Digital image correction device, digital image correction method, and program

Abstract

The present invention makes it possible to provide high-resolution DIC whereby measurement error can be further reduced.　The present invention comprises: an image acquisition unit that acquires a digital image in which the surface of an object to be measured has been captured in an angle-of-view capture range that includes a random pattern and a correction figure having a prescribed shape; an image correction unit that corrects distortion of the digital image on the basis of a matrix obtained when converting, in the digital image, the correction figure having distortion into the correction figure having the prescribed shape and having no distortion; and an image analysis unit that estimates displacement or strain of the object to be measured on the basis of image analysis in which the corrected digital image is used.

Description

Digital image correction device, digital image correction method and program

[0001] The present invention relates to a digital image correction device, a digital image correction method, and a program. This invention claims priority from Japanese Patent Application No. 2024-021950, filed on February 16, 2024, and the contents of that application are incorporated by reference into this application in designated states where incorporation by reference of documents is permitted.

[0002] Digital image correlation (DIC) is a well-known technique for measuring displacement and strain of structures, etc. In DIC, a random pattern of irregular spots is applied to the surface of a target area to be measured, a load is applied to the target object to deform it, the shape of the random pattern that changes before and after the deformation is photographed, and the amount of relative movement is analyzed using images to estimate the distribution of displacement and strain.

[0003] Incidentally, Patent Document 1 discloses technology related to DIC. Specifically, Patent Document 1 states that "This displacement measurement sheet is used to acquire images in a digital image correlation method. This displacement measurement sheet is made up of a flexible sheet of a finite shape, and the measurement field of view range of the displacement measurement sheet is divided into n areas vertically and m areas horizontally, and in each divided area, a pattern of an arbitrary shape and a color different from the background color is formed using digital data for measurement by a digital image correlation method, and the pattern is arranged on the sheet so as not to be symmetrical with respect to a line or a point."

[0004] JP 2023-71193 A

[0005] Because DIC uses image analysis, the measurement resolution of displacement and strain depends on the resolution of the digital image. In other words, the measurement resolution improves if the measurement area can be analyzed using a digital image with a larger number of pixels. Therefore, the upper limit of the measurement resolution is limited by the upper limit of the resolution of the camera used. On the other hand, the wider the measurement area in one image, the fewer the number of pixels per unit area, and therefore the lower the measurement resolution.

[0006] Therefore, when performing wide-area and high-resolution measurements using DIC, it is effective to divide the measurement area into multiple images rather than capturing a single image. In this case, for example, a method of moving the measurement object or the camera and capturing images while changing (scanning) the measurement area can be considered. However, this method involves moving either the camera or the measurement object when capturing images before and after deformation of the measurement object, which makes it easy for the positional relationship and orientation of the camera relative to the measurement object to change.

[0007] When the positional relationship and posture between the camera and the object being measured change, there is a concern that distortion in the digital image that occurs when an image is taken when the object being measured and the camera are not directly facing each other may be mistakenly recognized as being due to distortion or displacement of the object being measured during image analysis using DIC, which could result in measurement errors.

[0008] Patent Document 1 discloses a technique for creating a random pattern using digital data so that the random pattern used in DIC can be reproduced even if the random pattern is damaged. However, the technique in this document does not take into consideration the reduction of measurement errors due to distortion of the digital image. Therefore, even if the technique in this document is applied, it is difficult to solve the above-mentioned problem.

[0009] The present invention has been made in view of the above-mentioned problems, and has an object to provide a high-resolution DIC that can further reduce measurement errors.

[0010] The present application includes a plurality of means for solving at least part of the above-described problems, examples of which are as follows: A digital image correction device according to one aspect of the present invention for solving the above-described problems includes an image acquisition unit that acquires a digital image obtained by capturing an image of the surface of a measurement object within a shooting range having an angle of view that includes a random pattern and a correction figure of a predetermined shape, an image correction unit that corrects distortion of the digital image based on a matrix obtained when converting the distortion-containing correction figure in the digital image into a distortion-free correction figure of the predetermined shape, and an image analysis unit that estimates displacement or distortion of the measurement object based on image analysis using the corrected digital image.

[0011] According to the present invention, it is possible to provide a high-resolution DIC that can further reduce measurement errors.

