CN114758060A - Polarization three-dimensional imaging method capable of representing absolute depth of target - Google Patents

Polarization three-dimensional imaging method capable of representing absolute depth of target Download PDF

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CN114758060A
CN114758060A CN202210255211.4A CN202210255211A CN114758060A CN 114758060 A CN114758060 A CN 114758060A CN 202210255211 A CN202210255211 A CN 202210255211A CN 114758060 A CN114758060 A CN 114758060A
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polarization
angle
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pixel point
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李轩
刘志强
邵晓鹏
刘飞
蔡玉栋
蔡国成
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Xidian University
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Abstract

The invention discloses a polarization three-dimensional imaging method capable of representing the absolute depth of a target, which comprises the following steps: obtaining polarization images of a target under different polarization angles; obtaining the polarization degree of each pixel point on the surface of the target object in the polarization image; acquiring azimuth angle initial values and incidence angle initial values at different pixel points on the surface of a target; correcting the initial value of the azimuth angle and the initial value of the incidence angle; constructing a normal vector for each pixel point on the surface of the target by using the corrected azimuth angle and the corrected incident angle; reconstructing a three-dimensional contour of the target by utilizing normal vector integration to obtain a surface function of the target; and combining the calibration of the camera and the surface function to obtain the absolute depth information of the target. According to the method, the target surface normal vector is re-represented by taking the component of the target surface normal vector along the depth direction as a unit, and the three-dimensional model reconstructed on the basis of the surface normal vector and the target absolute depth information are determined change relations, so that the limitation that the display depth of the traditional polarization three-dimensional imaging is relative depth is broken.

Description

Polarization three-dimensional imaging method capable of representing absolute depth of target
Technical Field
The invention belongs to the technical field of optical imaging, and particularly relates to a polarization three-dimensional imaging method capable of representing the absolute depth of a target.
Background
At present, the application of the three-dimensional imaging technology in the fields of industrial production, face recognition, security detection and the like is increasingly wide, and the polarization three-dimensional imaging technology is taken as an important branch of three-dimensional imaging and has various advantages of simple equipment, higher precision, small application limit and the like, so that the polarization three-dimensional imaging technology has important significance for the research of the polarization three-dimensional imaging technology. The conventional polarization three-dimensional imaging technology obtains a normal vector of a target surface by interpreting polarization information of target reflected light, normalizes the normal vector, and finally integrates to obtain a target three-dimensional model. However, the depth in the three-dimensional model obtained by the traditional polarization three-dimensional imaging method for normal vector normalization processing is a relative depth, and cannot be changed along with the change of the target detection distance, so that the absolute depth of the target cannot be represented. Obviously, this does not follow the trend of future imaging development.
The method realizes three-dimensional reconstruction of a target by combining acquisition of target polarization information and depth information obtained by Kinect. The method has the advantages that the normal of the surface of the target obtained by acquiring the depth information of the target through the Kinect is used as a prior condition, and the multivalue problem of the normal of the surface of the target in the polarization three-dimensional imaging can be effectively solved The title is obtained. Specifically, first, polarization images at different angles are taken by using a camera, the polarization degree of the target surface is calculated according to the Stokes vector method, and the incident angle and the azimuth angle of the target incident light can be calculated according to the polarization degree. The incident angle and the azimuth angle obtained by the polarization method have uncertainty, so that the surface normal information obtained by obtaining the target depth information by using the Kinect is required to be corrected. The correction method is to make the component n of the object surface normal in the x-axis and the y-axis obtained by the polarization informationxAnd nyThe direction of (c) is kept consistent with the direction derived from the depth information. And finally, normalizing the corrected normal line, and integrating the components of the normal line in the x axis and the y axis to reconstruct the three-dimensional profile of the target.
