CN116773457B - Polarization measurement method, system, equipment and medium based on Stokes parameters - Google Patents
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Abstract
The present disclosure relates to a polarization measurement method, system, device and medium based on Stokes parameters, the method comprising the steps of: when white light is projected onto an object to be measured, an image of the object to be measured under different polarization angles by an analyzer shot by a camera is obtained; quantitatively calculating Stokes parameters according to images under different polarization angles shot by a camera to obtain a polarization angle pixel histogram, screening values of the Stokes parameters according to the polarization angle pixel histogram, and further determining an optimal polarization angle; and projecting the coded fringe pattern onto the measured object, adjusting the included angle of the analyzer according to the obtained optimal polarization angle, and shooting polarized images of the measured object under different polarization angles through a camera. The method solves the problem that the image signal to noise ratio is too low when the polarization filter is used for eliminating the interference of a high-light area, and can effectively improve the measurement efficiency, so that the selection of the polarization angle is faster and more accurate.
Description
Technical Field
The disclosure relates to the technical field of vision sensor measurement, in particular to a polarization measurement method, a polarization measurement system, polarization measurement equipment and polarization measurement media based on Stokes parameters.
Background
Today, high dynamic range measurement techniques offer a variety of solutions to many researchers. Some researchers can change the specular reflection of the surface of an object to diffuse reflection by coating a particle layer on the surface of the object to be measured, and the principle is that the image shot by a camera has errors caused by specular reflection due to the high reflectivity of the surface of the object, and the measurement of the object can be completed by coating the particle layer. However, the pre-treatment before the experiment is required to be carried out on the measured object, so that the measurement efficiency is greatly reduced, and the influence factors of measurement errors caused by uneven smearing exist.
To avoid the above effects, experts focus their attention on adjusting structured light code measurement systems to accomplish the measurement of HDR objects. Reducing the effect on oversaturated pixels on the image can be accomplished by adjusting the projection brightness and camera exposure time so that the captured image pixels maintain a relatively high gray level to improve the accuracy of the HDR object measurement. In the method, due to the fact that the fluctuation range of the surface reflectivity of the HDR object is too large, proper exposure time and projection pattern brightness cannot be accurately and rapidly predicted, a large number of pictures with different exposure time and projection brightness are required to be shot in the experiment, and the measurement efficiency is reduced. Based on the polarization characteristics of light, researchers have simulated a polarization filter in a measurement system in experiments, and the polarization filter can be used for eliminating interference caused by specular reflection on the surface of an HDR object in the measurement process. Because the attenuation of the polarized filter to the light intensity of the image is global, even if the polarized filter can eliminate the influence of high light, if the measured object has a diffuse reflection area, the partial area of the shot image is too dark, and the signal to noise ratio of the image is too low, so that the measurement result is influenced. In addition, a bicolor reflection model is also proposed by researchers, and the method mainly removes the influence of specular reflection on the surface of an HDR object through color information. However, the method has two problems of chromatic aberration and crosstalk, so that the accuracy of three-dimensional measurement can be greatly reduced.
Disclosure of Invention
The present disclosure provides a polarization measurement method, system, device and medium based on Stokes parameters, which can solve at least one problem mentioned in the background art. In order to solve the technical problems, the present disclosure provides the following technical solutions:
as an aspect of the embodiments of the present disclosure, there is provided a polarization measurement method based on Stokes parameters, including the steps of:
when white light is projected onto an object to be measured, an image of the object to be measured under different polarization angles by an analyzer shot by a camera is obtained;
Quantitatively calculating Stokes parameters according to images under different polarization angles shot by a camera to obtain a polarization angle pixel histogram, screening values of the Stokes parameters according to the polarization angle pixel histogram, and further determining an optimal polarization angle; the step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization; the expression form of the Stokes parameter consists of four vectors, which are expressed as follows:
，
Wherein, S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the ideal optimal polarization angle;
and projecting the coded fringe pattern onto the measured object, adjusting the included angle of the analyzer according to the obtained optimal polarization angle, and shooting polarized images of the measured object under different polarization angles through a camera.