[0012] Problems, configurations, effects, and the like other than those described above will become clear from the following description of the embodiments.

[0013] FIG. 1 is a diagram showing an example of a schematic configuration of a digital image correction system and a functional configuration of a digital image correction device. FIG. 2 is a diagram showing an example of a process for estimating displacement and strain by DIC for a measurement object. FIG. 3 is a diagram showing a schematic view of a measurement area after a patterning process. FIG. 4A and FIG. 4B are diagrams showing an example of a correction figure. FIG. 5A and FIG. 5B are diagrams showing an example of a correction figure. FIG. 4 is a schematic view showing an example of an imaging process. FIG. 5A is a schematic cross-sectional view of a camera and a measurement object in an imaging process. FIG. 6 is a plan view of a measurement area in which a plurality of correction figures are arranged. FIG. 7 is a diagram showing an example of the positional relationship between a plurality of correction figures arranged and an imaging range. FIG. 8 is an explanatory diagram of a correction process. FIG. 9 is a diagram showing an example in which one correction figure is formed by a plurality of correction figures. FIG. 10 is a diagram showing another example in which one correction figure is formed by a plurality of correction figures. FIG. 11 is a diagram showing an example of the hardware configuration of a digital image correction device.

[0014] The following embodiments are examples for explaining the present invention, and some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can be implemented in various other forms. Furthermore, unless otherwise specified, each component may be singular or plural.

[0015] Furthermore, in order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0016] Furthermore, various types of information may be described using expressions such as "table," "list," and "queue," but the various types of information may be expressed using data structures other than these. For example, various types of information such as "XX table," "XX list," and "XX queue" may be expressed as "XX information." When describing identification information, expressions such as "identification information," "identifier," "name," "ID," and "number" are used, but these are interchangeable.

[0017] In addition, when there are multiple components having the same or similar functions, they may be described by using the same reference numeral with different subscripts, or when there is no need to distinguish between these multiple components, the subscripts may be omitted.

[0018] In addition, in the embodiments, there may be cases where processing performed by executing a program is described. Here, a computer executes the program using a processor (e.g., a CPU or a GPU), and performs processing defined by the program while using storage resources (e.g., memory) and interface devices (e.g., communication ports). Therefore, the processor may be the entity that executes the program and performs the processing.

[0019] Similarly, the entity that executes the program and performs the processing may be a controller, device, system, computer, or node having a processor. The entity that executes the program and performs the processing may be any computing unit, and may include a dedicated circuit that performs specific processing. Here, the dedicated circuit is, for example, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a CPLD (Complex Programmable Logic Device).

[0020] A program may be installed on a computer from a program source. The program source may be, for example, a program distribution server or a computer-readable storage medium. When the program source is a program distribution server, the program distribution server may include a processor and storage resources for storing the program to be distributed, and the processor of the program distribution server may distribute the program to be distributed to other computers. In addition, in the embodiments, two or more programs may be realized as one program, or one program may be realized as two or more programs.

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] 1 is a diagram showing an example of the schematic configuration of a digital image correction system 1000 according to this embodiment and the functional configuration of a digital image correction device 100. As shown in the figure, the digital image correction system 1000 includes a digital image correction device 100 and a camera 200 that photographs an object to be measured, which are interconnected so as to be able to communicate with each other via a predetermined network N. The network N may be, for example, the Internet, an intranet, a WAN (Wide Area Network), a mobile phone network, or the like.

[0023] The digital image correction system 1000 is a system that uses a digital image of the object to be measured to measure the distribution of displacement and strain of the object to be measured by digital image correlation (hereinafter sometimes referred to as "DIC").

[0024] Camera 200 takes digital images of a measurement object having a random pattern on its surface before and after applying a load to deform it (hereinafter, sometimes referred to as "before and after deformation") and transmits these images to digital image correction device 100. If the entire measurement area of ​​the measurement object is wider than the imaging range (angle of view) of camera 200, the measurement area is virtually divided, and either camera 200 or the measurement object is moved to take a digital image of each divided measurement area, thereby taking a digital image of the entire measurement area.

[0025] The digital image correction device 100 performs image analysis by DIC using digital images before and after deformation, measures the displacement and strain of the object to be measured, and outputs output information that displays the distribution of the displacement and strain.