The binocular three-dimensional imaging technology based on the polarization information only uses the target depth information acquired by the Kinect as normal correction of the polarization three-dimensional imaging, and because the method integrates normalized surface normal vectors to achieve the effect of three-dimensional reconstruction, the depth information acquired by the reconstructed three-dimensional model is relative, only can reflect the distance between the target and a camera, and cannot represent the absolute depth information of the target.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides a polarized three-dimensional imaging method capable of characterizing the absolute depth of a target. The technical problem to be solved by the invention is realized by the following technical scheme:
one aspect of the present invention provides a polarized three-dimensional imaging method capable of characterizing an absolute depth of a target, comprising:
acquiring polarization images of a target under different polarization angles by using a polarization three-dimensional imaging system;
obtaining the polarization degree of each pixel point on the surface of the target object in the polarization image;
acquiring azimuth angle initial values and incidence angle initial values at different pixel points on the surface of the target according to the polarization images and the polarization degrees;
correcting the initial azimuth angle value and the initial incidence angle value to obtain a corrected azimuth angle and an incidence angle;
constructing a normal vector for each pixel point on the surface of the target by using the corrected azimuth angle and the corrected incident angle;
reconstructing a three-dimensional contour of the target by utilizing normal vector integration to obtain a surface height function of the target;
and obtaining absolute depth information of the target by combining the calibration of the camera in the polarized three-dimensional imaging system and the surface function.
In one embodiment of the present invention, acquiring polarized images of a target under different polarization angles by using a polarized three-dimensional imaging system comprises:
Acquiring reflected light of the surface of the target object by utilizing a polarized three-dimensional imaging system, and respectively acquiring polarized images I 'of the target object scene under four polarization angles of 0 degrees, 45 degrees, 90 degrees and 135 degrees'0、I′45、I′90、I′135；
Utilizing a threshold segmentation algorithm to carry out segmentation on the polarized image I'0、I′45、I′90、I′135The target object and the background in the image are segmented to obtain a polarization image I after threshold segmentation0、I45、I90、I135。
In one embodiment of the present invention, acquiring the degree of polarization at each pixel point on the surface of the target object in the polarization image comprises:
acquiring light intensity at each pixel point in the polarization image;
acquiring the maximum light intensity value, the minimum light intensity value and the polarization phase angle of reflected light at each pixel point in the polarization image by using the light intensity at each pixel point;
and obtaining the polarization value at each pixel point by using the maximum light intensity value and the minimum light intensity value.
In an embodiment of the present invention, acquiring initial values of an azimuth angle and an initial value of an incidence angle at different pixel points of a target surface according to the polarization image and the polarization degree includes:
obtaining an initial azimuth value of a pixel point u, wherein the initial azimuth value is equal to a polarization phase angle of reflected light of the pixel point u;
and obtaining an initial angle of incidence value of the incident light at each pixel point according to the relation between the polarization degree and the incident angle of the incident light on the target surface.
In an embodiment of the present invention, correcting the initial azimuth angle value and the initial incident angle value includes:
correcting the multivalue problem of the initial value of the incidence angle to obtain a corrected incidence angle, wherein the correction formula is expressed as:
Figure BDA0003548401910000041
GNrepresenting the gradient field variation reference information, G, solved using target surface intensity informationpolarRepresenting the gradient field parameters solved using the polarization information of the target reflected light,
Figure BDA0003548401910000042
represents a two-norm operation, if
Figure BDA0003548401910000043
The initial value of the azimuth angle is the corrected azimuth angle, if so
Figure BDA0003548401910000044
Then the initial value of the azimuth angle is turned for 180 degrees to obtain a corrected azimuth angle;
and optimizing the initial value of the incidence angle within a preset range adjacent to 90 degrees by utilizing an optimization algorithm to avoid the situation that the tan theta has a maximum value, and obtaining the optimized incidence angle theta.
In one embodiment of the present invention, the optimization algorithm is:
Figure BDA0003548401910000045
wherein, the first and the second end of the pipe are connected with each other,
Figure BDA0003548401910000046
f (x) is the initial value of the input angle of incidence, and 3 values are taken and are respectively denoted as T1，T0，T*Wherein, T0Approaches to T*；
The optimized incident angle is obtained as follows:
Figure BDA0003548401910000047
wherein the content of the first and second substances,
Figure BDA0003548401910000048
in an embodiment of the present invention, constructing a normal vector for each pixel point on the target surface by using the corrected azimuth angle and the corrected incident angle includes:
According to the corrected azimuth angle and the incidence angle, unitizing the depth direction components, and constructing a normal vector:
Figure BDA0003548401910000049
wherein, θ and
Figure BDA00035484019100000410
the optimized incident angle and the corrected azimuth angle are respectively used for the incident light on the target surface.
