JP6565601B2 - Image correction device - Google Patents

Description

  The present invention relates to an image correction apparatus, and in particular, an image for correcting a two-dimensional image obtained by measuring a predetermined physical quantity while scanning a measurement target region of a sample using a scanning microscope such as an electron beam microanalyzer. The present invention relates to a correction device.

  In a scanning microscope, a sample is placed on a sample mounting table, and the measurement target region is scanned while sequentially irradiating each minute region of the measurement target region of the sample with an electron beam. Observe the shape. Furthermore, the element distribution on the sample surface can be measured by detecting a predetermined physical quantity such as an X-ray emitted from each irradiation position.

  For example, an electron beam microanalyzer (EPMA), which is one of scanning microscopes, scans a measurement target region on a sample surface with an electron beam to detect secondary electrons and characteristic X-rays emitted from the sample. FIG. 1 shows a main configuration of the electron beam microanalyzer 101. The electron beam emitted from the electron beam source 102 sequentially passes through the focusing lens 103, the scanning coil 104, and the objective lens 105, and is irradiated on the surface of the sample 107 placed on the sample placing table 106. The irradiation position of the electron beam is moved when the driving unit 108 operates the scanning coil 104 based on a control signal from the control unit 110.

  Secondary electrons emitted from the measurement region on the sample surface by irradiation with the electron beam are detected by the electron detector 109, and characteristic X-rays are detected by the X-ray detector 111. Output signals from the electron detector 109 and the X-ray detector 111 are sent to the control unit 110, and based on the output signals, an image of the shape in the measurement target region and a two-dimensional image representing the element distribution are created.

Japanese Patent Laid-Open No. 62-115636

  In the electron microanalyzer, secondary electrons and characteristic X-rays are measured at a number of measurement points separated by a length on the order of nm, which is determined according to the scanning speed of the electron beam and the time interval for detecting secondary electrons and characteristic X-rays. The detection signal is obtained. Therefore, it is possible to obtain a two-dimensional image with a high resolution on the order of nm.

  However, if the sample itself moves or the scanning is disturbed while scanning a predetermined region of the sample, the irradiation position of the electron beam is deviated from the control measurement point. Then, the measurement point misalignment that the measurement value acquired at a certain measurement point is actually the measurement value of one or several measurement points shifted (for example, Patent Document 1). When such misalignment occurs, blurring occurs in the two-dimensional image that is a set of measurement values. Specifically, the blurring of the image appears as local whisker-like vibration or distortion of the entire image.

  Conventionally, each measurement point is measured by using a measuring instrument to prevent the displacement of the above measurement points using a vibration isolation table or a magnetic shield, or by measuring temporal changes in current and voltage values supplied to the electron beam irradiation system. However, if these are introduced, the apparatus becomes expensive. In addition, the cause of the displacement of the measurement point is not limited to the above, and there is a problem that the displacement of the measurement point cannot always be eliminated even if all of the above are introduced.

  Here, the electron beam microanalyzer has been described as an example, but in addition to scanning the measurement target area with an electron beam, the measurement target area is scanned with another charged particle beam (ion beam, etc.), current, voltage, etc. The same problem as described above also occurred when scanning the measurement target region with the probe while inputting the.

  The problem to be solved by the present invention is to provide an image correction device capable of inexpensively and reliably correcting a two-dimensional image obtained by measuring a predetermined physical quantity while scanning a measurement target region of a sample. It is.

The first aspect of the image correction apparatus according to the present invention, which has been made to solve the above problems,
a) A distribution of measured values of the physical quantity in the measurement target area obtained by measuring a predetermined physical quantity at each measurement point in the measurement target area while scanning the measurement target area of the sample at a predetermined speed. And a reference image representing a distribution of measured values of the physical quantity obtained by measuring the physical quantity at each measurement point while scanning the measurement target area at a speed higher than the predetermined speed. Storage unit
b) a difference calculation unit for obtaining a difference between measured values of the physical quantity at corresponding measurement points of the reference image and the main image;
c) a correction target region extraction unit that extracts a correction target region including a plurality of measurement points adjacent to each other whose difference is equal to or greater than a predetermined threshold;
d) The correction target area of the main image is moved in the plane by one measurement point, and the difference between the measurement values of the corresponding measurement points of the main image and the reference image at each moving position as the entire correction target area. A movement amount determination unit for determining a movement amount with which the predetermined statistic is minimized;
e) a correction execution unit that replaces the measurement value by moving the measurement value of each measurement point in the correction target area of the main image by the movement amount.