[0026] A correction figure is attached to the surface of the object to be measured together with a random pattern, and the digital image correction device 100 corrects the distortion of the correction figure photographed together with the random pattern, thereby correcting the distortion of the digital image caused by changes in the positional relationship and posture of the camera 200 relative to the object to be measured, and performs image analysis using DIC using the corrected digital image.

[0027] This allows the digital image correction device 100 to provide a high-resolution DIC that can further reduce measurement errors.

[0028] <Camera 200> The camera 200 is an imaging device that captures a digital image of the measurement object. The camera 200 captures a digital image of the measurement object (measurement area) including the random pattern and correction figures attached to the surface of the measurement object, and transmits the image to the digital image correction device 100.

[0029] The type of camera 200 is not particularly limited, and any known camera capable of capturing digital images used for image analysis by DIC (e.g., a high-resolution camera capable of fully recognizing the random pattern and correction figures in the captured digital image) may be used.

[0030] <Digital image correction device 100> The digital image correction device 100 is a device that measures the displacement and strain of a measurement object based on image analysis by DIC using a digital image of the measurement object. Specifically, the digital image correction device 100 estimates the distribution of displacement and strain by performing image analysis of the relative movement amount of a random pattern before and after deformation of the measurement object.

[0031] Furthermore, the digital image correction device 100 corrects the digital image by correcting distortion of the correction figure photographed together with the random pattern prior to image analysis by DIC.

[0032] 1, the digital image correction device 100 has various functional units. Specifically, the digital image correction device 100 has a processing unit 110, a storage unit 120, and a communication unit 130.

[0033] The processing unit 110 is a functional unit that performs processing executed by the digital image correction device 100. Specifically, the processing unit 110 has an image acquisition unit 111, an image correction unit 112, an image analysis unit 113, and an output information generation unit 114 as individual functional units that perform various processes.

[0034] The image acquisition unit 111 is a functional unit that acquires digital images of the measurement object from the camera 200. Specifically, the image acquisition unit 111 acquires digital images of the measurement object before and after deformation via the communication unit 130, and stores the images in the storage unit 120 (captured image DB).

[0035] The image correction unit 112 is a functional unit that corrects distortion of the digital image. Specifically, the image correction unit 112 performs homography transformation on the coordinates of the correction figure for each digital image obtained by photographing each measurement area of ​​the measurement object before and after deformation, thereby correcting distortion of the digital image caused by changes in the positional relationship and posture of the camera 200 with respect to the measurement object. Details of the correction method using the correction figure will be described later.

[0036] The image analysis unit 113 performs image analysis using DIC on the corrected digital image and calculates the distribution of displacement and strain of the measurement object. Note that DIC is a well-known technology and will not be described in detail here, but the image analysis unit 113 identifies random patterns within a subset (a rectangular area of ​​about several tens of pixels) identified from a digital image capturing the state of the measurement object before deformation from a digital image capturing the state after deformation, and calculates the displacement and strain of the measurement object based on the amount of displacement (amount of relative movement) and coordinate changes of the surrounding random patterns.

[0037] The output information generation unit 114 is a functional unit that generates a predetermined type of output information that visualizes the displacement and strain of the measurement object. For example, the output information generation unit 114 generates output information such as a contour diagram or a color map that shows the displacement and strain of the measurement object. The output information generation unit 114 also displays the output information on a display device (e.g., a display) included in the digital image correction device 100 or on an external display device connected via the communication unit 130.

[0038] Next, the storage unit 120 will be described. The storage unit 120 is a functional unit that stores various information. Specifically, the storage unit 120 has a captured image DB 121. The captured image DB 121 is a database that stores digital images of the measurement object captured by the camera 200 before and after deformation.

[0039] Next, the communication unit 130 will be described. The communication unit 130 is a functional unit that communicates information with an external device. Specifically, the communication unit 130 acquires a digital image of the measurement object from the camera 200. The communication unit 130 also outputs output information generated by the output information generation unit 114 to an external display device, for example.

[0040] The functional configuration of the digital image correction device 100 has been described above.

[0041] <Displacement and Strain Estimation Process Using DIC> Figure 2 shows an example of the displacement and strain estimation process using DIC. As shown in the figure, the process of estimating (calculating) the displacement and strain of a measurement region is broadly divided into a patterning process P1, an imaging process P2, an analysis process P3, and a display process P4. The imaging process P2 is performed by a camera 200, and the processes related to the analysis process P3 and display process P4 are performed by a digital image correction device 100.