In an embodiment of the present invention, the obtaining absolute depth information of the target by combining the calibration of the camera in the polarized three-dimensional imaging system and the surface function comprises:
obtaining the change matrix of the pixel point coordinate of the target surface in the world coordinate system, the camera coordinate system, the image coordinate system and the pixel coordinate system according to the camera calibration, and obtaining the coordinate (X) of the target surface in the world coordinate systemwYwZw)；
Establishing the coordinates of the target in the world coordinate system and the three-dimensional coordinates (X) reconstructed by the surface function Z (u)rYrZr) In relation to (2)
Figure BDA0003548401910000051
Calculating to obtain a scale change factor tau;
obtaining the coordinates (X) of the target in the camera coordinate system according to the coordinates of the target in the world coordinate systemcYcZc) And obtaining the absolute depth d of each point of the targetabs：
Figure BDA0003548401910000052
Wherein d isabs(u) represents the absolute depth of the target at pixel point u.
Another aspect of the present invention provides a storage medium having a computer program stored therein, the computer program being configured to perform the steps of any one of the above-mentioned embodiments of the polarized three-dimensional imaging method capable of characterizing an absolute depth of an object.
Yet another aspect of the present invention provides an electronic device, including a memory and a processor, where the memory stores a computer program, and the processor, when calling the computer program in the memory, implements the steps of the polarized three-dimensional imaging method capable of characterizing the absolute depth of the target as described in any one of the above embodiments.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the polarization three-dimensional imaging method, the target surface normal vector is re-represented by taking the component of the target surface normal vector along the depth direction as a unit, the three-dimensional model reconstructed based on the surface normal vector and the actual detection distance of the target, namely absolute depth information, are determined to be a change relation, and the change relation function is obtained by combining means such as camera calibration and the like, so that the absolute depth information of the target can be directly represented in the reconstructed polarization three-dimensional imaging model, the limitation that the traditional polarization three-dimensional imaging display depth is relative depth is broken through, and the direction is provided for the diversification of the function of the future polarization three-dimensional camera.
2. The polarization three-dimensional imaging method provided by the embodiment of the invention provides an optimization algorithm for the incident angle of incident light, and solves the problem that part of points of a normal vector represented by the incident angle are not available.
3. The polarization three-dimensional model constructed by the polarization three-dimensional imaging method reconstructs a three-dimensional surface which accords with the actual observation change along with the change of the target detection distance, and effectively shows the high-frequency change of the target.
The present invention will be described in further detail with reference to the drawings and examples.
Drawings
FIG. 1 is a flow chart of a method for polarized three-dimensional imaging capable of characterizing an absolute depth of a target according to an embodiment of the present invention;
FIG. 2 shows an azimuthal angle of light incident on a surface of an object according to an embodiment of the present invention
Figure BDA0003548401910000061
And an incident angle θ;
fig. 3 is a schematic diagram of a change matrix of an object in a world coordinate system, a camera coordinate system, an image coordinate system, and a pixel coordinate system according to an embodiment of the present invention.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined object, a three-dimensional polarization imaging method capable of representing the absolute depth of a target according to the present invention is described in detail below with reference to the accompanying drawings and the detailed description.
The foregoing and other technical matters, features and effects of the present invention will be apparent from the following detailed description of the embodiments, which is to be read in connection with the accompanying drawings. The technical means and effects of the present invention adopted to achieve the predetermined purpose can be more deeply and specifically understood through the description of the specific embodiments, however, the attached drawings are provided for reference and description only and are not used for limiting the technical scheme of the present invention.
It should be noted that, in this document, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Furthermore, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or device that comprises a list of elements does not include only those elements but may include other elements not expressly listed. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of additional like elements in the article or device in which the element is included.
