Optical image processing system based on six-step hybrid phase shifting

Abstract

The application discloses a photoelastic image processing system based on a six-step mixed phase shift, and the single-color light incident photoelastic image obtained by using the traditional six-step phase shift method is interfered by the noise of the equal-difference line, and errors are caused. The ten-step phase shift method increases four images of white light incidence, avoids the noise interference on the equal-inclination line, but the method is complicated in operation and low in efficiency because more images are collected. In order to balance the accuracy and the efficiency, a mixed six-step phase shift method is provided in the application, three white light incident photoelastic images and three single-color light incident photoelastic images are used to calculate the equal-inclination line and the equal-difference line respectively. Compared with the traditional six-step phase shift method, the method effectively avoids the problem that the equal-inclination line is interfered by the noise of the equal-difference line; compared with the ten-step phase shift method, four photoelastic images are reduced, and the collection efficiency is improved by 40%.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of digital photoelasticity, and particularly relates to a photoelastic image processing system based on six-step hybrid phase shifting. BACKGROUND

[0002] Digital photoelasticity (DP) is an optical technique for experimental mechanics analysis, which can intuitively give all information of a stress field in the form of a fringe pattern, i.e. isochromatic lines of the principal stress difference and isoclinic lines of the principal stress direction angle. The isochromatic and isoclinic parameters can be calculated by using a single photoelastic image and multiple photoelastic images. The Fourier transform method for analyzing a single image is less used due to the problems of high cost and limitation in simultaneously calculating isochromatic and isoclinic lines. The phase shifting technique for analyzing multiple images is widely used in stress analysis in the fields of dentistry, biology and fracture mechanics due to its simplicity and accuracy.

[0003] In 1991, Patterson and Wang proposed a six-step phase shifting method, which uses a monochromatic light source to obtain isoclinic parameters, and the extinction phenomenon occurs in the integer level and the half-integer region. The experimental use of a circularly polarized optical system has the influence of a quarter-wave plate matching error. In 1998, Aovalasit et al. proposed an improved six-step phase shifting method, which uses left and right circularly polarized light to collect images, thereby reducing the quarter-wave plate matching error. In 1990, Brown and Sullivan et al. proposed a four-step phase shifting method using a monochromatic light source and a plane polarized field to calculate the full-field isoclinic line, but the problem of isoclinic line coupling isochromatic line still exists. In 1997, Petrucci et al. used the idea of Brown and Sullivan, and used a white light source to replace the monochromatic light source to eliminate the problem of isoclinic line coupling isochromatic line. In 2006, Ramji et al. compared various methods, and concluded that the photoelastic image collected by the plane polarized field is more suitable for calculating the full-field isoclinic line. In 2008, Ramji and Ramesh et al. ingeniously proposed a ten-step phase shifting technology by mixing the four-step phase shifting method and the six-step phase shifting method. The method has become a commonly used method for photoelastic stress analysis, but it still has the problems of more interference images needing to be collected and calculated, and the experimental collection efficiency is slower than the six-step method. SUMMARY

[0004] The application aims to provide a photoelastic image processing system based on six-step hybrid phase shifting to solve the technical problems in the background art.

[0005] To solve the technical problems, the technical scheme of the application is as follows:

[0006] The photoelastic image processing system based on six-step hybrid phase shifting comprises a color photoelastic image collection device, a monochromatic photoelastic image collection device and an image processing device.

[0007] The color photoelastic image acquisition device acquires three color photoelastic images and sends them to the image processing device, and the monochromatic photoelastic image acquisition device acquires three monochromatic photoelastic images and sends them to the image processing device.

[0008] The image processing device pre-processes the received three color photoelastic images and three monochromatic photoelastic images to obtain three pre-processed color photoelastic images and three monochromatic photoelastic images.

[0009] The three pre-processed color photoelastic images are subjected to gray scale conversion processing to obtain three gray scale photoelastic images; based on the three gray scale photoelastic images, an isoclinal line solving model is established and solved using the inverse trigonometric function principle to obtain an isoclinal line wrapped phase image; the isoclinal line wrapped phase image is processed using a quality-guided path tracking algorithm to obtain an isoclinal line unwrapped phase image; the three pre-processed monochromatic photoelastic images and the isoclinal line unwrapped phase image are used to establish an equidifference line solving model and solve it using the inverse trigonometric function principle to obtain an equidifference line wrapped phase image; the equidifference line wrapped phase image is processed by the quality-guided path tracking algorithm to obtain a global fringe order image, thereby realizing extraction of isoclinal lines and equidifference lines from photoelastic images.

[0010] Further, the color photoelastic image acquisition device comprises a white light source S and a polarizer P, a load device M, an analyzer A, and an industrial CCD camera arranged in sequence along the axis direction of the white light source S.

