JP2011002401A - Correction coefficient calculating method in luminance measuring apparatus, and luminance measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To create precise correction data without using any expensive surface light source in a luminance measuring apparatus.SOLUTION: A correction coefficient calculating method in the luminance measuring apparatus having an imaging element equipped with a plurality of pixels is provided which includes: the step of photographing an object at a reference position; the step of photographing the object at a position shifted by at least one pixel from the reference position; the sensitivity ratio calculating step of calculating a sensitivity ratio of each pixel with respect to a prescribed reference pixel, based on a result of above photographing operations; and the sensitivity correction coefficient calculating step of calculating a sensitivity correction coefficient of each pixel, based on the sensitivity ratio.

Description

  The present invention relates to a luminance measuring apparatus, and more particularly, to a sensitivity characteristic correction technique for an image sensor provided in the luminance measuring apparatus.

  A luminance measuring device for measuring the luminance of an inspection object is known. FIG. 7 is a block diagram illustrating a configuration example of a conventional luminance measuring apparatus. As shown in the figure, a luminance measuring device 600 that measures the luminance and luminance distribution of the inspection object 700 includes an imaging device 610 and a control device 620. The inspection object 700 can be, for example, a flat panel display device, a flat light source, or the like.

  The imaging device 610 controls imaging processing in the imaging device 610 such as an optical system 611 including a lens, a diaphragm mechanism, an imaging element 612 such as a CCD and a CMOS, and exposure and imaging timing, and outputs captured image data. An imaging control unit 613.

  The control device 620 includes an image input unit 621 for inputting image data, an image correction unit 622, an image processing unit 623, a result display unit 624, and a correction data creation unit 625. The image processing unit 623 performs determination processing such as enhancement processing, binarization processing, feature amount calculation processing, and identification processing on the image data, and evaluates the luminance and luminance distribution of each display element of the inspection target. The result display unit 624 displays an evaluation result or the like as an image or outputs a file.

  In general, the image data output from the imaging device 610 is not the true luminance distribution of the inspection object but the luminance unevenness due to the peripheral dimming that is the characteristic of the optical system 611 and the variation in the sensitivity characteristic of each imaging element 612. Contains. The image correction unit 622 corrects the luminance unevenness to make an image showing the true luminance distribution of the inspection object. This correction is performed using correction data created by the correction data creation unit 625.

  The correction data can be created as follows. That is, a reference surface light source having a uniform luminance distribution is prepared, and the image capturing device 610 images the reference surface light source. Since the luminance distribution of the image data is based on the characteristics of the imaging device 610, the reciprocal of the luminance value of each pixel of the imaging element 612 is calculated and used as correction data. At this time, Median processing, smoothing processing, and the like may be performed.

JP 2008-76203 A

  An integrating sphere or the like is used as the reference surface light source having a uniform luminance distribution, but the correction accuracy based on the correction data depends on the accuracy of the in-plane luminance distribution of the reference surface light source. Therefore, in order to improve the correction accuracy based on the correction data, it is necessary to prepare a highly accurate reference surface light source having a uniform in-plane luminance distribution. However, large and highly accurate reference surface light sources are generally expensive.

  Accordingly, an object of the present invention is to create highly accurate correction data without using an expensive surface light source in a luminance measuring apparatus.

  In order to solve the above-described problem, a correction coefficient calculation method according to a first aspect of the present invention is a correction coefficient calculation method in a luminance measurement apparatus having an imaging device having a plurality of pixels, and an object is detected at a reference position. A step of imaging, a step of imaging the object by shifting by at least one pixel with respect to the reference position, and a sensitivity ratio calculating step of calculating a sensitivity ratio for each pixel with respect to a predetermined reference pixel based on the imaging result And a sensitivity correction coefficient calculation step of calculating a sensitivity correction coefficient for each pixel based on the sensitivity ratio.

  In the present invention, since the sensitivity ratio for each pixel is calculated by imaging the same area of the object with different pixels, high-precision correction is performed without using a high-precision reference surface light source with a uniform in-plane luminance distribution. Data can be created.