Optionally, the projecting white light onto the measured object includes: white light with the gray value of 255 and even distribution is projected onto the measured object through the polarizer by the structural light emitter.
Alternatively, the expression form of the Stokes parameter is composed of four vectors, expressed as:
，
Wherein S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data.
Optionally, the images captured by the camera under different polarization angles include: when the polarization angle is 0 DEG, the light intensity of polarized image radiation shot by the camera is expressed as:
，
Where θ is the linear polarizer angle.
Optionally, when white light is projected onto the measured object, after the image of the measured object under different polarization angles is obtained by the polarization analyzer shot by the camera, the method further includes: and fusing the polarized images under each optimal polarized angle through an image fusion algorithm to obtain a fused image, and then carrying out three-dimensional reconstruction on the object to be measured based on the fused image and the Gray code reconstruction principle.
As another aspect of an embodiment of the present disclosure, there is provided a polarization measurement system based on Stokes parameters, including:
the image acquisition module acquires images of the measured object under different polarization angles of the polarization analyzer shot by the camera when white light is projected onto the measured object;
The optimal polarization angle determining module is used for quantitatively calculating Stokes parameters according to images under different polarization angles shot by the camera to obtain a polarization angle pixel histogram, screening the Stokes parameters according to the polarization angle pixel histogram, and further determining an optimal polarization angle; the step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization; the expression form of the Stokes parameter consists of four vectors, which are expressed as follows:
，
Wherein, S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the ideal optimal polarization angle;
And the polarized image acquisition module projects the coded stripe pattern onto the measured object, adjusts the included angle of the analyzer according to the obtained optimal polarized angle, and shoots polarized images of the measured object under different polarized angles through the camera.
As another aspect of the embodiments of the present disclosure, there is provided an electronic device including a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the polarization measurement method based on Stokes parameters described above when the processor executes the computer program.
As another aspect of the embodiments of the present disclosure, there is provided a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements the polarization measurement method based on Stokes parameters described above.
Compared with the prior art, the beneficial effects of the present disclosure are:
1. The polarization measurement method or system based on Stokes parameters can well treat the problem that the signal to noise ratio is too low due to too dark of an image shot by a camera under the condition that a polarization filter is used for eliminating high light area interference in a traditional structured light measurement system, and can obviously improve the quality of stripe images;
2. the method and the device for calculating the polarization angle by the quantitative mathematical model can effectively improve the efficiency of system measurement, and enable the selection of the polarization angle to be quicker and more accurate in the experimental process.
Drawings
FIG. 1 is a flow chart of a polarization measurement method based on Stokes parameters in embodiment 1;
FIG. 2 is a schematic diagram of the line structure photosensor system of example 1;
FIG. 3 is a histogram of polarization angle pixels in example 1;
FIG. 4 is a schematic diagram of the image fusion algorithm in example 1;
Fig. 5 is a block diagram of a polarization measurement system based on Stokes parameters in embodiment 2.
Detailed Description
Various exemplary embodiments, features and aspects of the disclosure will be described in detail below with reference to the drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Although various aspects of the embodiments are illustrated in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The word "exemplary" is used herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
The term "and/or" is herein merely an association relationship describing an associated object, meaning that there may be three relationships, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In addition, the term "at least one" herein means any one of a plurality or any combination of at least two of a plurality, for example, including at least one of A, B, C, may mean including any one or more elements selected from the group consisting of A, B and C.
Furthermore, numerous specific details are set forth in the following detailed description in order to provide a better understanding of the present disclosure. It will be understood by those skilled in the art that the present disclosure may be practiced without some of these specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order not to obscure the present disclosure.
It will be appreciated that the above-mentioned method embodiments of the present disclosure may be combined with each other to form a combined embodiment without departing from the principle logic, and are limited to the description of the present disclosure.
In addition, the disclosure further provides a polarization measurement method, a system, a device and a medium based on Stokes parameters, and any one of the polarization measurement method based on Stokes parameters provided in the disclosure may be implemented, and corresponding technical schemes and descriptions and corresponding descriptions of method parts are omitted.