  The main image targeted by the image correction apparatus according to the present invention is an image obtained by scanning while irradiating a beam of charged particles such as an ion beam in addition to an image obtained by scanning the measurement target region with an electron beam. There are also images obtained by inputting current and voltage while scanning with a probe. The predetermined physical quantity is, for example, secondary electrons, reflected electrons, characteristic X-rays, fluorescence, current, voltage, or the like.

  The correction target region including the one to a plurality of adjacent measurement points may be the correction target region itself including the one to a plurality of adjacent measurement points, or the correction target region including the one to a plurality of adjacent measurement points. And a correction target area obtained by adding a predetermined number of measurement points adjacent in the scanning direction.

  In the first aspect of the image correction apparatus according to the present invention, a main image obtained by measuring a predetermined physical quantity while scanning the measurement target area at a predetermined speed is measured at high speed by scanning the measurement target area. Correction is performed using the reference image obtained as described above. In the main image, the measurement point is often misaligned due to the long measurement time. On the other hand, since the reference image is scanned at a high speed, the measurement point is less misaligned than the main image. In the image correction apparatus according to the first aspect, the measurement point where the magnitude of the difference between the measurement values of the main image and the reference image is equal to or larger than a predetermined threshold is set as a correction target region, and the positional deviation of the measurement point in the main image is It is determined that the position has occurred. Then, the correction target area is moved in the plane (in the xy direction) by one measurement point, and the difference (generally, a predetermined statistical value) from the measurement value of the reference image as the entire correction target area Find the minimum amount of movement. This is replaced by moving the measurement value of each measurement point of the main image by the movement amount as a movement amount due to the deviation of the main image, thereby correcting the positional deviation of the measurement point.

  In the image correction apparatus according to the present invention, when the positional deviation of the sample occurs at a relatively high speed, for example, even when the sample vibrates, the scanning speed for forming the reference image is set to such a (predicted) The correction can be performed in the same manner by performing at a higher speed than the vibration. Therefore, it is possible to correct the main image at a lower cost than in the prior art without using an additional device such as a vibration isolation table. In addition, the main image can be reliably corrected regardless of the cause of the displacement of the measurement point.

The image correction apparatus according to the first aspect further divides one image of the main image and the reference image into a plurality of divided images, and measures the measured value of each measurement point of each divided image to the measurement of the other image. A drift amount calculation unit for obtaining a drift amount of each divided image in comparison with the measured value of the point;
A drift correction unit that corrects drift of the one image by moving the divided image so as to cancel out the drift amount;
With
It is preferable that the difference calculation unit obtains a difference between measured values of the physical quantity at corresponding measurement points using the reference image or the main image after drift correction by the drift correction unit.

  In general, when acquiring a main image, it takes a long time (for example, several hours when measuring characteristic X-rays) to measure a predetermined physical quantity at each measurement point with sufficient intensity. Scan. When measurement is performed for a long time in a scanning microscope, in addition to the above-described positional deviation of the measurement point, there is often a deviation (so-called drift occurs) in the relative position between the scanning system such as an electron beam irradiation system and the sample. If the main image includes the effect of drift, the position of the sample in the measurement target area differs even at the same measurement point on the main image and the reference image. The correct difference cannot be obtained. When the image correction apparatus of the above aspect including the drift amount calculation unit and the drift correction unit is used, in order to eliminate the influence of drift before obtaining the difference between the measurement values of the main image and the reference image, the correct difference of the measurement values Can be requested.

  The drift correction unit may create a function for converting a coordinate representing a position in one of the main image and the reference image into a coordinate representing the other position.

The second aspect of the image correction apparatus according to the present invention, which has been made to solve the above problems,
a) A distribution of measured values of the physical quantity in the measurement target area obtained by measuring a predetermined physical quantity at each measurement point in the measurement target area while scanning the measurement target area of the sample at a predetermined speed. A storage unit storing a main image to be represented;
b) a reference image creation unit that creates a reference image by smoothing the main image;
c) a difference calculation unit for obtaining a difference between measured values of the physical quantity at corresponding measurement points of the reference image and the main image;
d) a correction target area extracting unit that extracts a correction target area including a plurality of measurement points adjacent to each other whose difference is equal to or greater than a predetermined threshold;
e) The correction target area of the main image is moved in the plane by one measurement point, and the difference between the measurement values of the corresponding measurement points of the main image and the reference image at each moving position as the entire correction target area. A movement amount determination unit for determining a movement amount with which the predetermined statistic is minimized;
and f) a correction execution unit that moves the measurement value of each measurement point in the correction target area of the main image by the movement amount and replaces the measurement value.