[0042] <<Patterning Process P1>> In the patterning process P1, a random pattern of irregular spots is applied to a measurement area of ​​the object to be measured. In addition, in the patterning process P1, unlike the random pattern, a correction figure having a predetermined shape is applied to the measurement area of ​​the object to be measured.

[0043] 3 is a diagram schematically illustrating the measurement area after the patterning step P1 has been performed. In the illustrated example, the random pattern 1 is applied to a measurement area 4 that is wider than the imaging range (angle of view) 2 of the camera 200. The correction figure 3 is applied in a size such that its outline (outline) fits within the imaging range 2.

[0044] The random pattern 1 is used to estimate the amount of movement of each coordinate on the surface of the measurement object before and after deformation using DIC. As long as the random pattern 1 is an irregular spotted pattern, it may be a pattern inherent in the material of the measurement object itself, or may be a pattern applied to the surface of the measurement object for other purposes, such as design or surface treatment of the measurement object.

[0045] Other methods for applying the random pattern 1 include spraying, applying with a brush, stamping with a random pattern, sealing, laser marking, etc. Usually, a white or black paint is applied as a base, and then a white or black color different from the base is applied on top of that as the random pattern 1, and image analysis is performed by DIC based on the black and white luminance distribution.

[0046] Note that the random pattern 1 is not limited to black and white or other visible colors, and may be displayed in, for example, the infrared or ultraviolet region, as long as image analysis by DIC is possible. In this case, there is an advantage that it is not necessary to remove the random pattern 1 from the measurement object after processing.

[0047] As shown in the figure, the correction figure 3 is a figure of a predetermined shape, such as a polygon (e.g., a rectangle or a triangle). Unlike the random pattern 1, the correction figure 3 preferably has a shape that makes it easy to perform image analysis of each individual shape. Furthermore, a plurality of correction figures 3 may be arranged within the measurement area 4.

[0048] The correction figure 3 may also be applied to the surface of the object to be measured for other purposes, such as design, surface treatment of the object to be measured, wiring for an electric circuit, etc. Other methods for applying the correction figure 3 include, for example, stamping, roller, printer, and laser marking.

[0049] Furthermore, the correction figure 3 is not limited to visible colors, and may be displayed in, for example, the infrared or ultraviolet region, as long as its shape can be recognized by the camera 200. In this case, there is an advantage that it is not necessary to remove the correction figure 3 after processing.

[0050] 4 to 6 are diagrams showing examples of correction figures. For example, as shown in Fig. 4A, a single correction figure 3 may be a figure in which multiple squares are arranged alternately within a rectangular frame. Alternatively, as shown in Fig. 4B, a single correction figure 3 may be a figure in which smaller squares are arranged inside a larger outer square.

[0051] 5A and 5B, the correction figure 3 may be formed as a set of a plurality of correction figures 3 arranged so as to fit within the shooting range 2. Also, as shown in Fig. 6, the correction figure 3 may be formed as a set of a plurality of correction figures 3 having different shapes.

[0052] Although not shown, the correction graphic 3 may be a two-dimensional barcode such as a QR code (registered trademark) or a two-dimensional digital matrix code such as a DM code (registered trademark).

[0053] <<Photographing Step P2>> In the photographing step P2, digital images including the random pattern 1 and the correction figure 3 before and after deformation of the measurement object are photographed by the camera 200.

[0054] 7 is a schematic diagram showing an example of the photographing step. As shown in the figure, in the photographing step P2, a camera 200 is placed in a position directly facing a measurement area 4 of the measurement object. Note that, for convenience, a flat measurement object 5 is shown in the figure, but the measurement object 5 may have a more complex shape. In the photographing step P2, the camera 200 or the measurement object 5 is moved so that the correction figure 3 falls within the photographing range 2 of the camera 200, and then the camera 200 photographs a digital image of the measurement area 4 included in the photographing range 2.

[0055] Fig. 8 is a cross-sectional schematic diagram of the camera 200 and the measurement object in the photographing process. Note that Fig. 7 shows the state in which the measurement object 5 is photographed by one camera 200, but as shown in Fig. 8, the digital image correction system 1000 may be configured using a pair of stereo cameras.

