CN108362469A - Size based on pressure sensitive paint and light-field camera and surface pressure measurement method and apparatus - Google Patents

Abstract

The invention provides a method for measuring three-dimensional dimensions and surface pressure based on pressure-sensitive paint and a light field camera, comprising the following steps: image acquisition step: respectively acquiring the pressure signal light field picture and the depth signal light field picture of the model; the surface pressure Distribution calculation step: calculate the model surface pressure distribution diagram from the pressure signal light field picture; surface depth distribution calculation step: calculate the model surface depth distribution diagram from the depth signal light field picture; three-dimensional pressure distribution generation step: fusion model The information of the surface pressure distribution map and the information of the model surface depth distribution map are used to generate a three-dimensional model pressure distribution map. The present invention also provides a measuring device for realizing the above measuring method. The invention can realize single-point shooting of a single light field camera to obtain the fusion data of the three-dimensional size of the model and the surface pressure distribution. Compared with other pressure-sensitive paints and three-dimensional reconstruction shooting requirements, the complexity of the system is obviously reduced, and the measurement efficiency is improved. efficiency.

Description

Method and device for measuring size and surface pressure based on pressure-sensitive paint and light field camera

technical field

The invention relates to the technical field of aerodynamic measurement, in particular to a method and device for measuring size and surface pressure based on pressure-sensitive paint and a light field camera.

Background technique

Pressure-sensitive paint (PSP), as a non-contact and high-resolution surface pressure measurement technology, has been widely used in aerodynamic experimental research since it was proposed in the 1980s. Unlike traditional pressure gauges or pressure sensors that can only obtain pressure data point by point, pressure-sensitive paint can measure the pressure distribution on the surface of complex models at one time. This technique takes advantage of the oxygen quenching properties of fluorescent molecules. Under suitable shooting conditions, the measurement accuracy is theoretically only limited by the accuracy of the photodetector used. By using suitable pressure-sensitive paint substrates and imaging devices, static or pressure measurements involving dynamic fluctuations can be accommodated.

The development of pressure-sensitive paint technology has been continuously improved, but errors caused by factors such as paint temperature sensitivity, model offset deformation, light source instability and photodegradation cannot be completely eliminated. In addition to improving the accuracy in low-speed flow and increasing the response frequency in high-speed flow, how to obtain the pressure distribution on the overall surface of a complex three-dimensional model is also the focus of research in this field.

In recent years, the development of light-field imaging offers a potential alternative to multi-camera imaging for 3D model pressure-sensitive paint measurements. A "light field" represents a collection of freely propagating light rays in space, usually by means of a five-dimensional parametric equation To describe, where L is a measure of the radiance density of light, (x, y, z) and represent the spatial and angular information of the ray, respectively. The five-dimensional light field can be simplified to four-dimensional through two parallel sampling planes, that is, L=L(u,v,s,t), where (u,v) and (s,t) are the light and the two planes respectively coordinates of the intersection point. In order to record the four-dimensional light field, it is necessary to place a microlens array at a distance in front of the photoelectric sensor of the camera. If this distance is equal to the focal length of the microlens, the resulting new camera structure is called a defocused light field camera (Defocused Plenoptic Camera). To eliminate ambiguity, the light field or light field camera mentioned below refer to the optical imaging system built on the basis of this structure. Any ray in space can be uniquely determined by its intersection with the camera main lens and the microlens plane. If the main lens plane is recorded as (u, v), the micro lens plane is (s, t). The light passing through the microlens can be regarded as having the ability to obtain the four-dimensional light field L(u,v,s,t) after being re-sampled by the microlens, and the original photo of the light field can be processed to obtain the depth of the object. information.

Nowadays, the measurement of the three-dimensional size and pressure distribution of complex geometric aerodynamic models is mostly achieved by multi-camera imaging. The multi-view pressure-sensitive paint technology puts forward high requirements on the installation, arrangement, calibration and number of optical windows of the model and multi-camera. These requirements are very unfavorable for aerodynamic tests, especially large-scale wind tunnel experiments.

Contents of the invention

Aiming at the defects in the prior art, the purpose of the present invention is to provide a method and device for measuring size and surface pressure based on pressure-sensitive paint and a light field camera.