  More specifically, the sensitivity ratio calculation step includes at least one pixel value corresponding to the luminance value acquired at the reference pixel when the pixels on the shift direction side of the reference pixel are sequentially set as the target pixel and imaged at the reference position. The product of the ratio of the luminance value acquired at the reference pixel side pixel (referred to as the “first comparison pixel”) of the target pixel and the sensitivity ratio of the first comparison pixel when the images are shifted and captured. It can be the sensitivity ratio of the pixel.

  In the sensitivity ratio calculation step, the pixels on the side opposite to the shifting direction of the reference pixel are sequentially set as the target pixel, and the luminance value acquired by the target pixel when the image is shifted by at least one pixel, and the reference position The product of the ratio of the luminance value acquired at the reference pixel side pixel (referred to as “second comparison pixel”) of the target pixel and the sensitivity ratio of the second comparison pixel when the image is captured It can be a sensitivity ratio.

  Furthermore, the sensitivity correction coefficient calculation step can calculate a reciprocal of the sensitivity ratio to obtain a sensitivity correction coefficient.

  In addition, the step of imaging the object includes a process of imaging by shifting at least one pixel in the horizontal direction and a process of imaging by shifting by at least one pixel in the vertical direction, and the sensitivity ratio calculating step includes: Alternatively, the sensitivity ratio for each pixel may be calculated in the vertical direction.

  Alternatively, the step of imaging the object includes a process of imaging with different brightness of the object, and the sensitivity ratio calculating step includes a correction coefficient corresponding to a change in brightness for each brightness of the object. The sensitivity ratio may be calculated.

  In order to solve the above-described problem, a luminance measuring apparatus according to a second aspect of the present invention is a luminance measuring apparatus having an imaging device including a plurality of pixels, and is shifted by at least one pixel from a reference position. A fine movement mechanism for moving an image sensor, and an image of an object at a reference position, an image of the object that is shifted by at least one pixel with respect to the reference position, and a pixel corresponding to a predetermined reference pixel based on the imaging result A correction data creation unit that calculates a sensitivity ratio for each pixel, calculates a sensitivity correction coefficient for each pixel based on the sensitivity ratio, and an image correction unit that corrects image data captured by the image sensor using the sensitivity correction coefficient And comprising.

  According to the present invention, it is possible to create highly accurate correction data without using an expensive surface light source in the luminance measuring apparatus.

It is a block diagram which shows the structure of the brightness | luminance measuring apparatus which concerns on this embodiment. It is a flowchart which shows the correction data creation procedure. It is a figure explaining the position of pixel shift. It is a figure which shows the imaging result in three places which shifted the pixel. It is a figure which shows the calculation area | region and calculation result of a sensitivity ratio. It is a figure which shows the calculation result of the brightness | luminance correction coefficient which is correction data. It is a block diagram which shows the structural example of the conventional brightness | luminance measuring apparatus.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a luminance measuring apparatus according to the present embodiment. As shown in this figure, the luminance measuring apparatus 100 that measures the luminance and the luminance distribution for each display element of the inspection object 200 includes an imaging device 110, a control device 120, and a fine movement mechanism 130. The inspection object 200 can be, for example, a flat panel display device, a surface light source, or the like.

  The imaging device 110 controls imaging processing in the imaging device 110 such as an optical system 111 including a lens, a diaphragm, an imaging element 112 such as a CCD and a CMOS, and exposure and imaging timing, and outputs captured image data. An imaging control unit 113. However, the imaging process may be controlled on the control device 120 side.

  The control device 120 includes an image input unit 121 for inputting image data, an image correction unit 122, an image processing unit 123, a result display unit 124, and a correction data creation unit 125. The control device 120 can use an information processing device such as a PC.

  The image correction unit 122 corrects the luminance unevenness of the image data captured by the imaging apparatus 110 using the correction data generated by the correction data generation unit 125. Here, the correction data is data in which a luminance correction coefficient is determined for each pixel of the image sensor 112, and the image correction unit 122 multiplies the luminance value of each pixel of the image data by the corresponding luminance correction coefficient. Thus, the luminance unevenness is corrected.

  The image processing unit 123 performs determination processing such as enhancement processing, binarization processing, feature amount calculation processing, and identification processing on the image data, and evaluates the luminance and luminance distribution of each display element of the inspection target. The result display unit 124 displays an evaluation result or the like as an image or outputs a file.

