A method for accurately extracting coal HRTEM lattice fringes

Abstract

The present invention relates to the field of image processing technology, and in particular to a method for accurately extracting coal HRTEM lattice stripes; comprising the following steps: 1) pre-processing a coal sample and photographing to obtain an HRTEM lattice stripe image; 2) cropping to obtain an image of an area of ​​interest; 3) using fast Fourier transform and inverse Fourier transform to reduce noise and enhance image contrast, and converting the image into a grayscale mode; 4) using the grayscale value when a single stripe is continuous and adjacent lattice stripes are isolated from each other as a threshold for binarization processing; 5) removing noise points and invalid edge lattice stripes; 6) extracting a vectorized coal HRTEM lattice stripe image, and outputting morphological parameter information of the lattice stripes; 7) using the same method and threshold to extract HRTEM lattice stripes in other areas of interest in the same photo. The present invention abandons the subjectivity of manual intervention in threshold selection, greatly improves the extraction accuracy and efficiency of coal HRTEM lattice stripes, and provides reliable data support for the quantitative description of coal HRTEM lattice stripe morphology.

Description

Technical Field

[0001] The present invention relates to the technical field of image processing, and in particular to a method for accurately extracting coal HRTEM lattice fringes. Background Art

[0002] Coal structure directly affects the industrial use and economic value of coal. The diverse composition of coal materials and the long geological history of evolution have led to the complexity and heterogeneity of coal structure. Coal structure research is the basis for the graded and quality-based utilization of coal and its clean, efficient and high value-added utilization. Vitrinite reflectance and bi-reflectance, coal pyrolysis / gas chromatography, X-ray diffraction, X-ray photoelectron spectroscopy, infrared spectroscopy, nuclear magnetic resonance, etc. indirectly explain the composition and structural characteristics of coal materials from different angles, and the research scale is limited to the micron and submicron level. The successful application of high-resolution transmission electron microscopy (HRTEM) in the field of coal structure research can directly observe the lattice fringe morphology of coal at the nanoscale and perform morphological analysis. It is an extremely attractive complementary technology in the field of direct observation of coal structure.

[0003] The HRTEM lattice fringes of coal provide rich information about the nanoscale structure of coal. It is a feasible technical means to directly study the structure of coal and can verify the accuracy of the indirect method of testing the structure of coal. The academic community has transitioned from the early qualitative description of coal HRTEM images to the quantitative interpretation of morphological characteristics. The difficulty lies in how to accurately identify the lattice fringes representing the real coal structure and quickly extract the lattice fringes morphological information. The existing invention patent CN112862816A has proposed an intelligent extraction method for coal lattice fringes. The lattice fringes and background noise are distinguished by block processing of the lattice fringes and further extracted to obtain the lattice fringes information. However, the extraction process does not distinguish between the overlapping areas and single-layer areas of the lattice fringes, and the identification of the lattice fringes depends on the one-to-one comparison of all pixels in the image. The extraction is time-consuming and the reliability and accuracy of the extraction results are difficult to guarantee. This is also a common drawback of the previous related coal HRTEM lattice fringes extraction methods.

[0004] The spacing between adjacent lattice fringes of coal is generally 0.335-0.360nm. Samples used for HRTEM photography are usually ground to pass through a 300-mesh standard sieve (particle size <48 microns). The sample thickness is much greater than the spacing between adjacent lattice fringes. Therefore, the actual HRTEM images often contain multiple layers of stacked lattice fringes, that is, most areas of the image are invalid information, and only the single-layer lattice fringes on the edge represent the real coal structure. At the same time, HRTEM images are greatly affected by electron scattering and thermal effects. Even in the thinner areas at the edge of coal particles, it is difficult to directly distinguish adjacent lattice fringes due to the limited instrument resolution. This is the difficulty in extracting HRTEM lattice fringes from coal. At present, there is a lack of rapid and accurate methods for extracting lattice fringes from HRTEM images of coal, which restricts the accuracy and reliability of coal macromolecular structure modeling and limits the accurate understanding of coal structure. Summary of the invention

[0005] In view of this, the purpose of the present invention is to propose a method for accurately extracting coal HRTEM lattice fringes, using the grayscale value determined when a single stripe is continuous and adjacent lattice fringes are isolated from each other as the threshold for image binarization, abandoning the subjectivity of manual intervention in threshold selection, and ensuring the authenticity and reliability of the extracted data. At the same time, the threshold can be applied to the extraction of other lattice fringes in the same photo, thereby improving the extraction efficiency of coal HRTEM lattice fringes and providing reliable data support for the quantitative description of the morphology of coal HRTEM lattice fringes.

