JP7213465B2 - Image processing method and measuring device - Google Patents

Description

The present invention relates to an image processing method and a measuring device, and more particularly to an image processing method and a measuring device used for measuring the three-dimensional shape of an object.

As a device for measuring the three-dimensional shape of an object to be measured, one using a scanning white light interferometer is known. A scanning white light interferometer is a device for non-contact measurement of the three-dimensional shape of the surface of an object to be measured using white light as a light source and an optical path interferometer such as a Michelson type or a Mirau type. be.

In a measurement method using a white light interferometer (hereinafter referred to as a white light interferometer), the range that can be imaged in one measurement is limited by the magnification of the objective lens used for measurement. For this reason, the object to be measured and the white light interferometer are relatively moved, images are taken a plurality of times, and a plurality of images of the object to be measured are combined to measure a wide range of three-dimensional shapes. (For example, Patent Document 1).

JP 2014-202651 A

In general, the resolution in the height direction in the white light interferometry is on the order of nanometers, whereas the moving accuracy (straightness) of the stage holding the object to be measured is on the order of micrometers. Since the accuracy of image stitching deteriorates depending on the movement accuracy of the stage with the lowest resolution, there is a problem that the measurement accuracy of the three-dimensional shape of the object to be measured deteriorates.

The present invention has been made in view of such circumstances, and is capable of preventing deterioration in the accuracy of stitching images due to stage movement accuracy and increasing the accuracy of measuring the three-dimensional shape of an object to be measured. An object of the present invention is to provide an image processing method and a measuring device.

In order to solve the above problems, an image processing method according to a first aspect of the present invention includes the steps of acquiring a plurality of images obtained by imaging an object to be measured for each region; acquiring a waveform; obtaining a cross-correlation function from interference waveforms of corresponding points in a plurality of images when synthesizing a plurality of images; calculating a correlation coefficient from the maximum value of the cross-correlation function; and an image processing step of aligning the plurality of images so that the number takes the higher value.

In the image processing method according to the second aspect of the present invention, in the image processing step of the first aspect, the distance between corresponding points in the plurality of images converges and the correlation coefficient takes a larger value. In addition, a plurality of images are aligned.

A measurement apparatus according to a third aspect of the present invention includes an image acquisition unit that acquires a plurality of images of an object to be measured for each region, and an interference waveform acquisition unit that acquires an interference waveform of each pixel included in the plurality of images. a calculation unit that, when synthesizing a plurality of images, obtains a cross-correlation function from interference waveforms of corresponding points in the plurality of images and calculates a correlation coefficient from the maximum value of the cross-correlation function; and an image processing unit that aligns a plurality of images so as to obtain a large value.

A measuring apparatus according to a fourth aspect of the present invention, in the third aspect, further includes a storage unit for storing interference waveforms, and the interference waveform acquisition unit includes pixels included in the plurality of images and used for alignment. The interference waveform is acquired for only the 100% and is stored in the storage unit.

According to the present invention, the correlation coefficient is obtained from the interference waveforms (interferogram) of corresponding points in a plurality of images, and the correlation coefficient takes a larger value so that the correlation of the interferogram becomes higher. can be done. As a result, it is possible to prevent a decrease in accuracy in stitching images due to movement accuracy in measuring the object to be measured.

FIG. 1 is a block diagram showing a measuring device according to one embodiment of the invention. FIG. 2 is a diagram for explaining image stitching processing. FIG. 3 is a diagram for explaining image stitching processing. FIG. 4 is a data block diagram showing image stitching processing. FIG. 5 is a graph showing an example of a model-side interferogram (m1). FIG. 6 is a graph showing an example of the data-side interferogram (d1). FIG. 7 is a graph showing an example of the data-side interferogram (d2). FIG. 8 is a graph showing an example of the cross-correlation function (c1) obtained from the model-side interferogram (m1) and the data-side interferogram (d1). FIG. 9 is a graph showing an example of the cross-correlation function (c2) obtained from the model-side interferogram (m1) and the data-side interferogram (d2). FIG. 10 is a histogram showing comparison results of the maximum values of the cross-correlation functions (c1 and c2). FIG. 11 is a flow chart showing steps of measuring an object to be measured and acquiring data in a measuring method according to an embodiment of the present invention. FIG. 12 is a flowchart illustrating an image processing method according to one embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an image processing method and a measuring apparatus according to the present invention will be described below with reference to the accompanying drawings.