The polarization measurement method based on the Stokes parameter may be implemented by a computer or other polarization measurement apparatus capable of implementing the Stokes parameter, for example, the method may be implemented by a terminal device or a server or other processing device, where the terminal device may be a User Equipment (UE), a mobile device, a User terminal, a cellular phone, a cordless phone, a Personal digital assistant (Personal DIGITAL ASSISTANT, PDA), a handheld device, a computing device, a vehicle-mounted device, a wearable device, and so on. In some possible implementations, the polarization measurement method based on Stokes parameters may be implemented by a processor invoking computer readable instructions stored in a memory.
Example 1
The embodiment provides a polarization measurement method based on Stokes parameters, which comprises the following steps:
S10, when white light is projected onto the measured object 1, the image of the measured object 1 under different polarization angles of the analyzer 4 shot by the camera 2 is obtained;
S20, quantitatively calculating Stokes parameters according to images under different polarization angles shot by the camera 2 to obtain a polarization angle pixel histogram, screening the Stokes parameters according to the polarization angle pixel histogram, and further determining an optimal polarization angle; the step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the ideal optimal polarization angle;
s30, projecting the coded stripe pattern onto the measured object 1, adjusting the included angle of the analyzer 4 according to the obtained optimal polarization angle, and shooting polarized images of the measured object 1 under different polarization angles through the camera 2.
In this embodiment, implementation of the polarization measurement method based on Stokes parameters specifically includes the following steps, a flowchart of which is shown in fig. 1, and each step of the embodiments of the disclosure is described in detail below.
S10, when white light is projected onto the measured object 1, the image of the measured object 1 under different polarization angles of the analyzer 4 shot by the camera 2 is obtained.
In this embodiment, the device used is composed of three parts of a camera 2, a structural light emitter 3 and a measured object 1, based on the principle of laser triangulation, wherein the camera 2 and the structural light emitter 3 are on a horizontal plane, the structural light emitter 3 emits structural light (i.e. white light) to intersect with two planes of the measured object 1 to form a light bar, the camera 2 and the structural light emitter 3 form a structural light vision sensor corresponding to a plane view field of the measured object 1, so as to form a set of linear structure light sensor system, and the measurement principle diagram is shown in fig. 2.
Wherein, the camera 2 can select a BFS-U3-23S3M-M type depth camera 2 (with HC1605 camera lens) with 8 bits, and the resolution is 1920 pixels×1200 pixels, which is produced by FLIR company; the structured light emitter 3 may be selected from a model TEXAS INSTRUMENTS DLP LIGHTCRAFTER 4500 projector with a resolution of 912 pixels x 1140 pixels. Two polarizing filter types were selected as opsp 25.4.4, manufactured by beijing Zolix. The object 1 to be measured may be a metal mask, and since the object 1 to be measured belongs to a metal object and has a dark area with a half of the surface, the surface reflectivity of the object is greatly changed, and a large area of supersaturated pixels exist under a traditional structured light measuring system, the metal mask is selected for experiments to verify the method in the disclosure. An 8-bit gray scale camera sensor is used, so the maximum light intensity of the structured light emitter 3 is 255.
Optionally, the projecting white light onto the measured object 1 includes: white light with the gray value of 255 and even distribution is projected by the structural light emitter 3 to the measured object 1 through the polarizer 5.
S20, according to images under different polarization angles shot by the camera 2, stokes parameters are quantitatively calculated to obtain a polarization angle pixel histogram, and according to the polarization angle pixel histogram, screening values are carried out on the Stokes parameters, so that the optimal polarization angle is determined. The step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization; the expression of Stokes parameters consists of four vectors, expressed as:
，
Wherein, S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the ideal optimal polarization angle;
Stokes vector method is applied to observe polarization state. Stokes vectors can analyze any light source in nature and represent their polarization states, including natural light, fully polarized light, and partially polarized light, as well as non-monochromatic light and monochromatic light can be represented by Stokes vectors.