[0006] Based on the above purpose, the present invention provides a method for accurately extracting coal HRTEM lattice fringes, comprising the following steps:

[0007] S1: coal sample pretreatment and photographing to obtain HRTEM lattice fringe images;

[0008] S2: Select the edge single-layer lattice fringe area and crop it to obtain the image of the area of ​​interest;

[0009] S3: Use fast Fourier transform and inverse Fourier transform to reduce noise and enhance contrast, and convert the image into grayscale mode;

[0010] S4: Binarization is performed based on the gray value when a single stripe is continuous and adjacent lattice stripes are isolated from each other;

[0011] S5: Remove noise and invalid lattice fringes at the edge;

[0012] S6: extracting the vectorized coal HRTEM lattice fringe image and outputting the morphological parameter information of the lattice fringe;

[0013] S7: Use the same method and threshold to extract HRTEM lattice fringes in other regions of interest in the same photo.

[0014] Preferably, the coal sample pretreatment step in step S1 is: grinding the coal sample with an agate mortar until it passes a 300-mesh standard sieve, then removing mineral impurities with a mixed acid method, and then using an ultrasonic oscillator to ultrasonicate the coal sample for 20 minutes to evenly disperse the coal sample to obtain a suspension, and using a dropper to draw 2-3 drops of the suspension onto a copper microgrid, and naturally drying to obtain a sample suitable for HRTEM observation.

[0015] Preferably, the HRTEM lattice fringe image in step S1 is a high-resolution lattice fringe photograph of the pretreated coal sample taken using a transmission electron microscope.

[0016] Preferably, the transmission electron microscope is a field emission transmission electron microscope, the acceleration voltage is not less than 200KV, the vacuum degree reaches 10 -8 Pa, has the capability to take high-resolution lattice fringe images.

[0017] Preferably, in step S1, the point resolution of the HRTEM lattice fringe image does not exceed 0.25 nm, and the line resolution does not exceed 0.15 nm.

[0018] Preferably, the selection of the region of interest image in step S2 is obtained by cutting in image processing software, and multiple region of interest images can be cut from the same photo.

[0019] Preferably, the image processing software for cutting the image of the region of interest in step S2 is Adobe Photoshop.

[0020] Preferably, in step S2, the image pixels of the region of interest are 256×256 pixels or 512×512 pixels.

[0021] Preferably, in step S3, the fast Fourier transform and the inverse Fourier transform are performed in the image processing software DigitalMicrograph, using Bandpass filtering, and the number of pixels for smooth edges does not exceed 5.

[0022] Preferably, the number of edge smoothing pixels is 3 or 4.

[0023] Preferably, the threshold in step S4 is a gray value determined by the Quantitative Image Analysis plug-in embedded in the image processing software Adobe Photoshop when a single stripe is continuous and adjacent lattice stripes are isolated from each other.

[0024] Preferably, the noise points in step S5 are removed by using a Quantitative Image Analysis plug-in embedded in the image processing software Adobe Photoshop to remove lattice fringes with a side length less than 0.28 nm.

[0025] Preferably, the invalid edge lattice fringes in step S5 are lattice fringes whose edges of the region of interest are partially sheared.

[0026] Preferably, in step S5, the invalid lattice fringes on the edges are removed by manually removing the lattice fringes whose edges are partially cut using the image processing software Adobe Photoshop.

[0027] Preferably, the morphological parameter information in step S6 includes length, relative position coordinates and angle, etc.

[0028] Beneficial effects of the present invention:

[0029] The present invention obtains multiple regions of interest representing the real structure of coal by cutting edge single-layer lattice fringe images, removes invalid lattice fringe information of multi-layer stacking, and ensures the authenticity and reliability of extracted data.

[0030] The present invention utilizes image processing software to identify and distinguish adjacent lattice fringes, and uses the grayscale value when a single fringes is continuous and adjacent lattice fringes are isolated from each other as the threshold of image binarization processing, thereby eliminating the subjectivity of manual intervention in threshold selection.

[0031] The present invention also uses the threshold value for lattice fringes extraction in other regions of interest in the same photo, avoiding setting different thresholds when processing images in different regions of the same photo, greatly improving the efficiency of coal HRTEM lattice fringes extraction, and providing reliable data support for the quantitative description of coal HRTEM lattice fringes morphology. The extraction results of different regions of interest can be compared horizontally to jointly reveal coal structure information.

