CN116402675B - Image registration method based on shale component calibration - Google Patents
Image registration method based on shale component calibration Download PDFInfo
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Abstract
The invention discloses an image registration method based on shale component calibration, which comprises the following steps: scanning the shale sample with high and low resolution to obtain a three-dimensional image and a partial image; importing the two images into the same coordinate system for registration; polishing the first surface to a region to be detected; determining a position of the polishing surface in a coordinate system based on a vertical distance from the polishing surface to the second surface; acquiring an SEM image of the polished surface; and carrying out overlay registration on the SEM image and the polished surface of the region to be detected in the coordinate system. According to the image registration method, the position relation between the shale sample and the region to be detected in the shale sample is determined in the same coordinate system, and the position of SEM scanning is accurately determined in the coordinate system through the vertical distance from the polishing surface to the second surface, so that registration is completed. The SEM image can be also in the range of CT scanning data volume in the rock, so that the success probability of registration between images with larger difference of two scanning instruments, observation scale and resolution is improved.
Description
Technical Field
The invention belongs to the technical field of rock analysis, and particularly relates to an image registration method based on shale component calibration.
Background
In recent years, with the development of fields such as unconventional oil and gas and nuclear waste disposal, dense rock typified by shale has been an object of intense study. Accurate and fine characterization of the internal microstructure and compositional features of shale is a common fundamental requirement for these research fields.
The current image interpretation analysis method for rock microstructure mainly relies on high-resolution local same-view images (such as SEM images) for reference and calibration, namely, images with different resolutions and different dimensions are registered. The existing CT and SEM scanning combined technical scheme can only ensure that images come from the same sample, if the SEM and CT images with the same vision are to be acquired, the cross-scale and the dimension are often needed, the difficulty of registration work is increased, and the existing solution method has two kinds: one is to expand the SEM or CT scan observation range (Li et al, 2022; sok et al, 2010), but this approach does not meet the objective of calibrating the shale CT image blur component with the SEM image, on the premise of losing image resolution; one is to directly SEM observe the outer surface of the sample and register with the corresponding CT data volume (De Boever, et al 2015), which is not friendly to CT image interpretation, because the outermost imaging effect of CT data volumes tends to be the worst, and component identification and interpretation is typically performed using relatively small-scale high-resolution sample internal scanning CT data volumes in shale.
Disclosure of Invention
Object of the invention
The invention aims to provide an image registration method based on shale component calibration so that a registered high-resolution SEM image can be used for calibrating low-gray-scale micro components in shale micron CT images.
(II) technical scheme
To solve the above problems, a first aspect of the present invention provides an image registration method based on shale component calibration, including: cutting shale raw materials to obtain shale samples; the shale sample is provided with a first face and a second face which are parallel to each other, and the first face and the second face are perpendicular to the bedding face of the shale sample; performing low-resolution CT scanning on the shale sample to obtain a three-dimensional image of the whole shale sample; performing high-resolution CT scanning on the shale sample to obtain a local image of a region to be detected of the shale sample; importing the three-dimensional image and the local image into the same coordinate system for registration; polishing the first face of the shale sample to the region to be tested; determining a position of the polishing surface in the coordinate system based on a vertical distance of the polishing surface to the second surface; carrying out SEM scanning on the polished surface of the region to be detected to obtain an SEM image; and carrying out overlay registration on the SEM image and the polished surface of the region to be detected in the coordinate system.
Further, the performing SEM scanning on the polished surface of the area to be measured, to obtain an SEM image includes: carrying out low-resolution SEM scanning on the polished surface to obtain an integral SEM image of the polished surface; obtaining the position of the region to be measured in the polished surface based on the position of the polished surface in the coordinate system; and carrying out high-resolution SEM scanning on the area to be detected in the polishing surface based on the position of the area to be detected in the polishing surface and the whole SEM image to obtain an SEM image.