  For the smoothing of the main image, for example, a smoothing filter such as a 3 × 3 or 5 × 5 median filter can be used.

  In the image correction apparatus of the first aspect, the reference image obtained by scanning the measurement target range at high speed is used. However, in the image correction apparatus of the second aspect, the reference image is obtained by smoothing the main image. create. The difference calculation unit, the correction target region extraction unit, the movement amount determination unit, and the correction execution unit of the image correction apparatus according to the second mode are common to the first mode, and the same effect as the first mode can be obtained. it can. In the second mode, since the reference image is created from the main image (that is, the original image is the same), it is not necessary to consider drift, and the main image can be corrected easily.

  By using the image correction apparatus according to the present invention, a two-dimensional image obtained by measuring a predetermined physical quantity while scanning a measurement target region of a sample can be corrected inexpensively and reliably.

The principal part block diagram of an electron beam microanalyzer. 1 is a main part configuration diagram of an image correction apparatus according to Embodiment 1. FIG. An example in which the reference image is deformed and drift correction is performed in the image correction apparatus according to the first embodiment. An example of obtaining a difference between measurement points of a main image and a reference image in the image correction apparatus according to the first embodiment. The figure explaining the threshold value for determining a correction target object correction point from the difference value of a measurement point. The figure explaining the relationship between a correction object measurement point, a correction object field, and a comparison field. An example of correcting an image by replacing measured values in a correction target area. Comparison of the main image before correction and the main image after correction. FIG. 6 is a configuration diagram of a main part of an image correction apparatus according to a second embodiment.

  Specific embodiments of the image correction apparatus according to the present invention will be described below with reference to the drawings. In the following, an example of correcting an image obtained by scanning a measurement target region on the sample surface with an electron beam in an electron beam microanalyzer will be described. However, scanning is performed while irradiating a charged particle beam such as an ion beam. It is possible to similarly correct an image obtained in this manner and an image obtained by inputting current and voltage while scanning with a probe.

<Example 1>
FIG. 2 shows a main configuration of the image correction apparatus 1 according to the first embodiment.
The image correction apparatus 1 includes a control unit 10, an input unit 18 connected to the control unit 10, and a display unit 19. In addition to the storage unit 11, the control unit 10 includes a drift amount calculation unit 12, a drift correction unit 13, a difference calculation unit 14, a correction target region extraction unit 15, a movement amount determination unit 16, and a correction execution unit 17 as functional blocks. I have. The entity of the control unit 10 is a personal computer in which required operating software (OS) or the like is installed.

  In the storage unit 11, a reference image that is an image obtained by measuring a secondary electron by scanning an area wider than the measurement target area with an electron beam in an electron beam microanalyzer, and the same measurement target area at a low speed. A main image (secondary electron image) and a target image (X-ray image), which are images obtained by scanning and measuring secondary electrons and characteristic X-rays, are stored in advance. The reference image may be acquired by measuring the same region as the measurement target region with an electron beam in an electron beam microanalyzer, but in order to perform drift correction described later more accurately, a region wider than the measurement target region. It is preferable that it is obtained by scanning.

  Hereinafter, a procedure for correcting the positional deviation between the main image and the target image in the image correction apparatus 1 of the present embodiment will be described.

  When the user instructs to start correction of the main image through the input unit 18, first, the drift amount calculation unit 12 reads out the main image and a reference image corresponding to the main image from the storage unit 11. Then, the main image is divided into a plurality of images (divided images) (FIG. 3A). Then, it is determined (template matching) at which position of the reference image each divided image corresponds to (refer to FIG. 3B), and the drift amount of the region is obtained. Template matching can be performed using, for example, a conventionally known normalized cross-correlation function. In FIG. 3A, a blank area is provided between the divided images in order to show the plurality of divided images in an easy-to-understand manner. However, the main image is divided into a plurality of images (divided images) in a lattice shape. It may be. Further, the size and number of the divided images may be appropriately determined in consideration of the shape of the sample on the image.