[0032] The method for accurately extracting HRTEM lattice fringes of coal provided by the present invention is not only applicable to the extraction of HRTEM lattice fringes of coal with different metamorphic degrees, but also applicable to the extraction of nanoscale lattice fringes of carbonaceous materials including petroleum coke, asphalt coke, coal-based graphite, carbon black, etc., providing a new idea for the high-precision and accurate interpretation of the nanostructure of carbon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 Schematic diagram of the HRTEM lattice fringe extraction process of an area of ​​interest in the lattice fringe photograph of Taixi anthracite in Ningxia Hui Autonomous Region in Example 1 of the present invention;

[0035] Figure 2 Schematic diagram of the HRTEM lattice fringes extraction process of another region of interest of the same photograph of Taixi anthracite in Ningxia Hui Autonomous Region in Example 1 of the present invention;

[0036] Figure 3 Schematic diagram of the process of extracting HRTEM lattice fringes of the region of interest in the lattice fringes photograph of Fujian Yong'an anthracite in Example 2 of the present invention;

[0037] Figure 4 This is a schematic diagram of the binarization processing results of the lattice fringe at different grayscale value thresholds in the same area of ​​interest in the Fujian Yong'an anthracite lattice fringe photograph in Example 3 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0039] Example 1: Taking the Taixi anthracite in Ningxia Hui Autonomous Region as an example, the method for accurately extracting coal HRTEM lattice fringes proposed in the present invention is verified. It can be seen that the lattice fringe image of the Taixi anthracite in Ningxia Hui Autonomous Region taken by high-resolution transmission electron microscopy is clear, the lattice fringes in the area of ​​interest are stacked in a single layer, and the grayscale of the HRTEM lattice fringe image in other areas of the photo is similar, the lattice fringe length, angle and distribution change continuously, and the morphological characteristics of the lattice fringes can be compared horizontally. See the schematic diagram of the HRTEM lattice fringe extraction process of the Taixi anthracite in Ningxia Hui Autonomous Region for details. Figure 1 , the specific extraction steps are as follows:

[0040] S1: The Taixi anthracite of Ningxia Hui Autonomous Region was pretreated to prepare a powder sample suitable for observation under a transmission electron microscope, wherein the pretreatment was performed by grinding with an agate mortar until it passed a 300-mesh standard sieve (particle size was less than 48 μm), and then the mineral impurities were removed by a mixed acid method, and the coal sample was evenly dispersed by ultrasonic oscillator for 20 minutes to obtain a suspension, and 2 drops of the translucent suspension were drawn onto a copper microgrid with a dropper, and the sample was obtained after natural drying to obtain a sample for observation under a transmission electron microscope, and then a high-resolution lattice fringe photograph of the pretreated sample was taken by a transmission electron microscope, and the transmission electron microscope was preferably a field emission transmission electron microscope, with an accelerating voltage of 200 KV and a vacuum degree of 10 -8 Pa level, the point resolution of the lattice fringe image is 0.25nm, and the line resolution is 0.15nm. The original HRTEM lattice fringe image of Taixi anthracite in Ningxia Hui Autonomous Region taken by transmission electron microscope (such as Figure 1 (shown in a);

[0041] S2: Select the edge single-layer lattice fringe area of ​​the photograph (such as Figure 1 In the image processing software Adobe Photoshop, a square image of the region of interest with a side length of 256 × 256 pixels is obtained by cutting (as shown in the white square box in Figure a). Figure 1 (as shown in b);

[0042] S3: The image of the region of interest is subjected to fast Fourier transform and inverse Fourier transform in the image processing software Digital Micrograph, and Bandpass filtering is used with 3 edge smoothing pixels to reduce noise and enhance image contrast. The lattice fringe length corresponding to a single pixel is calibrated and recorded according to the scale, and the image is converted to grayscale mode (such as Figure 1 (as shown in c);

[0043] S4: The Quantitative Image Analysis plug-in embedded in the image processing software Adobe Photoshop is used to obtain the gray value 52 when a single stripe is continuous and adjacent lattice stripes are isolated from each other, and the image is binarized with the gray value 52 as the threshold (e.g. Figure 1 (shown in (d));

[0044] S5: The image processing software Adobe Photoshop was used to manually remove the noise interference data with lattice fringe side length less than 0.28nm and the lattice fringes that were partially cut at the edge of the area of ​​interest, and the HRTEM lattice fringe vector image of an area of ​​interest of Taixi anthracite in Ningxia Hui Autonomous Region was obtained (see Figure 5). Figure 1 The vectorized lattice fringe image extracted with this threshold is shown in e). Figure 1 (e) and the region of interest obtained by cropping the original HRTEM image ( Figure 1 (b) The lattice fringes are distributed uniformly;

[0045] S6: Save and output the morphological parameter information of the lattice fringes of the Taixi anthracite in Ningxia Hui Autonomous Region (including length, relative position coordinates, angle, etc.) to a txt text, and obtain the lattice fringes morphological information data of an area of ​​interest of the Taixi anthracite in Ningxia Hui Autonomous Region (such as Figure 1 f in FIG. 1 );

[0046] S7: Use the same method and threshold to extract HRTEM lattice fringes in another region of interest in the same photo (such as Figure 2 The extraction steps are the same as S1-S6 in Example 1, and the HRTEM lattice fringe vectorized images and morphological data of multiple regions of interest are summarized to obtain the real coal structure information of Taixi anthracite in Ningxia Hui Autonomous Region.