The method for measuring the three-dimensional size and surface pressure based on the pressure-sensitive paint and the light field camera provided by the present invention comprises the following steps:

Image acquisition step: obtain the pressure signal light field picture and the depth signal light field picture of the model respectively;

Surface pressure distribution calculation steps: calculate the surface pressure distribution diagram of the model from the pressure signal light field picture;

Surface depth distribution calculation steps: Calculate the surface depth distribution map of the model from the depth signal light field picture;

The three-dimensional pressure distribution generation step: the information of the model surface pressure distribution map and the information of the model surface depth distribution map are fused to generate the three-dimensional model pressure distribution map.

Preferably, the image acquisition step includes the following steps:

Acquisition steps of the pressure signal light field picture: Under the closed and open conditions of the wind tunnel, use the light field camera to shoot the model coated with pressure-sensitive paint excited by the ultraviolet light source, respectively obtain the pressure signal light field picture, and record it as the first Pressure light field picture, second pressure light field picture;

Depth signal light field image acquisition steps: When the wind tunnel is closed, use a light field camera to capture the model of the projected pattern.

Preferably, the step of calculating the surface pressure distribution comprises the following steps:

Acquisition steps of the center perspective image: take out the pixels corresponding to the projection centers of all the microlenses in the first pressure light field image and the second pressure light field image, combine all the extracted pixels according to the position distribution of the microlenses, and obtain the first center perspective image respectively with the second center view image;

Rotation and translation correction step: perform rotation and translation correction on the first central perspective picture and the second central perspective picture, and respectively obtain the corrected first central perspective picture and the corrected second central perspective picture;

The step of obtaining the light intensity ratio image: take the deflection-corrected first central perspective picture as a reference picture, and divide the corresponding pixel value of the deflection-corrected first central perspective picture by the corresponding pixel value of the deflection-corrected second central perspective picture to obtain the light intensity Scale picture;

Calculation steps of model surface pressure: calculate and obtain model surface pressure based on light intensity ratio pictures.

Preferably, in the center angle of view picture acquisition step, the microlens projection center is obtained by shooting a whiteboard under the minimum aperture by using the principle of pinhole imaging;

In the rotation and translation deviation correction step, the rotation and translation parameters are obtained based on the following formula:

In the formula: W' _on is the image matrix after rotation and translation; T _{(Δx, Δy)} is the translation matrix _; Δx, Δy are the translation parameters; R _Δθ is the rotation matrix; Δθ is the rotation parameter; The picture matrix of the situation; (Δθ, Δx, Δy) is the rotation and translation parameters; argmin _{Δθ, Δx, Δy} () represents the value of Δθ, Δx, Δy when the substitution in the brackets takes the minimum value; sum() is the value of the calculation in the brackets Algorithm of the sum of matrix element values; W _off is the picture matrix of the wind tunnel closed working condition; .× represents the multiplication of elements at corresponding positions;

In the step of obtaining the light intensity ratio image, the light intensity ratio image is obtained by W _off ./W' _on , where ./ represents the division of the elements at the corresponding position;

In the model surface pressure calculation step, the model surface pressure is calculated based on the following formula:

In the formula: I is the fluorescence intensity recorded by the camera; ref is the reference value, and the value when the wind tunnel is closed is selected as the reference value; I _ref is the reference fluorescence intensity; A ₁ and A ₂ are the coefficients of performance of the pressure-sensitive paint; ₁ (T) and A ₂ (T) are the functions of coefficient of performance of pressure-sensitive paints with respect to temperature; P is the surface pressure; P _ref is the reference surface pressure.

Preferably, the step of calculating the surface depth distribution comprises the following steps:

Depth vision image acquisition step: perform a central viewing angle image acquisition operation on the depth signal light field image, and obtain a depth viewing angle image whose projection center of the microlens is symmetrical and centrally distributed, and whose size is a×a;

EPI slope output step: output the EPI slope k _epi of each pixel in the depth vision image;

Depth calculation step: calculate the actual depth d on the model according to k _epi .

Preferably, the EPI slope output step comprises the following steps:

Step S1: Perform sub-pixel translation for all viewing angles except the central viewing angle, and translate the vector Calculated according to the following formula:

In the formula: label _ind is the index number of the current label; label _total is the total number of labels set; label _ind ∈ [0, label _total ] and label _ind is an integer; label _step is the set label step; k _const is the set fixed translation constant term; is a vector of a non-central viewing angle position relative to the central viewing angle position;

Step S2: For each translation of a label _ind , calculate the cost value of the a×a translation image set, and calculate the slope k _{epi(x,y) of the pixel at (x,y} ) in the central view image in the EPI according to the following formula:

In the formula: Represents the value of the label _ind when the substitution in the brackets takes the minimum value; α is the proportional coefficient; _CD is the sum of the absolute value of the pixel difference between the shifted picture set and the central picture; C _G is the comparison of the shifted picture set The sum of the absolute values of gradient differences in the center image.