Referring to fig. 1, fig. 1 is a flowchart of a polarized three-dimensional imaging method capable of characterizing an absolute depth of a target according to an embodiment of the present invention. The polarization imaging method comprises the following steps:
s1: acquiring polarization images of a target under different polarization angles by using a polarization three-dimensional imaging system;
specifically, the S1 includes:
s11: the polarized three-dimensional imaging system is utilized to collect reflected light of the surface of the target object, and polarized images I 'of a target object scene under four polarization angles of 0 degrees, 45 degrees, 90 degrees and 135 degrees are respectively obtained' 0、I′45、I′90、I′135。
Specifically, in a natural light environment, reflected light of the surface of an object is acquired by a CMOS (Complementary Metal Oxide Semiconductor) camera in a polarization detector of the polarized three-dimensional imaging system, so that polarized images I 'of the object scene are acquired under four angles of 0 degrees, 45 degrees, 90 degrees and 135 degrees'0、I′45、I′90、I′135。
S12: utilizing a threshold segmentation algorithm to carry out segmentation on the polarized image I'0、I′45、I′90、I′135The target object and the background in the image are segmented to obtain a polarization image I after threshold segmentation0、I45、I90、I135。
Specifically, in order to reduce the amount of calculation, the acquired polarized image of the target object scene and the scene depth information need to be segmented separately, the target object is separated from the background,the background part is removed, so the present embodiment uses a threshold segmentation algorithm to segment the polarization image object of the object scene from the background, and the polarization images after threshold segmentation are I0、I45、I90、I135。
S2: and acquiring the polarization degree of each pixel point on the surface of the target object in the polarization image.
The method comprises the steps of firstly obtaining light intensity at each pixel point in the polarization image, and then obtaining the maximum value and the minimum value of the light intensity at each pixel point in the polarization image and the polarization phase angle of reflected light by using the light intensity at each pixel point.
Specifically, the light intensity and the rotation angle v of the polarizer in the polarization three-dimensional imaging system (v is an included angle between the transmission axis of the polarizer and the initial position) have the following relationship:
Figure BDA0003548401910000081
wherein u represents the number of the pixel point, and I (u, v) represents the light intensity at the pixel point u when the rotation angle v of the polarizer in the polarization three-dimensional imaging system is provided; I.C. AmaxAnd IminThe maximum light intensity and the minimum light intensity observed by the CMOS camera at the pixel point u are respectively represented by rotating the polaroid for one circle, and phi represents the polarization phase angle of reflected light at the pixel point u, namely the polarization angle corresponding to the maximum light intensity observed by each pixel point. Collecting polarization images under multiple polarization angles, and recording Ii(u) represents the intensity value at each pixel point u of the polarization image collected by the i-th rotating polarizer, and the above formula (1) can be rewritten as follows:
Figure BDA0003548401910000082
wherein, the first and the second end of the pipe are connected with each other,
Figure BDA0003548401910000091
vithe angle of the i-th rotation of the polarizer is shown.
When the polarizer rotates for several timesWhen the number is not less than three, because
Figure BDA0003548401910000092
Rotation angle v of polarization plate in matrixiKnown as matrix IiThe intensity value of each pixel in the acquired polarization image, denoted by (u), is also known, so the coefficient matrix x can be solved, denoted as x ═ x1x2x3]TThus, the maximum light intensity, the minimum light intensity, and the polarization phase angle at each pixel point in the polarization image are:
Figure BDA0003548401910000093
Then, calculating formula by degree of polarization
Figure BDA0003548401910000094
The polarization value at each pixel point can be derived.
S3: and acquiring initial values of azimuth angles and initial values of incidence angles at different pixel points of the target surface according to the polarization images and the polarization degrees.
Specifically, the S3 includes:
s31: and acquiring an initial azimuth value of the pixel point u, wherein the initial azimuth value is equal to a polarization phase angle phi of reflected light of the pixel point u.
In particular, polarized images I of the target at different angles are utilized0、I45、I90And I135According to step S2, the initial value of the azimuth angle of the pixel u can be obtained, i.e. the initial value is equal to the polarization phase angle phi of the reflected light at the pixel u. However, since the polarized image intensities obtained by two rotation angles spaced by 180 ° are the same during the process of rotating the polarizer, there is a 180 ° uncertainty problem between the incident azimuth angle of the target incident light to be reconstructed and the actual incident azimuth angle, that is:
Figure BDA0003548401910000101
wherein Λ represents one value of two of {0, 1}The meta operator, in this embodiment, needs to determine the value of Λ to eliminate the multivalue problem, which will be described in detail below.