  The correction data creation unit 125 calculates a sensitivity ratio for each pixel with respect to a predetermined reference pixel based on an imaging result obtained by imaging the reference surface light source at a position shifted by at least one pixel from the reference position and the reference position. Correction data is created by calculating a sensitivity correction coefficient for each pixel based on the sensitivity ratio.

  More specifically, when calculating the sensitivity ratio, the pixels on the reference pixel shift direction side are sequentially used as the target pixel, and the luminance value acquired at the target pixel when the image is captured at the reference position is shifted by at least one pixel. The sensitivity ratio of the target pixel is the product of the ratio of the luminance value acquired by the pixel on the reference pixel side of the target pixel (referred to as “first comparison pixel”) and the sensitivity ratio of the first comparison pixel. And

  In addition, the pixel on the opposite side of the reference pixel shift direction is sequentially set as the target pixel, and the luminance value acquired at the target pixel when the image is shifted by at least one pixel, and the reference pixel of the target pixel when the image is captured at the reference position The product of the ratio of the luminance value acquired by the pixel on the side (referred to as “second comparison pixel”) and the sensitivity ratio of the second comparison pixel is defined as the sensitivity ratio of the target pixel.

  The fine movement mechanism 130 moves the imaging position of the imaging device 110 in the horizontal direction and the vertical direction in units of pixels under the control of the correction data creation unit 125. When a so-called pixel-shifted image is captured, the dead zone of the image sensor is compensated by finely moving the image sensor by a movement amount that is less than one pixel such as 1/2, 1/3, or 1/4. The fine movement mechanism 130 moves the imaging position of the imaging device 110 in units of pixels, and moves at least one pixel. The fine movement mechanism 130 can be configured using, for example, an actuator in a fine movement stage described in Japanese Patent Application Laid-Open No. 2008-98968.

  In the above configuration, when the correction data creation unit 125 creates correction data, a reference surface light source (not shown) is imaged instead of the inspection object 200. In this embodiment, the luminance distribution of the reference surface light source does not have to be as uniform as required in the conventional configuration, and can be a surface light source, a screen, a white reference plate, or the like having a substantially uniform luminance distribution. . Therefore, correction data can be created without using an expensive reference surface light source.

  The correction data creation procedure in this embodiment will be described with reference to the flowchart of FIG. First, the imaging device 110 images the reference surface light source at the reference position A (S101). Here, the reference position A can be an arbitrary position at which each pixel of the image sensor 112 can photograph the reference surface light source.

  Next, the fine movement mechanism 130 is operated to move the imaging device 110 to a position B that has been moved by one pixel in the horizontal direction (S102). Here, as shown in FIG. 3, a position where the imaging device 110 is moved to the right by one pixel is defined as a position B. Then, the reference plane light source is imaged at position B (S103).

  When the reference surface light source is imaged at the position B, the fine movement mechanism 130 is operated to move the imaging device 110 to the position C moved by one pixel in the vertical direction with respect to the reference position A (S105). Here, as illustrated in FIG. 3, a position where the imaging apparatus 110 is moved upward by one pixel with respect to the reference position A is defined as a position C. Then, the reference plane light source is imaged at position C (S105).

  The reason why the horizontal direction and the vertical direction are shifted by one pixel is that the same area on the reference plane light source is captured with different pixels, and the sensitivity ratio for each pixel can be calculated. This is because the movement of about one pixel keeps the uniformity of the reference surface light source, and the influence of peripheral light reduction or the like can be reduced in the calculation of the sensitivity ratio. However, the shift amount is not limited to one pixel, and may be two or more pixels. In this case, in the calculation of the sensitivity ratio described later, the position of the pixel to be compared is adjusted according to the shift amount.

  When the imaging at the three positions where the pixels are shifted is finished, the horizontal direction sensitivity ratio is calculated (S106), and further the vertical direction sensitivity ratio is calculated (S107).

  Here, the horizontal direction sensitivity ratio and the vertical direction sensitivity ratio determine the reference pixel from among the pixels constituting the image sensor 612, and each other pixel is compared with the reference pixel in the imaging result of the reference surface light source. This is a value indicating how much sensitivity characteristic is provided.