Preferably, in the depth calculation step, the actual depth d is calculated according to the following formula:

In the formula: K is the number of pixels occupied by the size of the main lens corresponding to the unit viewing angle; D is the diameter of the clear aperture of the main lens; A is the micro-image size of the main lens; S _px is the side length of a single pixel; The focal length of the lens; f _n is the f-number of the main lens, u is the object distance; f is the focal length of the main lens; R is the scaling ratio of the number of pixels from the original image to the perspective transformation image, or Wherein, the size of the picture of the unit viewing angle is m×n, and the size of the original picture is M×N.

Preferably, the values of u and K are obtained by using metric calibration: the calibration plate is photographed multiple times, and before each shooting, the calibration plate is moved by a set distance Δd in a direction parallel to the main optical axis of the camera; the calibration plate is obtained For the k _epi of the upper feature point, within the set interval around the estimated value of u and K, use the least square method to find the sum of the squares of the residual values S(i, j) of the expression of u and K under the estimated value d, and take When S(i,j) is the minimum value, the values of u and K are the fitting values:

In the formula: K _final is the fitting value of K; u _final is the fitting value of u; () represents the value of K _i and u _j when the substitution in the brackets takes the minimum value; K _i is the value of the i-th K in the interval around the estimated value of K; u _j is the value of the i-th K in the interval near the estimated value of u j values of u; S is the sum of squares of the residual value; (i, j) is the coordinate position of the feature point in the set interval near the estimated value of u and K.

Preferably, in the step of generating the three-dimensional pressure distribution, spline curve fitting is used to convert the model surface depth results of the discrete distribution into continuous distribution according to different cross-section fittings;

The information of the surface pressure distribution map of the fusion model is coupled with the information of the depth distribution map of the model surface according to the corresponding positions to obtain the pressure distribution map of the three-dimensional model.

The present invention also provides a measuring device for realizing the above-mentioned three-dimensional dimension and surface pressure measurement method based on pressure-sensitive paint and light field camera, including a measured model, an ultraviolet light source, a light field camera and a projector, including only one A light field camera, the projector is capable of projecting patterns on the model under test.

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

1. The present invention can realize single-point shooting of a single light field camera to obtain the fusion data of the three-dimensional size of the model and the surface pressure distribution. Compared with other pressure-sensitive paints and three-dimensional reconstruction shooting requirements, it significantly reduces the complexity of the system and improves the Measured efficiency.

2. The present invention can realize the acquisition of the pressure distribution of the single-point shooting three-dimensional model under certain shooting conditions, effectively avoiding the incompatibility between the existing three-dimensional measurement technology and the pressure-sensitive paint technology in the experimental equipment and the experimental process, and providing further information for the follow-up Simplifying technical complexity and improving measurement efficiency has opened up a new path.

3. The present invention only uses one camera to realize the simultaneous measurement of the three-dimensional size of the model and the surface pressure distribution, which can effectively improve the efficiency of wind tunnel operation.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Fig. 1 is a device diagram for obtaining model surface pressure in an embodiment of the present invention;

Fig. 2 is a device diagram for obtaining the surface depth of a model in an embodiment of the present invention;

Fig. 3 is the application example that the present invention measures for a specific model;

Fig. 4 is the depth error value distribution on the axis of the application example model;

Fig. 5 is a flow chart of a measurement method for three-dimensional dimensions and surface pressure based on pressure-sensitive paint and a light field camera provided by the present invention;

The figure shows: the measured model 1; ultraviolet light source 2; light field camera 3; projector 4; image acquisition step 101; surface pressure distribution calculation step 102; surface depth distribution calculation step 103; three-dimensional pressure distribution generation step 104.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

In describing the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", The orientation or positional relationship indicated by "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the referred device Or elements must have a certain orientation, be constructed and operate in a certain orientation, and thus should not be construed as limiting the invention.

As shown in Figure 5, the method for measuring the three-dimensional size and surface pressure based on the pressure-sensitive paint and the light field camera provided by the present invention includes the following steps: the picture acquisition step: acquiring the pressure signal light field picture and the depth signal light field of the model respectively Picture; surface pressure distribution calculation steps: calculate the model surface pressure distribution map from the pressure signal light field picture; surface depth distribution calculation steps: calculate the model surface depth distribution map from the depth signal light field picture; three-dimensional pressure distribution generation Step: Fusing the information of the surface pressure distribution map of the model and the information of the depth distribution map of the model surface to generate a three-dimensional model pressure distribution map.