S32: the incident angle can be calculated according to the relation between the polarization degree and the incident angle of the incident light on the target surface, and the calculation formula is as follows:
Figure BDA0003548401910000102
Where n represents the refractive index of the target object surface, in this example implementation, the refractive index of the target object surface is typically taken to be 1.5.
S4: and correcting the initial value of the azimuth angle and the initial value of the incidence angle to obtain the corrected azimuth angle and the corrected incidence angle.
Specifically, step S4 of the present embodiment includes:
s41: and correcting the multivalue problem of the initial value of the incidence angle to obtain the corrected incidence angle.
Specifically, the variation relationship between the target reflected light intensity gradient field and the profile is utilized to convert the azimuth angle information of the target object surface into gradient field information, and then the correction process of the azimuth angle multivalue problem in the polarization three-dimensional imaging scene is represented as:
Figure BDA0003548401910000103
GNrepresenting the gradient field variation reference information solved by the target surface intensity information, GpolarRepresenting the gradient field parameters solved using the polarization information of the target reflected light,
Figure BDA0003548401910000104
represents a two-norm operation, if
Figure BDA0003548401910000105
The initial value of the azimuth angle is the corrected azimuth angle, if so
Figure BDA0003548401910000106
And turning the initial value of the azimuth angle by 180 degrees to obtain a corrected azimuth angle.
Specifically, the azimuthal information correction for a target surface micro-bin may be represented by:
Figure BDA0003548401910000111
Wherein, the first and the second end of the pipe are connected with each other,
Figure BDA0003548401910000112
and indicating azimuth information of the corrected target micro surface element (wherein one pixel point on the target surface indicates one micro surface element), and phi indicates a polarization phase angle of reflected light at the pixel point u. Finally, the normal vector information of the micro-surface element of the target surface can be uniquely solved.
S42: and optimizing the initial value of the incidence angle within a preset range adjacent to 90 degrees by using an optimization algorithm to avoid the situation that the tan theta has a maximum value, and obtaining the optimized incidence angle theta.
Specifically, in the following process of obtaining a normal vector, a tan θ parameter needs to be introduced into an expression of the normal vector, which causes a problem that some points are not preferable for an incident angle when the tan θ becomes infinite when the incident angle θ takes a value around 90 °. In view of this, the present embodiment proposes an optimization algorithm, which specifically includes the following:
the optimization algorithm is set as follows:
Figure BDA0003548401910000113
wherein the content of the first and second substances,
Figure BDA0003548401910000114
f (x) is the initial value of the input incident angle, and takes 3 values to be respectively marked as T1，T0，T*Wherein, T0Approaches to T*。
Then optimizedThe incident angles are:
Figure BDA0003548401910000115
wherein the content of the first and second substances,
Figure BDA0003548401910000116
in the present embodiment, T1Selecting 85.5 degrees and T*Select 85 DEG, T0And selecting 84.5 degrees, and after all the initial values of the incidence angles are optimized by the algorithm, the original value of the initial value of the incidence angle between 85 degrees and 90 degrees is reduced to 85 degrees, and the original angle is kept unchanged around and below 85 degrees. Therefore, the algorithm effectively solves the following problem of the inadaptability of the normal vector part points.
S5: and constructing a normal vector for each pixel point on the surface of the target by using the corrected azimuth angle and the corrected incidence angle.
Specifically, according to the corrected azimuth angle and incidence angle, the component in the depth direction, i.e., the z-axis direction, is unitized to construct a normal vector:
Figure BDA0003548401910000121
wherein, θ and
Figure BDA0003548401910000122
the optimized incident angle and the corrected azimuth angle are respectively used for the incident light on the target surface.
S6: and reconstructing the three-dimensional contour of the target by utilizing normal vector integration to obtain a surface height function of the target.
