Pressure value extraction method based on color-changing pressed film

Abstract

The invention discloses a pressure value extraction method based on a color-changing pressed film, and belongs to the technical field of pressure measurement film testing. The method comprises the following steps: carrying out image scanning on a pressure measurement film which is pressed and discolored by using an image measuring instrument to obtain a scanned image; processing the scanned image to generate a corresponding gray image and a gray value matrix; converting the generated gray value matrix into a pressure value matrix through the function relationship between the gray value and the pressure value of the pressure measurement film, wherein each element in the pressure value matrix represents the pressure value of each point position of the pressure measurement film image; giving colors to the gray value matrix according to the color mapping array, and visualizing the gray value matrix into a pressure cloud picture; wherein the color mapping array is used for determining the color of each gray value in the gray value matrix. By means of the method, the pressure cloud picture of the pressure measurement film and the pressure value of each point position after color change under pressure can be accurately obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of pressure measurement film testing, and in particular relates to a pressure value extraction method based on a color-changing pressure film. Background Art

[0002] When studying the influence of mold materials and configurations on pressure transmission performance, it is necessary to measure the pressure distribution on the mold surface and the pressure transmission efficiency. Researchers usually use the pressure measurement film (Pressure Measurement Film) of Fuji Corporation of Japan to measure the surface pressure of the mold. This film consists of two parts, A-film and C-film, both of which are made of polyethylene naphthalate as the matrix, in which A-film is coated with a layer of microencapsulated color-forming material and C-film is coated with a layer of color developer. During the test, the rough surfaces of A-film and C-film are placed face to face and fixed to the tested mold with tape. When pressure is applied to the mold, the microcapsules in A-film rupture, and the color-forming material reacts with the color-developing material in C-film, making it appear red. The depth of the film color change increases with the increase of the applied pressure value within its range, so the pressure value at that location can be extracted by the depth of color change. At present, the commonly used method for extracting pressure values ​​is mainly the colorimetric card comparison method. This method roughly estimates the pressure value by observing the similarity between the color of the color-changing film and the colorimetric card with the naked eye. It cannot accurately extract the pressure value of each point, nor can it draw a pressure cloud map of the film. Summary of the invention

[0003] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for extracting pressure values ​​based on a color-changing pressure film. The method of the present invention obtains the accurate pressure value of each point of the pressure measurement film after being compressed, and draws a pressure cloud map of the pressure measurement film, which greatly improves the accuracy and analyzability of the pressure value extraction. Its purpose is to accurately obtain the pressure value of each point of the pressure measurement film, and draw a pressure cloud map to facilitate subsequent analysis.

[0004] In order to achieve the above-mentioned invention object, the present invention specifically adopts the following technical solutions:

[0005] A method for extracting pressure values ​​based on a color-changing pressure film comprises the following steps:

[0006] S1. Scanning the pressure measurement film after the pressure change color by using an image measuring instrument to obtain a scanned image;

[0007] S2, processing the scanned image obtained in S1 to generate a corresponding grayscale image and grayscale value matrix;

[0008] S3, converting the gray value matrix generated by S2 into a pressure value matrix through the functional relationship between the gray value of the pressure measurement film and the pressure value, wherein each element in the pressure value matrix represents the pressure value of each point of the pressure measurement film image;

[0009] S4. Assign colors to the grayscale value matrix obtained in S2 according to the color mapping array and visualize the grayscale value matrix obtained in S2 as a pressure cloud map; wherein the color mapping array is used to determine the color of each grayscale value in the grayscale value matrix.

[0010] Based on the above scheme, each step can be implemented in the following preferred specific manner.

[0011] Preferably, the specific process of step S1 is as follows: place the pressure measurement film obtained by the experimental test and discolored under pressure on the workbench of the image measuring instrument, adjust the lighting and focal length of the image measuring instrument, use the scanning function of the image stitching in the image measuring instrument, start from the upper left corner of the pressure measurement film, and take pictures of the pressure measurement film in sequence as the lens of the image measuring instrument moves, and complete the image stitching until a complete and clear scanned image of the pressure measurement film is obtained.