[0011] Further, the monochromatic light photoelastic image acquisition device comprises a monochromatic light source S and a polarizer P, a first quarter-wave plate Q1, a load device M, a second quarter-wave plate Q2, an analyzer A, and an industrial CCD camera arranged in sequence along the axis direction of the monochromatic light source S.

[0012] Further, the color photoelastic image acquisition device specifically comprises placing the measured material on the load device M, rotating the load device M to apply pressure to the material, rotating the polarizer P to a fixed angle, changing the phase by rotating the analyzer A, and then using the industrial CCD camera to acquire three color photoelastic images.

[0013] Further, the monochromatic light photoelastic image acquisition device specifically comprises placing the measured material on the load device M, rotating the load device M to apply pressure to the material, adjusting the fixed angles of the polarizer P and the first quarter-wave plate Q1, rotating the second quarter-wave plate Q2 and the analyzer A by corresponding angles respectively, and then acquiring three monochromatic photoelastic images.

[0014] Further, the preprocessing treatment comprises: firstly, carrying out background information clipping on the three color photoelastic images and the three monochrome photoelastic images, obtaining, carrying out filtering noise treatment and image smoothing treatment on the clipped images, for eliminating photoelastic image bright spots or dark spots, bright bands or dark bands and high-frequency interference parts, obtaining the three color photoelastic images and the three monochrome photoelastic images after preprocessing.

[0015] Further, an isoclinic line solving model is established by using an inverse trigonometric function principle, and the model is specifically as follows:

[0016]

[0017] Further, an isochromatic line solving model is established by using an inverse trigonometric function principle, and the model is specifically as follows:

[0018]

[0019] Compared with the prior art, the present application has the following advantages:

[0020] Compared with the monochrome light six-step phase shift method, the same six-step method is used, but the present method effectively avoids the problems of isoclinic line coupling isochromatic line and wave plate mismatching error; compared with the ten-step phase shift method, four photoelastic images are reduced, the average deviation of the isoclinic line of the present method is about 0.01 rad, the average deviation of the isochromatic line is about 0.09 rad, and the measuring precision is ensured while the acquisition efficiency is improved by 40%.

[0021] The monochrome light incident photoelastic images obtained by the traditional six-step phase shift method are easily disturbed by isochromatic line noise, causing errors. The ten-step phase shift method increases four images of white light incidence, avoiding the disturbance of isoclinic line by noise, but the method is inefficient due to more collected images and complex operation. In order to balance the precision and efficiency, a hybrid six-step phase shift method is proposed in the present application, which uses three white light incident photoelastic images and three monochrome light incident photoelastic images to calculate the isoclinic line and the isochromatic line respectively. Compared with the traditional six-step phase shift method, the present method effectively avoids the problem of isoclinic line being disturbed by isochromatic line noise; compared with the ten-step phase shift method, four photoelastic images are reduced, and the acquisition efficiency is improved by 40%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 、 Six Step phase shift isoclinic line diagram;

[0023] Figure 2 Polarization optical system;

[0024] Figure 3 Digital photoelastic image acquisition system;

[0025] Figure 4 Color three photoelastic images;

[0026] Figure 5 , three images of photoelasticity of monochromatic light;

[0027] Figure 6 , isoclinic line wrapped phase map;

[0028] Figure 7 , isoclinic line unwrapped phase map;

[0029] Figure 8 , equidifference line wrapped phase map;

[0030] Figure 9 , equidifference line unwrapped phase map. DETAILED DESCRIPTION

[0031] The specific embodiments of the present application will be described below in conjunction with examples:

[0032] It should be noted that the structures, proportions, sizes, etc. shown in the present specification are only used to cooperate with the content disclosed in the present specification for understanding and reading by those skilled in the art, and are not used to limit the limiting conditions of the embodiments of the present application. Any modification of the structure, change of the proportional relationship or adjustment of the size, which does not affect the effects and purposes that can be achieved by the present application, should still fall within the scope of the technical content disclosed by the present application.

[0033] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" referred to in the present specification are only for the convenience of clear description, and are not used to limit the scope of the embodiments of the present application. The change or adjustment of the relative relationship, without substantially changing the technical content, is also considered as the scope of the embodiments of the present application.

[0034] Example 1:

[0035] Six-step phase shifting is used to collect six photoelastic images by circularly polarized optical system, and isoclinic line and equidifference line are calculated respectively. Corresponding to different light intensity equations, as shown in Table 1.

[0036] Table 1: Light intensity equation of six-step phase shifting

[0037]

[0038] In Table 1, I b is the background light intensity, I c is the monochromatic light intensity, θ represents the first principal stress direction angle, and δ represents the phase difference generated by the stress model. Then, the isoclinic line θ and the equidifference line δ are calculated by six-step phase shifting.

