A multi-object digital image detection method

Abstract

The present invention provides a special calibration ruler and method for multi-target digital image detection. The special calibration ruler includes a horizontal ruler and a vertical ruler perpendicular to the horizontal ruler. The plane formed by the horizontal ruler and the vertical ruler is set as the calibration plane, and a base is also provided. The horizontal ruler and the vertical ruler are fixed on the base. Then, the special calibration ruler is used to calibrate each target point of the test object separately to obtain the calibration parameters of each target point; by collecting and analyzing images, the pixel displacement and actual displacement of each target point can be obtained. By using the special calibration ruler to separately calibrate the plane where each target point of the test object is located, the calibration parameters of the plane where each target point is located are obtained, so that the same image acquisition instrument is used to collect images at certain time intervals for analysis, and the pixel displacement of the target point at each acquisition moment is obtained, saving the number of image acquisition instruments.

Description

Technical Field

[0001] The present invention belongs to the field of digital image detection, and particularly relates to a special calibration ruler and method for multi-target digital image detection. Background Art

[0002] Digital image detection is a non-contact and non-interfering full-field deformation optical measurement method based on the principles of computer vision, digital image processing, and numerical calculation. With its advantages of non-contact, high precision, convenience, strong platform scalability, and good connection with artificial intelligence technology, it shows an increasingly wide application prospect in the field of engineering structure detection.

[0003] In recent years, the research on high-precision digital image detection methods has become a hot field at home and abroad. However, a digital image detection method can only detect the displacement of target points in the same plane on a test object within that plane using one image acquisition device, as Figure 1 shown, and it cannot detect the displacement of target points in other planes of the test object. If it is necessary to detect target points in different planes, additional image acquisition devices need to be set up for image acquisition and analysis. Since one or more image acquisition devices require a high-performance laptop computer to be configured on-site, as Figure 2 shown, there are relatively many hardware facilities that need to be set up during image acquisition and analysis. Summary of the Invention

[0004] The purpose of the present invention is to provide a special calibration ruler and method for multi-target digital image detection to solve the technical problem in the prior art that the same image acquisition device cannot be used to detect different planes of a test object.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is:

[0006] A special calibration ruler for multi-target digital image detection, the special calibration ruler includes a horizontal ruler and a vertical ruler perpendicular to the horizontal ruler. The plane formed by the horizontal ruler and the vertical ruler is set as the calibration plane. The midlines of the horizontal ruler and the vertical ruler respectively represent the X-axis and Y-axis of the calibration plane. A base for placing the special calibration ruler on a certain surface is further provided on the special calibration ruler, and the horizontal ruler and the vertical ruler are fixed on the base.

[0007] Further, the horizontal ruler and the vertical ruler of the special calibration ruler are provided with easily recognizable unit scale grids, and the scale values on the horizontal line and the vertical line are obtained by reading the number of scale grids.

[0008] Further, the easily recognizable unit scale grids are scale grids of the same unit with significantly different colors for adjacent scale grids.

[0009] Furthermore, the base is provided with floor screws and a spirit level for adjusting the level of the spirit level.

[0010] The present invention also provides a multi-target digital image detection method using the special calibration ruler, comprising the following steps:

[0011] Step 1: Place the special calibration ruler on the upper surface of the target points of the test object respectively to calibrate each target point individually. The calibration plane formed by the special calibration ruler is the plane where each target point is located. Use an image acquisition device to collect the initial images of each target point during individual calibration and analyze them to obtain the calibration parameters corresponding to each target point.

[0012] Step 2: Collect images of the test object at preset time intervals, and use digital image correlation methods to analyze and calculate the images of the test object to obtain the pixel displacements within the planes where each target point is located.

[0013] Step 3: According to the pixel displacements within the planes where each target point is located, use the calibration parameters corresponding to each target point to calculate the actual displacements of each target point.

[0014] Furthermore, use an image acquisition device to collect the initial images of the target points where the special calibration ruler is placed. Use the known lengths of a certain horizontal line, a certain vertical line on the calibration ruler in the target point calibration image, and the hypotenuse of the right triangle formed by these two lines to calibrate the plane where the target point is located, and record the calibration parameters corresponding to the target point.

[0015] Furthermore, when the image acquisition device collects images, its optical axis is not perpendicular to the outer surface of the test object opposite to the image acquisition device.

