing unit 20 includes a preprocessing unit 21, a defect candidate extraction unit 22, and a determination unit 23.

The pre-processing unit 21 is a part that performs correction processing on an image captured by the camera 10 in order to perform processing by the defect candidate extraction unit 22 at the subsequent stage. Specific examples of processing include the following. Can be mentioned.
-Enlargement / reduction processing-Geometric correction-Shading correction-Noise removal (smoothing filter, median filter, etc.)
・ Pixel structure removal ・ Background image prediction removal

Further, the defect candidate extraction unit 22 is a part that extracts a candidate region of a defect portion corresponding to unevenness from the image that has passed through the preprocessing unit 21, and specific examples of processing include the following. Can be mentioned.
・ Enhancement processing ・ Edge detection (Laplacian filter, Sobel filter, etc.)
-First feature value calculation-Binarization-Isolated point removal-Expansion / contraction processing-Labeling

Furthermore, the determination unit 23 is a part that finally determines whether or not the candidate area extracted by the defect candidate extraction unit 22 is uneven. Specific examples of processing include the following. .
・ Second feature amount calculation ・ Identification (threshold judgment, classification, etc.)

  Here, the prior art related to the background image estimation process most relevant to the present application will be briefly described with reference to the drawings. FIG. 2 is an explanatory diagram related to a conventional background image estimation process, and shows a processing result by the pretreatment unit in steps S901 to S903 shown in FIG.

  FIG. 2A shows a non-uniformity detection target image after performing camera noise removal, removal of the pixel structure of the flat panel display, and the like on the output image of the camera 10 that has captured the flat panel display (inspection panel 1). . The image in FIG. 2A corresponds to an image generated by noise removal in step S901 in FIG.

  FIG. 2A illustrates a case where there is white (bright) unevenness in the lower left. A horizontal waveform passing through the cursor displayed to the right of the white unevenness is also shown in the lower part of FIG.

  Further, an estimated background image in FIG. 2B is obtained by applying a low-pass filter using a Gaussian filter to the output image of the camera 10. Note that the image in FIG. 2B corresponds to an image generated by the filter processing in step S902 in FIG. It can be seen that the white unevenness as shown in FIG. 2A is easily suppressed by a normal low-pass filter, but is still weak and remains broad (see the lower waveform in FIG. 2B).

  Therefore, in the background differential image of FIG. 2C obtained by subtracting the background image shown in FIG. 2B from the detection target image shown in FIG. (See the lower waveform in FIG. 2C). Note that the image in FIG. 2C corresponds to an image generated by the difference calculation in step S903 in FIG.

  Thus, in contrast to the conventional technique in which background image estimation is performed using a low-pass filter, in the present invention, a plurality of filters having different tap shapes and arrangements are used, and an appropriate filter based on a statistical method is used. And candidate selection and determination of estimated pixel values. As a result, the accuracy of the background image and the background difference image, which is the difference between the unevenness inspection target image and the background image, can be improved, thereby making it possible to detect unevenness with high accuracy.

  FIG. 3 is an explanatory diagram relating to background image estimation processing of the automatic unevenness detection apparatus for a flat panel display according to Embodiment 1 of the present invention. The outline of the background image estimation process in the first embodiment will be described in comparison with FIG. 2 relating to the prior art. The unevenness detection target image in FIG. 3A is the same as the image in FIG.

  In the estimated background image of FIG. 3B, the unevenness remaining weakly and broadly as in FIG. 2B is almost completely eliminated. Therefore, in the background difference image of FIG. 3C, compared to the previous FIG. 2C, the level remains as it is in the uneven portion, and the level is not lowered near the periphery of the unevenness, and is flat. It is. That is, it can be seen that the background image is estimated and the background difference image is generated with higher accuracy than in the past.

  Therefore, the background image estimation processing according to the present invention will be described in detail with reference to FIGS. FIG. 4 is an explanatory diagram relating to a plurality of filters used in the background image estimation processing according to Embodiment 1 of the present invention. The plurality of filters used in the first embodiment are different in tap shape and arrangement.