[0056] When the distance between the camera 200 and the measurement area 4 is unlikely to change before and after deformation of the measurement object, the use of a single camera 200 has the advantage of allowing for easier measurement. On the other hand, when it is better to consider changes in the distance between the camera 200 and the measurement area 4, a configuration using a stereo camera as shown in FIG. 8 is effective. When a stereo camera is used, the parallax between the two cameras 200 can be used to calculate the distance between the camera 200 and the measurement area 4. This allows the digital image correction device 100 to perform highly accurate correction (e.g., enlargement or reduction) that takes this distance into account in the analysis process.

[0057] As shown in the figure, a light 6 may be installed to illuminate the measurement area 4. When the camera 200 is moved to change the imaging range 2, it is preferable that the light 6 be fixed to the same jig as the camera 200 so that the camera 200 and the light can move simultaneously in conjunction with each other. This keeps the angle of the light 6 relative to the imaging range 2 constant, making it less likely that the way the light hits the image will change, and it is possible to prevent the brightness distribution of the digital image acquired for DIC from changing due to the position of the light.

[0058] Furthermore, the photographing step P2 is preferably performed in a darkroom or the like, or alternatively, a camera 200, a light 6, and a cover 7 covering at least the photographing range 2 above the measurement area 4 are preferably installed, as shown in the figure. Such a cover 7 can reduce the influence of light from the sun or lighting fixtures, thereby suppressing changes in the brightness distribution of the digital image due to differences in location and time. When moving the camera 200, it is preferable that the cover 7 be fixed to the same jig as the camera 200 so that the camera 200 and cover 7 can move simultaneously in unison. It is also preferable that the cover 7 and the measurement object 5 are in contact with each other. This reduces the gap between the cover 7 and the measurement object 5 and suppresses light intrusion. Furthermore, it is preferable that the contact surface between the cover 7 and the measurement object 5 be made of a cushioning material such as a soft brush or felt. This prevents the random pattern 1 and the correction figure 3 from being damaged by contact with the cover 7.

[0059] 9 is a plan view of a measurement area in which a plurality of correction figures are arranged. In the photographing step P2, the camera 200 or the measurement object 5 is moved to scan the measurement area 4. The camera 200 determines whether the correction figure 3 falls within a specific position in the photographing range 2, for example, based on image analysis such as template matching or contour detection, and photographs the measurement area 4 included in the photographing range 2 when it is determined that the correction figure 3 falls within the specific position. This allows digital images of the measurement area 4, including the random pattern 1 and the correction figures 3 before and after deformation, to be photographed again at the same position, even if the positional relationship changes due to the movement of the camera 200 or the measurement object 5.

[0060] 10 is a diagram showing an example of the positional relationship between a plurality of correction figures and the imaging range. As shown in the figure, a plurality of correction figures 3 are added to the measurement area 4 at intervals narrower than the width of the imaging range 2. By arranging the correction figures 3 at such intervals, when the camera 200 or the measurement object 5 is moved to change the imaging range 2, parts of the imaging range 2 overlap. This prevents gaps from occurring between the imaging ranges 2, which is effective when comprehensively measuring the measurement area 4.

[0061] The camera 200 transmits the captured digital image to the digital image correction device 100 via the network N. The image acquisition unit 111 of the digital image correction device 100 acquires the digital image from the camera 200 via the communication unit 130 and stores the acquired digital image in the captured image DB 121.

[0062] <<Analysis Step P3>> In the analysis step P3, the digital image correction device 100 corrects distortion of the digital image based on the correction figure 3. Furthermore, the digital image correction device 100 estimates displacement and distortion of the measurement object 5 by calculating the amount of relative movement of the random pattern 1 based on image analysis by DIC using the corrected digital image.

[0063] Fig. 11 is an explanatory diagram of the correction process based on the correction figure. Fig. 11A shows the shooting range 21 and correction figure 31 of a digital image without distortion, i.e., a digital image captured with the camera 200 facing the measurement object 5 substantially directly. Fig. 11B shows the shooting range 22 and correction figure 32 of a digital image with distortion, i.e., a digital image captured with the camera 200 not facing the measurement object 5 directly.