[Configuration of measuring device]
FIG. 1 is a block diagram showing a measuring device according to one embodiment of the invention.

As shown in FIG. 1, the measuring apparatus 1 according to the present embodiment includes a white interference microscope 50 for measuring the shape, surface roughness, etc. of an object W to be measured, and a control device 10 . In the following description, a three-dimensional orthogonal coordinate system in which the plane along the stage 78 on which the object W to be measured is placed is the XY plane will be used.

The control device 10 is a device that controls each part of the white interference microscope 50 and processes the results of measurement by the white interference microscope 50, and includes a control unit 12, an input/output unit 14, a storage unit 16, and a signal processing unit 18. I'm in. The control device 10 can be implemented by, for example, a general-purpose computer such as a personal computer or workstation.

The control unit 12 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control unit 12 receives operation inputs from the operator via the input/output unit 14 and controls each unit of the control device 10 . The control unit 12 also controls the output of the light source unit 52 of the white interference microscope 50 to adjust the amount of illumination light with which the object W to be measured is irradiated. The control unit 12 performs driving control of the stage driving unit 80 to move the stage 78 and adjust the observation target position (measurement position) of the object W to be measured. The control unit 12 also controls the relative position (distance) in the height direction (Z direction) between the lens barrel 56 and the stage 78 . The control unit 12 is an example of the calculation unit and the image processing unit of the present invention.

The input/output unit 14 includes an operation member (e.g., a keyboard, a pointing device, etc.) for receiving operation input by the operator, and a display unit ( For example, a liquid crystal display, etc.).

The signal processing unit 18 acquires a detection signal from the detector 76 of the white interference microscope 50, performs signal processing on this detection signal, and calculates the shape, amplitude, etc. of the interference fringes.

The storage unit 16 is a storage device for storing data such as measurement results of the object W to be measured. As the storage unit 16, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), or the like can be used.

A white light interference microscope 50 includes a light source section 52 , a light guide 54 and a lens barrel 56 . A turret 62 is attached to the lower end of the lens barrel 56 and a detector 76 is attached to the upper end of the lens barrel 56 . A plurality of (three in the example shown in FIG. 1) objective parts 64 are attached to the turret 62 . The interference objective lenses 66 included in the plurality of objective parts 64 have mutually different magnifications, and by rotating the turret 62, it is possible to switch the interference objective lens 66 used for measuring the object W to be measured. ing.

The light source unit 52 is a light source that outputs white light, and is, for example, a halogen lamp, a laser light source, or an LED (Light Emitting Diode) light source. Here, white light is light obtained by mixing visible light with a wavelength in the visible light region (wavelength of about 400 nm to about 720 nm). It may be light mixed at a ratio of

The light guide 54 is a member that forms an optical path for propagating the white light output from the light source unit 52 to the lens barrel 56, and is, for example, an optical fiber.

The lens barrel 56 has a coaxial epi-illumination optical system. An illumination lens 58 , a beam splitter 60 , an imaging lens 72 and a diaphragm 74 are arranged in the lens barrel 56 . The relative position (distance) between the lens barrel 56 and the stage 78 in the height direction (Z direction) can be changed by the controller 12 .

The illumination lens 58 has an optical system that guides (images) the white light (illumination light) incident on the lens barrel 56 through the light guide 54 to the pupil position of the interference objective lens 66 . The illumination light output from the illumination lens 58 is reflected by the beam splitter 60 and guided to the objective section 64 .

The illumination light guided through the beam splitter 60 is guided to the output side of the objective section 64 by the interference objective lens 66 . A component of the illumination light guided to the output side of the objective section 64 and transmitted through the half mirror 68 is guided to the object W placed on the stage 78 and reflected by the surface of the object W to be measured. be done. Reflected light from the surface of the object W to be measured passes through the half mirror 68 and reaches the imaging lens 72 . On the other hand, the component of the illumination light guided to the output side of the objective section 64 and reflected by the half mirror 68 is guided to the reference mirror 70 and reflected. The reference mirror 70 is arranged at a position conjugate with the focal position of the interference objective lens 66 on the exit side (on the side of the object to be measured W). Reflected light from the reference mirror 70 is reflected by the half mirror 68 and reaches the imaging lens 72 .