Optionally, the images captured by the camera 2 under different polarization angles include: when the polarization angle is 0 DEG, the light intensity of polarized image radiation shot by the camera 2 is expressed as:
，
Where θ is the linear polarizer angle.
In this embodiment, the value of the optimal polarization angle can be obtained after the calibration of the camera 2 is completed, and because the light rays can play a certain role in weakening the light intensity of the image after passing through the polarization filter and being captured by the camera 2, the three polarization angles in this embodiment can inhibit the highlight region, and meanwhile, the dark region can cause too low area brightness to affect the measurement result, so that the Stokes parameters are screened to obtain the value, and the optimal polarization angle is determined.
Optionally, the selecting the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization.
In this embodiment, a white light with a gray value 255 and uniform distribution passing through the polarizer 5 is projected to the surface of the measured object 1 by the structure light emitter 3, stokes parameters are quantitatively calculated again by shooting images with three required polarization angles by the camera 2, a distribution histogram of pixels corresponding to the polarization angles can be obtained, and the distribution histogram of pixels corresponding to the polarization angles obtained by quantitative calculation is shown in fig. 3. The image clearly reflects the distribution of the polarization angles corresponding to the pixel points on the image, wherein the polarization angle is 0-90 degrees, so that the abscissa value in the graph 3 is 0,1 and is divided into 9 effective intervals to represent 0-90 degrees, wherein [0.9,1] is an ineffective interval, and the ordinate value in the graph 3 is a pixel value.
The Stokes parameters are screened to obtain the value, and the final light intensity captured by the camera 2 and passing through the analyzer 4 is according to the Malus lawThe expression can be written as:
，
wherein, The light intensity of polarized light captured by the camera; /(I)For the intensity of unpolarized light captured by the camera, θ is the linear polarizer angle,/>Is the ideal polarization angle corresponding to each pixel point. /(I)The value of (2) can reach the minimum, the suppression to the highlight area of the image reaches the strongest at this moment, the image can be darker at the same time, and the optimal polarization angle is obtained as follows:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera 2, and/>The polarization angle after being orthogonal is the desired ideal optimal polarization angle.
S30, projecting the coded stripe pattern onto the measured object 1, adjusting the included angle of the analyzer 4 according to the obtained optimal polarization angle, and shooting polarized images of the measured object 1 under different polarization angles through the camera 2.
The included angle of the analyzer 4 is adjusted based on the above optimal polarization angle, the stripe projection pattern is photographed by the camera 2, and the images are subjected to image fusion based on an image fusion algorithm. An image fusion algorithm schematic is shown in fig. 4.
Optionally, after the angle camera 2 of the polarization analyzer 4 captures polarized images at different polarization angles, the method further includes: and fusing the polarized images under each optimal polarized angle through an image fusion algorithm to obtain a fused image, and then carrying out three-dimensional reconstruction on the measured object 1 based on the fused image and the Gray code reconstruction principle.
Gray code (Gray code) is a binary coding scheme characterized by only one digit changing between adjacent codewords. The range and resolution of the data that needs to be reconstructed in three dimensions is first determined. For example, assume that three-dimensional data ranges from 0 to 7 with a resolution of 1. A 3x3x3 cube grid is then created representing a three-dimensional space, each small cube representing a voxel (or pixel), for a total of 27 voxels, the 27 voxels being ordered in gray code order. The sequence of gray codes ensures that only one digit between adjacent voxels changes. Finally, according to the gray code ordering, different values are assigned to each voxel in turn. For example, the value of the first voxel is 0, the value of the second voxel is 1, and so on. In this way, the reconstruction principle of the gray code can be used for orderly assigning values to voxels in the three-dimensional space, thereby realizing three-dimensional reconstruction.
According to the polarization measurement method based on Stokes parameters, firstly, the conversion relation from an object world coordinate system to an image coordinate system is obtained through an imaging model of a camera 2; secondly, firstly calibrating the internal parameters and the external parameters of the camera 2, and then calibrating the structural light plane under the condition of knowing the internal and external parameters of the camera 2 to obtain the expression mode of the light plane in a world coordinate system; finally, the object 1 to be measured is scanned by the structured light to carry out three-dimensional reconstruction and three-dimensional measurement.