  In FIG. 4A, six filters 0 to 5 are illustrated as specific examples of the four-tap filter of the one-dimensional array. The filter 0 to the filter 5 have different tap intervals (s pixel, 2s pixel, 3s pixel: where s is an integer of 1 or more) and the orientation of the array (horizontal and vertical) as shown in FIG. ing.

  That is, the plurality of filters are configured as a one-dimensional or two-dimensional array that defines a plurality of pixel positions in the vicinity of the target pixel, and the interval between the plurality of pixels constituting the array and the direction of the array differ depending on each filter. ing. A plurality of pixels specified by the respective filters are referred to as “taps”.

  The relative positional relationship between these six filters is arbitrary. In addition, the filter of the present invention is not limited to the type illustrated in FIG. 4 (a), and other ones such as an oblique one-dimensional array and various two-dimensional arrays can be applied. Not exclusively.

Further, these six filters 0 to 5 can function as the following three types of first to third filters as shown in FIG. 4B.
First filter: first pixel value estimating means for approximating the pixel value at the tap position with, for example, a quadratic function and outputting an estimated value of the target pixel by approximation calculation. Second filter: above-mentioned The estimated value by the first pixel value estimating function is output, and the sum of squares of the difference value between the actual pixel value at each tap and the estimated value by the first pixel value estimating function or the sum of the absolute values of the differences (Hereinafter, collectively referred to as difference variance) calculating and further outputting difference variance evaluation means Third filter: second pixel for estimating and outputting a pixel value of interest based on the pixel value of each tap by interpolation Value estimation means

  When a part of the tap is uneven, the difference between the actual pixel value and the estimated value at each tap increases, or the error in the estimated value of the target pixel increases. In addition, each filter output is the timing at which each pixel of interest is the same pixel, and the following processing means (for example, the selectors in the first to third embodiments described later with reference to FIGS. 3, a delay unit (not shown) is used as appropriate.

  FIG. 5 is a diagram showing a first embodiment of the preprocessing unit of the automatic unevenness detection apparatus for a flat panel display according to the present invention. The preprocessing unit 21a in the first embodiment shown in FIG. 5 includes a noise removal unit 51, six second filters 52 (0) to 52 (5), a first determination unit 53, a selector 54, and A difference calculation unit 55 is provided.

  In the first embodiment, six second filters 52 (0) to 52 (5) having a difference variance evaluation unit are used as filters. And the 1st determination means 53 receives the output of the difference dispersion | distribution of each filter 52 (0) -52 (5), and determines those minimum values.

  Further, the selector 54 receives the determination result by the first determination unit 53 and each estimated pixel value by the first pixel value estimating unit in each of the filters 52 (0) to 52 (5), and the difference variance is minimized. Select an estimated pixel value by a certain filter.

  Then, the difference calculating unit 55 generates an estimated background image by using the estimated pixel value selected by the selector 54, and further, between the unevenness inspection target image from which the noise is removed by the noise removing unit 51 and the estimated background image. A background difference image is generated by taking the difference.

  Next, FIG. 6 is a figure which shows the 2nd Example in the pre-processing part of the automatic nonuniformity detection apparatus of the flat panel display of this invention. The pre-processing unit 21b in the second embodiment shown in FIG. 6 includes a noise removing unit 61, six second filters 62 (0) to 62 (5), a clustering unit 63, a second determination unit 64, The estimated value determination means 65 and the difference calculation part 66 are provided.

  In the second embodiment, six second filters 62 (0) to 62 (5) having difference variance evaluation means are used as filters. Then, the clustering unit 63 performs clustering on the estimated value of the target pixel by the filters 62 (0) to 62 (5).

  The second determination unit 64 receives each difference variance by the difference variance evaluation unit in each of the filters 62 (0) to 62 (5) and the clustering result by the clustering unit 63, and determines the optimum estimated value or the vicinity thereof. Which cluster is to be determined. For example, the second determination unit 64 calculates an average value of the difference variance corresponding to the estimated value for each cluster, and determines that the cluster having the smallest value is a cluster based on the optimal estimated value or a value in the vicinity thereof. .