Further, performing SEM scanning on the polished surface of the region to be detected to obtain an SEM image; performing overlay registration on the SEM image and the polished surface of the region to be measured in the coordinate system includes: carrying out low-resolution SEM scanning on the polished surface to obtain an integral SEM image of the polished surface; obtaining the position of the region to be measured in the polished surface based on the position of the polished surface in the coordinate system; based on the position of the region to be detected in the polishing surface and the whole SEM image, carrying out highest resolution SEM scanning in the region to be detected in the polishing surface to obtain an SEM image and the position of the SEM image; and determining the position of the SEM image in the coordinate system, and performing overlay registration based on the local image and the SEM image of the position.
Further, performing overlay registration between the SEM image and the polished surface of the region to be measured in the coordinate system includes: selecting a plurality of slices of the partial images along the direction of the first surface and/or the direction of the second surface based on the position of the polishing surface in the coordinate system, and acquiring the slices of the position of the polishing surface in the coordinate system; extracting the characteristics of each slice; comparing the features extracted from each slice with the features of the SEM image, and determining a registration slice with the same features or the closest features; and carrying out overlay registration on the SEM image and the registration slice.
Further, the feature extraction is performed on each slice; comparing the extracted features of each slice with the features of the SEM image, and determining the registered slice with the same or closest features comprises: calculating the area and the position of the low gray part in each slice to obtain the contrast characteristic of each slice; calculating the area and the position of the low gray scale part in the SEM image as standard features; and comparing the contrast characteristic of each slice with the standard characteristic, and determining the registration slices with the same characteristics or the closest characteristics.
Further, the cutting the shale raw material to obtain a shale sample comprises: cutting the shale raw material into rectangular blank samples by adopting a linear cutting instrument or a lapping integrated machine; and mechanically polishing the blank samples in sequence to obtain shale samples.
Further, the high-resolution CT scanning is performed by replacing an objective lens after the low-resolution CT scanning, and the positions of the shale samples are unchanged during the low-resolution CT scanning and the high-resolution CT scanning.
Further, the low-resolution CT scanning is performed by adopting a highest-resolution objective lens capable of integrally scanning the shale sample in CT; the high resolution CT scan uses the highest resolution objective of CT for scanning.
Further, said registering said three-dimensional image and said local image in the same coordinate system comprises: reconstructing the three-dimensional image in software of a CT scanning instrument to form a low-resolution three-dimensional data volume; reconstructing the local image into a high resolution three-dimensional data volume in software of a CT scanning instrument; and importing the low-resolution three-dimensional data volume and the high-resolution three-dimensional data volume into three-dimensional image processing software for registration.
Further, polishing the first face of the shale sample for the first time by adopting a lapping integrated machine; performing secondary polishing on the shale sample subjected to the primary polishing by adopting an argon ion polisher; the first polishing and the second polishing polish the first face of the shale sample to the area under test.
(III) beneficial effects
The technical scheme of the invention has the following beneficial technical effects:
according to the image registration method, the position relation between the shale sample and the region to be detected in the shale sample is determined in the same coordinate system, and the polishing surface is determined in the coordinate system through the perpendicular distance from the polishing surface to the second surface. By knowing the position relation between the shale sample and the area to be measured and combining the polished surface, the position of the polished surface in the area to be measured can be determined in a coordinate system, so that the position of SEM scanning can be accurately obtained, and registration is completed. The SEM image can be also in the range of CT scanning data volume in the rock, so that the success probability of registration between images with larger difference of two scanning instruments, observation scale and resolution is improved.
Drawings
Fig. 1 is a flowchart of an image registration method according to an embodiment of the present invention.
Fig. 2 is a schematic representation of a shale sample according to an embodiment of the invention.
Fig. 3 is a schematic representation of a polished shale sample in accordance with an embodiment of the present invention.
Fig. 4 is a schematic diagram of a comparison of a slice and SEM image according to an embodiment of the invention.