Example 2
As another aspect of the embodiments of the present disclosure, there is also provided a polarization measurement system 100 based on Stokes parameters, as shown in fig. 5, including:
the image acquisition module 10 acquires images of the measured object under different polarization angles of the polarization analyzer shot by the camera when white light is projected onto the measured object;
The optimal polarization angle determining module 20 quantitatively calculates Stokes parameters according to images under different polarization angles shot by a camera to obtain a polarization angle pixel histogram, and screens the Stokes parameters according to the polarization angle pixel histogram to determine an optimal polarization angle; the step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization;
the expression of Stokes parameters consists of four vectors, expressed as:
，
Wherein, S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the ideal optimal polarization angle;
The polarized image obtaining module 30 projects the coded stripe pattern onto the measured object, adjusts the included angle of the analyzer according to the obtained optimal polarized angle, and shoots polarized images of the measured object under different polarized angles through the camera.
Based on the module, the embodiment of the disclosure constructs a polarization measurement system based on Stokes parameters, and when white light is projected onto a measured object, an analyzer shot by a camera acquires images of the measured object under different polarization angles; quantitatively calculating Stokes parameters according to images under different polarization angles shot by a camera to obtain a polarization angle pixel histogram, screening values of the Stokes parameters according to the polarization angle pixel histogram, and further determining an optimal polarization angle; the coding fringe pattern is projected onto the measured object, the included angle of the analyzer is adjusted according to the obtained optimal polarization angle, and the polarized images of the measured object under different polarization angles are shot by the camera, so that the problem that the signal-to-noise ratio of the images is too low when the interference of a high-light area is eliminated by using the polarized filter is solved, the measurement efficiency can be effectively improved, and the selection of the polarization angles is faster and more accurate.
The following describes each module of the embodiments of the present disclosure in detail.
The image acquisition module 10 acquires images of the measured object under different polarization angles, taken by the camera, of the analyzer when white light is projected onto the measured object.
In this embodiment, the device used is composed of a camera, a structural light emitter and a measured object, based on the principle of laser triangulation, wherein the camera and the structural light emitter are on a horizontal plane, the structural light emitter emits structural light (i.e. white light) and intersects two planes of the measured object to form a light bar, and the camera and the structural light emitter form a structural light vision sensor corresponding to a plane view field of the measured object, thereby forming a set of line structure light sensor.
Wherein the camera can select an 8-bit BFS-U3-23S3M-M type depth camera (with HC1605 camera lens), and the resolution is 1920 pixels×1200 pixels, which is produced by FLIR company; the structured light emitter may be selected from a model TEXAS INSTRUMENTS DLP LIGHTCRAFTER 4500 projector with a resolution of 912 pixels x 1140 pixels. Two polarizing filter types were selected as opsp 25.4.4, manufactured by beijing Zolix. The object to be measured can be selected as a metal mask, and since the object to be measured belongs to a metal object and has a dark area with a half of the surface, the surface reflectivity of the object to be measured has a large change, and a large area of supersaturated pixels exist under a traditional structured light measuring system, the metal mask is selected for experiments to verify the method in the disclosure. An 8-bit gray scale camera sensor is used, so the maximum light intensity of the structured light emitter 3 is 255.
Optionally, the projecting white light onto the measured object includes: white light with the gray value of 255 and even distribution is projected onto the measured object through the polarizer by the structural light emitter.
The optimal polarization angle determining module 20 quantitatively calculates Stokes parameters according to images under different polarization angles shot by a camera to obtain a polarization angle pixel histogram, and screens the Stokes parameters according to the polarization angle pixel histogram to determine an optimal polarization angle. The step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization;
the expression of Stokes parameters consists of four vectors, expressed as:
，
Wherein, S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the desired ideal optimal polarization angle.
Stokes vector method is applied to observe polarization state. Stokes vectors can analyze any light source in nature and represent their polarization states, including natural light, fully polarized light, and partially polarized light, as well as non-monochromatic light and monochromatic light can be represented by Stokes vectors.