Specifically, after obtaining the normal vector of the target surface constructed through correction, the target surface is reconstructed through surface integration, and the normal vector is represented by a gradient field, where the normal vector is represented as:
Figure BDA0003548401910000123
where z (u) ═ f (x, y) denotes the height of the target surface. For a globally continuous normal gradient field, a global or local integration method is usually adopted, wherein the global integration has better robustness to noise and the reconstructed surface is smoother. However, for a general target surface, there are discrete non-integrable regions, and a three-dimensional curved surface cannot be reconstructed directly by integration. At this time, the distance function between the normal gradient field and the continuous integrable micro-bin can be defined by projecting the non-integrable region in the target normal vector gradient field information to the integrable surface slope subspace:
D{(p,q),(zx,zy)}＝∫∫|zx-p|2+|zy-q|2dxdy (10)
Wherein p and q represent the gradient fields of the normal vector of the target micro-surface element in the x and y directions, respectively, and zxAnd zyRepresenting the partial derivatives of the surface function z (u) in the x and y directions, respectively.
When the above equation is solved to the minimum, the normal vector gradient field and the integrable micro-bin are orthogonally projected. The surface function z (u) may be represented as a linear combination of a series of orthogonal basis functions ψ (x, y; w) ((w))x,wy) Representing a two-dimensional index. The surface function can be expressed as:
Figure BDA0003548401910000131
wherein C (w) is an expansion coefficient of z (u). The surface function gradient field is then expressed as follows:
Figure BDA0003548401910000132
Figure BDA0003548401910000133
wherein p isg(u) gradient field of the surface function in the x-direction, qg(u) represents the gradient field of the surface function along the y-axis,
Figure BDA0003548401910000134
and
Figure BDA0003548401910000135
representing the optimal set of coefficients in the x and y directions, respectively. Selecting a Fourier coefficient expansion with perfect orthogonal basis, the basis function can be characterized as:
Figure BDA0003548401910000136
where M and N represent the dimensions of the target two-dimensional image along the x-axis and along the y-axis, respectively. The surface function gradient field is then expressed as follows:
Figure BDA0003548401910000137
Figure BDA0003548401910000138
where α, β represent the fourier coefficients of the discrete micro-operators in the x and y directions, respectively.
Substituting the expressions (12), (13) and (14) into the expression (11), namely establishing the relation between the discrete gradient field information in the space domain and the surface function information in the Fourier domain to reconstruct the surface function, constructing a polarized three-dimensional model of the surface of the object, wherein the calculation formula is as follows:
Figure BDA0003548401910000139
Wherein F { } and F-1{ } denotes discrete fourier transform and inverse transform, respectively.
S7: and combining the calibration of a camera in the polarization three-dimensional imaging system and the surface function to obtain the absolute depth information of the target.
In order to characterize the absolute depth of the target, this embodiment combines with a camera calibration method, and the camera calibration is used to determine the correlation between the three-dimensional geometric position of a certain point on the surface of the spatial target and its corresponding point in the image, i.e. the change matrix of the target in the world coordinate system, the camera coordinate system, the image coordinate system, and the pixel coordinate system can be found, as shown in fig. 3.
The specific camera calibration process mainly comprises the following steps:
(a) preparing a calibration picture
The calibration picture is shot by using the calibration plate at different positions, different angles and different postures, and at least 3 pictures are shot, preferably 10-20 pictures. The calibration plate uses a chessboard pattern formed by alternate black and white rectangles.
(b) Extracting angular point information from each calibration picture
The corner points are inner corner points on the calibration plate, which are not in contact with the edges of the calibration plate, and are extracted by using the find Chessboard Corners function.
(c) For each calibration picture, further extracting sub-pixel information
And sub-pixel information is further extracted on the basis of the preliminarily extracted corner information by using a cornerSubPix function, so that the calibration error of the camera is reduced.
(d) Drawing found internal angle points on the chessboard calibration chart
Drawing successfully calibrated corner points by using a drawChessboardCorres function.
(e) Camera calibration
Calibrating by using a calibretacarama function, and calculating the internal and external parameters of the camera by calculating the internal and external parameter coefficients of the camera through the steps, wherein the internal parameters are as follows:
Figure BDA0003548401910000151
the external reference is as follows:
Figure BDA0003548401910000152
wherein d isxAnd dyRespectively representing an image on the abscissa and on the ordinateThe distance, in mm, is represented by the elements, f represents the camera focal length, R represents a third order rotation matrix, and T represents a third order translation matrix.
The change from the world coordinate system to the pixel coordinate system is represented by:
Figure BDA0003548401910000153
wherein (X)wYwZw) And the coordinates of the target world coordinate system obtained by calibrating the camera are represented.