Fig. 5 is a schematic diagram of a slice versus SEM image according to another embodiment of the invention.
Fig. 6 is a schematic diagram of a combination of a registered CT scan image and an SEM image according to an embodiment of the present invention.
The right side in fig. 3 is a partial enlarged view of the E-plane.
Reference numerals:
a is a first surface; b is a second surface; s is a region to be measured; g is a polished surface; e is the overlapping part of the polishing surface and the area to be tested (namely the polishing surface in the area to be tested); f is part of the SEM scan.
Detailed Description
The objects, technical solutions and advantages of the present invention will become more apparent by the following detailed description of the present invention with reference to the accompanying drawings. It should be understood that the description is only illustrative and is not intended to limit the scope of the invention. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the present invention.
A layer structure schematic diagram according to an embodiment of the present invention is shown in the drawings. The figures are not drawn to scale, wherein certain details may be exaggerated and some details may be omitted for clarity. The shapes of the various regions, layers and relative sizes, positional relationships between them shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.
It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In addition, the technical features of the different embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The invention will be described in more detail below with reference to the accompanying drawings. Like elements are denoted by like reference numerals throughout the various figures. For clarity, the various features of the drawings are not drawn to scale. The current image interpretation analysis method for rock microstructure mainly relies on gray threshold segmentation, and besides manual threshold determination, the method also comprises various automatic threshold determination methods such as Ostu, watershed and the like. With the development of machine learning technology, an image segmentation method based on a deep learning model such as U-net is further developed, and the method integrates various information such as gray level and geometric form of a target component to perform component identification and image segmentation. However, whichever of the above image segmentation methods is required to be completed on the basis of accurate knowledge of the rock image component categories. Even with the machine learning method employing the leading edge, it is necessary to provide accurate image recognition and segmentation results as sample data for training of the deep learning model.
In shale micron CT images, low-gray scale micro-components represented by pores, organic matter, clay minerals tend to be intermixed and indistinguishable, which makes these image segmentation techniques difficult to develop in such image data interpretation analysis.
The invention establishes an experimental technical process and an image registration technical analysis method for combining SEM and micron CT, reduces the data analysis workload required by image registration by changing a sample preparation method and optimizing an image scanning process, and rapidly positions CT slices containing the same view field as a high-resolution SEM image in a CT data volume, so that the registered high-resolution SEM image can be used for calibrating low-gray micro components in a shale micron CT image, and the identification and interpretation of the micro components of the shale micron CT image are completed on the basis. The method can be used as a quality evaluation reference of shale micron CT data volume interpretation results, and can also provide a basic training sample for image segmentation interpretation technologies such as deep learning.
In one embodiment of the invention, an image registration method based on shale component calibration is provided, comprising: cutting shale raw materials to obtain shale samples; the shale sample is provided with a first face and a second face which are parallel to each other, and the first face and the second face are perpendicular to the bedding face of the shale sample; performing low-resolution CT scanning on the shale sample to obtain a three-dimensional image of the whole shale sample; performing high-resolution CT scanning on the shale sample to obtain a local image of a region to be detected of the shale sample; importing the three-dimensional image and the local image into the same coordinate system for registration; polishing the first face of the shale sample to the region to be tested; determining a position of the polishing surface in the coordinate system based on a vertical distance of the polishing surface to the second surface; carrying out SEM scanning on the polished surface of the region to be detected to obtain an SEM image; and carrying out overlay registration on the SEM image and the polished surface of the region to be detected in the coordinate system.
According to the image registration method, the position relation between the shale sample and the region to be detected in the shale sample is determined in the same coordinate system, and the polishing surface is determined in the coordinate system through the perpendicular distance from the polishing surface to the second surface. By knowing the position relation between the shale sample and the area to be measured and combining the polished surface, the position of the polished surface in the area to be measured can be determined in a coordinate system, so that the position of SEM scanning can be accurately obtained, and registration is completed. The SEM image can be also in the range of CT scanning data volume in the rock, so that the success probability of registration between images with larger difference of two scanning instruments, observation scale and resolution is improved.
