A dic assisted fpp measurement method based on intensity-color space analysis

Abstract

The application discloses a DIC auxiliary FPP measurement method based on intensity-color space analysis. The application first uses fluorescent pigments to make a speckle pattern, then obtains a gray structure light pattern deformed by the surface modulation of an object through projection, then obtains a color image of the deformed gray structure light pattern and the speckle pattern, and uses an intensity-color space analysis method to separate stripe information and speckle information of the color image and modulate the stripe information in an intensity space and the speckle information in a chroma space, obtains an intensity component and chroma difference data of the color image, and obtains three-dimensional topography, deformation and strain information of the measured object through the DIC auxiliary FPP measurement method based on the intensity component and the chroma difference data. The application fundamentally overcomes the inherent contradiction of FPP and DIC in surface reflectivity requirements, can simultaneously ensure the measurement accuracy of shape and deformation, and obtain complete and fine surface geometry and strain distribution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of computer vision three-dimensional measurement calculation, and particularly relates to a DIC assisted FPP measurement method based on intensity-color space analysis. BACKGROUND

[0002] With the continuous improvement of three-dimensional profile reconstruction efficiency and measurement robustness, the existing fringe projection technology can realize efficient and high-precision three-dimensional profile measurement of complex dynamic scenes. However, since the projected pattern is not attached to the surface of the object, it is impossible to accurately establish the point-to-point mapping relationship of the reconstructed three-dimensional profile information at different times, so it is impossible to accurately calculate the displacement and deformation of the measured surface in the experimental mechanics field.

[0003] Digital image correlation is a recognized method for analyzing object deformation and mechanical properties. Digital image correlation uses the natural texture or artificially made marker points on the surface of the object to accurately track the point-to-point relationship by calculating the gray correlation degree before and after the deformation of the analysis area. The fringe projection profilometry which can obtain the dense three-dimensional profile of the scene and the digital image correlation technology which can realize accurate deformation tracking are combined together to form a new method for simultaneous measurement of three-dimensional profile and deformation.

[0004] However, fringe projection profilometry expects the reflectivity of the measured surface to be uniform enough to ensure the accuracy of the profile measurement, while digital image correlation technology expects the measured surface to provide high-contrast texture information to ensure the accuracy of image matching and the accuracy of deformation calculation. There is a contradiction in the reflectivity distribution of the measured surface between the two, and the existing combined technology cannot solve the contradictory requirements of the reflectivity distribution of the measured surface, thereby greatly limiting the measurement accuracy, and lacking further effective three-dimensional strain analysis algorithm. SUMMARY

[0005] The present application aims to overcome the problem that the existing technology cannot simultaneously meet the reflectivity requirements of FPP and DIC on the surface of the measured object, which limits the measurement accuracy when using DIC assisted FPP measurement, and provides a DIC assisted FPP measurement method based on intensity-color space analysis.

[0006] In order to achieve the above-mentioned application purpose, the present application provides the following technical solutions:

[0007] A DIC assisted FPP measurement method based on intensity-color space analysis, comprising the following steps:

[0008] S1, using fluorescent pigments to make a speckle pattern on the surface of the measured object;

[0009] S2, project a gray-scale structured light pattern to a surface of a measured object to obtain a deformed gray-scale structured light pattern modulated by the surface of the object, the deformed gray-scale structured light pattern comprising a fringe pattern and an encoded structured light pattern;

[0010] S3, obtain a color image of the deformed gray-scale structured light pattern and the speckle pattern;

[0011] S4, separate an intensity component of the color image from an intensity space of the color image using an intensity-color space analysis method, the intensity component having fringe information of the color image, and separate chrominance difference data of the color image from a color space of the color image, the chrominance difference data having speckle information of the color image;

[0012] S5, obtain three-dimensional topography, deformation and strain information of the measured object based on a DIC-assisted FPP measurement method according to the intensity component and the chrominance difference data.

[0013] As a preferred scheme of the present application, the DIC-assisted FPP measurement method based on intensity-color space analysis uses an intensity-color space including LAB, lαβ space, HSV space and YCbCr space in a commonly used intensity-color space.