[0012] Preferably, in step S1, the pressure measuring film model is LLLW normal temperature type, the pressure measuring range is 0.2-0.6 MPa, the size is 20 mm*100 mm, and the pressure measuring film is tested at a temperature of 25° C. and a humidity of 30%.

[0013] Preferably, in step S1, the model of the image measuring instrument is QVME-3020G.

[0014] Preferably, in step S2, the grayscale image and the preset grayscale value threshold array are processed by the grayslice function, and the grayscale image is converted into a pseudo-color image with a specific grayscale range as a grayscale value matrix; wherein the grayscale value threshold array is used to store the grayscale value thresholds used for classification in the grayscale image.

[0015] Preferably, in step S3, the functional relationship between the grayscale value of the pressure measurement film and the pressure value is obtained by querying the official website of Fuji pressure measurement film.

[0016] Preferably, in step S3, the method of converting the gray value matrix into the pressure value matrix is ​​as follows: each item in the gray value matrix is ​​substituted into the functional relationship between the gray value and the pressure value, and then the re-output matrix is ​​used as the pressure value matrix.

[0017] Preferably, in step S3, the pressure value matrix is ​​used to draw a pressure value curve of a certain area in the pressure measurement film along the length direction of the film to obtain the change of the pressure value in the area.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] In the present invention, a clear and accurate color change image of the pressure measurement film can be obtained by scanning with an image measuring instrument, thereby avoiding the color misjudgment caused by human eyes observing under different light; MATLAB software extracts the gray value matrix of the image, and converts the gray value matrix into a pressure value matrix through the functional relationship between the gray value and the pressure value, so as to accurately obtain the pressure value of each point of the pressure measurement film; and the gray image is converted into a pressure cloud image according to a certain pressure value interval, which is convenient for analyzing the pressure test results and summarizing the pressure change law. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the method of the present invention;

[0021] Figure 2 A schematic diagram of a scanned image obtained by scanning a pressure measurement film using an image measuring instrument;

[0022] Figure 3 This is a schematic diagram of the grayscale image obtained after processing by MATLAB software;

[0023] Figure 4 is a schematic diagram of a pressure value variation curve of a row extracted from the pressure value matrix;

[0024] Figure 5 Schematic diagram of the pressure cloud diagram of the pressure measurement film obtained. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0026] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for the purpose of distinguishing descriptions, and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0027] like Figure 1As shown, in a preferred implementation of the present invention, the above-mentioned method for extracting pressure values ​​based on a color-changing pressure film includes the following steps S1 to S4. The specific implementation process is described in detail below.

[0028] S1. Use an image measuring instrument to scan the pressure measurement film after it changes color under pressure to obtain a scanned image.

[0029] As a preferred embodiment of the present invention, step S1 can specifically adopt the following method:

[0030] Place the pressure measurement film that changes color under pressure obtained in the experimental test on the workbench of the image measuring instrument, adjust the lighting and focal length of the image measuring instrument, use the scanning function of picture stitching in the image measuring instrument, start from the upper left corner of the pressure measurement film, and take pictures of the pressure measurement film in sequence as the lens of the image measuring instrument moves, and complete the image stitching until a complete and clear scanned image of the pressure measurement film is obtained.

[0031] It should be noted that in step S1 of the present invention, the pressure measuring film model is LLLW normal temperature type, the pressure measuring range is 0.2-0.6 MPa, the size is 20 mm*100 mm, and the pressure measuring film is tested at a temperature of 25°C and a humidity of 30%.

[0032] It should be noted that in step S1 of the present invention, the model of the image measuring instrument is QVME-3020G.