[0016] Furthermore, the included angle between the optical axis of the image acquisition device and the outer surface of the test object is 30 to 45 degrees.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] A special calibration ruler for multi-target digital image detection provided by the present invention places the special calibration ruler on the upper surface of the target point through the provided base. Through the spirit level and the vertical ruler, both the calibration plane of the target point can be determined, and the scale values can be read from the images collected by the image acquisition device through the easily recognizable scales on the spirit level and the vertical ruler, so as to obtain the calibration parameters of the target point.

[0019] A multi-target digital image detection method provided by the present invention separately calibrates the plane where each target point of the test object is located by using a special calibration ruler to obtain the calibration parameters of the plane where each target point is located. Then, the same image acquisition instrument is used to collect images of the object to be measured at certain time intervals. The digital image correlation (DIC) technology is used to analyze each target point in the image with each target point in the initial image to obtain the pixel displacement of the target point at each acquisition moment. Then, the actual displacement of each target point is calculated by using the calibration parameters.

[0020] Since the calibration planes of each target point can be calibrated according to the special calibration ruler, and the calibration parameters can be calculated from the lengths of three known line segments on the special calibration ruler, the separate calibration of the planes where multiple target points are located is realized, so that each target point uses an independent calibration plane to analyze its displacement at different moments. Compared with the prior art, the displacement of target points on different planes can be detected by using the same image acquisition instrument, rather than only detecting and analyzing different target points in the same plane, reducing the number of image acquisition instruments used. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of detecting target points in only one plane of the test object in the prior art;

[0022] Figure 2 It is the relationship among the test object, the digital image acquisition instrument, and the computer in the prior art;

[0023] Figure 3 It is a schematic diagram of collecting different target points in different planes by using one image acquisition instrument;

[0024] Figure 4 It is a schematic diagram of the structure of the special calibration ruler;

[0025] Figure 5 It is a schematic diagram of three line segments on the special calibration ruler;

[0026] Figure 6 It is a schematic diagram of the bottom structure of the special calibration ruler;

[0027] Figure 7 It is a schematic diagram of coordinates. Detailed Embodiment

[0028] Next, the technical solution of the present invention will be clearly and completely described in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] A special calibration ruler for multi-target digital image detection according to the present invention, the special calibration ruler includes a horizontal ruler and a vertical ruler perpendicular to the horizontal ruler, and a plane formed by the horizontal ruler and the vertical ruler is set as a calibration plane. The midlines of the horizontal ruler and the vertical ruler respectively represent the X-axis and Y-axis of the calibration plane. A base for placing it on a certain surface is further provided on the special calibration ruler, and the horizontal ruler and the vertical ruler are fixed on the base.

[0030] In this embodiment, as Figure 4 shown, unit scale grids that are easy to identify are provided on the horizontal ruler and the vertical ruler of the special calibration ruler. The scale values on the horizontal line and the vertical line are obtained by reading the number of scale grids. Since the calibration parameters of the target points need to be analyzed through the images of the image acquisition device, unit scale grids that are easy to identify are adopted to facilitate reading the scales from the images. The easy-to-identify unit scale grids are scale grids of the same unit with obvious color contrast between adjacent scale grids. In this embodiment, scale grids with obvious black and white contrast are used to facilitate obtaining the lengths of the line segments on the horizontal ruler and the vertical ruler by counting the scale grids in the image, and then obtaining the length of the hypotenuse. As Figure 5 the lengths of line segments OA, OB, and AB in.

[0031] In this embodiment, as Figure 6 shown, floor screws and a spirit level for adjusting the horizontality of the horizontal ruler are provided on the base. The setting of the floor screws and the spirit level facilitates adjusting the horizontality of the horizontal ruler, making the calibration more accurate.

[0032] The present invention also provides a multi-target digital image detection method using the special calibration ruler, including the following steps:

[0033] Step 1: Place the special calibration ruler on the upper surface of the target points of the test object respectively to perform individual calibration on each target point. As Figure 3 shown, the calibration plane formed by the special calibration ruler is the plane where each target point is located. Use an image acquisition device to collect the initial images of each target point during individual calibration and perform analysis to obtain the calibration parameters corresponding to each target point. The target points in this embodiment refer to cylindrical bases that are pre-set at each target position of the test object as the target points, and the upper surface refers to the upper surface of the cylindrical base.