[0014] As a preferred scheme of the present application, the DIC-assisted FPP measurement method based on intensity-color space analysis includes a selection method of a color fluorescent pigment with an optimal fluorescent color, which specifically comprises:

[0015] When the background color difference of the measured object is not less than a color difference threshold, the selection of the color of the fluorescent pigment should make the speckle color difference take a minimum value; when the background color difference of the measured object is less than the color difference threshold, the selection of the color of the fluorescent pigment should make the speckle color difference take a maximum value; at the same time, the modulation degree of the fringe pattern always takes a maximum value; the above method ensures that the color contrast obtained finally is the highest.

[0016] As a preferred scheme of the present application, the DIC-assisted FPP measurement method based on intensity-color space analysis specifically comprises:

[0017] S21, obtain the gray-scale structured light pattern, the gray-scale structured light pattern comprising a fringe pattern and an encoded structured light pattern;

[0018] S22, arrange the fringe pattern and the encoded structured light pattern in sequence and interleave to generate a gray-scale structured light sequence pattern S;

[0019] S23, the sequence pattern S is cyclically projected onto the surface of the object under test. The sequence pattern S will be deformed by the object under test to obtain a deformed sequence pattern S. The deformed sequence pattern S includes a deformed stripe pattern and a deformed coded structured light pattern.

[0020] As a preferred embodiment of the present invention, a DIC-assisted FPP measurement method based on intensity-color space analysis, step S4 specifically includes:

[0021] S41, based on the calculation of the R, G, and B channel components of the stripe pattern, the image sequence is converted from RGB space to YCbCr space, and the luma component Y representing brightness is obtained. The Y component retains the modulated stripe information, and at the same time, the red component Cr and the blue component Cb expressing the difference compared with the luma component are obtained.

[0022] S42, calculate the modulation degree Mo(Cr) and Mo(Cb) of Cr and Cb respectively, and calculate the color difference data Dc with high contrast based on the absolute value of the difference between the modulation degree Mo(Cr) and Mo(Cb), wherein Dc retains the speckle information;

[0023] S43, calculate and obtain the modulation index M of the Y component based on the Y component. Y And based on the aforementioned modulation M Y Evaluate the stripe quality of the modulated stripe pattern;

[0024] As a preferred embodiment of the present invention, a DIC-assisted FPP measurement method based on intensity-color space analysis, M Y The method for evaluating the stripe quality of the modulated stripe pattern is as follows: Observe M Y If speckle is not present in the image, it indicates that the modulation and separation were successful, and the stripe pattern obtained by the modulation and separation has high stripe quality.

[0025] As a preferred embodiment of the present invention, a DIC-assisted FPP measurement method based on intensity-color space analysis, step S5 specifically includes:

[0026] S51, the three-dimensional shape of the object under test is reconstructed based on the FPP system using the stripe pattern obtained by modulation and separation;

[0027] S52, based on the pattern Dc, the two-dimensional coordinate association of the corresponding points before and after deformation is completed according to the DIC technology, and based on the three-dimensional morphology of the corresponding points before and after deformation, the three-dimensional point cloud association of the corresponding points before and after deformation is completed, so as to obtain the three-dimensional deformation information of the measured object.

[0028] S53, performing differential calculation on the three-dimensional deformation information based on the chain rule to obtain three-dimensional strain information of the measured object.

[0029] As a preferred scheme of the present application, the DIC-assisted FPP measurement method based on intensity-color space analysis specifically comprises the following steps S51:

[0030] S511, obtaining phase representing height information of the measured object surface based on the Y component obtained after modulation and separation of the deformed fringe pattern;

[0031] S512, obtaining height value of the measured object in the color image in the three-dimensional world coordinate system point by point according to the phase-height algorithm based on the phase of the height information;

[0032] S513, obtaining three-dimensional world coordinates of the measured object in the color image point by point according to the camera imaging model to solve the remaining two dimension values of the measured object surface in the three-dimensional world coordinate system, and reconstructing the three-dimensional morphology of the measured object.

[0033] As a preferred scheme of the present application, the DIC-assisted FPP measurement method based on intensity-color space analysis specifically comprises the following steps S52:

[0034] S521, obtaining the point p*(x*, y*) on the deformed pattern Dc of the point p(x, y) in the pattern Dc by the DIC method;

[0035] S522, mapping each point on the deformed and un-deformed patterns Dc to three-dimensional coordinates in the world coordinate system by the FPP method, wherein the point p in the un-deformed pattern Dc is (X(x, y), Y(x, y), Z(x, y)) in the world coordinate system, the point p* in the deformed pattern Dc is (X(x*, y*), Y(x*, y*), Z(x*, y*)) in the world coordinate system, and the two points are the same point on the object in the world coordinate system, and the difference in coordinates is caused by deformation.