Further, the surface function z (u) reconstructed in the unit of the depth direction component in step S6 has a certain scale change relationship with the coordinates of the target in the world coordinate system, that is:
Figure BDA0003548401910000154
wherein (X)rYrZr) For the three-dimensional coordinates of the target reconstructed by the surface function Z (u), the scale change factor tau can be obtained by the internal and external parameters and the corresponding coordinates in the pixel coordinate system through the belt formula (16), so that the three-dimensional world coordinates of the target can be represented, and the world coordinate system is changed to the camera coordinate system through the external parameter matrix to obtain the corresponding point on the camera coordinate system, wherein the coordinates are (X) and (u) cYcZc) Finally, the absolute depth d of each target point can be obtainedabs：
Figure BDA0003548401910000161
Wherein d isabs(u) represents the absolute depth of the target at pixel point u. It should be noted that, when the camera is far away from Δ d along the depth direction, the scale change factor τ does not change, but the translation matrix T in the external reference matrix changes correspondingly, and the change is:
Figure BDA0003548401910000162
the absolute depth information will change accordingly. That is to say, the polarization three-dimensional model constructed by the polarization three-dimensional imaging method in the embodiment of the present invention reconstructs a three-dimensional surface conforming to the actual observation change along with the change of the target detection distance, and effectively shows the high-frequency change of the target.
In summary, the polarization three-dimensional imaging method according to the embodiment of the present invention re-characterizes the normal vector of the target surface by using the component of the normal vector of the target surface along the depth direction as a unit, obtains the change relation function by combining the camera calibration and other means based on the change relation determined by the three-dimensional model reconstructed by the normal vector of the target and the actual detection distance of the target, and further directly characterizes the absolute depth information of the target in the reconstructed polarization three-dimensional imaging model, breaks through the limitation that the display depth of the traditional polarization three-dimensional imaging is the relative depth, and provides a direction for the diversification of the functions of the future polarization three-dimensional camera.
A further embodiment of the present invention provides a storage medium having stored therein a computer program for performing the steps of the polarized three-dimensional imaging method capable of characterizing an absolute depth of an object described in the above embodiments. Yet another aspect of the present invention provides an electronic device, which includes a memory and a processor, where the memory stores a computer program, and the processor, when calling the computer program in the memory, implements the steps of the polarized three-dimensional imaging method capable of characterizing an absolute depth of a target as described in the above embodiments. Specifically, the integrated module implemented in the form of a software functional module may be stored in a computer readable storage medium. The software functional module is stored in a storage medium and includes several instructions to enable an electronic device (which may be a personal computer, a server, or a network device) or a processor (processor) to execute some steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (10)

1. A polarized three-dimensional imaging method capable of characterizing the absolute depth of an object, comprising:
acquiring polarization images of a target under different polarization angles by using a polarization three-dimensional imaging system;
obtaining the polarization degree of each pixel point on the surface of the target object in the polarization image;
acquiring azimuth angle initial values and incidence angle initial values at different pixel points of the target surface according to the polarization images and the polarization degrees;
correcting the initial value of the azimuth angle and the initial value of the incidence angle to obtain a corrected azimuth angle and an incidence angle;
constructing a normal vector for each pixel point on the surface of the target by using the corrected azimuth angle and the corrected incidence angle;
reconstructing a three-dimensional contour of the target by utilizing normal vector integration to obtain a surface height function of the target;
And combining the calibration of a camera in the polarization three-dimensional imaging system and the surface function to obtain the absolute depth information of the target.
2. The method of claim 1, wherein acquiring polarized images of the target at different polarization angles using a polarized three-dimensional imaging system comprises:
acquiring reflected light of the surface of the target object by using a polarized three-dimensional imaging system, and respectively acquiring polarized images I 'of a target object scene under four polarization angles of 0 degrees, 45 degrees, 90 degrees and 135 degrees'0、I′45、I′90、I′135；
Utilizing a threshold segmentation algorithm to carry out segmentation on the polarized image I'0、I′45、I′90、I′135The target object and the background in the image are segmented to obtain a polarization image I after threshold segmentation0、I45、I90、I135。
3. The method of claim 1, wherein obtaining the degree of polarization at each pixel point on the surface of the target object in the polarization image comprises:
acquiring light intensity at each pixel point in the polarization image;
acquiring the maximum light intensity value, the minimum light intensity value and the polarization phase angle of reflected light at each pixel point in the polarization image by using the light intensity at each pixel point;
and obtaining the polarization value at each pixel point by using the maximum light intensity value and the minimum light intensity value.