The imaging lens 72 has an optical system that forms an image of the reflected light from the surface of the object W to be measured and the reflected light from the reference mirror 70 on the photodetection surface of the detector 76 .

The diaphragm 74 is provided between the imaging lens 72 and the detector 76 and blocks part of the reflected light guided from the imaging lens 72 to the detector 76 .

The detector 76 includes, for example, a photodetection array element (hereinafter referred to as an image sensor) such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor). The detector 76 generates an analog or digital detection signal indicating the light intensity detected by each light receiving element of the image sensor and outputs it to the signal processing section 18 . Thereby, an image of the surface to be measured of the object W to be measured is acquired. Also, the detector 76 acquires an interference waveform (interferogram) of each pixel of this image. The detector 76 is an example of the image acquisition section and the interference waveform acquisition section of the present invention.

The detector 76 receives the first reflected light L1 from the surface of the object W to be measured and the second reflected light L2 from the reference mirror 70 to generate a detection signal and output it to the signal processing section 18 . do.

The signal processing unit 18 acquires a detection signal from the detector 76 of the white interference microscope 50, performs predetermined signal processing on the detection signal, and calculates the shape, amplitude, etc. of the interference fringes. Here, a luminance change curve (interference waveform) obtained when the interference objective lens 66 is scanned in the height direction (Z direction) is called an interferogram.

When the interference objective lens 66 is scanned in the height direction (Z direction), the control unit 12 controls the surface to be measured of the object W to be measured based on the shape and amplitude of the interference fringes calculated by the signal processing unit 18. Measure the shape, surface roughness, etc. Specifically, the controller 12 determines the difference between the distance between the surface to be measured of the object W to be measured and the half mirror 68 and the distance between the reference mirror 70 and the half mirror 68 (hereinafter referred to as optical path difference). ) is used to measure the shape, surface roughness, etc. of the surface of the object W to be measured. Such a measurement method is called vertical scanning interferometry (VSI). Vertical scanning is described, for example, in US Pat. No. 4,340,306. The vertical scanning method is standardized as CSI (Coherence Scanning Interferometry) by the International Organization for Standardization (ISO) (ISO25178-604:2013).

When the optical path difference changes, the phase difference between the first reflected light L1 and the second reflected light L2 changes, and the interference fringes change according to the change in the phase difference. When the optical path difference is zero, that is, when the surface of the object W to be measured is in focus, no phase difference occurs between the first reflected light L1 and the second reflected light L2. Therefore, the interference intensity is maximized and the amplitude of the interference fringes is maximized. On the other hand, as the optical path difference increases, the interference intensity decreases.

The control unit 12 acquires, for example, the position (Z-axis height) in the height direction (Z direction) of the interference objective lens 66 when the amplitude of the interference fringes calculated by the signal processing unit 18 is maximized. Here, the height direction position of the interference objective lens 66 when the amplitude of the interference fringes is maximized can be obtained from the envelope in the interferogram. Then, based on the position of the interference objective lens 66, the control unit 12 calculates the height position (focus position) of the surface to be measured of the object W to be measured, and the shape of the surface to be measured of the object W to be measured, Measure the surface roughness, etc. The control unit 12 can store the measurement result in the storage unit 16 and display it on the display unit of the input/output unit 14 .

Note that the method for measuring the height position of the surface to be measured of the object W to be measured is not limited to VSI or CSI. As a method of measuring the height position of the surface to be measured of the object W to be measured, for example, a frequency domain analysis (FDA) or a phase shifting interferometry (PSI) may be applied. The frequency domain method is a method of obtaining the height position of the surface of the object W to be measured by Fourier transforming the interferogram and obtaining the phase gradient with respect to the wave number near the peak position of the amplitude spectrum. Frequency domain methods are described, for example, in US Pat. No. 5,398,113. The phase shift method is a method of obtaining the height position of the surface of the object W to be measured based on the change in the density value of the pixel when the focal position of the interference objective lens 66 is shifted in the optical axis direction. Phase-shifting methods are described, for example, in J. H. Bruning et al.: "Digital Wavefront Measuring Interferometer for Testing Optical Surfaces and Lenses, Applied Optics, Vol. 13, Issue 11, pp. 2693-2703 (1974).

Scanning along the XY directions of the object W to be measured is performed by the stage driving section 80 . The stage driving section 80 includes a driving mechanism (such as an actuator) for moving the stage 78 in the XY directions. The light irradiation position (observation target position) on the object W to be measured can be changed by moving the stage 78 in the XY directions by the stage driving unit 80 .