[0039] The formulas are as follows:

[0040]

[0041]

[0042] Disadvantages of six-step phase shift:

[0043] Under monochromatic light incidence, extinction occurs in the region where sinδ=0 in formula (1), causing noise interference from isochoric lines in the integer and half-integer regions, affecting the accuracy of isochoric line development, such as... Figure 1 As shown.

[0044] The ten-step phase shift method uses a four-step phase shift method to calculate isoclinal parameters, and a six-step phase shift method to calculate isoartic parameters. The four-step phase shift method uses a plane polarization system to acquire four photoelastic images, corresponding to different light intensity equations, as shown in Table 2.

[0045] Table 2. Light intensity equations for color four-step phase-shifting technology

[0046]

[0047] Among them, I in Table 1 s Let be the intensity of white light. The formula for calculating the isoclin θ is:

[0048]

[0049] In formula (3) The average value of the R, G, and B channels of the image is taken to obtain the isoclinal θ in the range of [-π / 8, π / 8] across the entire field. After unwrapping, the isoclinal θ is extended to the range of [-π / 2, π / 2]. u The isochronous lines δ in the range [-π / 2, π / 2] are obtained by calculating using the six-step phase shift formula (2).

[0050] The ten-step phase shift increases the number of four color images, resulting in a larger number of photoelastic stripe images to be acquired, leading to low acquisition efficiency.

[0051] And this invention:

[0052] Table 3. Light intensity equations for the six-step phase shift in the hybrid system.

[0053]

[0054]

[0055] Table 3, I b For background light intensity, I s It is the intensity of white light, I c Let θ represent the intensity of monochromatic light, θ represent the direction angle of the first principal stress (isoclimax), and δ represent the phase difference (isodiameter) generated through the stress model.

[0056]

[0057]

[0058] The image R, G, B three channel average value (converted gray image) is represented.

[0059] Example 2:

[0060] The isoclinic line and the isochromatic line are realized by the phase shift technology, and the technical route is: photoelastic image acquisition, image processing, isoclinic line calculation, isoclinic line unwrapping, isochromatic line calculation, and isochromatic line unwrapping.

[0061] Photoelastic image acquisition:

[0062] As shown in Figure 3 , the experiment needs three color photoelastic images and three monochromatic photoelastic images, and the experimental devices used are a plane polarized optical system and a circular polarized optical system, as shown in Figure 2 , (a) plane polarized optical system; (b) circular polarized optical system.

[0063] The plane polarized optical system is provided with: a white light source (S), a polarizer (P), a load device (M), an analyzer (A), and an industrial CCD camera.

[0064] The circular polarized optical system is provided with: a monochromatic light source (S), a polarizer (P), a first quarter wave plate (Q1), a load device (M), a second quarter wave plate (Q2), an analyzer (A), and an industrial CCD camera.

[0065] Experimental steps:

[0066] (1) Place the measured material on the load device (M), and rotate the load device (M) to apply pressure to the material.

[0067] (2) Rotate the polarizer (P) to a fixed angle, and after changing the phase by rotating the analyzer (A), use the industrial CCD camera to respectively collect three color photoelastic images, as shown in Figure 4 .

[0068] (3) Insert the quarter wave plates (Q1, Q2) between the polarizer (P) and the load device (M), and the load device (M) and the analyzer (A) respectively, and change the plane polarized optical system to a circular polarized optical system.

[0069] (4) Adjust the fixed angle of the polarizer (P) and the first quarter wave plate (Q1), respectively rotate the second quarter wave plate (Q2) and the analyzer (A) by corresponding angles, and respectively collect three monochromatic photoelastic images, as shown in Figure 5 .

[0070] Image processing:

[0071] First, the image is cropped, cutting off most of the background information, in the cropped part of the filter noise processing and image smoothing, eliminate the photoelastic image bright (dark) points, bright (dark) band and high frequency interference part.

[0072] The isoclinic line θ is calculated:

[0073]

[0074] The present technology reduces the number of color four-step phase shift images, only three color photoelastic images are needed to calculate the isoclinic line. The processed photoelastic image is first converted into a gray-scale image, which is substituted into the above formula to calculate the isoclinic line wrapped phase map, as shown in Figure 6 .

[0075] Isoclinic line unwrapping:

[0076] The unwrapped isoclinic line phase map can be obtained by processing the isoclinic line unwrapping phase map with a quality-guided phase unwrapping algorithm, as shown in Figure 7 .