  When template matching is performed for all the divided images and the drift amount is determined, the drift correction unit 13 deforms the reference image based on the respective drift amounts. Specifically, from the obtained drift amount, the coordinate position of each measurement point of the reference image (more precisely, the center of the minute region representing the minute region on the reference image corresponding to each measurement point) is determined as the main image. A polynomial (for example, a cubic polynomial) that is converted into the coordinate position of each measurement point is created, and the reference image is deformed by using this polynomial (FIG. 3 (c)). This eliminates the effect of drift that occurs when acquiring the main image (and the target image). In the following description, a minute area on an image corresponding to a measurement point is also referred to as a measurement point for convenience.

  When the drift correction is completed, the difference calculation unit 14 compares the measurement value (detected intensity of secondary electrons) at each measurement point of the main image with the measurement value at the corresponding measurement point of the reference image after the deformation, and the difference Ask for. Then, the correction target region extraction unit 15 extracts measurement points (correction target measurement points) whose difference values exceed a predetermined threshold value. 4 (a) is an example of a main image, FIG. 4 (b) is an example of the above-described modified reference image, and FIG. 4 (c) is a white measurement point to be corrected based on a difference value between the main image and the reference image. It is an example displayed by painting.

  The above-mentioned threshold value can be obtained by obtaining an average value and standard deviation σ of differences at all measurement points, and adding a value obtained by multiplying the standard deviation by a predetermined coefficient n to the average value (average value + nσ). The statistical method can be determined (see FIG. 5). The coefficient may be determined before image correction is performed. However, the coefficient may be determined while confirming the number of measurement points extracted and the change in location by changing the coefficient. .

  When the correction target area extraction unit 15 extracts the correction target measurement points as shown in FIG. 4C, the correction target area extraction unit 15 subsequently groups the correction target measurement points adjacent to each other (FIG. 6A). A measurement point added at three measurement points on both sides in the electron beam scanning direction at the time of measurement is defined as a correction target region (FIG. 6B).

  When the correction target area is determined, the movement amount determination unit 16 expands two measurement points on both sides in the electron beam scanning direction during measurement and one measurement point in the non-scanning direction from the correction target area (FIG. 6B). The region is set as a comparison region (FIG. 6 (c)). Then, the correction target area is moved by one measurement point within the comparison area, and the square sum of the difference between the measurement value of each measurement point constituting the correction target area and the corresponding measurement point of the reference image is obtained. Determine the minimum amount of movement. In this embodiment, the amount of movement is determined so that the sum of squared differences is minimized, but the amount of movement can also be determined by various methods such as using the sum of absolute values of differences or a normalized correlation function.

  When the movement amount is determined by the above procedure for all the correction target areas, the correction execution unit 17 cuts out the measurement values of each correction target area from the main image (FIG. 7A), and is obtained for the correction target area. Move it by the amount of movement and replace it with the measured value at that measurement point. At this time, a measurement point at which the measurement value is missing is generated as the measurement value of the measurement point in the correction target region is cut out and moved. Accordingly, the measurement values at the measurement points located on both sides of the measurement point in the electron beam scanning direction are used to supplement the measurement values at these measurement points (for example, the average value of the measurement values at the measurement points on both sides) ( FIG. 7 (b)).

  The main image correction is completed by the above procedure. FIG. 8 shows a main image before correction (FIG. 8A) and a main image after correction (FIG. 8B). In the main image before correction in FIG. 8 (a), jagged disturbance can be confirmed at the edge portion of the object, whereas in the main image after correction in FIG. 8 (b), this disturbance is corrected. .

  As in the present embodiment, when there is an image (target image) that is a correction target other than the main image, the correction execution unit 17 further targets the correction target area related to the main image and the movement amount of the area as it is. Apply to the image to correct the target image. Since the main image and the target image are obtained from the same measurement, and the location and amount of misalignment are the same for both images, the correction target area and the movement amount of the main image are used as they are and the measurement points of the target image are measured. Misalignment can be corrected.