The control unit 12 causes the stage driving unit 80 to move the object W to be measured in the XY directions, and sequentially capture images of the surface to be measured. Then, the control unit 12 can create a composite image of the entire measurement target range of the object W by connecting the sequentially captured images. As a result, it is possible to measure the three-dimensional shape of the entire measurement target range of the object W to be measured.

In this embodiment, the stage 78 is movable in the XY directions, but the stage 78 may be fixed and the lens barrel 56 may be movable in the XY directions, or both the lens barrel 56 and the stage 78 may be movable. good too.

[Image stitching processing (compositing processing)]
Next, image stitching processing will be described with reference to FIGS. 2 to 10. FIG. 2 and 3 are diagrams for explaining image stitching processing.

In the present embodiment, the stage driving unit 80 moves the object W to be measured in the XY directions, and sequentially picks up images of the surface to be measured. Here, when imaging the surface to be measured, the object W to be measured is scanned such that adjacent measurement images partially overlap each other (so that adjacent measurement images have corresponding points). When imaging the surface to be measured, an interferogram for each pixel of the surface to be measured is acquired and stored. Note that interferograms for each pixel may be stored only for pixels in mutually overlapping regions of adjacent measurement images.

When performing image stitching processing, first, two measurement images are selected, and one of the two measurement images is used as a reference to position the other. At this time, the model image P _Model (P _Model (1, 1)) is used as a reference measurement image, and the measurement image (before the coordinates are fixed with respect to the model image P _Model ) is aligned with the model image P _Model . ) is defined as a data image P _Data .

Then, as shown in FIG. 2, the positions of the data images P _Data are sequentially aligned with the first model image P _Model (1, 1) as a starting point. Here, the data image P _Data after alignment whose coordinates are fixed with respect to the model image P _Model are represented by P _Model (1, 2), P _Model (1, 3), . . . , P _Model (2, 1), Let P _Model (2, 2), . . . Also, images P _Model (1, 1), P _Model (1, 2), P _Model (1, 3), . . . , P _Model (2, 1), P _Model (2, 2), . Let the image that is displayed be a model image P _Model . By sequentially synthesizing the model image P _Model with the data image P _Data , a synthesized image of the entire measurement target range is created.

Alignment between the model image P _Model and the data image P _Data is performed by, for example, an ICP (Iterative Closest Point) algorithm. That is, the closest points (nearest neighbor pixels) between the point groups (pixel groups) in the two images of the model image P _Model and the data image P _Data are obtained as corresponding points, and the corresponding points are brought closer to each other (or superimposed). The two images are aligned by performing the transformation. The ICP algorithm is described, for example, in IEEE (Institute of Electrical and Electronics Engineers) Transactions on Pattern Analysis and Machine Intelligence (Volume: 14, Issue: 2, Feb. 1992).

Specifically, first, a pixel group (hereinafter referred to as a model pixel group G _Model ) to be used as a reference for alignment is selected from the model image P _Model . Also, in the data image P _Data , a pixel group (hereinafter referred to as data point group G _Data ) to be transformed so as to be closer to the model pixel group G _Model is selected. Here, the model pixel group G _Model and the data pixel group G _Data are regions in which the model image P _Model and the data image P _Data overlap each other based on the positional relationship between the white interference microscope 50 and the object W during imaging. may be identified and selected from among them (see FIG. 2). When selecting the model pixel group G _Model and the data pixel group G _Data , it is not necessary to select all the pixels in the overlapping regions of the model image P _Model and the data image P _Data . Alternatively, selection may be made from a partial area (for example, the central area) of the overlapping areas.

Next, for pixel E _Model (X _Model , Y _Model , Z _Model ) in model pixel group G _Model , three-dimensional data for all pixels E _Data (X _Data , Y _Data , Z _Data ) in data pixel group G _Data Find the target distance (see Figure 3). Then, a set of nearest neighbor points (E _Model , E _Data ) that minimizes the distance between the pixel E _Model and the pixel E _Data is obtained for all pixels of the model pixel G _Model group.

Next, using the pair of nearest neighbor points (E _Model , E _Data ) as corresponding points in alignment, a transformation that brings the corresponding points closer to each other is obtained. This conversion can be obtained, for example, by minimizing (converging) the sum of squares of distances between corresponding points through iterative calculation.