Fig. 1 is a flowchart of an image registration method according to an embodiment of the present invention.
As shown in fig. 1, in an embodiment of the present invention, there is provided an image registration method based on shale component calibration, at least comprising the steps of:
s100, cutting the shale raw material to obtain shale samples.
S200, performing low-resolution CT scanning on the shale sample to obtain a three-dimensional image of the whole shale sample.
S300, performing high-resolution CT scanning on the shale sample to obtain a local image of a region to be detected of the shale sample.
S400, importing the three-dimensional image and the local image into the same coordinate system for registration.
S500, polishing the first surface of the shale sample to the area to be detected.
S600, determining the position of the polishing surface in the coordinate system based on the vertical distance from the polishing surface to the second surface.
S700, carrying out SEM scanning on the polished surface of the region to be detected to obtain an SEM image.
S800, performing overlay registration on the SEM image and the polished surface of the region to be detected in the coordinate system.
In an alternative embodiment, the low resolution CT scan employs the highest resolution objective lens of the CT scan that is capable of fully scanning the entire shale sample. Although called low resolution CT scan, the highest resolution objective lens that is capable of fully scanning the shale sample is actually employed as opposed to high resolution CT scan.
In an alternative embodiment, the high resolution CT scan uses the highest resolution objective lens of the CT scan.
According to the invention, the rock sample with parallel opposite faces (the first face and the second face) is manufactured, and the sample thinning direction of the sample SEM scanning observation face can be rapidly determined in a CT data body through the flow of mechanical polishing-CT multistage scanning-ion thinning-SEM scanning.
In an alternative embodiment, the performing SEM scanning on the polished surface of the area to be measured, and obtaining an SEM image includes: carrying out low-resolution SEM scanning on the polished surface to obtain an integral SEM image of the polished surface; obtaining the position of the region to be measured in the polished surface based on the position of the polished surface in the coordinate system; and carrying out high-resolution SEM scanning on the area to be detected in the polishing surface based on the position of the area to be detected in the polishing surface and the whole SEM image to obtain an SEM image.
In an alternative embodiment, the SEM scanning is performed on the polished surface of the area to be measured to obtain an SEM image; performing overlay registration on the SEM image and the polished surface of the region to be measured in the coordinate system includes: carrying out low-resolution SEM scanning on the polished surface to obtain an integral SEM image of the polished surface; obtaining the position of the region to be measured in the polished surface based on the position of the polished surface in the coordinate system; based on the position of the region to be detected in the polishing surface and the whole SEM image, carrying out highest resolution SEM scanning in the region to be detected in the polishing surface to obtain an SEM image and the position of the SEM image; and determining the position of the SEM image in the coordinate system, and performing overlay registration based on the local image and the SEM image of the position.
In an alternative embodiment, the performing overlay registration between the SEM image and the polished surface of the region to be measured in the coordinate system includes: selecting a plurality of slices of the partial images along the direction of the first surface and/or the direction of the second surface based on the position of the polishing surface in the coordinate system, and acquiring the slices of the position of the polishing surface in the coordinate system; extracting the characteristics of each slice; comparing the features extracted from each slice with the features of the SEM image, and determining a registration slice with the same features or the closest features; and carrying out overlay registration on the SEM image and the registration slice.
In an alternative embodiment, the feature extraction is performed on each slice; comparing the extracted features of each slice with the features of the SEM image, and determining the registered slice with the same or closest features comprises: calculating the area and the position of the low gray part in each slice to obtain the contrast characteristic of each slice; calculating the area and the position of the low gray scale part in the SEM image as standard features; and comparing the contrast characteristic of each slice with the standard characteristic, and determining the registration slices with the same characteristics or the closest characteristics. According to the invention, through identification of the marker boundary, an image difference evaluation algorithm is used for analyzing the result, and therefore, the CT slice with the highest similarity with the SEM image is determined to be used for registration.