4. The method of claim 3, wherein obtaining initial azimuth and initial incidence angles at different pixel points on the surface of the target according to the polarization image and the polarization degree comprises:
obtaining an initial azimuth value of a pixel point u, wherein the initial azimuth value is equal to a polarization phase angle of reflected light of the pixel point u;
and obtaining an initial incident angle value of the incident light at each pixel point according to the relation between the polarization degree and the incident angle of the incident light on the target surface.
5. The method of polarized three-dimensional imaging capable of characterizing absolute depth of a target of claim 3, wherein correcting the initial value of azimuth angle and the initial value of angle of incidence comprises:
correcting the multivalue problem of the initial value of the incidence angle to obtain a corrected incidence angle, wherein the correction formula is expressed as:
Figure FDA0003548401900000021
wherein G isNRepresenting the gradient field variation reference information solved by the target surface intensity information, GpolarRepresenting the gradient field parameters solved using the polarization information of the target reflected light,
Figure FDA0003548401900000022
represents a two-norm operation, if
Figure FDA0003548401900000023
The initial value of the azimuth angle is the corrected azimuth angle, if so
Figure FDA0003548401900000024
Then the initial value of the azimuth angle is turned for 180 degrees to obtain a corrected azimuth angle;
and optimizing the initial value of the incidence angle within a preset range adjacent to 90 degrees by using an optimization algorithm to avoid the situation that the tan theta has a maximum value, and obtaining the optimized incidence angle theta.
6. The method of polarized three-dimensional imaging capable of characterizing absolute depth of an object of claim 5, wherein the optimization algorithm is:
Figure FDA0003548401900000031
wherein, the first and the second end of the pipe are connected with each other,
Figure FDA0003548401900000032
f (x) is the initial value of the input incident angle, and takes 3 values to be respectively marked as T1，T0，T*Wherein, T0Approach to T*；
The optimized incident angle is obtained as follows:
Figure FDA0003548401900000033
wherein the content of the first and second substances,
Figure FDA0003548401900000034
7. the method of claim 1, wherein constructing a normal vector for each pixel on the surface of the target using the corrected azimuth and incidence angle comprises:
according to the corrected azimuth angle and the corrected incidence angle, unitizing the depth direction components, and constructing a normal vector:
Figure FDA0003548401900000035
wherein, θ and
Figure FDA0003548401900000036
the optimized incident angle and the corrected azimuth angle are respectively used for the incident light on the target surface.
8. The polarized three-dimensional imaging method capable of characterizing the absolute depth of the target according to claim 1, wherein obtaining the absolute depth information of the target by combining the calibration of the camera in the polarized three-dimensional imaging system and the surface function comprises:
Obtaining the change matrix of the pixel point coordinate of the target surface in the world coordinate system, the camera coordinate system, the image coordinate system and the pixel coordinate system according to the camera calibration, and obtaining the coordinate (X) of the target surface in the world coordinate systemw Yw Zw)；
Establishing the coordinates of the target in the world coordinate system and the three-dimensional coordinates (X) reconstructed by the surface function Z (u)r Yr Zr) In relation to (2)
Figure FDA0003548401900000041
Calculating to obtain a scale change factor tau;
obtaining the coordinates (X) of the target in the camera coordinate system according to the coordinates of the target in the world coordinate systemc Yc Zc) And obtaining the absolute depth d of each point of the targetabs：
Figure FDA0003548401900000042
Wherein d isabs(u) represents the absolute depth of the target at pixel point u.
9. A storage medium, characterized in that a computer program is stored in the storage medium for performing the steps of the method of polarized three-dimensional imaging capable of characterizing the absolute depth of an object according to any one of claims 1 to 8.
10. An electronic device, comprising a memory in which a computer program is stored and a processor, wherein the processor, when calling the computer program in the memory, implements the steps of the method of polarized three-dimensional imaging capable of characterizing the absolute depth of an object according to any one of claims 1 to 8.
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