[0034] In this embodiment, use an image acquisition device to collect the initial images of the target points where the special calibration ruler is placed, and use the known lengths of a certain horizontal line segment, a certain vertical line segment, and the hypotenuse of a right triangle formed by these two lines on the calibration ruler in the target point calibration image to calibrate the plane where the target point is located, and record the calibration parameters corresponding to the target point.

[0035] Step 2: Collect images of the test object at preset time intervals, analyze and calculate the images of the test object using digital image correlation method to obtain the pixel displacements in the plane where each target point is located, and calculate the actual displacements of each target point using the calibration parameters.

[0036] In this embodiment, when the image acquisition device collects images, its optical axis is not perpendicular to the outer surface of the test object opposite to the image acquisition device. The included angle between the optical axis of the image acquisition device and the outer surface of the test object is 30 to 45 degrees. As Figure 7 shown in the coordinates, the reason why the optical axis of the image acquisition device is not perpendicular to the outer surface of the test object opposite to the image acquisition device when collecting images is that digital image measurement is currently two-dimensional and can measure the displacements of target points in the XY plane along the X and Y directions, but cannot measure the displacement along the Z axis. However, in order to measure the displacements of target points in the YZ plane along the Y and Z directions, the optical axis of the image acquisition device cannot be perpendicular to the XY plane (i.e., cannot be parallel to the Z axis), but should form a certain angle with the XY plane, so as to take into account both the XY and YZ planes.

[0037] Since the calibration planes of each target point can be calibrated according to a special calibration ruler, and the calibration parameters can be calculated from the lengths of three known line segments on the special calibration ruler, individual calibration of multiple target points can be realized, so that each target point uses an independent calibration plane to analyze its displacements at different times. Compared with the prior art, the displacements of target points on different planes can be detected using the same image acquisition device, rather than only detecting and analyzing different target points on the same plane, reducing the number of image acquisition devices used. Furthermore, the number of high-performance computers used is reduced.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-object digital image detection method, characterized in that It includes the following steps: Step 1: Place the special calibration ruler on the upper surface of the target points of the test object respectively to calibrate each target point individually. The calibration plane formed by the special calibration ruler is the plane where each target point is located. Use an image acquisition device to collect the initial images of each target point during individual calibration and analyze them to obtain the calibration parameters corresponding to each target point; The special calibration ruler includes a horizontal ruler and a vertical ruler perpendicular to the horizontal ruler. The plane formed by the horizontal ruler and the vertical ruler is set as the calibration plane. The midlines of the horizontal ruler and the vertical ruler represent the X-axis and Y-axis of the calibration plane respectively. A base for placing it on a certain surface is also provided on the special calibration ruler. The horizontal ruler and the vertical ruler are fixed on the base; Unit scale grids that are easy to identify are provided on the horizontal ruler and the vertical ruler of the special calibration ruler. The scale values on the horizontal line and the vertical line are obtained by reading the number of scale grids; The method for individually calibrating each target point is: Use an image acquisition device to collect the initial image of the target point with the special calibration ruler placed on it. Calibrate the plane where the target point is located by using a certain section of the horizontal line, a certain section of the vertical line of the special calibration ruler in the target point calibration image, and the known length of the hypotenuse of the right triangle formed by these two lines, and record the calibration parameters corresponding to the target point; Step 2: Collect images of the test object at preset time intervals. Use the digital image correlation method to analyze and calculate the images of the test object to obtain the pixel displacements within the plane where each target point is located, and calculate the actual displacements of each target point according to the calibration parameters.

2. The multi-object digital image detection method according to claim 1, characterized in that, The easily identifiable unit scale grids are scale grids of the same unit with significantly different colors for adjacent scale grids.

3. A multi-object digital image detection method according to claim 2, characterized in that, Foot screws and a level bubble for adjusting the horizontality of the horizontal ruler are provided on the base.

4. A multi-object digital image detection method according to claim 3, characterized in that When the image acquisition device collects images, its optical axis is not perpendicular to the outer surface of the test object opposite to the image acquisition device.

5. A multi-object digital image detection method according to claim 4, characterized in that, The included angle between the optical axis of the image acquisition device and the outer surface of the test object is 30 to 45 degrees.

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