[0077] The isochromatic line δ is calculated:

[0078]

[0079] In the process of calculating the isochromatic line, the present technology reduces the number of original monochromatic light six-step photoelastic images, only three images and the above unwrapped isoclinic line phase map are selected and substituted into the above formula to calculate the isochromatic line wrapped phase map, as shown in Figure 8 .

[0080] Isochromatic line unwrapping: the global fringe order can be obtained by processing the isochromatic line wrapped phase map with a quality-guided phase unwrapping algorithm, as shown in Figure 9 .

[0081] Compared with the monochromatic light six-step phase shift method, the same six-step method effectively avoids the problems of isoclinic line coupling isochromatic line and wave plate mismatch error; compared with the ten-step phase shift method, four photoelastic images are reduced, the average deviation of the isoclinic line of the present method is 0.01 rad, and the average deviation of the isochromatic line is 0.09 rad, which improves the collection efficiency by 40% while ensuring the measurement accuracy.

[0082] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

[0083] Many other changes and modifications can be made to the application without departing from the spirit and scope of the application. It is to be understood that the application is not limited to particular embodiments described, and is intended in its broadest aspect to cover all such changes and modifications thereof. The scope of the application is defined by the appended claims.

Claims

1. A photoelastic image processing system based on a six-step hybrid phase shift, characterized in that, include: Color photoelastic image acquisition device, monochrome photoelastic image acquisition device and image processing device; The color photobulb image acquisition device acquires three color photobulb images and sends them to the image processing device; the monochrome photobulb image acquisition device acquires three monochrome photobulb images and sends them to the image processing device. The image processing device preprocesses the received three color photobulb images and three monochrome photobulb images to obtain three preprocessed color photobulb images and three monochrome photobulb images. Three preprocessed color photoelastic images are converted to grayscale to obtain three grayscale photoelastic images. Based on these three grayscale images, an isoclinal solution model is established and solved using the inverse trigonometric function principle to obtain an isoclinal-wrapped phase map. A quality-guided path tracing algorithm is then used to process the isoclinal-wrapped phase map to obtain an isoclinal-unwrapped phase map. For the three preprocessed monochromatic photoelastic images and the isoclinal-unwrapped phase map, an isoarithmic line solution model is established and solved using the inverse trigonometric function principle to obtain an isoarithmic-wrapped phase map. Finally, a quality-guided path tracing algorithm is used to process the isoarithmic-wrapped phase map to obtain a global fringe series map, thus realizing the extraction of isoclinal and isoarithmic lines from the photoelastic image. A solution model for isoclinals is established using the principle of inverse trigonometric functions, specifically as follows: ， Indicates isochoric lines; This represents the phase difference generated by the stress model; A model for solving isometric lines is established using the principle of inverse trigonometric functions, specifically as follows: ， The intensity of monochromatic light.

2. The photoelastic image processing system based on a six-step hybrid phase shift as described in claim 1, characterized in that, The color photoelastic image acquisition device includes: a white light source (S) and a polarizer (P), a load device (M), an analyzer (A), and an industrial CCD camera arranged sequentially along the axis of the white light source (S).

3. The photoelastic image processing system based on a six-step hybrid phase shift as described in claim 1, characterized in that, The monochromatic light photoelastic image acquisition device includes: a monochromatic light source (S) and a polarizer (P), a first quarter-wave plate (Q1), a load device (M), a second quarter-wave plate (Q2), an analyzer (A), and an industrial CCD camera arranged sequentially along the axis of the monochromatic light source (S).

4. The photoelastic image processing system based on a six-step hybrid phase shift according to claim 2, characterized in that, The specific steps for acquiring color photoelastic images using the color photoelastic image acquisition device are as follows: placing the material to be tested on the load device (M), rotating the load device (M) to apply pressure to the material, rotating the polarizer (P) to a fixed angle, changing the phase by rotating the analyzer (A), and then acquiring three color photoelastic images using an industrial CCD camera.

5. The photoelastic image processing system based on a six-step hybrid phase shift according to claim 3, characterized in that, The monochromatic photoelastic image acquisition device specifically acquires monochromatic photoelastic images by: placing the material to be tested on the load device (M), applying pressure to the material using the load device (M), adjusting the fixed angles of the polarizer (P) and the first quarter-wave plate (Q1), rotating the corresponding angles of the second quarter-wave plate (Q2) and the analyzer (A), and acquiring three monochromatic photoelastic images respectively.

6. The photoelastic image processing system based on a six-step hybrid phase shift according to claim 1, characterized in that, The preprocessing includes: firstly, cropping the background information of the three color photobullet images and the three monochrome photobullet images; then, performing noise filtering and image smoothing on the cropped images to eliminate bright or dark spots, bright or dark bands, and high-frequency interference in the photobullet images, resulting in the preprocessed three color photobullet images and three monochrome photobullet images.

Images