In an alternative embodiment, an image is selected that includes the region to be measured in each slice.
In a preferred embodiment, the polishing of the first face of the shale sample into the area to be polished is a1+a2/2 thickness.
And taking the marker area in the SEM image as a standard area, calculating the relative error between the corresponding marker area in each slice and the standard area, counting the relative error average value of all the marker areas in each slice, and selecting the slice to be screened with the minimum relative error average value as a registration slice.
And moving the rotating SEM image in a mode of overlapping images in the same coordinate system so as to perform position registration on the slice group to be screened.
In an alternative embodiment, the cutting the shale material to obtain shale samples comprises: cutting the shale raw material into rectangular blank samples by adopting a linear cutting instrument or a lapping integrated machine; and mechanically polishing the blank sample by adopting sand paper to obtain a shale sample.
In an alternative embodiment, the mechanically polishing the blank sample with sandpaper may include: and mechanically polishing the blank sample by adopting sand paper with the granularity from coarse to fine in sequence to obtain a shale sample. According to the shale component calibration-based image registration method, an experimental technical flow of SEM (electron scanning microscope) and micron CT combined and an image registration technical analysis method are established, data analysis workload required by image registration is reduced by changing a sample preparation method and optimizing an image scanning flow, CT slices which contain the same view field as a high-resolution SEM image are rapidly positioned in a CT data body, so that the registered high-resolution SEM image can be used for calibrating low-gray micro components in a shale micron CT image, and identification and interpretation of the shale micron CT image micro components are completed on the basis. The method can be used as a quality evaluation reference of shale micron CT data volume interpretation results, and can also provide a basic training sample for image segmentation interpretation technologies such as deep learning.
In an alternative embodiment, the high resolution CT scan is performed by changing an objective lens after the low resolution CT scan, and the positions of the shale samples are unchanged during the low resolution CT scan and the high resolution CT scan.
In an alternative embodiment, the low resolution CT scan is performed using the highest resolution objective lens in CT that is capable of scanning the shale sample in its entirety; the high resolution CT scan uses the highest resolution objective of CT for scanning.
In an alternative embodiment, said registering said importing said three-dimensional image and said local image into the same coordinate system comprises: reconstructing the three-dimensional image in software of a CT scanning instrument to form a low-resolution three-dimensional data volume; reconstructing the local image into a high resolution three-dimensional data volume in software of a CT scanning instrument; and importing the low-resolution three-dimensional data volume and the high-resolution three-dimensional data volume into three-dimensional image processing software for registration. The reconstructed high-resolution partial image and the low-resolution three-dimensional image are imported into the same coordinate system, and because the position of the sample in the micrometer CT instrument is unchanged in the two scanning processes, the reconstructed data volume (the coordinate system with the three-dimensional image and the partial image at the same time) can be directly registered in the same coordinate system.
In an alternative embodiment, the partial image is a three-dimensional high resolution image of the region to be measured.
In an alternative embodiment, the CT scan is performed using a Seiss Xradia 510Versa scanner to obtain projection images (the three-dimensional image and the partial image) of the entirety of the shale sample; because the shale sample position is unchanged during two CT scans (low-resolution CT Scan and high-resolution CT Scan), the three-dimensional image and the local image can be imported into the same coordinate system by using scanning instrument matching software (Scout-and-Scan), and the three-dimensional image and the local image can be automatically registered in the coordinate system by virtue of matching software thereof, and the local image with high resolution is matched in the position of the three-dimensional image with low resolution.
In an alternative embodiment, the three-dimensional image and the local image are imported into the same coordinate system using Scout-and-Scan to reconstruct a 3D data volume of the object.