[0036] S523, dividing the three-dimensional world coordinates into UVW three directions, and the UVW deformation calculation formula is:

[0037] ;

[0038] wherein x and y are two-dimensional plane image coordinates before and after deformation, X, Y and Z are three-dimensional world coordinates of corresponding two-dimensional points of the reference image and the deformed image, and U(x, y), V(x, y) and W(x, y) are the three-dimensional deformation information.

[0039] As a preferred scheme of the present application, the DIC-assisted FPP measurement method based on intensity-color space analysis specifically comprises the following steps S53:

[0040] S531, calculating the differential of the three-dimensional deformation information U(x, y) and V(x, y) with respect to pixel coordinates (u, v);

[0041] S532, calculating the partial derivative of pixel coordinates (u, v) with respect to three-dimensional world coordinates (x, y) according to the camera imaging model and the point-by-point three-dimensional world coordinates of the measured object;

[0042] S533, calculating the partial derivative of U(x, y) and V(x, y) with respect to three-dimensional world coordinates (x, y) according to the chain rule of differentiation based on the differential of the three-dimensional deformation information U(x, y) and V(x, y) with respect to pixel coordinates and the partial derivative of the pixel coordinates with respect to three-dimensional world coordinates, i.e. the three-dimensional strain information of the measured object.

[0043] Compared with the prior art, the present application has the following beneficial effects:

[0044] The present application fundamentally overcomes the inherent contradiction between FPP and DIC in surface reflectivity requirements, and further completes the strain analysis at a lower calculation cost by introducing the chain rule, which not only ensures the measurement accuracy of shape and deformation at the same time, but also obtains complete and fine surface geometry and strain distribution, thereby providing an alternative method for bridging the three-dimensional geometry and mechanical state of complex test pieces. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 It is a flowchart of the DIC-assisted FPP measurement method based on intensity-color space analysis;

[0046] Figure 2 It is a schematic diagram of the projection sequence image of experimental example 1 and example 2 of the present application;

[0047] Figure 3 It is a commonly used intensity-chroma space schematic diagram;

[0048] Figure 4 It is a schematic diagram of using luminance-chroma space YCbCr for intensity-space analysis;

[0049] Figure 5 It is a fringe and speckle diagram separated based on the intensity-space analysis method in experimental example 1 of the present application;

[0050] Figure 6 It is a three-dimensional topography, deformation and strain result diagram of the real object in experimental example 1 of the present application;

[0051] Figure 7The diagram shows the three-dimensional morphology, deformation, and strain results of the actual object in Experimental Example 2 of this invention. Detailed Implementation

[0052] The present invention will now be described in detail with reference to the accompanying drawings.

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0054] Example 1

[0055] like Figure 1 The diagram shows a DIC-assisted FPP measurement method based on intensity-color space analysis. The specific steps are as follows:

[0056] In this embodiment, a single-camera FPP system is built using a camera (Baumer VCXU-23M, resolution: 2448×2048 pixels) and a DLP projector (Lightcrafter DLP4500, resolution: 912×1140 pixels) to perform dynamic measurements on a composite woven structure object.

[0057] S1. Select the best fluorescent pigment and use the pigment to make a speckle pattern and spray it onto the surface of the object to be tested.

[0058] Specifically, the method for selecting the optimal fluorescent color of a colored fluorescent pigment includes:

[0059] The color of the fluorescent dye and the background color of the object being tested must satisfy the following formula:

[0060]

[0061] Among them, R R R G and R B M represents the reflectance of the tested object to colors R, G, and B, respectively. Y The modulation depth of the stripe pattern represents the grayscale image of the object after removing ambient light interference, D. CB D represents the color difference of the background of the object being measured in the color space. CS The color difference of the speckle pattern in the color space. As a gradient operator, when the background color difference D of the measured object... CB When the value is not less than 0.5B, the choice of fluorescent pigment color should ensure that the speckle color difference D CS Take the minimum value when the background color difference D of the measured object is... CBWhen the speckle color difference D is less than 0.5B, the selection of the fluorescent color should be such that the speckle color difference D CS Taking the maximum value, thereby obtaining the highest color contrast D C The selection of the optimal fluorescent color can ensure high fringe intensity modulation and speckle color difference at the same time, lay a good image foundation for subsequent intensity-space analysis, and make the fringe and speckle images obtained after intensity-space analysis have higher quality.

