JP2006210043A - Image evaluation method of plasma display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to appropriately evaluate and inspect the luminance unevenness of discharge cell unit occurring in a plasma display panel by distinguishing it from disconnection due to contact failure. <P>SOLUTION: The image evaluation method comprises a step in which an image of the plasma display panel is photographed by an imaging means and an isolation point removal processing is applied to the image photographed, a step in which a peripheral comparison processing is applied wherein the values based on the differential between the image data of the object pixel and the image data of the peripheral pixel are made the image data of the object pixel, a step in which binary processing is applied for extracting as a detection part the region in which a pixel having the image data in a prescribed relation with an established threshold exists, and a step in which, thereafter the detection part is determined whether it is a non-lighting region or not and the image of the plasma display panel is evaluated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image evaluation method for evaluating an image displayed on a plasma display panel.

  The plasma display panel is configured such that a front substrate and a rear substrate are arranged to face each other so that a discharge space is formed therebetween, a peripheral portion is sealed, and a rare gas is sealed in the discharge space. A plurality of display electrodes composed of scan electrodes and sustain electrodes are formed on the front substrate, and a plurality of address electrodes are formed on the rear substrate in a direction orthogonal to the display electrodes. A discharge cell which is a unit light emitting region is formed in the part. In this plasma display panel, a predetermined voltage is applied to the display electrode and the address electrode to generate a discharge selectively in each discharge cell, and the phosphor layer formed in each discharge cell emits light by discharge, An image is displayed.

When manufacturing such a plasma display panel, it is necessary to evaluate the performance of the panel. For example, Patent Document 1 discloses a method for evaluating the performance of a plasma display panel.
JP 11-86731 A

  A plasma display panel is desired to have a uniform display image with no variation in luminance. However, in the actual display image, luminance unevenness occurs because the difference in emission luminance between discharge cells becomes large due to factors such as significant variations in the discharge start voltage in each discharge cell constituting the plasma display panel. If a person views the display image at this time, the display image feels rough. The brightness unevenness referred to here is brightness unevenness (brightness unevenness in units of discharge cells) caused by a brightness difference for each discharge cell, and is brightness unevenness occurring in a minute range. Such uneven brightness needs to be evaluated in the panel inspection process.

  Therefore, a method for quantitatively evaluating and inspecting such luminance unevenness in units of discharge cells using camera imaging and image processing has been studied. However, when the plasma display panel is lit in the panel inspection process, a lighting signal is supplied to the panel by bringing the inspection device side terminal into contact with the panel side terminal. The electrical connection between the panel side terminal and the inspection device side terminal When a connection failure (contact failure) occurs, the above-described method using image processing has a problem that it is difficult to distinguish between disconnection due to contact failure and luminance unevenness in discharge cell units.

  The present invention has been made to solve the above-described problems, and makes it possible to perform appropriate evaluation and inspection by distinguishing luminance unevenness occurring in a discharge cell unit in a plasma display panel from disconnection caused by contact failure. For the purpose.

  In order to achieve the above object, an image evaluation method for a plasma display panel according to the present invention includes a step of imaging an image of a plasma display panel by an imaging means, performing isolated point removal processing on the captured image, and then a target pixel A step of performing a peripheral comparison process in which a value based on a difference between the image data of the pixel and the image data of the peripheral pixels is used as the image data of the target pixel, and thereafter, a pixel having image data having a predetermined relationship with a set threshold value A step of performing binarization processing for extracting a region in which a light source exists as a detection unit, and a step of determining whether or not the detection unit is a non-lighting region and evaluating an image of the plasma display panel. Features.

  According to the present invention, it is possible to quantitatively evaluate the brightness unevenness in units of discharge cells that can occur in the plasma display panel, in distinction from the disconnection due to contact failure, and to appropriately evaluate the brightness unevenness, Inspection can be performed.

  According to a first aspect of the present invention, there is provided an image evaluation method for a plasma display panel having a plurality of discharge cells between a pair of substrates and displaying an image by generating a discharge in each discharge cell. Capturing an image of the plasma display panel, performing isolated point removal processing on the captured image, and then calculating a value based on the difference between the image data of the target pixel and the image data of the surrounding pixels of the target pixel. A step of performing a peripheral comparison process as image data, a step of performing a binarization process of extracting, as a detection unit, an area where pixels having image data having a predetermined relationship with a set threshold value are present, and Determining whether or not the detection unit is a non-lighting region and evaluating an image of the plasma display panel. And wherein the door.