  In the image correction apparatus according to the first embodiment, the main image obtained by measuring the secondary electrons while scanning the measurement target region at a predetermined speed is obtained by measuring the secondary electrons by scanning the measurement target region at high speed. Correction is performed using the reference image. Furthermore, using the correction result of the main image (correction target region and movement amount), the target image obtained by detecting characteristic X-rays in the measurement simultaneously with the main image is also corrected. In the image correction apparatus according to the first embodiment, the main image can be corrected at a low cost without using an additional apparatus such as a vibration isolator as in the prior art. In addition, regardless of the cause of the displacement of the measurement point, both distortion of the entire image caused by slow vibrations such as drift, and local whisker-like disturbances caused by fast vibrations in the apparatus itself or its surroundings. Can be reliably corrected.

<Example 2>
Next, an image correction apparatus 20 according to the second embodiment will be described with reference to the drawings. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

FIG. 9 shows a main configuration of the image correction apparatus 2 according to the second embodiment.
The image correction apparatus 2 includes a control unit 20, an input unit 18 connected to the control unit 20, and a display unit 19. In addition to the storage unit 21, the control unit 20 includes a reference image creation unit 22, a difference calculation unit 14, a correction target region extraction unit 15, a movement amount determination unit 16, and a correction execution unit 17 as functional blocks. The entity of the control unit 20 is a personal computer in which required operating software (OS) or the like is installed.

  The storage unit 21 stores in advance a target image that is an image obtained by scanning a measurement target region with an electron beam at a low speed and measuring characteristic X-rays in an electron beam microanalyzer. This target image corresponds to the main image in the image correction apparatus according to the second aspect.

  Hereinafter, a procedure for correcting the positional deviation of the target image in the image correction apparatus 2 of the present embodiment will be described. In the image correction apparatus 1 of the first embodiment, the main image is corrected using the reference image, and the target image is corrected from the correction result of the main image. However, in the image correction apparatus 2 of the second embodiment, the target image is corrected only from the target image. Correct the image.

  When the user instructs correction of the target image through the input unit 18, the reference image creation unit 22 reads the target image from the storage unit 21. Then, smoothing processing is performed on the target image to create a reference image. That is, in the second embodiment, the reference image is acquired by reducing the disturbance in the edge portion of the target object caused by the positional deviation by intentionally blurring the target image. For this smoothing processing, various conventionally known media such as a 3 × 3 (3 measurement points on all sides) or 5 × 5 (5 measurement points on all sides) median filter, an averaging filter, a weighted averaging filter, a Gaussian filter, etc. Can be used.

  Since the procedure related to image correction after creating the reference image is the same as that in the first embodiment, description thereof is omitted.

  Similar to the first embodiment, the image correction apparatus according to the second embodiment has an advantage that the target image can be directly corrected in addition to being able to correct the image inexpensively and reliably. For example, when the target image is obtained by detecting characteristic X-rays, it is difficult to obtain a reference image by high-speed scanning because the intensity of characteristic X-rays emitted from the sample is small. Therefore, in the first embodiment, it is necessary to acquire the reference image and the main image for the secondary electrons and correct the target image using the correction result related to the main image. On the other hand, when the image correction apparatus according to the second embodiment is used, the target image can be directly corrected, so that it is not necessary to acquire a reference image or a main image for secondary electrons. Further, since the reference image is created by smoothing the target image itself, there is no need to eliminate the influence of drift as in the first embodiment (the reference image is deformed to correct drift), and the image correction is performed. Processing is simple. In the image correction apparatus according to the second embodiment, it is possible to reliably correct both local whisker-like disturbances generated in an image due to fast vibration or the like in the apparatus itself or in the vicinity thereof regardless of the cause of the positional deviation of the measurement point. it can.

Each of the above-described embodiments is an example, and can be appropriately changed in accordance with the gist of the present invention.
For example, in the above embodiment, the correction target region including the measurement point adjacent to the correction target measurement point is used, but the correction target measurement point itself (not including the adjacent measurement point) may be used as the correction target region.

  In the first embodiment, the drift amount of the main image is obtained and the reference image is deformed based on the drift amount. However, in the measurement for acquiring the main image, the relative relationship between the scanning system such as an electron beam and the sample changes. When it is considered that no drift has occurred (that is, no drift has occurred), the calculation of the drift amount and the deformation of the reference image based on the drift amount do not have to be performed. However, when measuring characteristic X-rays as in the above example, it is common to measure the characteristic X-rays by scanning the measurement target region over several hours even if the size is several μm square, and drift is Since it is considered that the possibility of the occurrence is high, it is preferable to calculate the drift amount and to deform the reference image (drift correction).