[0062] S2, projecting a gray-scale structured light pattern to the surface of the measured object to obtain a deformed gray-scale structured light pattern modulated by the surface of the measured object

[0063] The gray-scale structured light pattern, the structured light pattern comprising a fringe pattern and an encoded structured light pattern;

[0064] Specifically, S2 comprises the following steps:

[0065] S21, the gray-scale structured light pattern comprising a fringe pattern and an encoded structured light pattern, the fringe pattern I1, I2, I3 being expressed by the formula as follows:

[0066]

[0067] Wherein, A(x, y) is the background light intensity, B(x, y) is the fringe modulation, (x, y) represents the phase carrying the object topography information;

[0068] S22, the encoded structured light pattern comprising 6 patterns, using Gray code encoding, comprising GC1, GC2, GC3, GC4, GC5, GC6, the encoded structured light pattern being arranged in each group of the fringe pattern to generate a gray-scale structured light sequence pattern S as shown in Figure 2 The sequence pattern S can be expressed as: S = I1I2I3GC1; I1I2I3GC2; I1I2I3GC3; I1I2I3GC4; I1I2I3GC5; I1I2I3GC6; I1I2I3GC1; I1I2I3GC2;...;

[0069] S23, the sequence pattern S being projected to the surface of the measured object in a loop, the sequence pattern S being deformed by the measured object to obtain a deformed sequence pattern S, the deformed sequence pattern S comprising a deformed fringe pattern and a deformed encoded structured light pattern;

[0070] S3, acquiring a color image of the deformed gray-scale structured light pattern and the speckle pattern;

[0071] Specifically, the color camera synchronously takes photos at intervals of the cyclic projection to obtain photos including the speckle pattern and the sequence of gray structured light patterns S deformed by the measured object, and generates a sequence of color images in sequence of the sequence of patterns.

[0072] S4, separating an intensity component of the color image from an intensity space of the color image using an intensity-color space analysis method, the intensity component having fringe information of the color image, and separating chrominance difference data of the color image from a color space of the color image, the chrominance difference data having speckle information of the color image;

[0073] Specifically, the intensity-color space used in the intensity-space analysis method includes LAB, Figure 3 space, HSV space and YCbCr space in a commonly used intensity-color space as shown in the following table.

[0074] Further, in the embodiment, the sequence of color images is converted from RGB space to YCbCr space, and the conversion formula is as follows:

[0075]

[0076] wherein I R , I G , I B are components of R, G and B channels of the deformed fringe image respectively, Y is a luma component representing luminance, the Y component retains the modulated fringe information, Cb and Cr are chrominance component differences of blue component and red component compared with the Y component respectively; the Y component retains high-quality phase-shifted fringe and Gray code modulated by the object topography, and the Cb and Cr components retain information of the fluorescent speckle. To further eliminate residual fringe and background components, the following formula is used:

[0077] ;

[0078] The modulation degrees Mo(Cr) and Mo(Cb) of Cb and Cr are calculated respectively, the chrominance difference data Dc with high contrast is calculated based on the absolute value of the difference between the modulation degrees Mo(Cr) and Mo(Cb), the Dc retains the modulated speckle information, and the modulation degree M Y of the Y component is calculated based on the Y component, and the fringe pattern and the speckle pattern separated by the intensity-chrominance space analysis method are as shown in the following table. Figure 4

[0079] Further, the fringe quality of the modulated fringe pattern is evaluated based on the modulation degree M Y , and the specific steps include: observing M​​Y whether speckle still exists in the image, and if not, it means that the modulation and separation are successful, and the fringe quality of the fringe pattern obtained by the modulation and separation is high.

[0080] S5, as shown in the DIC assisted FPP measurement method, the three-dimensional topography, deformation and strain information of the measured object are obtained according to the intensity component and chrominance difference data. Figure 5

[0081] Specifically, S5 includes the following steps:

[0082] S511, the phase representing the surface height information of the measured object is obtained based on the Y component obtained after the modulation and separation of the deformed fringe pattern, and the calculation formula is:

[0083]

[0084] wherein Y1, Y2 and Y3 correspond to the fringes obtained by separating the color image, k is the order corresponding to the truncated phase, and the luminance component of the deformed Gray code encoded structured light pattern is calculated.