Optionally, the images captured by the camera under different polarization angles include: when the polarization angle is 0 DEG, the light intensity of polarized image radiation shot by the camera is expressed as:
，
Where θ is the linear polarizer angle.
In this embodiment, the value of the optimal polarization angle can be obtained after the calibration of the camera is completed, and because the light rays can play a certain role in weakening the light intensity of the image after passing through the polarization filter and capturing by the camera, the three polarization angles in this embodiment can inhibit the highlight region, and meanwhile, the dark region can cause too low area brightness to affect the measurement result, so that the Stokes parameter is screened, and the optimal polarization angle is determined.
Optionally, the selecting the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization.
In this embodiment, a white light with a gray value of 255 and uniformly distributed through the polarizer is projected to the surface of the measured object by the structural light emitter, and then the Stokes parameters are quantitatively calculated again by shooting the required images under three polarization angles by the camera, so that the distribution histogram of the pixels corresponding to the polarization angles can be obtained, and the distribution histogram of the pixels corresponding to the polarization angles, which is obtained by quantitative calculation, is obtained. The image clearly reflects the distribution of the polarization angles corresponding to the pixel points on the image, wherein the polarization angle is 0-90 degrees, so that the abscissa of the image is 0,1 and divided into 9 effective sections, and 0.9,1 is an ineffective section.
The Stokes parameters are screened, and according to the Malus law, the finally captured light intensity expression after passing through the analyzer by the camera can be written as follows:
，
wherein, The light intensity of polarized light captured by the camera; /(I)For the intensity of unpolarized light captured by the camera, θ is the linear polarizer angle,/>Is the ideal polarization angle corresponding to each pixel point. /(I)The value of (2) may be minimized where the suppression of the highlight areas of the image is maximized while the image may be darker. The optimal polarization angle is obtained as follows:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the desired ideal optimal polarization angle.
The polarized image obtaining module 30 projects the coded stripe pattern onto the measured object, adjusts the included angle of the analyzer according to the obtained optimal polarized angle, and shoots polarized images of the measured object under different polarized angles through the camera.
And adjusting the included angle of the polarization analyzer based on the optimal polarization angle, shooting the stripe projection pattern by a camera, and carrying out image fusion on the images based on an image fusion algorithm.
Optionally, when white light is projected onto the measured object, after the image of the measured object under different polarization angles is obtained by the polarization analyzer shot by the camera, the method further includes: and fusing the polarized images under each optimal polarized angle through an image fusion algorithm to obtain a fused image, and then carrying out three-dimensional reconstruction on the object to be measured based on the fused image and the Gray code reconstruction principle.
Gray code (Gray code) is a binary coding scheme characterized by only one digit changing between adjacent codewords. The range and resolution of the data that needs to be reconstructed in three dimensions is first determined. For example, assume that three-dimensional data ranges from 0 to 7 with a resolution of 1. A 3x3x3 cube grid is then created representing a three-dimensional space, each small cube representing a voxel (or pixel), for a total of 27 voxels, the 27 voxels being ordered in gray code order. The sequence of gray codes ensures that only one digit between adjacent voxels changes. Finally, according to the gray code ordering, different values are assigned to each voxel in turn. For example, the value of the first voxel is 0, the value of the second voxel is 1, and so on. In this way, the reconstruction principle of the gray code can be used for orderly assigning values to voxels in the three-dimensional space, thereby realizing three-dimensional reconstruction.
According to the polarization measurement system based on Stokes parameters, firstly, a conversion relation from an object world coordinate system to an image coordinate system is obtained through an imaging model of a camera; secondly, firstly calibrating internal parameters and external parameters of the camera, and then calibrating a structural light plane under the condition of knowing the internal and external parameters of the camera to obtain an expression mode of the light plane in a world coordinate system; finally, the object 1 to be measured is scanned by the structured light to carry out three-dimensional reconstruction and three-dimensional measurement.
In some embodiments, the polarization measurement system 100 based on Stokes parameters described above operates in use in the following manner:
s1: the image acquisition module 10 is run. When white light is projected onto an object to be measured, an analyzer 4 shot by a camera is used for obtaining images of the object to be measured under different polarization angles;
S2: the optimal polarization angle determination module 20 is operated. Quantitatively calculating Stokes parameters according to images under different polarization angles shot by a camera to obtain a polarization angle pixel histogram, screening values of the Stokes parameters according to the polarization angle pixel histogram, and further determining an optimal polarization angle;
S3: the polarized image acquisition module 30 is operated. And projecting the coded fringe pattern onto the measured object, adjusting the included angle of the analyzer according to the obtained optimal polarization angle, and shooting polarized images of the measured object under different polarization angles through a camera.
Based on the description of the above embodiments, the embodiments of the present disclosure can achieve the following technical effects:
(1) The polarization measurement method or system based on Stokes parameters can well treat the problem that the signal to noise ratio is too low due to too dark of an image shot by a camera under the condition that a polarization filter is used for eliminating high light area interference in a traditional structured light measurement system, and can obviously improve the quality of stripe images;
(2) The method and the device for calculating the polarization angle by the quantitative mathematical model can effectively improve the efficiency of system measurement, and enable the selection of the polarization angle to be quicker and more accurate in the experimental process.
Example 3
An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the Stokes parameter-based polarization measurement method of embodiment 1 when the computer program is executed.
Embodiment 3 of the present disclosure is merely an example, and should not be construed as limiting the functionality and scope of use of the embodiments of the present disclosure.
The electronic device may be in the form of a general purpose computing device, which may be a server device, for example. Components of an electronic device may include, but are not limited to: at least one processor, at least one memory, a bus connecting different system components, including the memory and the processor.
The buses include a data bus, an address bus, and a control bus.
The memory may include volatile memory such as Random Access Memory (RAM) and/or cache memory, and may further include Read Only Memory (ROM).
The memory may also include program means having a set (at least one) of program modules including, but not limited to: an operating system, one or more application programs, other program modules, and program data, each or some combination of which may include an implementation of a network environment.
The processor executes various functional applications and data processing by running computer programs stored in the memory.
The electronic device may also communicate with one or more external devices (e.g., keyboard, pointing device, etc.). Such communication may be through an input/output (I/O) interface. And, the electronic device may also communicate with one or more networks such as a Local Area Network (LAN), a Wide Area Network (WAN), and/or a public network, such as the Internet, through a network adapter. The network adapter communicates with other modules of the electronic device via a bus. It should be appreciated that other hardware and/or software modules may be used in connection with an electronic device, including but not limited to: microcode, device drivers, redundant processors, external disk drive arrays, RAID (disk array) systems, tape drives, data backup storage systems, and the like.
It should be noted that although several units/modules or sub-units/modules of an electronic device are mentioned in the above detailed description, such a division is merely exemplary and not mandatory. Indeed, the features and functionality of two or more units/modules described above may be embodied in one unit/module in accordance with embodiments of the present application. Conversely, the features and functions of one unit/module described above may be further divided into ones that are embodied by a plurality of units/modules.
Example 4
A computer-readable storage medium storing a computer program which, when executed by a processor, implements the steps of the Stokes parameter-based polarization measurement method of embodiment 1.
More specifically, among others, readable storage media may be employed including, but not limited to: portable disk, hard disk, random access memory, read only memory, erasable programmable read only memory, optical storage device, magnetic storage device, or any suitable combination of the foregoing.
In a possible embodiment, the disclosure may also be implemented in the form of a program product comprising program code for causing a terminal device to carry out the steps of implementing the Stokes parameter based polarization measurement method as described in embodiment 1, when said program product is run on the terminal device.
Wherein the program code for carrying out the present disclosure may be written in any combination of one or more programming languages, which program code may execute entirely on the user device, partly on the user device, as a stand-alone software package, partly on the user device, partly on the remote device or entirely on the remote device.
Although embodiments of the present disclosure have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.