In an alternative embodiment, the reconstructed 3D data volume (with the coordinate system of the three-dimensional image and the local image at the same time) is stored as a format file (txm in this example) with the spatial coordinate information of the scanned sample, which file is imported into the three-dimensional image processing software (Dragonfly in this example) to view the three-dimensional image. In an alternative embodiment, the coordinate system takes the direction vertical to the first surface/the second surface of the shale sample as a coordinate Z axis, takes orthogonal straight lines in a plane passing through the origin of coordinates and parallel to the first surface and the second surface as an X axis and a Y axis, and the coordinate system is kept unchanged after being selected.
And selecting the region to be detected on the basis of the lithology characteristics provided by the three-dimensional image of the shale sample, and importing the three-dimensional image and the local image into a coordinate system to finish registration.
In an alternative embodiment, a lapping machine is used to first polish the first face of the shale sample; performing secondary polishing on the shale sample subjected to the primary polishing by adopting an argon ion polisher; the first polishing and the second polishing polish the first face of the shale sample to the area under test.
Example 1:
cutting the shale raw material into cubes with a side length of about 1mm (as shown in fig. 2) by using a wire cutter or a lapping integrated machine, requiring that one set of opposite faces (the first face and the second face) are perpendicular to the shale layer arranging direction and parallel to each other, the angle error is not more than 0.5 mu m, and then carrying out simple mechanical polishing on the first face by using sand paper with a granularity ranging from coarse to fine (the minimum granularity is less than 4000 meshes) in sequence to obtain shale samples.
And standing the first surface and the second surface of the shale sample and fixing the first surface and the second surface on a micrometer CT sample rotary table to perform continuous scanning twice, wherein the resolution adopted by the first scanning is required to be capable of performing complete three-dimensional imaging (the resolution used in the example is 1.2 mu m) on the whole sample, the position of the sample is not moved during the second scanning, only the high-power objective lens is changed to enable the resolution to be improved to be close to the highest resolution (the resolution used in the example is 0.6 mu m) of an instrument by 0.3-1, and the region to be detected inside the shale sample is selected to perform local high-resolution scanning imaging, so that a three-dimensional image of the whole shale sample and a local image of the region to be detected of the shale sample are obtained.
In this embodiment, the selected regions to be measured are cylindrical (generally, the regions to be measured selected for analysis of the components are all cylindrical).
Reconstructing the three-dimensional image to obtain a first data body; the partial image is reconstructed to obtain a second data volume (the data reconstruction software used in this example is the micrometer CT scanner self-contained program).
The reconstructed low-resolution data volume and the high-resolution data volume are imported into the same coordinate system to directly obtain the registered low-resolution data volume (corresponding to the first data volume) and high-resolution data volume (corresponding to the second data volume) (the coordinate system used in the example is provided by Dragonfly software), the minimum distance a1 (223 μm in the example) between the first surface of the sample and the region to be measured in the low-resolution data volume is measured in the coordinate system, and the diameter a2 (106 μm in the example) of the high-resolution data volume (i.e. the diameter of the cylinder region to be measured) is measured (as shown in fig. 2).
The shale sample is put into a lapping machine and the first surface is polished again to the region to be measured (the thickness of the mechanical polishing reduction is about 250 μm in the example) by using a minimum particle size sand paper (6000 mesh in the example), the polished surface is put upwards into an argon ion polisher for large-area ion polishing to remove stress damage caused by the mechanical polishing on the sample surface, the ion polishing time is preferably not more than 4h (4 kv and 2 hours in the example), the total thickness of the mechanical polishing and the ion polishing reduction is not less than the minimum distance a1 measured in the step 3 and not more than a1+a2 (the thickness of the mechanical polishing reduction is about 250 μm in the example), and the vertical distance from the polished surface to the second surface observed in the lapping machine after polishing is recorded as a3 (shown in fig. 3).