  According to a second aspect of the present invention, in the first aspect of the invention, it is determined whether or not the detection unit is a non-lighting region using at least one of the aspect ratio of the detection unit or the average difference sum of the detection units. It is characterized by performing.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  First, the structure of the plasma display panel will be described with reference to FIG. As shown in FIG. 1, the front panel 1 includes a plurality of display electrodes made up of scanning electrodes 3 and sustain electrodes 4 formed on a glass front substrate 2, and a dielectric made of dielectric glass so as to cover the display electrodes. The body layer 5 is formed, and the protective layer 6 made of magnesium oxide (MgO) is formed on the dielectric layer 5.

  On the other hand, the back panel 7 disposed opposite to the front panel 1 has a plurality of address electrodes 9 formed on a glass back substrate 8, and a dielectric layer 10 is formed so as to cover the address electrodes 9. A plurality of partition walls 11 parallel to the address electrodes 9 are formed on the body layer 10, and phosphor layers that emit light of red (R), green (G), and blue (B) colors between the adjacent partition walls 11. 12 is formed. The address electrode 9 is located between the adjacent partition walls 11.

  The front substrate 2 and the rear substrate 8 which are a pair of substrates are arranged to face each other so that the scan electrodes 3 and the sustain electrodes 4 and the address electrodes 9 are orthogonal to each other, and a peripheral member of these substrates is a sealing member (not shown). A discharge gas composed of neon and xenon is sealed in a discharge space formed between the front substrate 2 and the back substrate 8. A discharge cell is formed at the three-dimensional intersection of scan electrode 3 and sustain electrode 4 and address electrode 9. The discharge cell is a unit light emitting region for displaying an image, and one pixel is formed by three adjacent discharge cells formed with phosphor layers 12 that emit light in R, G, and B colors.

  The front substrate 2 and the rear substrate 8 have a rectangular planar shape. Normally, the scan electrodes 3 and the sustain electrodes 4 are formed in parallel (horizontal direction) with respect to the long sides of the front substrate 2, and the address electrodes 9 are formed on the rear substrate 8. It is formed in parallel (perpendicular direction) to the short side. A terminal connected to the scanning electrode 3 or the sustain electrode 4 is formed at the short side end (left end, right end) of the front substrate 2, and the long side end (upper end) of the back substrate 8 is formed. , The lower end portion) is formed with a terminal connected to the address electrode 9. These terminals are the panel side terminals described above. The terminal connected to the address electrode 9 is formed on either the upper end or the lower end of the rear substrate 8 (single scan type), and the address electrode 9 is formed on the upper half and the lower half of the rear substrate 8. A type in which the terminals connected to the upper half address electrodes 9 are formed at the upper end of the rear substrate 8 and the terminals connected to the lower half address electrodes 9 are formed at the lower end of the rear substrate 8 (dual Scan type).

  In this plasma display panel, a discharge cell to be displayed is selected by sequentially applying a scan pulse to the scan electrode 3 and applying an address pulse to the address electrode 9 based on image data. Thereafter, sustain pulses are alternately applied to scan electrode 3 and sustain electrode 4 to cause sustain discharge in the selected discharge cells. As a result, ultraviolet rays are generated in the discharge cells in which the sustain discharge has occurred, and visible light of each color is emitted from the phosphor layer 12 excited by the ultraviolet rays, and image display is performed.

  Next, a method for evaluating luminance unevenness in units of discharge cells when performing panel inspection on such a plasma display panel will be described. FIG. 2 is an overall configuration diagram of a system that quantitatively evaluates luminance unevenness in units of discharge cells in an embodiment of the present invention.

  As shown in FIG. 2, the plasma display panel 13 to be inspected is mounted on the panel holding unit 14 and driven by the drive circuit 15. The power supply 16 supplies power to the drive circuit 15, and the signal generator 17 supplies signals to the drive circuit 15, and the power supply 16 and the signal generator 17 are controlled by the control device 18. Further, a camera 19 such as a CCD camera as an imaging means captures an image displayed on the plasma display panel 13 and outputs it as digital image data having intensity data of R, G and B for each pixel of the camera 19. To do. Here, it is desirable that the camera 19 has a resolution that allows the pixels of the camera 19 to measure at least one pixel with respect to one pixel of the plasma display panel 13. The image memory 20 as image storage means temporarily stores an image of the plasma display panel 13 captured by the camera 19 as image data. The image processing unit 21 is configured mainly with a CPU, for example, and performs various processes using the image data stored in the image memory 20 and outputs an evaluation result.

  FIG. 3 is a flowchart of image evaluation in this embodiment. Steps 1 to 7 are sequentially performed, and an evaluation result is output. Using this evaluation method, the quality of the panel can be determined in the panel inspection process when the plasma display panel 13 is manufactured. Hereinafter, each step will be described.

  First, in step 1, an image corresponding to a signal from the signal generator 17 is displayed on the plasma display panel 13 installed in the panel holding unit 14. At this time, an inspection apparatus side terminal (for example, a terminal of a flexible printed circuit board) electrically connected to the drive circuit 15 is brought into contact with a panel side terminal of the plasma display panel 13, and the plasma display panel 13 is driven by the drive circuit 15. Then, an image displayed on the plasma display panel 13 is picked up using the camera 19, and digital image data R (red data), G (red data), which are intensity data of red, green, and blue in each pixel of the camera 19, respectively. Green data) and B (blue data) are stored in the image memory 20. Here, the image displayed on the plasma display panel 13 is, for example, displayed in white by lighting all the discharge cells.

  Next, in step 2, luminance conversion processing is performed on the image data stored in the image memory 20. In the luminance conversion process, image data Y representing the luminance of each pixel is obtained by converting the image data R, G, and B of each pixel in the captured image using, for example, the following Equation 1.

  In the next step 3, isolated point removal processing is performed on the image having the image data Y obtained in step 2. It is desirable to use one of the two methods shown in FIG. 4 or 5 for the isolated point removal processing. 4 and 5, the input image is an image before the isolated point removal process is performed, and the numerical values in the drawings are the values of the image data Y for a part of the pixels, that is, the image data f (x, y) of the input image. Represents the value of. Here, x and y specify the position of the pixel, and the horizontal direction is x and the vertical direction is y. The output image is an image after the isolated point removal process is performed on the input image, and the numerical values in the figure are the values of the image data for the target pixel, that is, the image data F (x, y) of the output image. Represents a value. Here, the target pixel is a pixel to be subjected to isolated point removal processing, and a pixel to be subjected to each processing in step 4 and subsequent steps is referred to as a target pixel.

  As shown in FIG. 4, the first method of the isolated point removal process is an intermediate value filter process in which the image data in the target pixel of the input image is replaced with the intermediate value of the image data in the pixels in the vicinity region. In the example of FIG. 4, the target pixel and eight pixels surrounding the target pixel are employed as the pixels in the vicinity region. That is, although the x-direction filter size and the y-direction filter size are both 3, this value can be changed as appropriate. Then, the value of the image data F (x, y) after the intermediate value filter processing in the target pixel is arranged in order of the size of the image data f (x, y) in the target pixel in the input image and the surrounding eight pixels. It is the value (19) that comes to the center.

  As shown in FIG. 5, the second method of the isolated point removal process is a smoothing filter process that replaces the image data in the target pixel of the input image with the average value of the image data in the pixels in the vicinity region. In FIG. 5, as in the case of FIG. 4, the target pixel and eight pixels surrounding the target pixel are adopted as the pixels in the vicinity region, but can be changed as appropriate. Then, the value of the image data F (x, y) after the smoothing filter processing in the target pixel is the average value (24) of the image data f (x, y) in the target pixel and the surrounding eight pixels in the input image. It has become.

  These intermediate value filter processing and smoothing filter processing are both isolated point removal processing for the purpose of removing isolated points and removing and suppressing noise in the image.

  In the next step 4, peripheral comparison processing is performed on the image that has undergone isolated point removal processing in step 3. As the peripheral comparison process, a primary differentiation process for comparing the image data of the target pixel of the input image with the image data of the pixel existing in the two directions, or a secondary differentiation process for comparing with the image data of the pixel existing in the four directions. Can be used. Hereinafter, the peripheral comparison process will be described with reference to FIGS. 6 and 7. In each figure, the image data of the input image at the pixel specified by x and y is f (x, y), and the image data of the output image Is F (x, y).

  As shown in FIG. 6, the first-order differentiation process is f (x, y) for image data of a certain target pixel, f (x + 1, y) for image data of a pixel located right next to the target pixel, Assuming that the image data of the pixel located below the target pixel is f (x, y + 1), for example, the absolute value of G (x, y) obtained by the following equation 2 is the image data F (x, y). To do. Here, the pixels located on the right side and the lower side of the target pixel are selected as the peripheral pixels.

Then, when calculating the data example of the input image shown in FIG.
G (x, y) = 2 × 11−30−5 = −13
Thus, the image data F (x, y) of the output image at the target pixel is 13.

  Further, as shown in FIG. 7, the second-order differential processing is performed by using f (x, y) for the image data of a certain target pixel and f (x-1, y) for the image data of the pixel located to the left of the target pixel. y), f (x + 1, y) is the image data of the pixel located right next to the target pixel, f (x, y-1) is the image data of the pixel located next to the target pixel, and the target pixel Assuming that the image data of the pixel located below is f (x, y + 1), for example, the absolute value of G (x, y) obtained by the following equation 3 is set as the image data F (x, y) It is. Here, the pixels located on the left side, the right side, the upper side, and the lower side of the target pixel are selected as the peripheral pixels.

Then, when calculating the data example of the input image shown in FIG.
G (x, y) = 4 × 11−51−30−55−5 = −97
Therefore, the image data F (x, y) of the output image at the target pixel is 97.

  As described above, in the peripheral comparison process, the sum of the differences between the image data of the target pixel and the image data of the peripheral pixel is used as the image data of the target pixel. When such peripheral comparison processing is performed, if the luminance of the target pixel is significantly different from the luminance of the peripheral pixels, the image data of the output image at the target pixel becomes a large value. In other words, in the output image when the peripheral comparison process is performed, pixels having a large luminance difference with the surrounding pixels have large image data, and pixels having a small luminance difference with the peripheral pixels have small image data. is doing. For this reason, it can be determined that there is a possibility that luminance unevenness occurs in units of discharge cells in the pixel having large image data and in the vicinity thereof.

  In the above description, as an example when the peripheral comparison process is performed, the target pixel and the peripheral pixel are adjacent to each other. However, for example, a pixel located three pixels to the right of the target pixel or a pixel located five pixels above. The peripheral comparison processing may be performed using the image data of the target pixel and the image data of the peripheral pixel, with the pixel to be processed as the peripheral pixel. However, since the detection target is uneven luminance in units of discharge cells, it is desirable that the number of pixels existing between the target pixel and the peripheral pixels is 10 pixels or less.

  Next, a binarization process is performed on the image obtained by performing the peripheral comparison process in step 4, in which pixels in which the image data is equal to or greater than a predetermined threshold value are extracted in step 5. . An example when the result is represented in an image is shown in FIG. In FIG. 8, areas represented by black dots (black areas existing inside broken lines 22a and 22b) are areas extracted by binarization processing (detection units), and the image data is equal to or greater than the threshold value. This is a region where pixels exist, that is, a region where pixels with a large luminance difference from surrounding pixels exist. As described above, in the binarization processing, a region where pixels having image data having a predetermined relationship with a certain threshold value are extracted as a detection unit, and pixels whose image data is larger than the threshold value. May be extracted.

  Here, if the extracted regions are scattered like the portions surrounded by the broken lines 22a and 22b in FIG. 8, it is difficult to accurately evaluate the luminance unevenness in units of discharge cells. Therefore, in the next step 6, the image subjected to the binarization process in step 5 is subjected to a combination process in which a plurality of detection units existing in a short distance are combined and handled as one detection unit, and the discharge is performed. Make it possible to accurately evaluate luminance unevenness in cell units. Here, for example, a combination process may be performed for a detection unit that is within a range of m pixels (m = 10) in the horizontal direction and n pixels (n = 10) in the vertical direction. It can be set appropriately. In FIG. 8, the extracted areas 23a and 23b represent disconnection points due to contact failure between the panel side terminals and the inspection apparatus side terminals, which is a case of the dual scan type.

  FIG. 9 shows an example of an output image after the combining process in step 6 is performed on the image of FIG. In FIG. 9, the detection unit A to detection unit D are regions where pixels having image data equal to or greater than the threshold exist, but the detection unit A and the detection unit B are portions where luminance unevenness exists in units of discharge cells, The detection part C and the detection part D are detecting the disconnection by a contact defect.

  In the next step 7, using the detection unit A to the detection unit D extracted by the series of processing of step 1 to step 6, a determination process is performed to determine luminance unevenness in units of discharge cells of the plasma display panel 13. Here, it is necessary to distinguish luminance unevenness in units of discharge cells from disconnection due to contact failure.

  As the determination index used in this determination process, a detection unit area, a detection unit total difference sum, a detection unit average difference sum, an aspect ratio, and the like, which are feature amounts representing the characteristics of the detection unit, are used. Here, when a plurality of detection units are detected (four in the case of FIG. 9), the detection unit area, the detection unit total difference sum, the detection unit average difference sum, and the aspect ratio are defined for each detection unit. The Although the detection unit A will be described below, the detection units B to D are also defined in the same manner.