[0085] S512, the two-dimensional plane pixel coordinates on the image are converted to three-dimensional coordinates in the real world based on the camera calibration data obtained by the camera calibration technology, and the three-dimensional coordinate values of each point in the image are obtained, and the reconstruction of the three-dimensional topography is completed. The phase-height algorithm calculation formula is:

[0086]

[0087] wherein a, b and c are obtained by four-plane calibration, is the phase, and thus the height value h in the world coordinate system is obtained, and there are still two dimensions to be solved, i.e. x and y.

[0088] S513, the remaining two dimension values of the measured object surface in the three-dimensional world coordinate system are obtained according to the camera imaging model, the three-dimensional world coordinates of the measured object point by point in the color image are obtained, and the three-dimensional topography of the measured object is reconstructed.

[0089] Specifically, according to the camera imaging model:

[0090]

[0091] ​Wherein, the calibration parameters include A is a camera internal parameter and R, t is a camera external parameter, u, v is the color image coordinates, x, y, z is a three-dimensional world coordinate, and lambda is a scaling factor at the corresponding point, at this time, u, v, z and the camera internal and external parameters are known, the corresponding x, y can be solved by the formula, that is, the remaining two dimensions are obtained, so as to obtain the three-dimensional world coordinate value of each point in the image, and the three-dimensional topography reconstruction is completed.

[0092] S52, using the extracted high-contrast chrominance difference pattern D on the three-dimensional topography C The three-dimensional point cloud correlation before and after deformation is completed through the DIC technology, and the three-dimensional deformation information of the measured object is obtained. When a sprayed speckle object deforms, the speckle will change with the object. By shooting images at different times before and after deformation and matching the speckles, the displacement, that is, the deformation information, can be obtained. In the traditional method, the speckle and the stripe interfere with each other, while in the present application, due to the selection of the fluorescent pigment and the conversion of the color space, the chrominance difference is higher-quality speckle information.

[0093] Specifically, the three-dimensional topography reconstruction step is:

[0094] The three-dimensional topography information is divided into UVW three directions to express the three-dimensional deformation information of the measured object, and the UVW deformation calculation formula is:

[0095]

[0096] Wherein, x, y and x*, y* are two-dimensional plane image coordinates before and after the deformation of the gray structured light pattern, and X, Y, Z are three-dimensional world coordinates of corresponding two-dimensional points of the reference image and the deformed image. Through the DIC method, the point p*(x*, y*) on the deformed image is obtained based on the point p(x, y) in the two-dimensional plane image before deformation. Using the FPP method, each point on the image before and after deformation is mapped to the three-dimensional coordinates in the world coordinate system. The p point in the image is (X(x, y), Y(x, y), Z(x, y)) in the world coordinate system, and the corresponding p* is (X(x*, y*), Y(x*, y*), Z(x*, y*)) in the world coordinate system. The two points p and p* are the same point on the object in the world coordinate system. Due to the difference in coordinates caused by deformation, the UVW, that is, the three-dimensional deformation information of the measured object, can be obtained by subtracting the corresponding dimensions of the coordinates.

[0097] S53, based on the chain rule, the three-dimensional deformation information is subjected to differential calculation of the three-dimensional coordinates in the real world and the two-dimensional plane pixel coordinates, and the three-dimensional strain information of the measured object is obtained, and the calculation formula is:

[0098]

[0099] wherein, corresponding to the deformation UV, x, y, z are three-dimensional real coordinates, u, v are two-dimensional pixel coordinates, , , and The pixel coordinates are differentiated by the displacement field, and the pixel coordinates have the property of uniform distribution. The algorithm for differential operation is simpler; , , and The partial derivative of the pixel coordinates of the image with respect to the three-dimensional surface coordinates is calculated by the following formula, and the calculation formula is as follows:

[0100]

[0101] wherein m ij from the camera imaging model, uv is the corresponding pixel coordinate, and xyz is the world coordinate of the corresponding point. The deformation and strain measurement results of the obtained composite woven structure object are as shown in Figure 6 .

[0102] Example 2

[0103] This embodiment measures an object with a large depth change of a laminated structure, and a fast color camera (Emergent HB-1800-SC, resolution: 1600x1096 pixels) is used for dynamic measurement. The steps of a DIC assisted FPP measurement method based on intensity-color space analysis are as shown in Figure 1 .