In the high-resolution data volume registration coordinate system and the low-resolution data volume registration coordinate system, the opposite surface of the polishing surface of the low-resolution data volume is positioned, a high-resolution CT data volume slice (namely, E surface and polishing surface in a to-be-detected area) corresponding to the thickness a3 is reserved after a sample is taken and thinned along the direction perpendicular to the surface, and the length and width of the view area and the relative positions in the low-resolution CT data volume slice at the same position are calculated, namely, the distances c1, c2, c3 and c4 (shown in fig. 3) of four direction boundaries of the view area of the high-resolution slice from the corresponding direction boundary of the view area of the low-resolution slice are recorded. Determining the position of the polishing surface in the coordinate system based on the vertical distance from the polishing surface to the second surface; based on the position of the polishing surface, the position of the E-surface can be determined in the coordinate system.
Placing the polished surface of the shale sample subjected to ion polishing upwards into a Scanning Electron Microscope (SEM), positioning the position of an E surface in a low resolution mode and defining a boundary range; and then reducing the scanning view field to improve the resolution, carrying out continuous scanning imaging or large-area scanning imaging on the premise of ensuring that low gray scale components such as pores, organic matters and the like can be resolved, and measuring the position of the imaging view field in a delimited SEM scannable imaging area (namely the position of an F surface in an E surface) in a low resolution mode, namely recording distances d1, d2, d3 and d4 (shown in figure 3) of four direction boundaries of the SEM imaging view field from corresponding direction boundaries of a high resolution slice view field. Based on d1, d2, d3, d4, the position of the F-plane can be determined in the coordinate system.
The position of the F-plane is determined in the coordinate system, and a number of adjacent serial slices (6 slices in this example) are extracted as a slice group to be screened having a similar view to the SEM image and an image is derived (as shown in fig. 4).
Setting the same threshold value to extract low gray components in a slice group to be screened, selecting a plurality of discrete distribution units as markers (shown in figure 5), and calculating the area size of each selected marker in each CT slice to be screened (table 1); as shown in table 1, slice 3 is a registration slice.
The SEM image is registered with the registration slice in a superimposed manner (as shown in fig. 6).
TABLE 1 statistical table of marker areas and errors of to-be-screened and registered SEM images
The invention provides an image registration method based on shale component calibration, which comprises the following steps: cutting shale raw materials to obtain shale samples; the shale sample is provided with a first face and a second face which are parallel to each other, and the first face and the second face are perpendicular to the bedding face of the shale sample; performing low-resolution CT scanning on the shale sample to obtain a three-dimensional image of the whole shale sample; performing high-resolution CT scanning on the shale sample to obtain a local image of a region to be detected of the shale sample; importing the three-dimensional image and the local image into the same coordinate system for registration; polishing the first face of the shale sample to the region to be tested; determining a position of the polishing surface in the coordinate system based on a vertical distance of the polishing surface to the second surface; carrying out SEM scanning on the polished surface of the region to be detected to obtain an SEM image; and carrying out overlay registration on the SEM image and the polished surface of the region to be detected in the coordinate system. According to the image registration method, the position relation between the shale sample and the region to be detected in the shale sample is determined in the same coordinate system, and the polishing surface is determined in the coordinate system through the perpendicular distance from the polishing surface to the second surface. By knowing the position relation between the shale sample and the area to be measured and combining the polished surface, the position of the polished surface in the area to be measured can be determined in a coordinate system, so that the position of SEM scanning can be accurately obtained, and registration is completed. The SEM image can be also in the range of CT scanning data volume in the rock, so that the success probability of registration between images with larger difference of two scanning instruments, observation scale and resolution is improved.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explanation of the principles of the present invention and are in no way limiting of the invention. Accordingly, any modification, equivalent replacement, improvement, etc. made without departing from the spirit and scope of the present invention should be included in the scope of the present invention. Furthermore, the appended claims are intended to cover all such changes and modifications that fall within the scope and boundary of the appended claims, or equivalents of such scope and boundary.