The image acquisition step includes the following steps: pressure signal light field image acquisition step: under the closed working condition and the open working condition of the wind tunnel, use the light field camera to shoot the model coated with pressure-sensitive paint excited by the ultraviolet light source, and obtain the pressure signal light respectively Field pictures, and recorded as the first pressure light field picture and the second pressure light field picture respectively; the acquisition step of the depth signal light field picture: when the wind tunnel is closed, use the light field camera to take pictures of the model of the projected pattern. In the embodiment, the image acquisition step adopts a pressure measurement method based on the excitation intensity of the pressure-sensitive paint, and the three-dimensional light-field pressure-sensitive paint technology consists of two parts. The first is the acquisition of the fluorescent light field image on the model surface and the pressure calculation, and the second is the acquisition of the three-dimensional light field image on the model surface and the depth reconstruction. Place the area of the model to be tested somewhere within the focal plane, turn on the ultraviolet light source, so that the pressure-sensitive paint is excited to emit fluorescence, and use the light field camera to obtain the fluorescence image of the model surface when the wind tunnel is opened and closed. As shown in Figure 1, the three-dimensional light-field pressure-sensitive paint technology is similar to the two-dimensional pressure-sensitive paint system, the only difference is that the former uses a light-field camera instead of the traditional camera used by the latter to obtain pictures when the wind tunnel is opened and closed. There is no strict sequence between the acquisition of the three-dimensional light field image on the model surface and the acquisition of the pressure information image. As shown in Figure 2, turn off the ultraviolet light source, turn on the projector, and select a black dot and white background pattern with proper density to project on the surface of the model to be tested, so that the black dots are evenly distributed in a honeycomb hexagonal shape, and the total area of the black dots accounts for about 100% of the total area. 40% to 50% of the projected area. Without moving the position of the light field camera, take pictures to obtain the surface map of the model under this projection.

The calculation step of the surface pressure distribution includes the following steps: the central viewing angle picture acquisition step: take out the pixels corresponding to the projection centers of all the microlenses in the first pressure light field picture and the second pressure light field picture, and press all the taken out pixels according to the microlens The position distribution is combined to obtain the first central perspective picture and the second central perspective picture; the rotation and translation correction step: perform rotation and translation correction on the first central perspective picture and the second central perspective picture, and respectively obtain the first central perspective after correction Angle of view picture and second center angle of view picture after deviation correction; light intensity ratio picture acquisition step: take the first center angle of view picture after deviation correction as a reference picture, and the pixel value corresponding to the first center angle of view picture after deviation correction and the second center angle of view picture after deviation correction The corresponding pixel value of the center view image is divided to obtain the light intensity ratio image; the calculation step of the model surface pressure: calculate the model surface pressure based on the light intensity ratio image.

In the embodiment, before performing division on the corresponding pixels to obtain the light intensity ratio image, preprocessing needs to be performed on the light field original picture. The first step in preprocessing is to obtain the projection center of each microlens on the camera's photosensor. Put a uniform whiteboard in front of the camera, adjust the aperture to the minimum and take a picture of the whiteboard, use a 9×9 Gaussian distribution to fit each bright spot, and calculate the sub-pixel microlens projection center coordinates. Using the coordinates of each center, the subsequent corresponding pixel set can be artificially encoded. Under the condition that the length is in pixels, the size of the original image is M×N, the side length of the circumscribed square of the circle where the microlenses are located is A; the number of microlenses is X×Y. According to the four-dimensional light field imaging principle L=L(u, v, s, t) mentioned in the background technology, the coordinates of each pixel under the microlens relative to its projection center represent a definite (u, v ) value, and the projection center of the microlens on the pixel plane determines the value of (s, t). The meaning of the (u,v) value can be regarded as the light passing through different positions of the main lens, so take out a certain pixel with the same (u,v) value under all microlenses, and place it on the photoelectric sensor plane according to the center of the microlens Combining the rules of arrangement, an image of a viewing angle can be obtained. During the combination process, in view of the fact that the actual picture pixel does not fall in the center of the microlens projection, an interpolation algorithm based on adjacent sampling points is used to calculate the pixel value at that point. The size of the generated picture from a certain perspective can be set manually, here it is set to m×n. Theoretically, for this light field imaging system, images from all viewing angles on the inscribed circle of the A×A area can be acquired. For the original picture of the model light field obtained under the open and closed conditions of the wind tunnel, only the central viewing angle of the two is taken for subsequent processing, that is, the picture obtained by interpolating the pixel at the center of the microlens projection.