[0064] In the distortion-free digital image (FIG. 11A), two axes parallel to sides 10 and 11 defining shooting range 21 are defined in advance as x and y. Also, assume that the contour of distortion-free correction figure 31 is rectangular (FIG. 11A), and that a trapezoidal correction figure 32 is photographed because camera 200 is not directly facing measurement area 4 (FIG. 11B).

[0065] In this case, if the trapezoidal correction figure 32 is transformed so that it matches the contour (rectangle) of the distortion-free correction figure 31, it is possible to correct the influence of the orientation of the camera 200. An example of the transformation method is homography transformation.

[0066] When homography transformation is used, the transformation from the coordinates (x, y) of an arbitrary quadrangle with distortion (corresponding to correction figure 32) to the coordinates (x', y') of an arbitrary quadrangle without distortion (corresponding to correction figure 31) can be calculated based on the following equations (1) and (2): x'=(ax+by+c) / (gx+hy+1) (1) y'=(dx+ey+f) / (gx+hy+1) (2)

[0067] Here, a, b, c, d, e, f, g, and h represent the components of the homography transformation matrix. For these eight unknowns, a, b, c, d, e, f, g, and h, the x and y coordinates of the four vertices of the quadrangle (the trapezoidal correction figure 32 before transformation) and the x and y coordinates of the four vertices of the quadrangle (the rectangular correction figure 31 after transformation) can be determined based on the pixel positions of the digital image. Therefore, eight equations can be formulated to determine the homography transformation matrix. In particular, since the dimensions of the distortion-free quadrangle (correction figure 31) are predetermined and known, using this known dimensional information assigned to the surface of the measurement object 5 as coordinate information after the homography transformation can further improve the accuracy of the transformation, i.e., the correction accuracy of the digital image itself. Note that this homography transformation can be applied to quadrangles of any shape, not just trapezoids and rectangles. Furthermore, the above explanation of the homography transformation has been based on the assumption that the correction figure is a quadrilateral, but the homography transformation can also be applied to polygons of any shape (for example, a triangle) in a similar manner.

[0068] Using the homography transformation matrix thus obtained, the coordinates of each pixel in the distorted capture range 22 ( FIG. 11B ), which is captured as a trapezoid, can be converted into the coordinates of the undistorted rectangular capture range 21, thereby correcting the digital image to reduce the influence of changes in the posture of the camera 200. Note that this correction process is performed by the image correction unit 112. Specifically, the image correction unit 112 performs the correction process on all digital images stored in the captured image DB 121, which are images of the measurement area 4 before and after deformation of the measurement object 5.

[0069] Next, a correction method for when a single correction figure is formed by combining a plurality of correction figures 3 will be described with reference to FIGS.

[0070] 12 is a diagram showing an example in which one correction figure is formed from a plurality of correction figures. As shown in the figure, one rectangle and three triangles, which are individual correction figures 3, are located at the four corners of the imaging range 2, and one virtual correction figure 52 is formed by connecting the vertices 51 of each correction figure 3. In this case, the image correction unit 112 applies homography transformation to the four vertices 51 of the virtual correction figure 52, thereby correcting the distorted digital image in the same manner as described above.

[0071] 13 shows another example in which a single correction figure is formed from a plurality of correction figures. As shown in the figure, correction figures 3 having the shape shown in FIG. 4B are located at the four corners of the imaging range 2. In this case, correction vertices 51 are defined in advance for the rectangles inside each correction figure 3, and a single virtual correction figure 52 is formed by connecting the correction vertices 51. In this case, the image correction unit 112 also applies homography transformation to the four vertices 51 of the virtual correction figure 52, thereby correcting the distorted digital image in the same manner as described above.

[0072] In this way, the digital image correction device 100 can achieve correction with higher accuracy by correcting a digital image using a single virtual correction figure 52 that is a combination of multiple correction figures 3. This is because the greater the distance from the center of the imaging range 2 to the correction figure 3, the more error is caused by applying the same homography transformation matrix to both the correction figure 3 and the imaging range 2.

[0073] 11 , one correction figure 32 is positioned away from the center of the imaging range 22, and therefore, applying a homography transformation matrix calculated using this correction figure 32 to the imaging range 22 results in a large error. In contrast, if a single virtual correction figure 52 formed by combining multiple correction figures 3 is used, the center of the imaging range 22 can be positioned inside the virtual correction figure 52, thereby narrowing the distance between them. Therefore, the digital image correction device 100 can improve the accuracy of digital image correction by calculating a homography transformation matrix using this virtual correction figure 52.