In this embodiment, when obtaining this conversion, in addition to bringing corresponding points closer together, interferograms of the model pixel group G _Model and the data pixel group G _Data (hereinafter referred to as a model-side interferogram and a data-side interferogram, respectively). ferrogram) is made to be highly correlated. As a result, it is possible to prevent deterioration in the accuracy of stitching images due to the movement accuracy of the stage 78 and the stage drive section 80 .

FIG. 4 is a data block diagram showing image stitching processing using an interferogram.

Let f be the interferogram of the pixel E _Model of the model image P _Model and g be the interferogram of the pixel E _Data of the data image P _Data . ).

(f*g)(m)=∫f(t)・g(m−t) (1)
where t is the sampling time and m is the delay. Note that the interferograms f and g may be expressed as a function of the height (Z coordinate) of the interference objective lens 66. FIG.

As shown in FIG. 4, the control unit 12 according to this embodiment includes delayers, multipliers and adders. When the model-side interferogram m1 and the data-side interferograms d1 and d2 are input, the control unit 12 performs the calculation of formula (1) using the delay unit, multiplier, and adder. Thus, a cross-correlation function c1 is calculated from the model-side interferogram m1 and the data-side interferogram d1, and a cross-correlation function c2 is calculated from the model-side interferogram m1 and the data-side interferogram d2.

Next, the control unit 12 performs envelope detection on the cross-correlation functions c1 and c2 to obtain the maximum value _Imax of the signal intensity. The maximum value of signal strength can be determined by identifying the point where the slope of the envelope is zero.

Next, when the control unit 12 minimizes (converges) the sum of squares of the distances between the corresponding points by iterative calculation, the correlation coefficients in the X and Y directions of _Imax calculated from the interferogram of the corresponding pixels ρ(X) and ρ(Y) (hereinafter collectively referred to as ρ) are obtained. Then, the model image P _Model and the data image P _Data are aligned so that the correlation coefficient ρ takes a larger value, that is, a value closer to one.

FIG. 5 is a graph showing an example of the model-side interferogram (m1), and FIGS. 6 and 7 are graphs showing examples of the data-side interferograms (d1 and d2), respectively. 5 to 7, the horizontal and vertical axes indicate sampling time and signal intensity (luminance), respectively.

FIG. 6 shows the interferogram d1 at the data pixel E _Data1 which is the _{closest point to the model pixel E Model ,} and FIG. Fig. 2 shows an interferogram d2 in _Data2 ;

8 and 9 are graphs showing examples of cross-correlation functions (c1 and c2) respectively obtained from the model-side interferogram (m1) and the data-side interferogram (d1 and d2). By performing envelope detection on the cross-correlation functions c1 and c2 shown in FIGS. 8 and 9 and specifying the point where the slope of the envelope becomes zero, the maximum value of the signal intensity can be asked for.

FIG. 10 is a histogram showing comparison results of the maximum values of the cross-correlation functions (c1 and c2). As shown in FIG. 10, the maximum value of the cross-correlation function c1 corresponding to the data pixel E _Data1 , which is the closest point of the model pixel E _Model , is at the data pixel E _Data2 located slightly farther than the closest point. larger than the corresponding cross-correlation function c2.

In this embodiment, the model image P _Model and the data image P _Data are aligned so that the correlation coefficient ρ obtained from the maximum value takes a larger value (closer to 1).

According to this embodiment, when aligning the model image P _Model and the data image P _Data , the three-dimensional distance between the corresponding points is converged (minimized) and obtained from the interferogram of the corresponding points. The correlation coefficient ρ is set to take a larger value (increase the correlation of the interferogram). As a result, it is possible to prevent deterioration in the accuracy of stitching images due to the movement accuracy of the stage 78 and the stage drive section 80 .

In this embodiment, the case of aligning two images has been described. It suffices to calculate the relational coefficient ρ and converge.

[Measuring method]
Next, a measuring method according to this embodiment will be described.

First, the process of measuring an object to be measured and obtaining data will be described. FIG. 11 is a flow chart showing steps of measuring an object to be measured and acquiring data in the measuring method according to the present embodiment.

In this embodiment, the surface to be measured of the object W to be measured is divided into a plurality of areas and images are taken. First, the white interference microscope 50 is used to image a partial area N (N=1) of the surface to be measured of the object W (steps S10 and S12), and the measurement image of the area N and the interference waveform for each pixel are (interferogram) is stored in the storage unit 16 (step S14).