Claims (8)
1. An image registration method based on shale component calibration, which is characterized by comprising the following steps:
cutting shale raw materials to obtain shale samples; the shale sample is provided with a first face and a second face which are parallel to each other, and the first face and the second face are perpendicular to the bedding face of the shale sample;
performing low-resolution CT scanning on the shale sample to obtain a three-dimensional image of the whole shale sample;
performing high-resolution CT scanning on the shale sample to obtain a local image of a region to be detected of the shale sample;
importing the three-dimensional image and the local image into the same coordinate system for registration;
polishing the first face of the shale sample to the region to be tested;
determining a position of the polishing surface in the coordinate system based on a vertical distance of the polishing surface to the second surface;
carrying out SEM scanning on the polished surface of the region to be detected to obtain an SEM image;
carrying out overlay registration on the SEM image and a polished surface of the region to be detected in the coordinate system;
performing SEM scanning on the polished surface of the region to be detected to obtain an SEM image; performing overlay registration on the SEM image and the polished surface of the region to be measured in the coordinate system includes: carrying out low-resolution SEM scanning on the polished surface to obtain an integral SEM image of the polished surface; obtaining the position of the region to be measured in the polished surface based on the position of the polished surface in the coordinate system; based on the position of the region to be detected in the polishing surface and the whole SEM image, carrying out highest resolution SEM scanning in the region to be detected in the polishing surface to obtain an SEM image and the position of the SEM image; and determining the position of the SEM image in the coordinate system, and performing overlay registration based on the local image and the SEM image of the position.
2. The image registration method according to claim 1, wherein performing overlay registration of the SEM image with a polished surface of the region to be measured in the coordinate system includes:
selecting a plurality of slices of the partial images along the direction of the first surface and/or the direction of the second surface based on the position of the polishing surface in the coordinate system, and acquiring the slices of the position of the polishing surface in the coordinate system;
extracting the characteristics of each slice;
comparing the features extracted from each slice with the features of the SEM image, and determining a registration slice with the same features or the closest features;
and carrying out overlay registration on the SEM image and the registration slice.
3. The image registration method according to claim 2, wherein the feature extraction is performed on each slice; comparing the extracted features of each slice with the features of the SEM image, and determining the registered slice with the same or closest features comprises:
calculating the area and the position of the low gray part in each slice to obtain the contrast characteristic of each slice;
calculating the area and the position of the low gray scale part in the SEM image as standard features;
and comparing the contrast characteristic of each slice with the standard characteristic, and determining the registration slices with the same characteristics or the closest characteristics.
4. The image registration method of claim 1, wherein the cutting the shale material to obtain shale samples comprises:
cutting the shale raw material into rectangular blank samples by adopting a linear cutting instrument or a lapping integrated machine;
and mechanically polishing the blank sample by adopting sand paper to obtain a shale sample.
5. The method of image registration according to claim 1, wherein,
and after the low-resolution CT scanning, the high-resolution CT scanning is performed by replacing an objective lens, and the positions of the shale samples are unchanged during the low-resolution CT scanning and the high-resolution CT scanning.
6. The method of image registration according to claim 5, wherein,
the low-resolution CT scanning adopts a highest-resolution objective lens capable of integrally scanning the shale sample in CT for scanning;
the high resolution CT scan uses the highest resolution objective of CT for scanning.
7. The image registration method according to claim 1, wherein the introducing the three-dimensional image and the partial image into the same coordinate system for registration includes:
reconstructing the three-dimensional image in software of a CT scanning instrument to form a low-resolution three-dimensional data volume;
reconstructing the local image into a high resolution three-dimensional data volume in software of a CT scanning instrument;
and importing the low-resolution three-dimensional data volume and the high-resolution three-dimensional data volume into three-dimensional image processing software for registration.
8. The method of image registration according to claim 1, wherein,
polishing the first surface of the shale sample for the first time by adopting a lapping integrated machine;
performing secondary polishing on the shale sample subjected to the primary polishing by adopting an argon ion polisher;
the first polishing and the second polishing polish the first face of the shale sample to the area under test.
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