  A method of calculating the horizontal direction sensitivity ratio and the vertical direction sensitivity ratio will be described with reference to FIGS. Here, for the sake of simplicity of explanation, the image sensor 612 includes nine pixels 1 to 9 in the horizontal direction and nine pixels 1 to 9 in the vertical direction, and is configured by a total of 81 pixels. And The reference pixel is the center (5, 5) pixel.

  FIG. 4 shows the imaging result at the reference position A, the imaging result at the position B, and the imaging result at the position C, and shows the luminance value of each pixel. First, the horizontal direction sensitivity ratio is calculated using the imaging result at the reference position A and the imaging result at the position B. In calculating the horizontal direction sensitivity ratio, the sensitivity ratio is calculated for each of the horizontal pixels (1, 5) to (9, 5) including the reference pixel. Since the sensitivity ratio is the ratio to the reference pixel (5, 5), the ratio of the reference pixel (5, 5) is 1.0.

  In the horizontal direction sensitivity ratio, the pixels (4, 5) to (1, 5) on the left side from the reference pixel indicated by the area 2 in FIG. 5 and the pixels (6, 5) to (9) on the right side from the reference pixel indicated in the area 1 are displayed. , 5) and the calculation method is different.

  First, a method of calculating the horizontal direction sensitivity ratio of the pixels (6, 5) to (9, 5) on the right side from the reference pixel indicated by the region 1 in FIG. 5 will be described. These pixels are pixels on the shifting direction side of the reference pixel. First, the pixel (6, 5) is set as a target pixel. In this case, the pixel (5, 5) is the first comparison pixel.

  As can be seen from the imaging result at the reference position A and the imaging result at the position B shown in FIG. 4, the area of the reference surface light source captured by the pixel (6, 5) at the reference position A is the reference pixel ( 5 and 5) are imaging. The luminance value of the pixel (6, 5) is 64 and the luminance value of the reference pixel (5, 5) is 48 even though the same region is imaged. That is, the sensitivity of the pixel (6, 5) is 64/48 = 1.33 with respect to the reference pixel (5, 5).

  Next, the pixel (7, 5) is set as a target pixel. In this case, the pixel (6, 5) is the first comparison pixel. Similarly to the case where the pixel (6, 5) is the target pixel, the area of the reference surface light source captured by the pixel (7, 5) at the reference position A is captured by the pixel (6, 5) at the position B. Will be. The luminance value of the pixel (7, 5) is 49 and the luminance value of the pixel (6, 5) is 56 even though the same area is imaged. That is, the sensitivity of the pixel (7, 5) is 49/56 = 0.88 with respect to the pixel (6, 5). Here, since the sensitivity of the pixel (6, 5) is 1.33 with respect to the reference pixel (5, 5), the sensitivity of the pixel (7, 5) to the reference pixel (5, 5) is 0.88. × 1.33 = 1.17.

From the above, the horizontal direction sensitivity ratio in the pixels (6, 5) to (9, 5) on the right side from the reference pixel indicated by the region 1 is
Sensitivity ratio (x, 5) = position A (x, 5) / position B (x−1, 5) × sensitivity ratio (x−1, 5)
Can be obtained.

  Next, a method of calculating the horizontal sensitivity ratio of the pixels (4, 5) to (1, 5) on the left side from the reference pixel indicated by the region 2 in FIG. 5 will be described. These pixels are pixels on the side opposite to the shifting direction of the reference pixel. First, the pixel (4, 5) is set as a target pixel. In this case, the pixel (5, 5) is the second comparison pixel.

  As can be seen from the imaging result at the reference position A and the imaging result at the position B shown in FIG. 4, the area of the reference surface light source captured by the reference pixel (5, 5) at the reference position A is the pixel ( 4 and 5) are imaging. The luminance value of the reference pixel (5, 5) is 60 and the luminance value of the pixel (4, 5) is 80 despite the image of the same region. That is, the sensitivity of the pixel (4, 5) is 80/60 = 1.33 with respect to the reference pixel (5, 5).