[0033] S2, processing the scanned image obtained in S1 to generate a corresponding grayscale image and grayscale value matrix;

[0034] As a preferred embodiment of the present invention, in step S2, the scanned image obtained by the image measuring instrument in S1 can be accurately processed into a grayscale image using MATLAB software, and the grayscale value of each point is extracted and the grayscale value matrix is ​​output. Specifically, first, the scanned image named figname.jpg is read in using the packaged imread function in MATLAB software, and stored in the variable Im, which is a three-dimensional matrix, in which the color information of each pixel is represented by the values ​​of three channels of RGB (red, green, and blue), so the scanned image in the present invention is a color image. Then, the packaged rgb2gray function is used to convert the scanned image into a grayscale image, and the grayscale image B=rgb2gray (Im) is extracted, in which the value of each pixel represents the brightness (grayscale value) of the corresponding pixel. Finally, the packaged imshow function is used to visualize the grayscale value matrix B. Then, the grayscale image and the preset grayscale value threshold array are processed by the grayslice function, and the grayscale image is converted into a pseudo-color image G2C with a specific grayscale range as a grayscale value matrix. The gray value threshold array is used to store gray value thresholds used for classification in the gray image.

[0035] In this embodiment, the MATLAB software used is the genuine software MATLAB R2022b.

[0036] S3. Convert the gray value matrix generated by S2 into a pressure value matrix through the functional relationship between the gray value of the pressure measurement film and the pressure value. Each element in the pressure value matrix represents the pressure value of each point of the pressure measurement film image.

[0037] It should be noted that in step S3, the functional relationship between the grayscale value of the pressure measurement film and the pressure value can be obtained by searching the official website of Fuji pressure measurement film.

[0038] It should be noted that in step S3, the method of converting the gray value matrix into the pressure value matrix is ​​specifically: each item in the gray value matrix is ​​substituted into the functional relationship between the gray value and the pressure value, and then the re-output matrix is ​​used as the pressure value matrix.

[0039] It should be noted that, in step S3, the pressure value matrix is ​​used to draw a pressure value curve of a certain area in the pressure measurement film along the length direction of the film to obtain the change of the pressure value of the area.

[0040] In this embodiment, the pressure value matrix obtained by gray value matrix conversion has a high degree of accuracy and can clearly reflect the pressure value of each point of the pressure measurement film. In practical applications, by outputting a row or a column of data in the pressure value matrix obtained in step S3, the pressure value change curve can be drawn, which is more convenient for analyzing and summarizing the pressure transmission efficiency and pressure distribution law obtained by the test.

[0041] S4. Assign colors to the grayscale value matrix obtained in S2 according to the color mapping array and visualize the grayscale value matrix obtained in S2 as a pressure cloud map; wherein the color mapping array is used to determine the color of each grayscale value in the grayscale value matrix.

[0042] As a preferred embodiment of the present invention, the pressure distribution law obtained by the test can be clearly reflected by the generated pressure cloud map, and the pressure value interval of the output pressure cloud map is usually 0.02MPa.

[0043] It should be noted that in step S4 of the present invention, a new graphics window is opened by the figure command to prepare for displaying a new image or graphic. A color mapping array mymap is preset to store the color mapping to determine the color of each gray value in the gray value matrix. The color mapping defined by mymap is applied and the gray value matrix G2C is visualized by using the imshow function, i.e., imshow(G2C,colormap(mymap)), and the pressure cloud map is output.

[0044] In order to better demonstrate the specific implementation and technical effect of the present invention, a pressure value extraction method based on a color-changing compressed film shown in steps S1 to S4 in the above preferred implementation is applied to a specific example.

[0045] Example

[0046] In this embodiment, the pressure value of the pressure measuring film after the pressure transmission performance test of the aircraft hat-shaped long stringer core mold is completed is extracted, and a pressure cloud diagram and a pressure value change curve on the central axis are drawn. The pressure measuring film model used is LLLW, the pressure value applied to the mold in the test is 0.6MPa, the test temperature is 25°C, the test humidity is 40%, and the image measuring instrument model is QVME-3020G. The specific processing process is as follows:

[0047] First, place the pressure measurement film that has been tested and has changed color on the workbench of the image measuring instrument, adjust the lighting and focal length, use the image stitching scanning function, start from the upper left corner of the pressure measurement film, and take pictures of it in turn as the image measuring instrument lens moves and complete the image stitching until a complete and clear scanned image is obtained. The obtained scanned image is as follows: Figure 2 shown.