[0074] The image analysis unit 113 uses the corrected digital image to estimate (calculate) the displacement and strain of the measurement object 5 based on image analysis by DIC.

[0075] <<Display Step P4>> In the display step P4, output information for displaying the displacement and strain of the measurement object 5 estimated in the analysis step P3 is generated and displayed on a predetermined device. Specifically, the output information generation unit 114 generates output information that visualizes the displacement and strain of the measurement object 5, such as a contour diagram or a color map diagram. The output information generation unit 114 also displays the output information on, for example, a display device included in the digital image correction device 100 or a display device of an external device connected via the communication unit 130.

[0076] The process of estimating the displacement and strain of the measurement object 5 using DIC has been described above.

[0077] This digital image correction device can provide a high-resolution DIC that can further reduce measurement errors. In particular, the digital image correction device uses a correction graphic attached to the measurement object along with a random pattern to pre-correct the digital image to be used for image analysis using DIC. This allows the digital image correction device to perform image analysis using DIC using a corrected digital image in which distortion caused by changes in the positional relationship between the camera and the measurement object or changes in posture has been corrected. Therefore, the digital image correction device can estimate the displacement and strain of the measurement object with high resolution and precision.

[0078] In image analysis using DIC (digital image correlation), calibration is sometimes performed during the imaging process. For example, it is known that in an imaging process using two or more cameras, a checkerboard with a black and white checkerboard pattern is captured, and the position and orientation of the measurement target relative to the camera can be estimated based on calibration using the image information. However, measurement errors may occur during calibration, or due to changes in the measurement environment after calibration. Furthermore, the above-mentioned general calibration alone is prone to errors, such as distance in the depth direction.

[0079] For this reason, the present invention achieves more accurate correction of the digital image by using known dimensional information of the measurement object 5. This known dimensional information of the measurement object 5 refers to dimensional information of the correction figure 3 applied to the surface of the measurement area 4, and since the dimensions of the correction figure 3 are known (because a figure of a predetermined shape and size is applied to the surface of the measurement object 5), this dimensional information is used for correction (as a transformation matrix during correction), thereby improving the correction accuracy of the digital image.

[0080] DIC is a technology for measuring displacement and strain of a measurement object, and when the camera is moved, more accurate estimation is required than ever before. The digital image correction device 100 can meet this requirement by achieving more accurate correction of digital images based on the above-described correction. Furthermore, the technology related to digital image correction of the present invention does not exclude the possibility of combining it with conventional general calibration, and the digital image correction device 100 may perform both the above-described correction process and conventional calibration.

[0081] <Hardware Configuration of Digital Image Correction Device 100>

[0082] 14 is a diagram showing an example of the hardware configuration of a digital image correction device 100. As shown in the figure, the digital image correction device 100 has an input device 310, a display device 320, a processing device 330, a main memory device 340, an auxiliary memory device 350, a communication device 360, and a bus 370 that electrically interconnects these devices.

[0083] The input device 310 is, for example, a touch panel, a keyboard, a mouse, etc. The display device 320 is a display device such as a liquid crystal display or an organic display.

[0084] The processing device 330 is, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). The main storage device 340 is a memory device (memory resource) such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The digital image correction device 100 has at least one processor and one or more memory resources.

[0085] The auxiliary storage device 350 is a non-volatile storage device capable of storing digital information, such as a so-called hard disk drive, a solid state drive (SSD), or a flash memory.

[0086] The communication device 360 ​​is a wired communication device that performs wired communication via a network cable, or a wireless communication device that performs wireless communication via an antenna.

[0087] An example of the hardware configuration of the digital image correction device 100 has been described above.

[0088] The processing unit 110 of the digital image correction device 100 is realized by a program that causes the processing device 330 to perform processing. This program is stored in the main storage device 340 or the auxiliary storage device 350, and is loaded onto the main storage device 340 and executed by the processing device 330 when the program is executed.

[0089] The storage unit 120 is realized by a main storage device 340, an auxiliary storage device 350, or a combination of these. The communication unit 130 is realized by a communication device 360.