The second step of preprocessing needs to account for the translation and rotation of the model due to the opening of the wind tunnel. Firstly, the area of the model is divided by threshold segmentation, the background is set to zero, the picture matrix of the wind tunnel open condition is W _on , and the picture matrix of the wind tunnel open condition is W _off . Estimate the deflection angle of the model when the wind tunnel is open relative to when the wind tunnel is closed, and use the reverse two-dimensional rotation matrix R _θ to rotate the model at this angle to eliminate the angle difference between the two models; then estimate the translation distance and introduce the translation matrix T _{(Δx, Δy)} , the model after translation and rotation, let the coordinates of a point in W _on be Then the coordinates after translation and rotation After traversing all non-zero points on W _on , the distribution of the model after translation and rotation when the wind tunnel is turned on is W _on ′. Calculate the dot product for the corresponding positions of W _off and W _on ′, and take the sum of the elements of the result, then the deflection and translation parameters (Δθ, Δx, Δy) should be the parameters when the sum value is the largest, namely:

In the formula: W' _on is the image matrix after rotation and translation; T _{(Δx, Δy)} is the translation matrix _; Δx, Δy are the translation parameters; R _Δθ is the rotation matrix; Δθ is the rotation parameter; The picture matrix of the situation; (Δθ, Δx, Δy) is the rotation and translation parameters; argmin _{Δθ, Δx, Δy} () represents the value of Δθ, Δx, Δy when the substitution in the brackets takes the minimum value; sum() is the value of the calculation in the brackets The algorithm of the sum of matrix element values; W _off is the picture matrix of the wind tunnel closed working condition; .× represents the multiplication of elements at corresponding positions.

After determining the deflection and translation parameters, use the deflected result to obtain the light intensity ratio image, that is, obtain it through W _off ./W' _on , where ./ represents the element division of the corresponding position.

Based on the improved Stern-Volmer equation, by calculating the ratio of the pixel value of the corresponding position of the image under the two working conditions of the wind tunnel closed condition and the open condition, combined with the calibration formula and parameters of the pressure-sensitive paint at the experimental temperature, the calculated Pressure distribution on the surface of the 3D model:

In the formula: I is the fluorescence intensity recorded by the camera; ref is the reference value, and the value when the wind tunnel is closed is selected as the reference value; I _ref is the reference fluorescence intensity; A ₁ and A ₂ are the coefficients of performance of the pressure-sensitive paint; ₁ (T) and A ₂ (T) are the functions of coefficient of performance of pressure-sensitive paints with respect to temperature; P is the surface pressure; P _ref is the reference surface pressure.

The calculation step of the surface depth distribution includes the following steps: Depth visual image acquisition step: perform a central viewing angle image acquisition operation on the depth signal light field image, and obtain a depth viewing angle image whose projection center of the microlens is a symmetrical center distribution and a size of a×a; EPI slope Output step: output the EPI slope k _epi of each pixel in the depth vision image, EPI (Epipolar Plane Image) is a polar geometric map, and the EPI slope is a measure of the displacement of the same object as the viewing angle changes; depth calculation steps: The actual depth d on the model is calculated according to k _epi .

In the embodiment, similar to the above-mentioned pressure image processing process, before processing the depth information, in order to meet the requirements of the subsequent depth estimation algorithm, it is necessary to take out a part of all viewing angles and use them. , on a square of size a×a (a<A, and a is an integer). After taking these picture sets as the input of the depth estimation algorithm, the result form of the depth estimation is to output the EPI slope k _epi of each point on the center picture with the center view picture as a model. The meaning of this slope can be regarded as per unit view angle The number of pixels displaced by a certain point is positive if it is within the focus plane, and negative if it is within the focal plane. The main body of the depth estimation algorithm is divided into the following steps:

Step S1: Perform sub-pixel translation for all viewing angles except the central viewing angle, and translate the vector Where label _ind is the index number of the current label, label _ind ∈ [0, label _total ] and is an integer; label _total is the total number of labels artificially set, generally 60-100; label _step is the artificially set label step; k _const is an artificially set translation constant item, its purpose is to make the final translation distance involved include the depth range occupied by the model, and at the same time not exceed the range too much; is the vector of the viewing angle position relative to the central viewing angle position, for the central viewing angle, Can be seen as zero.