  Next, the pixel (3, 5) is set as a target pixel. In this case, the pixel (4, 5) is the second comparison pixel. As in the case where the pixel (4, 5) is the target pixel, the area of the reference surface light source captured by the pixel (4, 5) at the reference position A is captured by the pixel (3, 5) at the position B. Will be. The luminance value of the pixel (4, 5) is 64 and the luminance value of the pixel (3, 5) is 56 even though the same area is imaged. That is, the sensitivity of the pixel (3, 5) is 56/64 = 0.88 with respect to the pixel (4, 5). Here, since the sensitivity of the pixel (4, 5) is 1.33 with respect to the reference pixel (5, 5), the sensitivity of the pixel (3, 5) to the reference pixel (5, 5) is 0.88. × 1.33 = 1.17.

From the above, the horizontal direction sensitivity ratio in the pixels (4, 5) to (1, 5) on the left side from the reference pixel indicated by the region 2 in FIG.
Sensitivity ratio (x, 5) = position B (x, 5) / position A (x + 1, 5) × sensitivity ratio (x + 1, 5)
Can be obtained.

  The vertical direction sensitivity ratio is determined in the horizontal direction using the imaging result at the reference position A and the imaging result at the position C with reference to the column (hereinafter referred to as “reference column”) from which the horizontal direction sensitivity ratio is calculated. It can be calculated in the same manner as the sensitivity ratio.

  That is, the pixels (x, 4) to (x, 1) on the upper side from the reference column indicated by the region 3 in FIG. 5 which is the shifting direction side, and the lower side from the reference column indicated by the region 4 on the opposite side to the shifting direction. The calculation method is different for the pixels (x, 6) to (x, 9). Note that x is the vertical direction sensitivity ratio for each of 1 to 9 with reference to the reference column.

The vertical direction sensitivity ratios of the pixels (x, 4) to (x, 1) on the upper side from the reference column indicated by the region 3 in FIG.
Sensitivity ratio (x, y) = position A (x, y) / position C (x, y + 1) × sensitivity ratio (x, y + 1)
Can be obtained.

On the other hand, the vertical direction sensitivity ratios of the pixels (x, 6) to (x, 9) below the reference column indicated by the region 4 in FIG.
Sensitivity ratio (x, y) = position C (x, y) / position A (x, y−1) × sensitivity ratio (x, y−1)
Can be obtained. As a result, the sensitivity ratio of each pixel becomes a value as shown in FIG.

  When the sensitivity ratio with respect to the reference pixel is calculated for each pixel by the above procedure, the correction data creation unit 125 generates correction data (S108). Here, the correction data is a luminance correction coefficient for each pixel, and can be obtained by the reciprocal of the sensitivity ratio. FIG. 6 is a diagram showing the calculated luminance correction coefficient.

  The image correction unit 122 corrects each luminance value of the image data of the inspection object 200 imaged by the imaging device 110 in accordance with the correction data generated by the correction data generation unit 125, thereby obtaining image data without luminance unevenness. be able to.

  In the above-described example, a two-dimensional image sensor has been described as an example. However, the present invention can also be applied to a case where a one-dimensional line-type image sensor is used. When a line-type image sensor is used, a sensitivity ratio calculation process and a luminance correction coefficient calculation process for either the horizontal direction or the vertical direction may be performed.

  Further, although the sensitivity ratio of the reference pixel (5, 5) is 1.0, the sensitivity ratio may be determined in consideration of a characteristic difference with other imaging devices. For example, if the imaging device A has twice the sensitivity as compared with the imaging device B, the sensitivity ratio of the reference pixel (5, 5) in the imaging device A is set to 1.0, and the reference in the imaging device B The sensitivity ratio of the pixel (5, 5) may be set to 0.5. The sensitivity difference between the imaging devices can be obtained by comparing the luminance of the reference pixel with respect to the same object, calculating the average luminance value of the pixels in the predetermined area, or the like.

  Further, although the imaging positions are set at three positions shifted by one pixel, the entire imaging element may be corrected by moving the entire imaging element in the vertical and horizontal directions and imaging at each position. Further, the image correction unit 122 may be configured by hardware and provided on the imaging device 110 side so as to perform correction processing at high speed in real time.

  The correction data can be created by the correction data creation unit 125 not only before shipment of the luminance measuring apparatus but also after the shipment by the user, or by a service person during maintenance.

  As described above, according to the present embodiment, since the correction data is created by shifting the pixels and calculating the sensitivity ratio for each pixel, high accuracy can be achieved without using an expensive surface light source. Correction data can be created.