  Further, the estimated value determining means 65 receives the determination result by the second determining means 64 and each estimated pixel value by the first pixel value estimating means in each of the filters 62 (0) to 62 (5). One estimated value is output based on the configured estimated value. For example, the estimated value determining means 65 can obtain, for example, an average value or a median for the estimated values constituting the cluster specified by the second determining means 64, and can output it as one estimated value.

  Then, the difference calculation unit 66 generates an estimated background image by using one estimated value output by the estimated value determining unit 65, and further, the unevenness inspection target image from which noise is removed by the noise removing unit 61 A background difference image is generated by taking the difference from the estimated background image.

  Next, FIG. 7 is a figure which shows the 3rd Example in the pre-processing part of the automatic nonuniformity detection apparatus of the flat panel display of this invention. The preprocessing unit 21c in the third embodiment shown in FIG. 7 includes a noise removal unit 71, six filters 72 (0) to 72 (5), a clustering unit 73, a third determination unit 74, and an estimated value determination. Means 75 and a difference calculation unit 76 are provided.

  In the third embodiment, six filters 72 (0) to 72 (5) configured by any of the first, second, and third filters are used as filters. Then, the clustering unit 73 performs clustering on the estimated value of the pixel of interest by each of the filters 72 (0) to 72 (5).

  Further, the third determination unit 74 receives the estimated value of the target pixel by the first pixel estimation unit in each of the filters 72 (0) to 72 (5) and the clustering result by the clustering unit 73, and receives the optimum estimated value. And which cluster is composed of and its neighbors. For example, the third determination unit 74 determines that the cluster having the largest number of estimated values constituting the cluster is the optimum cluster.

  Further, the estimated value determining means 75 receives the result of determination by the third determining means 74 and the estimated value of the target pixel by the first pixel estimating means in each of the filters 72 (0) to 72 (5). One estimated value is output based on the configured estimated value. For example, the estimated value determining means 75 can obtain, for example, an average value or a median for the estimated values included in the cluster specified by the third determining means 74 and output it as one estimated value.

  Then, the difference calculation unit 76 generates an estimated background image by using one estimated value output by the estimated value determining unit 75, and further, the unevenness inspection target image from which noise is removed by the noise removing unit 71 A background difference image is generated by taking the difference from the estimated background image.

  The clustering means 63 shown in FIG. 6 or the clustering means 73 shown in FIG. 7 does not particularly specify a method, and for example, a k-average method may be applied. It is also possible to use a simple method shown in FIG. FIG. 8 is an explanatory diagram of the clustering process according to the first embodiment of the present invention.

First, in step S801, the clustering unit sorts N estimated pixel values P _i (i = 0, 1,..., N−1) that are integers of 2 or more, in descending order of values, and p _j (j = 0, 1,..., N−1) is obtained.

Next, in step S _< b> 802, the clustering unit calculates a distance between adjacent estimated pixel values (corresponding to a pixel value difference) d _ij = p _i −p _j (= −dji) with respect to p _j after sorting. Next, in step S803, the clustering means calculates a standard deviation σ of the distance d _ij . Finally, in step S804, the clustering means can set a cluster boundary between pi and pj that is represented by the following expression (1). For example, k = 2 can be set as k.
| D _ij |> k * σ (1)

  In the first to third embodiments described above, although not shown in FIGS. 5 to 7, a median filter or other low-pass filter may be applied to the estimated background image. Thereby, it is possible to obtain a background image in which the influence of the case where the characteristics of the applied filter are shifted between adjacent pixels due to noise or the like can be obtained, and the accuracy of the background difference image can be improved.