[0047] Example 2: The method for accurately extracting coal HRTEM lattice fringes proposed in the present invention is verified by taking Fujian Yong'an anthracite as an example. The extraction steps are the same as S1-S6 in Example 1. The Fujian Yong'an anthracite HRTEM lattice fringes in the area of ​​interest are stacked in a single layer, and have similar grayscale to the HRTEM lattice fringes in other areas of the photo. The length, angle and distribution of the lattice fringes change continuously. The threshold in step S4 uses the grayscale value 48 determined by the Quantitative Image Analysis plug-in embedded in the image processing software Adobe Photoshop based on the continuous single fringes and the isolated adjacent lattice fringes. See the schematic diagram of the Fujian Yong'an anthracite HRTEM lattice fringes extraction process. Figure 3 ( Figure 3 The corresponding step images and Figure 1 and Figure 2The corresponding relationship is the same). It can be seen that the vectorized lattice fringe image ( Figure 3 Figure e) and the region of interest obtained by cropping the original HRTEM image ( Figure 3 The distribution of lattice fringes in (Fig. b) is consistent, and the extraction results are accurate and reliable.

[0048] Example 3: Select the region of interest image of step S3 in Example 2, and compare and explore the lattice fringe binarization result images when different grayscale thresholds are set, see Figure 4 , the thresholds are set to 20( Figure 4 As shown in a), 30( Figure 4 As shown in b), 40( Figure 4 As shown in c), 48( Figure 4 As shown in d), 50( Figure 4 As shown in e), 60( Figure 4 f), 70( Figure 4 As shown in Figure 5g), it can be seen that the region of interest ( Figure 3 Compared with the lattice fringes shown in (b), when the threshold is 20, 30, and 40, the number of extracted lattice fringes is relatively small, and a single lattice fringes is discontinuous inside. When the threshold is 50, 60, and 70, the number of extracted lattice fringes is relatively large, and adjacent lattice fringes are connected together. When the threshold is 48, the extracted lattice fringes are closest to the actual ones, indicating that the gray value threshold determined based on the continuity of a single fringes and the isolation of adjacent lattice fringes is reliable, and the accuracy of the lattice fringe extraction results is high.

[0049] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0050] Therefore, any omission, modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for accurately extracting coal HRTEM lattice fringes, characterized in that: The following steps are involved: S1: coal sample pretreatment and photographing to obtain HRTEM lattice fringe images; S2: Select the edge single-layer lattice fringe area and crop it to obtain the image of the area of ​​interest; S3: Use fast Fourier transform and inverse Fourier transform to reduce noise and enhance contrast, and convert the image into grayscale mode; S4: Binarization is performed based on the gray value when a single stripe is continuous and adjacent lattice stripes are isolated from each other; S5: Remove noise and invalid lattice fringes at the edge; S6: extracting the vectorized coal HRTEM lattice fringe image and outputting the morphological parameter information of the lattice fringe; S7: Use the same method and threshold to extract HRTEM lattice fringes in other regions of interest in the same photo.

2. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: The coal sample pretreatment steps in step S1 are as follows: using an agate mortar to grind the coal sample until it passes a 300-mesh standard sieve, then using a mixed acid method to remove mineral impurities, and then using an ultrasonic oscillator to ultrasonicate the coal sample for 20 minutes to evenly disperse the coal sample to obtain a suspension, using a dropper to draw 2-3 drops of the suspension onto a copper microgrid, and naturally drying to obtain a sample suitable for HRTEM observation.

3. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: In step S1, the point resolution of the HRTEM does not exceed 0.25 nm, and the line resolution does not exceed 0.15 nm.

4. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: The pixels of the ROI image in step S2 are 256×256 pixels or 512×512 pixels.

5. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: In step S3, the fast Fourier transform and the inverse Fourier transform are performed in the image processing software Digital Micrograph, using Bandpass filtering, and the number of pixels for edge smoothing does not exceed 5.

6. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: In step S3, the number of edge smooth pixels is 3 or 4.

7. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: The threshold in step S4 is a gray value obtained by the Quantitative Image Analysis plug-in embedded in the image processing software Adobe Photoshop based on the fact that a single stripe is continuous and adjacent lattice stripes are isolated from each other.

8. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: In step S5, the noise points are removed by using the Quantitative Image Analysis plug-in embedded in the image processing software Adobe Photoshop to remove the lattice fringes with a side length less than 0.28 nm.

9. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: In step S5, the invalid lattice fringes on the edges are removed by manually removing the lattice fringes whose edges are partially cut using the image processing software Adobe Photoshop.

10. The method for accurately extracting coal HRTEM lattice fringes according to claim 1, characterized in that: The morphological parameter information in step S6 includes lattice fringe length, relative position coordinates and angle, etc.

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