[0090] Furthermore, the above-described configurations, functions, processing units, and processing means of the digital image correction device may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations and functions may also be implemented in software, with a processor interpreting and executing programs that implement the respective functions. Information such as programs, tables, and files that implement the respective functions may be stored in a storage device such as a memory, hard disk, or SSD, or in a recording medium such as an IC card, SD card, or DVD.

[0091] Furthermore, the present invention is not limited to the above-described embodiments and modifications, and includes various modifications within the scope of the same technical concept. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0092] In addition, in the above explanation, the control lines and information lines are those that are considered necessary for the explanation, and do not necessarily show all the control lines and information lines in the product. In reality, it can be considered that almost all components are interconnected.

[0093] 1000: Digital image correction system, 100: Digital image correction device, 110: Processing unit, 111: Image acquisition unit, 112: Image correction unit, 113: Image analysis unit, 114: Output information generation unit, 120: Storage unit, 121: Captured image DB, 130: Communication unit, 310: Input device, 320: Display device, 330: Processing device, 340: Main memory device, 350: Auxiliary memory device, 360: Communication device, 370: Bus, 200: Camera, N: Network

Claims

1. A digital image correction device comprising: an image acquisition unit that acquires a digital image of the surface of a measurement object within a shooting range with an angle of view that includes a random pattern and a correction figure of a predetermined shape; an image correction unit that corrects distortion in the digital image based on a matrix obtained when converting the distortion-containing correction figure in the digital image into a distortion-free correction figure of the predetermined shape; and an image analysis unit that estimates displacement or distortion of the measurement object based on image analysis using the corrected digital image.

2. A digital image correction device according to claim 1, wherein the matrix is ​​a homography transformation matrix, and the image correction unit corrects distortion of the digital image based on the homography transformation matrix.

3. A digital image correction device according to claim 1, characterized in that the image analysis unit estimates the displacement or strain based on image analysis using a digital image correlation method.

4. A digital image correction device according to claim 1, characterized in that the imaging range includes at least one of the correction figures.

5. A digital image correction device according to claim 1, characterized in that the imaging range includes a plurality of correction figures of the same shape or different shapes.

6. A digital image correction device according to claim 4, characterized in that, when the imaging range includes a plurality of said correction figures, said plurality of correction figures are arranged at intervals narrower than the imaging range.

7. A digital image correction device according to claim 1, characterized in that the imaging range includes a plurality of said correction figures positioned at the four corners of said imaging range.

8. A digital image correction device according to claim 7, wherein the image correction unit corrects distortion of the digital image based on a matrix obtained when converting a virtual correction figure formed by connecting the vertices of each of the correction figures located at the four corners of the shooting range, the virtual correction figure having distortion, into a virtual correction figure of a predetermined shape without distortion.

9. A digital image correction device according to claim 1, characterized in that the distortion of the digital image is caused by changes in the positional relationship and posture between the camera that captured the digital image and the object to be measured when the capturing range moves.

10. A digital image correction device according to claim 1, characterized in that at least one of the random pattern and the correction figure is displayed in a visible color or in the infrared or ultraviolet region.

11. A digital image correction device according to claim 1, further comprising an output information generation unit that generates output information indicating the displacement or strain of the object to be measured estimated based on the image analysis and outputs the output information to a specified display device.

12. A digital image correction method performed by a digital image correction device, characterized in that the digital image correction device performs the following steps: an image acquisition step of acquiring a digital image of the surface of a measurement object within a shooting range with an angle of view that includes a random pattern and a correction figure of a predetermined shape; an image correction step of correcting distortion of the digital image based on a matrix obtained when converting the distortion-containing correction figure in the digital image into a distortion-free correction figure of the predetermined shape; and an image analysis step of estimating displacement or distortion of the measurement object based on image analysis using the corrected digital image.

13. A program that causes a computer to function as a digital image correction device, the program causing the computer to function as: an image acquisition unit that acquires a digital image of the surface of a measurement object within a shooting range with an angle of view that includes a random pattern and a correction figure of a predetermined shape; an image correction unit that corrects distortion in the digital image based on a matrix obtained when converting the distortion-containing correction figure in the digital image into a distortion-free correction figure of the predetermined shape; and an image analysis unit that estimates displacement or distortion of the measurement object based on image analysis using the corrected digital image.

Images