  As described above, according to the first embodiment, by using a statistical process in the background image estimation process in the preprocessing, an appropriate result is obtained from among the calculation results using a plurality of filters for each target pixel. The estimated value can be selected adaptively. Thereby, an appropriate filter process can be performed according to the pixel position, and the estimation accuracy of the background image can be improved. As a result, it is possible to obtain an automatic unevenness detecting device and an automatic unevenness detecting method for a flat panel display capable of realizing high accuracy when automatically detecting a non-uniformity (unevenness) region by image processing in an inspection process. .

  DESCRIPTION OF SYMBOLS 1 Inspection panel, 10 cameras, 20 Image processing part, 21, 21a, 21b, 21c Preprocessing part, 22 Defect candidate extraction part, 23 Judgment part, 30 Display part, 51 Noise removal part, 52 Each filter, 53 1st Determination means, 54 selector, 55 difference calculation section, 61 noise removal section, 62 filters, 63 clustering means, 64 second determination means, 65 estimation value determination means, 66 difference calculation section, 71 noise removal section, 72 filters 73 Clustering means, 74 Third determination means, 75 Estimated value determination means, 76 Difference calculation section.

Claims (3)

A two-dimensional image of a light emission state of a flat panel display captured by a camera is captured as a non-uniformity inspection target image, a non-uniform background image is generated based on the non-uniformity inspection target image, and the non-uniformity inspection target image and the background image A pre-processing unit that generates a difference image of the defect, a defect candidate extraction unit that performs an extraction process of a non-uniformity candidate region on the difference image generated by the pre-processing unit, and the unevenness candidate extracted by the defect candidate extraction unit An automatic unevenness detection device for a flat panel display that determines the presence or absence of an uneven region by performing image processing with a determination unit that performs authenticity determination of the region,
The pre-processing unit is
A plurality of filters for calculating a background pixel estimated value of the target pixel from pixel values at a plurality of pixel positions in the vicinity of the target pixel;
The plurality of filters are configured as a one-dimensional or two-dimensional array that defines the plurality of pixel positions in the vicinity of the pixel of interest, and an interval between the plurality of pixels constituting the array and an orientation of the array are respectively It depends on the filter,
Using each of the plurality of filters for the unevenness inspection target image, based on pixel values at a plurality of pixel positions specified by the respective filters, calculating respective background pixel estimated values in the target pixel, By performing statistical processing on each of the calculated background pixel estimated values, a background image is generated by selecting one background pixel estimated value suitable for the background pixel for each target pixel ,
The pre-processing unit is
The first pixel value estimation means includes first pixel value estimation means for calculating an estimated value of the pixel of interest by function approximation calculation for pixel values at the plurality of pixel positions specified by the respective filters. A second difference variance evaluation unit that calculates a sum of squares of a difference value between the estimated value calculated by the unit and an actual pixel value at the plurality of pixel positions or a sum of absolute values of the differences as a difference variance. Filtering processing section of
First determination means for determining a minimum value of the difference variance of each filter calculated by using each of the plurality of filters by the difference variance evaluation means in the second filtering processing unit;
An estimation calculated by using the filter having the minimum value determined by the first determination unit from among the respective estimation values calculated by the first pixel value estimation unit in the second filtering processing unit. A selector that selects a value as one background pixel estimate suitable for the background pixel;
An automatic unevenness detection apparatus for a flat panel display. A two-dimensional image of a light emission state of a flat panel display captured by a camera is captured as a non-uniformity inspection target image, a non-uniform background image is generated based on the non-uniformity inspection target image, and the non-uniformity inspection target image and the background image A pre-processing unit that generates a difference image of the defect, a defect candidate extraction unit that performs an extraction process of a non-uniformity candidate region on the difference image generated by the pre-processing unit, and the unevenness candidate extracted by the defect candidate extraction unit An automatic unevenness detection device for a flat panel display that determines the presence or absence of an uneven region by performing image processing with a determination unit that performs authenticity determination of the region,
The pre-processing unit is
A plurality of filters for calculating a background pixel estimated value of the target pixel from pixel values at a plurality of pixel positions in the vicinity of the target pixel;
The plurality of filters are configured as a one-dimensional or two-dimensional array that defines the plurality of pixel positions in the vicinity of the pixel of interest, and an interval between the plurality of pixels constituting the array and an orientation of the array are respectively It depends on the filter,