  In addition, in Example 1, it is determined which position of the reference image the divided image corresponds to, a correction target measurement point is extracted, the correction target region is moved within the comparison region, or the correction target region is moved. The contents may be appropriately displayed on the display unit 19 when performing various processes such as replacing measured values. Similarly, in the second embodiment, when each process is performed, the contents may be appropriately displayed on the display unit 19.

DESCRIPTION OF SYMBOLS 1, 2 ... Image correction apparatus 10, 20 ... Control part 11, 21 ... Memory | storage part 12 ... Drift amount calculation part 13 ... Drift correction part 14 ... Difference calculation part 15 ... Correction object area | region extraction part 16 ... Movement amount determination part 17 ... Correction execution unit 22 ... Reference image creation unit 18 ... Input unit 19 ... Display unit

Claims (7)

a) A distribution of measured values of the physical quantity in the measurement target area obtained by measuring a predetermined physical quantity at each measurement point in the measurement target area while scanning the measurement target area of the sample at a predetermined speed. And a reference image representing a distribution of measured values of the physical quantity obtained by measuring the physical quantity at each measurement point while scanning the measurement target area at a speed higher than the predetermined speed. Storage unit
b) a difference calculation unit for obtaining a difference between measured values of the physical quantity at corresponding measurement points of the reference image and the main image;
c) a correction target region extraction unit that extracts a correction target region including a plurality of measurement points adjacent to each other whose difference is equal to or greater than a predetermined threshold;
d) The correction target area of the main image is moved in the plane by one measurement point, and the difference between the measurement values of the corresponding measurement points of the main image and the reference image at each moving position as the entire correction target area. A movement amount determination unit for determining a movement amount with which the predetermined statistic is minimized;
e) An image correction apparatus comprising: a correction execution unit that moves a measurement value of each measurement point in the correction target area of the main image by the movement amount and replaces the measurement value. One image of the main image and the reference image is divided into a plurality of divided images, and the measured value of each measurement point of each divided image is compared with the measured value of the measurement point of the other image. A drift amount calculation unit for obtaining a drift amount;
A drift correction unit that corrects drift of the one image by moving the divided image so as to cancel the drift amount;
The difference calculation unit obtains a difference between measured values of the physical quantity at corresponding measurement points using the reference image or the main image after drift correction by the drift correction unit. Image correction device.   The drift correction unit creates a function for converting coordinates representing a position in one of the main image and the reference image into coordinates representing the other position. 2. The image correction apparatus according to 2. In the storage unit, the distribution of the measurement value of another type in the measurement target region obtained by measuring the physical quantity of another type different from the predetermined physical quantity in the measurement for acquiring the main image is represented. The target image is saved,
The image correction apparatus according to claim 1, wherein the correction execution unit corrects the target image using a correction target region and a movement amount in the main image. a) A distribution of measured values of the physical quantity in the measurement target area obtained by measuring a predetermined physical quantity at each measurement point in the measurement target area while scanning the measurement target area of the sample at a predetermined speed. A storage unit storing a main image to be represented;
b) a reference image creation unit that creates a reference image by smoothing the main image;
c) a difference calculation unit for obtaining a difference between measured values of the physical quantity at corresponding measurement points of the reference image and the main image;
d) a correction target area extracting unit that extracts a correction target area including a plurality of measurement points adjacent to each other whose difference is equal to or greater than a predetermined threshold;
e) The correction target area of the main image is moved in the plane by one measurement point, and the difference between the measurement values of the corresponding measurement points of the main image and the reference image at each moving position as the entire correction target area. A movement amount determination unit for determining a movement amount with which the predetermined statistic is minimized;
f) An image correction apparatus comprising: a correction execution unit that moves a measurement value at each measurement point in the correction target area of the main image by the movement amount and replaces the measurement value.   The image correction apparatus according to claim 1, wherein the threshold value is obtained by statistically processing differences between the measurement values at all measurement points.   The threshold value is obtained by adding a value obtained by multiplying a standard deviation of the difference between the measurement values at all measurement points by a predetermined coefficient to an average value of the difference between the measurement values at all the measurement points. The image correction apparatus according to claim 1, wherein the image correction apparatus is an image correction apparatus.