The detection unit area is the total number of pixels included in the detection unit A. Further, the total detection unit difference is the sum of the image data for all the pixels of the detection unit A in the output image at the end of step 4. The detection unit average difference sum is an average value for the image data of all the pixels of the detection unit A in the output image at the end of step 4,
The sum of the detection part average difference = the total difference of the detection part / the area of the detection part. The aspect ratio is a ratio (W / L) of the length (W) in the horizontal direction to the length (L) in the vertical direction of the detection unit. By using any one of these determination indexes or a combination of a plurality of determination indexes, it is possible to inspect the luminance unevenness of the discharge cell unit of the plasma display panel quantitatively and accurately. For example, a predetermined determination reference value is determined for each of the detection unit area, the detection unit total difference sum, and the detection unit average difference sum that are determination indexes, and the detection unit area, the detection unit total difference sum, and the detection unit average difference sum If any one of them is larger than the determination reference value, the luminance unevenness in discharge cell units is large, and it is determined that the panel is defective. Can be judged.

  Next, a method for distinguishing between regions having unevenness of brightness in units of discharge cells (detection unit A, detection unit B) and regions representing disconnection due to contact failure (detection unit C, detection unit D) will be described.

  The detection unit C and the detection unit D, which are portions that detect a disconnection due to a contact failure, have a feature that the aspect ratio is small. That is, when a contact failure occurs, the discharge cell formed by the electrode that has caused the contact failure (in the case of FIG. 9, the address electrode) does not light up. The disconnection area is a line area in the vertical direction, and the aspect ratio is smaller than that of the detection unit A and the detection unit B. In addition, when the electrode having a contact failure is a scan electrode or a sustain electrode, the region of disconnection due to the contact failure is a horizontal line-shaped region, and the aspect ratio is larger than that of the detection unit A and the detection unit B. Therefore, in the aspect ratio, a new threshold value that can distinguish between uneven brightness in discharge cells and disconnection due to contact failure is set as appropriate, and determination is made using the threshold value. And can be distinguished.

  Moreover, the part which has detected the disconnection due to the contact failure has a feature that the detection part average difference sum is large. This is because the luminance of the broken portion due to contact failure is almost 0, and the luminance is clearly lower than the portion where the luminance due to luminance unevenness is small. Therefore, in the detection unit average difference sum, by setting a new threshold value that can distinguish between luminance unevenness in discharge cell units and disconnection due to contact failure, and determining using the threshold value, luminance unevenness and contact failure in discharge cell units It can be distinguished from disconnection due to.

  Furthermore, determination may be made using both the aspect ratio and the detection unit average difference sum. Thereby, for example, when a region having luminance unevenness in units of discharge cells overlaps with a region representing disconnection due to contact failure, they can be effectively distinguished.

  As described above, in the determination process of step 7, the detection unit A to the detection unit D are determined as to whether or not they are non-lighting areas, and the image of the plasma display panel is evaluated. It is possible to determine whether or not the detection unit A to the detection unit D are non-lighting regions by using at least one of the ratio or the detection unit average difference sum.

  As described above, according to the present invention, it is possible to quantitatively evaluate brightness unevenness in units of discharge cells, which can occur in a plasma display panel, by distinguishing from disconnection due to contact failure, and for plasma display panel inspection. Useful.

The perspective view which shows a part of plasma display panel in one embodiment of this invention 1 is an overall configuration diagram of a system for evaluating brightness unevenness in units of discharge cells according to an embodiment of the present invention. The flowchart explaining the flow of the image processing in one embodiment of the present invention Explanatory drawing of intermediate value filter processing Illustration of smoothing filter processing Explanatory drawing of first derivative processing Explanatory drawing of the secondary differentiation process The figure which shows an example of the image when the image data after a periphery comparison process is binarized The figure which shows an example of the image after a joint process

Explanation of symbols

2 Front substrate 8 Rear substrate 19 Camera 20 Image memory 21 Image processing unit

Claims (2)

In an image evaluation method for a plasma display panel that has a plurality of discharge cells between a pair of substrates and displays an image by generating a discharge in each discharge cell, the image of the plasma display panel is picked up by an image pickup means and picked up Performing an isolated point removal process on the image, and thereafter performing a peripheral comparison process using a value based on a difference between the image data of the target pixel and the image data of the peripheral pixels as the image data of the target pixel; Thereafter, a step of performing binarization processing for extracting a region where pixels having image data having a predetermined relationship with a set threshold value exist as a detection unit, and then determining whether or not the detection unit is a non-lighting region And a step of evaluating an image of the plasma display panel. Image evaluation method of Ipaneru. 2. The image evaluation method for a plasma display panel according to claim 1, wherein at least one of the aspect ratio of the detection unit and the average difference sum of the detection units is used to determine whether or not the detection unit is a non-lighting region. .

Images