Claims (5)
1. A polarization measurement method based on Stokes parameters is characterized by comprising the following steps:
when white light is projected onto an object to be measured, an image of the object to be measured under different polarization angles by an analyzer shot by a camera is obtained;
Quantitatively calculating Stokes parameters according to images under different polarization angles shot by a camera to obtain a polarization angle pixel histogram, wherein the polarization angle pixel histogram reflects the distribution condition of polarization angles corresponding to all pixel points on the image, and screening values are carried out on the Stokes parameters according to the polarization angle pixel histogram so as to determine the optimal polarization angle; the step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization;
the expression form of the Stokes parameter consists of four vectors, which are expressed as follows:
，
Wherein, S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the ideal optimal polarization angle;
Projecting the coded fringe pattern onto a measured object, adjusting the included angle of the analyzer according to the obtained optimal polarization angle, and shooting polarized images of the measured object under different polarization angles through a camera;
the images shot by the camera under different polarization angles comprise: when the polarization angle is 0 DEG, the light intensity of polarized image radiation shot by the camera is expressed as:
，
Wherein θ is the linear polarizer angle;
When white light is projected onto the measured object, after the image of the measured object under different polarization angles is obtained by the polarization analyzer shot by the camera, the method further comprises the following steps: and fusing the polarized images under each optimal polarized angle through an image fusion algorithm to obtain a fused image, and carrying out three-dimensional reconstruction on the measured object based on the fused image and the Gray code reconstruction principle.
2. The Stokes parameter-based polarization measurement method of claim 1, wherein the projecting white light onto the object under measurement comprises: white light with the gray value of 255 and even distribution is projected onto the measured object through the polarizer by the structural light emitter.
3. A Stokes parameter based polarization measurement system comprising:
the image acquisition module acquires images of the measured object under different polarization angles of the polarization analyzer shot by the camera when white light is projected onto the measured object;
The optimal polarization angle determining module is used for quantitatively calculating Stokes parameters according to images under different polarization angles shot by the camera to obtain a polarization angle pixel histogram, wherein the polarization angle pixel histogram reflects the distribution condition of polarization angles corresponding to all pixel points on the image, and screening values are carried out on the Stokes parameters according to the polarization angle pixel histogram so as to determine an optimal polarization angle; the step of screening the Stokes parameter according to the polarization angle pixel histogram includes: total intensity screening for selecting light waves having a particular intensity range, horizontal polarization screening for selecting light waves having a particular degree of horizontal polarization, and vertical polarization screening for selecting light waves having a particular degree of vertical polarization;
the expression form of the Stokes parameter consists of four vectors, which are expressed as follows:
，
Wherein, S 0 represents the intensity of the whole white light wave, S 1,S2,S3 represents the polarization states of three different angles independent of each other, and S 1,S2,S3 is the actual measurement data;
The optimal polarization angle is expressed as:
，
wherein, For the polarization angle corresponding to each pixel point in the ideal, the method is that-Is the ideal light intensity captured by the camera, and/>The polarization angle after being orthogonal is the ideal optimal polarization angle;
The polarized image acquisition module projects the coded stripe pattern onto the measured object, adjusts the included angle of the analyzer according to the obtained optimal polarized angle, and shoots polarized images of the measured object under different polarized angles through the camera;
the images shot by the camera under different polarization angles comprise: when the polarization angle is 0 DEG, the light intensity of polarized image radiation shot by the camera is expressed as:
，
Wherein θ is the linear polarizer angle;
When white light is projected onto the measured object, after the image of the measured object under different polarization angles is obtained by the polarization analyzer shot by the camera, the method further comprises the following steps: and fusing the polarized images under each optimal polarized angle through an image fusion algorithm to obtain a fused image, and carrying out three-dimensional reconstruction on the measured object based on the fused image and the Gray code reconstruction principle.
4. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor implements the Stokes parameter-based polarization measurement method of any one of claims 1 to 2 when the computer program is executed.
5. A computer readable storage medium, on which a computer program is stored, characterized in that the program, when being executed by a processor, implements the Stokes parameter based polarization measurement method of any one of claims 1 to 2.
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