[0104] S1, select a color fluorescent pigment with the best fluorescent color, and use the pigment to make a speckle pattern and spray it on the surface of the measured object;

[0105] Specifically, when the background color difference of the measured object is not less than 0.5B, the selection of the fluorescent pigment color should make the speckle color difference take the minimum value; when the background color difference of the measured object is less than 0.5B, the selection of the fluorescent pigment color should make the speckle color difference take the maximum value; at the same time, the modulation of the stripe pattern is always taken as the maximum value; the above method ensures that the final obtained color contrast is the highest.

[0106] S2, project a gray-scale structured light pattern onto the surface of the measured object to obtain a deformed

[0107] The gray-scale structured light pattern, the structured light pattern includes a stripe pattern and an encoded structured light pattern;

[0108] Specifically, S2 includes the following steps:

[0109] S21, the gray-scale structured light pattern comprises a fringe pattern and an encoded structured light pattern, the fringe pattern I1, I2, I3 is represented based on the background light intensity, fringe pattern modulation degree of the fringe pattern and the phase carrying object topography information;

[0110] S22, the encoded structured light pattern is six, including GC1, GC2, GC3, GC4, GC5, GC6, the encoded structured light pattern is arranged in each group of the fringe pattern, generating as Figure 2 Gray-scale structured light sequence pattern S, which can be represented as: S=I1I2I3GC1; I1I2I3GC2; I1I2I3GC3; I1I2I3GC4; I1I2I3GC5; I1I2I3GC6; I1I2I3GC1; I1I2I3GC2;...;

[0111] S23, the sequence pattern S is projected to the surface of the measured object, and the sequence pattern S is deformed by the measured object;

[0112] S3, the deformed gray-scale structured light pattern and the color image of the speckle pattern are acquired;

[0113] Specifically, the color camera synchronously takes pictures at intervals of the cyclic projection, acquires a photo including the speckle pattern and the sequence gray-scale structured light pattern S deformed by the measured object, and generates a color image sequence according to the sequence pattern.

[0114] S4, the intensity component of the color image is separated from the intensity space of the color image using an intensity-color space analysis method, the intensity component has the fringe information of the color image, and the chrominance difference data of the color image is separated from the color space of the color image, and the chrominance difference data has the speckle information of the color image;

[0115] Specifically, S41, the color image sequence is converted from RGB space to YCbCr space based on the calculation of R, G and B channel components of the fringe pattern, the luma component Y representing brightness is acquired, the Y component retains the modulated fringe information, and the red component Cr and the blue component Cb representing the difference from the luma component are acquired;

[0116] S42, the modulation degree Mo(Cr) and Mo(Cb) of Cr and Cb are calculated respectively, the chrominance difference data Dc with high contrast is calculated based on the absolute value of the difference between the modulation degrees Mo(Cr) and Mo(Cb), and the Dc retains the modulated speckle information;

[0117] S43, the modulation degree M of the Y component is calculated based on the Y componentY and based on the modulation depth M Y evaluate the fringe quality of the modulated fringe pattern;

[0118] Further, M Y For evaluating the fringe quality of the modulated fringe pattern, the specific evaluation method is: observing whether there is speckle in the image, if there is no speckle, it means that the modulation and separation are successful, and the fringe quality of the fringe pattern obtained by the modulation and separation is high. Y

[0119] S5, as Figure 5 The DIC auxiliary FPP measurement method shown in the figure obtains the three-dimensional topography, deformation and strain information of the measured object according to the intensity component and chrominance difference data.

[0120] Specifically, S5 includes the following steps:

[0121] S51, based on the FPP system, reconstructing the three-dimensional topography of the measured object by using the fringe pattern obtained by the modulation and separation;

[0122] Further, the specific steps of S51 include:

[0123] S511, based on the Y component obtained after the modulation and separation of the deformed fringe pattern, obtaining the phase representing the height information of the measured object surface;

[0124] S512, based on the phase of the height information, obtaining the height value of each point of the measured object in the three-dimensional world coordinate system according to the phase-height algorithm in the color image;

[0125] S513, according to the camera imaging model, solving the remaining two dimension values of the measured object surface in the three-dimensional world coordinate system, obtaining the three-dimensional world coordinates of each point of the measured object in the color image, and reconstructing the three-dimensional topography of the measured object.