Step S2: For each translation of a label _ind , calculate the cost value (Cost volume) of the a×a translation image set. The size of the cost value is divided into two parts: the first part is the pixel set at the image set (x, y) compared to the center The sum C _D of the absolute value of the pixel difference at the picture (x, y), and the second part is the sum C _G of the absolute value of the gradient at the picture set (x, y) compared to the gradient at the center picture (x, y). The two are coupled through the proportional coefficient α to obtain the final cost value αC _D +(1-a)C _G , α∈[0,1], and α is generally 0.5. Calculate the replacement value of all pixels in the center image under the label _ind , and traverse all the label _inds to obtain a multi-label cost set of m×n×label _total . For k _epi(x,y) , that is, the slope of the pixel at (x,y) in the central view image in the EPI is:

In the formula: Represents the value of the label _ind when the substitution in the brackets takes the minimum value; α is the proportional coefficient; _CD is the sum of the absolute value of the pixel difference between the shifted picture set and the central picture; C _G is the comparison of the shifted picture set The sum of the absolute values of gradient differences in the center image.

Using the thin lens imaging formula and the structural characteristics of the light field camera, the relationship between k _epi and the actual depth d can be deduced as

In the formula: K is the number of pixels occupied by the size of the main lens corresponding to the unit viewing angle; D is the diameter of the clear aperture of the main lens; A is the micro-image size of the main lens; S _px is the side length of a single pixel; The focal length of the lens; f _n is the f-number of the main lens, u is the object distance; f is the focal length of the main lens; R is the scaling ratio of the number of pixels from the original image to the perspective transformation image, or Wherein, the size of the picture of the unit viewing angle is m×n, and the size of the original picture is M×N. In theory and The two should be equal, but in practice, not all camera photosensors can be covered by microlenses, or the quality of microlenses on the edges is not good, resulting in the need to remove the poor quality edges of the M×N original image in use Assuming that the size of the image after removing the edge is M′×N′, the actual zoom size of the image should be:

In the above formula, F and f _n can be accurately read from the parameters of the main lens, and S _px , as the pixel size, can also be accurately read from the production parameters of the camera. In the formula, the value of the object distance u is unknown, and the value of the side length A of the square circumscribed by the microlens projected spot can be obtained by estimating the diameter of the microlens projected circular spot under the aperture size. This estimated value can be calculated in the subsequent measurement calibration calculation. K is used as the initial value, and the optimal solution of u and K is obtained.

The purpose of metric calibration is to obtain accurate u and A values. The method is to take multiple shots of the calibration plate that is easy to obtain k _epi and calculate the k _epi of some feature points on the calibration plate. Before each shooting, the calibration plate is placed along the Move a known distance Δd in a direction parallel to the principal optical axis of the camera. The pattern of the calibration board must be conducive to the accurate acquisition of _kepi , and the pattern used in the present invention is a black and white checkerboard pattern commonly used in camera calibration. The moving distance Δd is freely set by a high-precision linear stage, and the initial position is generally set to a place slightly away from the focal plane, namely Slightly less than zero, the end position is generally artificially adjusted at =2-2.5, assuming that the total number of shots is G, the total moving distance is (G-1)·Δd, in a certain interval near the estimated value K _esti of K such as (95%K _esti , 105%K _esti ), take K _i in ), and solve the equation about the corresponding estimated object distance u _esti :

Take u _j in a certain interval near the estimated value u _esti of u, such as (95% u _esti , 105% u _esti ), and use the least square _method to obtain (K _i ,u _j ) parameters, the residual sum of squares of the following formula (4), denoted as S(i,j), when the residual sum of squares is the smallest, it can be regarded that the fitting result is closest to the real value, that is:

In the formula: K _final is the fitting value of K; u _final is the fitting value of u; () represents the value of K _i and u _j when the substitution in the brackets takes the minimum value; K _i is the value of the i-th K in the interval around the estimated value of K; u _j is the value of the i-th K in the interval near the estimated value of u j values of u; S is the sum of squares of the residual value; (i, j) is the coordinate position of the feature point in the set interval near the estimated value of u and K.

In the step of generating the three-dimensional pressure distribution, the spline curve fitting is used to transform the discrete distribution model surface depth results into continuous distribution according to different cross-section fittings, and the information of the fusion model surface pressure distribution map and the information of the model surface depth distribution map are combined according to Corresponding to the position coupling, the pressure distribution map of the 3D model is obtained.