[0048] The scanned image obtained by S1 is processed by MATLAB software to generate the corresponding grayscale image (such as Figure 3 Then, through the functional relationship between the gray value of the pressure measurement film and the pressure value, the gray value matrix generated by S2 is converted into a pressure value matrix to obtain the pressure value of each point of the pressure measurement film image. The matrix of a certain row in the pressure value matrix can be extracted to draw a curve of the pressure value change along this path (as shown in Figure 4 In addition, the grayscale image obtained by S2 is assigned colors according to certain pressure value intervals, thereby obtaining the pressure cloud map of the image (as shown in Figure 5 shown).

[0049] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for extracting pressure values ​​based on a color-changing pressure film, characterized in that: The following steps are involved: S1. Scanning the pressure measurement film after the pressure change color by using an image measuring instrument to obtain a scanned image; S2, processing the scanned image obtained in S1 to generate a corresponding grayscale image and grayscale value matrix; S3, converting the gray value matrix generated by S2 into a pressure value matrix through the functional relationship between the gray value of the pressure measurement film and the pressure value, wherein each element in the pressure value matrix represents the pressure value of each point of the pressure measurement film image; S4. Assign colors to the grayscale value matrix obtained in S2 according to the color mapping array and visualize the grayscale value matrix obtained in S2 as a pressure cloud map; wherein the color mapping array is used to determine the color of each grayscale value in the grayscale value matrix.

2. A method for extracting pressure values ​​based on a color-changing pressure film according to claim 1, characterized in that: The specific process of step S1 is as follows: put the pressure measurement film obtained by the experimental test and the color change under pressure on the workbench of the image measuring instrument, adjust the lighting and focal length of the image measuring instrument, use the scanning function of the image stitching in the image measuring instrument, start from the upper left corner of the pressure measurement film, and take pictures of the pressure measurement film in sequence as the lens of the image measuring instrument moves, and complete the image stitching until a complete and clear scanned image of the pressure measurement film is obtained.

3. A method for extracting pressure values ​​based on a color-changing pressure film according to claim 1, characterized in that: In step S1, the pressure measuring film model is LLLW normal temperature type, the pressure measuring range is 0.2-0.6 MPa, the size is 20 mm*100 mm, and the pressure measuring film is tested at a temperature of 25° C. and a humidity of 30%.

4. A method for extracting pressure values ​​based on a color-changing pressure film according to claim 1, characterized in that: In step S1, the model of the image measuring instrument is QVME-3020G.

5. A method for extracting pressure values ​​based on a color-changing pressure film according to claim 1, characterized in that: In step S2, the grayscale image and the preset grayscale value threshold array are processed by the grayslice function, and the grayscale image is converted into a pseudo-color image with a specific grayscale range as a grayscale value matrix; wherein the grayscale value threshold array is used to store the grayscale value thresholds used for classification in the grayscale image.

6. A method for extracting pressure values ​​based on a color-changing pressure film according to claim 1, characterized in that: In step S3, the functional relationship between the grayscale value of the pressure measurement film and the pressure value is obtained by searching the official website of Fuji pressure measurement film.

7. A method for extracting pressure values ​​based on a color-changing pressure film as claimed in claim 1, characterized in that: In step S3, the method of converting the gray value matrix into the pressure value matrix is ​​specifically: each item in the gray value matrix is ​​brought into the functional relationship between the gray value and the pressure value, calculated, and then the re-output matrix is ​​used as the pressure value matrix.

8. A method for extracting pressure values ​​based on a color-changing pressure film according to claim 1, characterized in that: In step S3, the pressure value matrix is ​​used to draw a pressure value curve of a certain area in the pressure measurement film along the length direction of the film to obtain the change of the pressure value in the area.

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