Using each of the plurality of filters for the unevenness inspection target image, based on pixel values at a plurality of pixel positions specified by the respective filters, calculating respective background pixel estimated values in the target pixel, By performing statistical processing on each of the calculated background pixel estimated values, a background image is generated by selecting one background pixel estimated value suitable for the background pixel for each target pixel ,
The pre-processing unit is
The first pixel value estimation means includes first pixel value estimation means for calculating an estimated value of the pixel of interest by function approximation calculation for pixel values at the plurality of pixel positions specified by the respective filters. A second difference variance evaluation unit that calculates a sum of squares of a difference value between the estimated value calculated by the unit and an actual pixel value at the plurality of pixel positions or a sum of absolute values of the differences as a difference variance. Filtering processing section of
Clustering means for performing clustering on each estimated value calculated by the first pixel value estimating means in the second filtering processing unit;
Regarding the difference variance of each filter calculated by each of the plurality of filters by the difference variance evaluation unit in the second filtering processing unit, an average value of the difference variances for each cluster clustered by the clustering unit And a second determination means for determining a cluster with the calculated average value being minimum,
Among the estimated values calculated by the first pixel value estimating unit in the second filtering processing unit, the estimated value included in the cluster having the minimum average value determined by the second determining unit An estimated value determining means for calculating an average value or a median of one as a background pixel estimated value suitable for the background pixel;
An automatic unevenness detection apparatus for a flat panel display. A two-dimensional image of a light emission state of a flat panel display captured by a camera is captured as a non-uniformity inspection target image, a non-uniform background image is generated based on the non-uniformity inspection target image, and the non-uniformity inspection target image and the background image A pre-processing unit that generates a difference image of the defect, a defect candidate extraction unit that performs an extraction process of a non-uniformity candidate region on the difference image generated by the pre-processing unit, and the unevenness candidate extracted by the defect candidate extraction unit An automatic unevenness detection device for a flat panel display that determines the presence or absence of an uneven region by performing image processing with a determination unit that performs authenticity determination of the region,
The pre-processing unit is
A plurality of filters for calculating a background pixel estimated value of the target pixel from pixel values at a plurality of pixel positions in the vicinity of the target pixel;
The plurality of filters are configured as a one-dimensional or two-dimensional array that defines the plurality of pixel positions in the vicinity of the pixel of interest, and an interval between the plurality of pixels constituting the array and an orientation of the array are respectively It depends on the filter,
Using each of the plurality of filters for the unevenness inspection target image, based on pixel values at a plurality of pixel positions specified by the respective filters, calculating respective background pixel estimated values in the target pixel, By performing statistical processing on each of the calculated background pixel estimated values, a background image is generated by selecting one background pixel estimated value suitable for the background pixel for each target pixel ,
The pre-processing unit is
A first filtering processing unit having first pixel value estimating means for calculating an estimated value of the target pixel by function approximation calculation for pixel values at the plurality of pixel positions specified by the respective filters;
A sum of squares of differences between the estimated values calculated by the first pixel value estimating means and actual pixel values at the plurality of pixel positions, or a difference. A second filtering processing unit having difference variance evaluation means for calculating a sum of absolute values of the values as a difference variance, or
A third filtering processing unit having second pixel value estimating means for calculating an estimated value of the target pixel by interpolation processing based on pixel values at the plurality of pixel positions specified by the respective filters.
A filtering processing unit that is any one of
Clustering means for performing clustering for each estimated value calculated by the filtering processing unit;
For each estimated value calculated by the filtering processing unit, third determining means for determining a cluster having the largest number of estimated values constituting each cluster clustered by the clustering means;
Among the estimated values calculated by the filtering processing unit, an average value or median of estimated values included in a cluster having the largest number of estimated values determined by the third determining unit is used as the background pixel. Estimated value determining means for calculating as one background pixel estimated value suitable for
An automatic unevenness detection apparatus for a flat panel display.

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