Due to the discreteness of the labels, the depth distribution cannot match the surface well. The spline curve fitting in Matlab is used to transform the surface depth results of the discrete distribution model into continuous distribution according to different cross-section fittings, which improves the accuracy due to the existence of discrete labels. Reduced sampling precision. Finally, the final pressure distribution result of the 3D model can be obtained by fusing the pressure and post-processed depth data. The specific application example is shown in Figure 3. The fusion process involves matching the corresponding points on the model. The method used is similar to the above method.

Fig. 4 shows the comparison error distribution diagram of the depth calculation results according to the embodiment of the present invention and the real model size on the central axis of the model, where the direction of the X-axis is the direction pointed by the top of the model. It can be seen that in the case of a large model cross-sectional area, the error of depth estimation can be effectively controlled within ±1mm. The part near the top of the model has a smaller cross-sectional area, resulting in a large increase in the surface curvature of the model. Due to the global camera resolution The ratio is a constant value, so the smaller cross-sectional area causes the decline of the actual resolution, which makes the depth calculation result deviate from the true value more.

But generally speaking, the present invention can realize the acquisition of the pressure distribution of the single-point shooting three-dimensional model under certain shooting conditions, effectively avoiding the incompatibility between the existing three-dimensional measurement technology and the pressure-sensitive paint technology in the experimental equipment and experimental process, This opens up a new path for further simplifying technical complexity and improving measurement efficiency.

The present invention provides a measurement device for realizing the above-mentioned three-dimensional dimension and surface pressure measurement method based on pressure-sensitive paint and light field camera, which includes a measured model, an ultraviolet light source, a light field camera and a projector, and only includes one A light field camera, the projector is capable of projecting patterns on the model under test. In the step of obtaining the light field picture of the pressure signal, turn on the ultraviolet light source, turn off the projector, and use the light field camera to take pictures; in the step of obtaining the light field picture of the depth signal, turn off the ultraviolet light source, turn on the projector to project on the measured model, and use the light field camera field camera to take pictures.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims (10)