Next, as N=N+1 (No in step S16 and step S18), steps S12 to S18 are repeated. Here, the control unit 12 controls the stage driving unit 80 to pick up measurement images so that adjacent regions N partially overlap each other. In addition, regarding the interferogram for each pixel, the pixels included in the mutually overlapping regions of the region N or the pixels used for alignment of a part thereof (the pixels selected as the model pixel group G _Model and the data pixel group G _Data ) may be saved. Then, when the imaging of all regions of the surface to be measured of the object W to be measured is completed (Yes in step S16), the measurement is completed.

Next, the process of synthesizing measurement images will be described. FIG. 12 is a flowchart illustrating an image processing method according to one embodiment of the invention.

First, the control unit 12 selects two images from the measurement images acquired in the process of FIG. 11, and sets one as the model image P _Model and the other as the data image P _Data (step S30).

Next, the control unit 12 selects the model pixel group G _Model and the data pixel group G _Data from the model image P _Model and the data image P _Data , respectively (step S32).

Next, the control unit 12 calculates a three-dimensional distance for each set of pixels of the model pixel group G _Model and the data pixel group G _Data . In addition, the control unit 12 calculates a cross-correlation function from the interference waveforms (interferograms) of the pixels of the model pixel group G _Model and the data pixel group G _Data , and the cross-correlation function obtained from the set of interferograms of each pixel. Calculate the correlation coefficient ρ from the maximum value of Then, the control unit 12 aligns the model image P _Model and the data image P _Data so that the three-dimensional distance between the corresponding points converges and the correlation coefficient ρ takes a larger value ( step S34: image processing step).

Next, another data image is selected (No in step S36 and S38), steps S32 to S38 are repeated, and when the composition of all measurement images is completed (Yes in step S36), the image composition processing ends. .

In this embodiment, the model image P _Model and the data image P _Data are aligned using the three-dimensional distance used in the ICP algorithm, but the present invention is not limited to this. The image processing method according to the present invention can also be realized by combining a registration method for a three-dimensional point group other than the ICP algorithm with the correlation coefficient ρ obtained from the interferogram. For example, when using a SIFT (Scale-Invariant Feature Transform) algorithm (for example, US Pat. No. 6,711,293) as a registration method for a three-dimensional point cloud, feature points (pixels) , the correlation coefficient .rho. should be set to a larger value.

DESCRIPTION OF SYMBOLS 1... Measuring apparatus 10... Control apparatus 12... Control part 14... Input/output part 16... Storage part 18... Signal processing part 50... White interference microscope 52... Light source part 54... Light guide 56... Lens barrel 58 Illumination lens 60 Beam splitter 62 Turret 64 Objective part 66 Interference objective lens 68 Half mirror 70 Reference mirror 72 Imaging lens 74 Diaphragm 76 ... detector, 78 ... stage, 80 ... stage drive unit

Claims (4)

a step of acquiring a plurality of images obtained by imaging the object to be measured for each region;
obtaining an interference waveform of each pixel included in the plurality of images;
obtaining a cross-correlation function from interference waveforms of corresponding points in the plurality of images when synthesizing the plurality of images, and calculating a correlation coefficient from the maximum value of the cross-correlation function;
an image processing step of aligning the plurality of images so that the correlation coefficient takes a larger value;
An image processing method including 2. The image processing step according to claim 1, wherein the plurality of images are aligned such that distances between corresponding points in the plurality of images converge and the correlation coefficient takes a larger value. image processing method. an image acquisition unit that acquires a plurality of images obtained by imaging an object to be measured for each region;
an interference waveform acquisition unit that acquires an interference waveform of each pixel included in the plurality of images;
a calculation unit that obtains a cross-correlation function from interference waveforms of corresponding points in the plurality of images when synthesizing the plurality of images, and calculates a correlation coefficient from the maximum value of the cross-correlation function;
an image processing unit that aligns the plurality of images so that the correlation coefficient takes a larger value;
A measuring device comprising a Further comprising a storage unit for storing the interference waveform,
4. The measuring apparatus according to claim 3, wherein said interference waveform acquisition unit acquires said interference waveform only for pixels used for said alignment among pixels included in said plurality of images, and stores said interference waveform in said storage unit.

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