[0126] S52, based on the pattern DC, completing the two-dimensional coordinate correlation of the same named points before and after the deformation according to the DIC technology, and based on the three-dimensional topography of the same named points before and after the deformation, completing the three-dimensional point cloud correlation of the same named points before and after the deformation, and obtaining the three-dimensional deformation information of the measured object;

[0127] Further, the specific steps of S52 include:

[0128] S521, obtaining the point p*(x*, y*) of the point p(x, y) in the pattern Dc on the deformed pattern Dc by the DIC method;

[0129] ​S522, mapping each point on the pattern Dc before and after deformation to a three-dimensional coordinate in the world coordinate system using the FPP method, the p point in the pattern Dc before deformation is (X(x,y), Y(x,y), Z(x,y)) in the world coordinate system, and the p* point in the pattern Dc after deformation is (X(x*,y*), Y(x*,y*), Z(x*,y*)) in the world coordinate system, the two points are the same point on the object in the world coordinate system, and the difference in coordinates is caused by deformation.

[0130] S523, dividing the three-dimensional world coordinate into UVW three directions, and the UVW deformation calculation formula is:

[0131] ;

[0132] Wherein, x, y and x*, y* are two-dimensional plane image coordinates before and after deformation respectively, X, Y, Z are three-dimensional world coordinates of corresponding two-dimensional points of the reference image and the deformation image, and U(x,y), V(x,y), and W(x,y) are obtained, which are the three-dimensional deformation information.

[0133] S53, performing differential calculation of the three-dimensional deformation information in the real world three-dimensional coordinate and two-dimensional plane pixel coordinate based on the chain rule, to obtain the three-dimensional strain information of the measured object.

[0134] S531, calculating the differential of the three-dimensional deformation information U(x,y) and V(x,y) with respect to the pixel coordinates;

[0135] S532, calculating the partial derivative of the pixel coordinates with respect to the three-dimensional world coordinates according to the camera imaging model and the three-dimensional world coordinates of the measured object point by point;

[0136] S533, calculating the partial derivative of U(x,y) and V(x,y) with respect to the three-dimensional world coordinates (x,y) according to the chain rule of differential based on the differential of the three-dimensional deformation information U(x,y) and V(x,y) with respect to the pixel coordinates and the partial derivative of the pixel coordinates with respect to the three-dimensional world coordinates, that is, the three-dimensional strain information of the measured object. The final deformation and strain measurement results of the object with large depth change of the laminated structure are as shown in Figure 7

[0137] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A DIC-assisted FPP measurement method based on intensity-color space analysis, characterized in that, The method includes the following steps: S1, using fluorescent pigments to create speckle patterns on the surface of the object being tested; S2, Project a grayscale structured light pattern onto the surface of the object being measured to obtain a grayscale structured light pattern that is modulated and deformed by the object surface. The deformed grayscale structured light pattern includes a deformed stripe pattern and a deformed coded structured light pattern. S3, acquire color images of the deformed grayscale structured light pattern and the speckle pattern; S4, using an intensity-color space analysis method, the intensity component of the color image is separated in the intensity space of the color image. The intensity component has the stripe information of the color image. The chromaticity difference data of the color image is separated in the color space of the color image. The chromaticity difference data has the speckle information of the color image. S5. Based on the DIC-assisted FPP measurement method, the three-dimensional morphology, deformation and strain information of the measured object are obtained according to the intensity component and color difference data.

2. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 1, characterized in that, The intensity-color space used in the intensity-color space analysis method includes commonly used intensity-color spaces such as LAB, lαβ, HSV, and YCbCr.

3. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 1, characterized in that, The specific methods for selecting the optimal fluorescent color of a colored fluorescent pigment include: When the background color difference of the object being tested is not less than the color difference threshold, the selection of the fluorescent pigment color should minimize the speckle color difference; when the background color difference of the object being tested is less than the color difference threshold, the selection of the fluorescent pigment color should maximize the speckle color difference; at the same time, the modulation degree of the stripe pattern should always be maximized; the above methods ensure that the final obtained color contrast is the highest.

4. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 1, characterized in that, Step S2 specifically includes: S21, Obtain the grayscale structured light pattern, the grayscale structured light pattern including a stripe pattern and an encoded structured light pattern; S22, the stripe pattern and the encoded structured light pattern are arranged alternately in sequence to generate a grayscale structured light sequence pattern S; S23, the sequence pattern S is cyclically projected onto the surface of the object under test. The sequence pattern S will be deformed by the object under test to obtain a deformed sequence pattern S. The deformed sequence pattern S includes a deformed stripe pattern and a deformed coded structured light pattern.

5. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 2, characterized in that, Step S4, performed using the YCbCr space, specifically includes: S41, based on the calculation of the R, G, and B channel components of the stripe pattern, the color image sequence is converted from RGB space to YCbCr space, and the luma component Y representing brightness is obtained. The Y component retains the modulated stripe information, and at the same time, the red component Cr and the blue component Cb expressing the difference compared with the luma component are obtained. S42, calculate the modulation degree Mo(Cr) and Mo(Cb) of Cr and Cb respectively, and calculate the color difference data Dc with high contrast based on the absolute value of the difference between the modulation degree Mo(Cr) and Mo(Cb), wherein Dc retains the speckle information; S43, calculate and obtain the modulation index M of the Y component based on the Y component. Y And based on the aforementioned modulation M Y Evaluate the stripe quality of the modulated stripe pattern.

6. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 5, characterized in that, M Y The method for evaluating the stripe quality of the modulated stripe pattern is as follows: Observe M Y If speckle is not present in the image, it indicates that the modulation and separation were successful, and the stripe pattern obtained by the modulation and separation has high stripe quality.

7. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 5, characterized in that, Step S5 specifically includes: S51, the three-dimensional shape of the object under test is reconstructed based on the FPP system using the stripe pattern obtained by modulation and separation; S52, based on the pattern DC, the two-dimensional coordinate association of the corresponding points before and after deformation is completed according to the DIC technology, and based on the three-dimensional morphology of the corresponding points before and after deformation, the three-dimensional point cloud association of the corresponding points before and after deformation is completed, so as to obtain the three-dimensional deformation information of the measured object. S53, based on the chain rule, perform differential calculations on the three-dimensional deformation information using the three-dimensional coordinates and two-dimensional plane pixel coordinates in the real world to obtain the three-dimensional strain information of the measured object.

8. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 7, characterized in that, Step S51 specifically includes: S511, Based on the Y component obtained after modulation and separation of the deformed stripe pattern, obtain the phase representing the surface height information of the measured object. S512, Based on the phase of the height information, the height value of the measured object in the color image is obtained point by point in the three-dimensional world coordinate system according to the phase-height algorithm; S513, based on the camera imaging model, the remaining two dimensions of the surface of the object under test in the three-dimensional world coordinate system are obtained, the three-dimensional world coordinates of the object under test point by point in the color image are obtained, and the three-dimensional shape of the object under test is reconstructed.

9. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 7, characterized in that, S52 specifically includes: S521, obtain the point p*(x*,y*) of the point p(x,y) in the pattern Dc on the deformed pattern Dc by the DIC method; S522, using the FPP method, each point on the pattern Dc before and after deformation is mapped to three-dimensional coordinates in the world coordinate system. Before deformation, point p in the pattern Dc is (X(x,y),Y(x,y),Z(x,y)) in the world coordinate system, and after deformation, point p* in the pattern Dc is (X(x*,y*),Y(x*,y*),Z(x*,y*)) in the world coordinate system. These two points are the same point on the object in the world coordinate system, and the difference in coordinates is caused by the deformation. S523, the three-dimensional world coordinates are divided into three directions: UVW. The UVW deformation calculation formula is as follows: ； Where x, y and x*, y* are the coordinates of the two-dimensional planar images before and after deformation, respectively, and X, Y, Z are the three-dimensional world coordinates of the corresponding two-dimensional points in the reference image and the deformed image. The obtained U(x,y), V(x,y), W(x,y) are the three-dimensional deformation information.

10. The DIC-assisted FPP measurement method based on intensity-color space analysis according to claim 7, characterized in that, Step S53 specifically includes: S531, calculate the derivatives of the three-dimensional deformation information U(x,y) and V(x,y) with respect to the pixel coordinates (u,v); S532, calculate the partial derivative of the pixel coordinates (u,v) with respect to the three-dimensional world coordinates (x,y) based on the camera imaging model and the point-by-point three-dimensional world coordinates of the measured object; S533, based on the differentials of the three-dimensional deformation information U(x,y) and V(x,y) with respect to the pixel coordinates and the partial derivatives of the pixel coordinates with respect to the three-dimensional world coordinates, calculate the partial derivatives of U(x,y) and V(x,y) with respect to the three-dimensional world coordinates (x,y) according to the chain rule of differentiation, that is, the three-dimensional strain information of the measured object.

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