1. A method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera, is characterized in that, comprises the following steps: Image acquisition step: obtain the pressure signal light field picture and the depth signal light field picture of the model respectively; Surface pressure distribution calculation steps: calculate the surface pressure distribution diagram of the model from the pressure signal light field picture; Surface depth distribution calculation steps: Calculate the surface depth distribution map of the model from the depth signal light field picture; The three-dimensional pressure distribution generation step: the information of the model surface pressure distribution map and the information of the model surface depth distribution map are fused to generate the three-dimensional model pressure distribution map. 2. the method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 1, is characterized in that, described picture acquisition step comprises the following steps: Acquisition steps of the pressure signal light field picture: Under the closed and open conditions of the wind tunnel, use the light field camera to take pictures of the model coated with pressure-sensitive paint excited by the ultraviolet light source, obtain the pressure signal light field picture respectively, and record them as the first Pressure light field picture, second pressure light field picture; Depth signal light field image acquisition steps: When the wind tunnel is closed, use a light field camera to capture the model of the projected pattern. 3. the method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 2, is characterized in that, described surface pressure distribution calculation step comprises the following steps: Acquisition steps of the center perspective image: take out the pixels corresponding to the projection centers of all the microlenses in the first pressure light field image and the second pressure light field image, combine all the extracted pixels according to the position distribution of the microlenses, and obtain the first center perspective image respectively with the second center view image; Rotation and translation correction step: perform rotation and translation correction on the first central perspective picture and the second central perspective picture, and respectively obtain the corrected first central perspective picture and the corrected second central perspective picture; The step of obtaining the light intensity ratio image: take the deflection-corrected first central perspective picture as a reference picture, and divide the corresponding pixel value of the deflection-corrected first central perspective picture by the corresponding pixel value of the deflection-corrected second central perspective picture to obtain the light intensity Scale picture; Calculation steps of model surface pressure: calculate and obtain model surface pressure based on light intensity ratio pictures. 4. The method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 3, characterized in that, in the step of acquiring the picture from the center angle of view, the small hole imaging principle is used to capture the whiteboard under the minimum aperture Obtain the microlens projection center; In the rotation and translation deviation correction step, the rotation and translation parameters are obtained based on the following formula: W' _on ＝T _{(Δx, Δy} )R _Δθ W _on In the formula: W′ _on is the image matrix after rotation and translation; T _{(Δx, Δy)} is the translation matrix; Δx, Δy are the translation parameters; R _Δθ is the rotation matrix; Δθ _is the rotation parameter; (Δθ, Δx, Δy) is the rotation and translation parameters; argmin _{Δθ, Δx, Δy} () represents the value of Δθ, Δx, Δy when the substitution formula in brackets takes the minimum value; sum() is to calculate the values in brackets Algorithm of the sum of matrix element values; W _off is the picture matrix of the wind tunnel closed working condition; .× represents the multiplication of elements at corresponding positions; In the light intensity ratio image acquisition step, the light intensity ratio image is obtained by W _off ./W' _on , where ./ represents the division of elements at corresponding positions; In the model surface pressure calculation step, the model surface pressure is calculated based on the following formula: In the formula: I is the fluorescence intensity recorded by the camera; ref is the reference value, and the value when the wind tunnel is closed is selected as the reference value; I _ref is the reference fluorescence intensity; A ₁ and A ₂ are the coefficients of performance of the pressure-sensitive paint; ₁ (T) and A ₂ (T) are the functions of coefficient of performance of pressure-sensitive paints with respect to temperature; P is the surface pressure; P _ref is the reference surface pressure. 5. the method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 2, is characterized in that, described surface depth distribution calculation step comprises the following steps: Depth vision image acquisition step: perform a central viewing angle image acquisition operation on the depth signal light field image, and obtain a depth viewing angle image whose projection center of the microlens is symmetrical and centrally distributed, and whose size is a×a; EPI slope output step: output the EPI slope k _epi of each pixel in the depth vision image; Depth calculation step: calculate the actual depth d on the model according to k _epi . 6. the method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 5, is characterized in that, described EPI slope output step comprises the following steps: Step S1: Perform sub-pixel translation for all viewing angles except the central viewing angle, and translate the vector Calculated according to the following formula: In the formula: label _ind is the index number of the current label; label _total is the total number of labels set; label _ind ∈ [0, label _total ] and label _ind is an integer; label _step is the set label step; k _const is set fixed translation constant term; is a vector of a non-central viewing angle position relative to the central viewing angle position; Step S2: For each translation of a label _ind , calculate the cost value of the a×a translation image set, and calculate the slope k _{epi(x, y) of the pixel at (x, y} ) in the central view image in the EPI according to the following formula: In the formula: Represents the value of the label _ind when the substitution in the brackets takes the minimum value; α is the proportional coefficient; _CD is the sum of the absolute value of the pixel difference between the shifted picture set and the central picture; C _G is the comparison of the shifted picture set The sum of the absolute values of gradient differences in the center image. 7. The method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 6, characterized in that, in the depth calculation step, the actual depth d is calculated according to the following formula: In the formula: K is the number of pixels occupied by the size of the main lens corresponding to the unit viewing angle; D is the diameter of the clear aperture of the main lens; A is the micro-image size of the main lens; S _px is the side length of a single pixel; The focal length of the lens; f _n is the f-number of the main lens, u is the object distance; f is the focal length of the main lens; R is the scaling ratio of the number of pixels from the original image to the perspective transformation image, or Wherein, the size of the picture of the unit viewing angle is m×n, and the size of the original picture is M×N. 8. The method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 7, characterized in that, the value of u and K is obtained by metric calibration: the calibration plate is photographed multiple times, every Before the second shooting, move the calibration plate by a set distance Δd along the direction parallel to the main optical axis of the camera; obtain the k _epi of the feature points on the calibration plate, and use the least squares method in the set interval around the estimated value of u and K Multiplication calculates the sum of the squares of the residual values S(i, j) of the expression of u and K under the estimated value d, and takes the value of u and K when S(i, j) is the minimum value as the fitting value: In the formula: K _final is the fitting value of K; u _final is the fitting value of u; Represents the value of K _i and u _j when the substitution in the brackets takes the minimum value; K _i is the value of the i-th K in the interval around the estimated value of K; u _j is the j-th value in the interval near the estimated value of u The value of u; S is the sum of squares of the residual value; (i, j) is the coordinate position of the feature point in the set interval near the estimated value of u and K. 9. The method for measuring the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera according to claim 1, characterized in that, in the step of generating three-dimensional pressure distribution, spline curve fitting is adopted, and the model of discrete distribution is The surface depth results are transformed into continuous distribution according to different cross-section fittings; The information of the surface pressure distribution map of the fusion model is coupled with the information of the depth distribution map of the model surface according to the corresponding positions to obtain the pressure distribution map of the three-dimensional model. 10. A measuring device that realizes the measurement method of the three-dimensional size and surface pressure based on pressure-sensitive paint and light field camera described in any one of claims 1 to 9, comprising a measured model, an ultraviolet light source, a light field camera and The projector is characterized in that it only includes a light field camera, and the projector can project patterns on the measured model.