  Further, the correction data may be created with two or more different luminances, and not only the luminance distribution correction data but also the “inclination” and “intercept” of the sensitivity of each image sensor. That is, using two or more reference surface light sources with different luminances, correction data is created for each luminance, and if there is a difference in the correction data depending on the luminance, the sensitivity of the image sensor is corrected, or depending on the luminance By providing the correction coefficient term, it is possible to correct the luminance change. Further, “inclination” and “intercept” for each image sensor can be obtained by another method, and correction of the luminance distribution according to the present invention can be performed to perform correction with higher accuracy.

DESCRIPTION OF SYMBOLS 100 ... Luminance measuring apparatus 110 ... Imaging device 111 ... Optical system 112 ... Imaging element 113 ... Imaging control part 120 ... Control apparatus 121 ... Image input part 122 ... Image correction part 123 ... Image processing part 124 ... Result display part 125 ... Correction data Creation unit 130 ... fine movement mechanism 200 ... inspection object 600 ... luminance measuring device 610 ... imaging device 611 ... optical system 612 ... imaging element 613 ... imaging control unit 620 ... control device 621 ... image input unit 622 ... image correction unit 623 ... image Processing unit 624 ... Result display unit 625 ... Correction data creation unit 700 ... Inspection object

Claims (7)

A method for calculating a correction coefficient in a luminance measuring apparatus having an imaging device having a plurality of pixels,
Imaging a target object at a reference position;
Imaging the object with a shift of at least one pixel with respect to the reference position;
A sensitivity ratio calculating step of calculating a sensitivity ratio for each pixel with respect to a predetermined reference pixel based on the imaging result;
And a sensitivity correction coefficient calculation step of calculating a sensitivity correction coefficient for each pixel based on the sensitivity ratio. The correction coefficient calculation method according to claim 1,
The sensitivity ratio calculating step includes:
The pixel on the shift direction side of the reference pixel is sequentially set as the target pixel, and the luminance value acquired at the target pixel when imaged at the reference position and the reference pixel side of the target pixel when imaged at least one pixel apart A correction coefficient characterized in that a product of a ratio of a luminance value acquired at a pixel (referred to as a “first comparison pixel”) and a sensitivity ratio of the first comparison pixel is a sensitivity ratio of the target pixel. Calculation method. The correction coefficient calculation method according to claim 1 or 2,
The sensitivity ratio calculating step includes:
The pixel on the side opposite to the shifting direction of the reference pixel is sequentially set as the target pixel, and the luminance value acquired at the target pixel when the image is shifted by at least one pixel, and the reference of the target pixel when the image is captured at the reference position. The product of the ratio of the luminance value acquired by the pixel on the pixel side (referred to as “second comparison pixel”) and the sensitivity ratio of the second comparison pixel is used as the sensitivity ratio of the target pixel. Correction coefficient calculation method. The correction coefficient calculation method according to any one of claims 1 to 3,
The sensitivity correction coefficient calculation step includes:
A correction coefficient calculation method comprising calculating a reciprocal of the sensitivity ratio to obtain a sensitivity correction coefficient. A correction coefficient calculation method according to any one of claims 1 to 4,
The step of imaging the object includes a process of imaging by shifting at least one pixel in the horizontal direction and a process of imaging by shifting by at least one pixel in the vertical direction,
The sensitivity ratio calculating step calculates a sensitivity ratio for each pixel in the horizontal direction and the vertical direction. A correction coefficient calculation method according to any one of claims 1 to 5,
The step of imaging the object includes a process of imaging with different brightness of the object,
The correction factor calculation means characterized in that the sensitivity ratio calculation step calculates the sensitivity ratio for each luminance of the object in order to provide a correction factor corresponding to the luminance change. A luminance measuring device having an imaging device including a plurality of pixels,
A fine movement mechanism that moves the image sensor with a shift of at least one pixel with respect to a reference position;
An object is imaged at a reference position, the object is imaged by shifting by at least one pixel with respect to the reference position, a sensitivity ratio for each pixel with respect to a predetermined reference pixel is calculated based on the imaging result, A correction data creation unit that calculates a sensitivity correction coefficient for each pixel based on the sensitivity ratio;
An image correction unit that corrects image data captured by the image sensor using the sensitivity correction coefficient;
A luminance measuring apparatus comprising: