CN109059800B - Light source position calibration method of three-dimensional reconstruction device - Google Patents
Light source position calibration method of three-dimensional reconstruction device Download PDFInfo
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Abstract
The invention provides a light source position calibration method of a three-dimensional reconstruction device, which comprises a light source group, a camera, a controller, a plane template and an image processor, wherein the light source position calibration of the three-dimensional reconstruction device comprises three links.
Description
Technical Field
The invention relates to the technical field of three-dimensional reconstruction correlation, in particular to a light source position calibration method of a three-dimensional reconstruction device.
Background
Nowadays, the three-dimensional reconstruction device is widely applied to production practice and daily life. At present, a common three-dimensional reconstruction method is to estimate the normal vector of the surface of an object through the gray level difference of the object under different illumination conditions, and has the advantages of outstanding recovery capability for texture details, high calibration requirement for light source parameters, and influence of the installation error of a light source and a camera on the reduction accuracy, so that a light source calibration method which uses the influence of the installation error of the light source and the camera on the reduction accuracy needs to be designed.
Disclosure of Invention
The technical problem is as follows: in order to solve the above problems, the present invention provides a method for calibrating a light source position of a three-dimensional reconstruction apparatus, which includes a light source set, a camera, a controller, a planar template and an image processor, and can reduce the influence of the installation error of the light source and the camera on the reconstruction accuracy,
the technical scheme is as follows: the invention relates to a light source position calibration method of a three-dimensional reconstruction device, wherein the three-dimensional reconstruction device comprises a light source group, a camera, a controller, a plane template and an image processor, wherein the camera is positioned in the middle, the light source group comprises a first light source, a second light source, a third light source and a fourth light source which are respectively positioned on 4 sides of the camera, and the plane template is positioned above the camera and the light source group;
the light source position calibration method of the three-dimensional reconstruction device comprises a shooting link, a preparation link and an operation link; in the preparation link, the shot plane image is grayed, and the offset coordinate when the error coefficient obtained in the operation link takes the minimum value is recorded as the optimum coordinate; if the detection step length is larger than 2 pixels after the operation link is finished, deleting the lattice points in the detection grid, the lattice point distance of which is superposed with the optimal coordinate and is larger than the detection step length; halving the detection step length and adding new lattice points in the detection grid; after the grid points are added to the detection grid, the distance between adjacent grid points is a detection step length, and the area of the detection grid is not increased; then repeating the operation link; and after the operation link is finished, if the detection step length is less than 2 pixels, recording the optimal coordinate as an optimal offset coordinate.
Wherein:
the shooting link is as follows: the controller controls all light sources in the light source group to be sequentially lightened, and immediately controls the camera to shoot the plane template placed in front of the light source group and the camera after each light source is lightened, and a group of pictures obtained are called as a first plane image.
The preparation link establishes a three-dimensional rectangular coordinate system by taking the plane of the first plane image as an xy plane and the upper left corner of the first plane image as an origin; setting detection step length in the image processor, establishing a detection grid parallel to an xy plane along the directions of x and y axes, wherein the distance between adjacent grid points is the detection step length, the z axis of the three-dimensional rectangular coordinate system passes through one of the grid points, the position of a camera is coplanar with the detection grid, and the projection of the detection grid to the z =0 plane is totally positioned in the first plane image.
In the operation link, the image processor sets the (x, y) coordinates of the offset coordinates as the (x, y) coordinates of each grid point in the detection grid in sequence, and sets the z coordinates of the offset coordinates as the distance between the camera and the plane template; carrying out three-dimensional reconstruction on the plane template according to a three-dimensional reconstruction algorithm built in the image processor and the first plane image to obtain a first plane model; vertically projecting the first plane model to an x-y plane, and uniformly dividing a projection area into error grids with the size of m x n along x and y axes; the collection of points in the first plane model, which have the same (x, y) coordinates as the error grid points, is recorded as a first point cloud;
in the operation link, the image processing unit fits the first point cloud into a plane in the three-dimensional rectangular coordinate system, and the plane is called as a second plane; calculating the square sum of the distances between all the points in the first point cloud and the second plane, and the square sum is called as an error coefficient; and comparing error coefficients obtained when the offset coordinates are positioned at each grid point in the detection grid, recording the minimum value of the error coefficients, and recording the offset coordinates when the error coefficients take the minimum value as the optimal coordinates.
The light source group comprises 4 light sources and is arranged at the middle point of 4 sides of a square with the side length s; the camera (2) is arranged at the center of the square and the direction of the optical axis of the camera is vertical to the square; when shooting, only one of the light sources is in a lighting state; the brightness of the individual light sources is the same and the distance between each other can be measured accurately.
The image processing unit calculates the first plane model by the gray scale information in the first plane image, the distance between the light sources in the light source group, the coordinates of the camera and the distance between the camera and the plane template.
The first plane image comprises 4 pictures, 4 gray-scale images are obtained after the 4 pictures are grayed, and pixels at the same position in the 4 gray-scale images correspond to the same point in the plane model; setting the size of the gray scale image as m pixel by n pixel, taking the pixel at the upper left corner of the gray scale image as an origin, horizontally and rightwards as a y-axis direction, vertically and downwards as an x-axis direction, and establishing a rectangular coordinate system in the direction facing the camera as the positive direction of a z axis; the length of 1 mm in the plane template corresponds to r pixels in the gray scale image, the distance between the camera and the plane template is d mm, and the camera coordinate in the rectangular coordinate system is (m/2, n/2, d r);
in the gray-scale map as described above,
a gray matrix representing the k-th gray map,
the coordinates of the pixel of the ith row and the jth column in the rectangular coordinate system are represented,
represents a direction vector from the kth light source to the pixel of the jth row and the jth column in the gray scale image,
a surface normal vector of a point, corresponding to the pixel of the ith row and the jth column in the gray scale image, on the plane template in the rectangular coordinate system is represented; according to the lambertian reflection law, when the reflected light of the planar template is diffuse reflection, the following equation exists for any point of the surface of the planar template:
solving the equation to obtain
And then solving the gradient of any point on the surface of the plane template; and integrating the gradient to calculate the z coordinate of any point on the surface of the planar template, namely restoring the first planar model.
The center of the light source group coincides with the optimal offset coordinate.
Has the advantages that: the invention provides a light source position calibration method of a three-dimensional reconstruction device, which adjusts light source position parameters in an algorithm through a built-in three-dimensional reconstruction algorithm, performs three-dimensional reconstruction on a plane template by utilizing a group of pictures shot by taking the plane template as an object in a shooting link, fits a reconstruction result into a plane, calculates the difference between the reconstruction result and the plane, determines the optimal light source position parameters, can effectively correct the influence of errors in the installation process of the device on the reconstruction result, and improves the quality of the three-dimensional reconstruction.
Drawings
Fig. 1 is a schematic mechanical structure diagram of a three-dimensional reconstruction apparatus for light source position calibration according to an embodiment of the present application;
the reference numbers illustrate:
the light source system comprises a plane template 1, a camera 2, a first light source 3, a second light source 4, a third light source 5 and a fourth light source 6.
Detailed Description
The invention is described in further detail below with reference to the following detailed description and accompanying drawings:
the invention provides a light source position calibration method of a three-dimensional reconstruction device, which comprises a light source group, a camera, a controller, a plane template and an image processor, wherein the light source position calibration of the three-dimensional reconstruction device comprises three links. The following describes embodiments of the present application in further detail with reference to the accompanying drawings.
Referring to fig. 1, the mechanical structure of the present application includes a planar template 1, a camera 2, a first light source 3, a second light source 4, a third light source 5, and a fourth light source 6.
The invention relates to a light source position calibration method of a three-dimensional reconstruction device, which comprises a light source group, a camera, a controller, a plane template and an image processor, and is characterized in that: the working state of the device comprises a shooting link, a preparation link and an operation link;
the shooting link is as follows:
in the shooting link, the controller controls all light sources in the light source group to be sequentially lightened, and immediately controls the camera to shoot the plane template placed in front of the light source group and the camera after each light source is lightened, and a group of pictures obtained are called as first plane images;
the preparation process comprises the following steps:
in the preparation link, a three-dimensional rectangular coordinate system is established by taking the plane where the first plane image is located as an x-y plane and taking the upper left corner of the first plane image as an origin; setting a suitable detection step size in said image processor, establishing a detection grid parallel to the (x, y) plane along the x, y axis direction, wherein the distance between adjacent grid points is said detection step size, the z axis of said three-dimensional rectangular coordinate system passes through one of said grid points, said camera position is coplanar with said detection grid, and the projection of said detection grid to the z =0 plane is entirely within said first plane image;
the operation link is as follows:
in the operation link, the image processor sequentially sets the (x, y) coordinates of the offset coordinates as the (x, y) coordinates of each grid point in the detection grid, and sets the z coordinates of the offset coordinates as the distance between the camera and the plane template; carrying out three-dimensional reconstruction on the plane template according to a three-dimensional reconstruction algorithm built in the image processor and the first plane image to obtain a first plane model; vertically projecting the first plane model to an x-y plane, and uniformly dividing a projection area into error grids with the size of m x n along x and y axes; the collection of points in the first plane model, which have the same (x, y) coordinates as the error grid points, is recorded as a first point cloud;
and in the operation link, the image processing unit fits the first point cloud into a plane in the three-dimensional rectangular coordinate system, and the plane is called as a second plane. Calculating the square sum of the distances between all the points in the first point cloud and the second plane, and the square sum is called as an error coefficient; comparing error coefficients obtained when the offset coordinates are located at each grid point in the detection grid, recording the minimum value of the error coefficients, and recording the offset coordinates when the error coefficients take the minimum value as the optimal coordinates;
if the detection step length is larger than 2 pixels after the operation link is finished, deleting the lattice points in the detection grid, the lattice point distance of which is superposed with the optimal coordinate and is larger than the detection step length; halving the detection step length and adding new lattice points in the detection grid; the distance between adjacent grid points of the detection grid after the grid points are added is a detection step length, and the area of the detection grid is not increased; then repeating the operation link;
and after the operation link is finished, if the detection step length is less than 2 pixels, recording the optimal coordinate as an optimal offset coordinate.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, but any modifications or equivalent variations made according to the technical spirit of the present invention are within the scope of the present invention as claimed.
Claims (5)
1. A light source position calibration method of a three-dimensional reconstruction device is characterized by comprising the following steps: the three-dimensional reconstruction device comprises a light source group, a camera (2), a controller, a plane template (1) and an image processor, wherein the camera (2) is located in the middle, the light source group comprises a first light source (3), a second light source (4), a third light source (5) and a fourth light source (6) which are respectively located on 4 sides of the camera (2), and the plane template (1) is located above the camera (2) and the light source group;
the light source position calibration method of the three-dimensional reconstruction device comprises a shooting link, a preparation link and an operation link; in the preparation link, the shot plane image is grayed, the light source position parameters are adjusted through a built-in three-dimensional reconstruction algorithm, a group of pictures shot by taking the plane template as an object in the shooting link are utilized to carry out three-dimensional reconstruction on the plane template, and the optimal light source position parameters are determined through the reconstruction result;
the offset coordinate when the error coefficient is the minimum value obtained in the operation link is recorded as the optimal coordinate; if the detection step length is larger than 2 pixels after the operation link is finished, deleting the lattice points, the distance of which is larger than the detection step length, of the lattice points in the detection grid, which are overlapped with the optimal coordinates; halving the detection step length and adding new lattice points in the detection grid; the distance between adjacent grid points of the detection grid after the new grid point is added is a detection step length, and the area of the detection grid is not increased; then repeating the operation link; after the operation link is finished, if the detection step length is less than 2 pixels, recording the optimal coordinate as an optimal offset coordinate;
the shooting link is as follows: the controller controls all light sources in the light source group to be sequentially lightened, and immediately controls the camera to shoot the plane template placed in front of the light source group and the camera after each light source is lightened, and a group of obtained photos are called as a first plane image;
the preparation link establishes a three-dimensional rectangular coordinate system by taking the plane where the first plane image is located as an xy plane and the upper left corner of the first plane image as an origin; setting a detection step length in an image processor, establishing a detection grid parallel to an xy plane along the directions of x and y axes, wherein the distance between adjacent grid points is the detection step length, a z axis of a three-dimensional rectangular coordinate system passes through one of the grid points, the position of a camera is coplanar with the detection grid, and the projection of the detection grid to the z-0 plane is totally positioned in the first plane image;
in the operation link, the image processor sets the (x, y) coordinates of the offset coordinates as the (x, y) coordinates of each grid point in the detection grid in sequence, and sets the z coordinates of the offset coordinates as the distance between the camera and the plane template; carrying out three-dimensional reconstruction on the plane template according to a three-dimensional reconstruction algorithm built in the image processor and the first plane image to obtain a first plane model; vertically projecting the first plane model to an x-y plane, and uniformly dividing a projection area into error grids with the size of m x n along x and y axes; the collection of points in the first plane model, which have the same (x, y) coordinates as the error grid points, is recorded as a first point cloud;
in the operation link, the image processing unit fits the first point cloud into a plane in a three-dimensional rectangular coordinate system, and the plane is called as a second plane; calculating the square sum of the distances between all points in the first point cloud and the second plane, and the square sum is called as an error coefficient; comparing error coefficients obtained when the offset coordinates are located at each grid point in the detection grid, recording the minimum value of the error coefficients, and recording the offset coordinates when the error coefficients take the minimum value as the optimal coordinates;
the center of the light source group coincides with the optimal offset coordinate.
2. The method for calibrating the light source position of the three-dimensional reconstruction device according to claim 1, wherein: the light source group comprises 4 light sources and is arranged at the middle point of 4 sides of a square with the side length s; the camera (2) is arranged at the center of the square and the direction of the optical axis of the camera is vertical to the square; when shooting, only one of the light sources is in a lighting state; the brightness of the individual light sources is the same and the distance between each other can be measured accurately.
3. The method for calibrating the light source position of the three-dimensional reconstruction device according to claim 1, wherein: the image processing unit calculates a first plane model according to the gray information in the first plane image, the distance between the light sources in the light source group, the coordinate of the camera and the distance between the camera and the plane template.
4. The method for calibrating the light source position of the three-dimensional reconstruction device according to claim 1, wherein: the first plane image comprises 4 pictures, 4 gray-scale images are obtained after the 4 pictures are grayed, and pixels at the same position in the 4 gray-scale images correspond to the same point in the plane model; setting the size of a gray scale image as m x n pixels, taking the pixel at the upper left corner of the gray scale image as an origin, horizontally and rightwards as a y-axis direction, vertically and downwards as an x-axis direction, and establishing a rectangular coordinate system in the direction facing the camera as the positive direction of a z-axis; the length of 1 mm in the plane template corresponds to r pixels in the gray scale map, the distance between the camera and the plane template is d mm, and the camera coordinate in the rectangular coordinate system is (m/2, n/2, d r).
5. The method for calibrating the light source position of the three-dimensional reconstruction device according to claim 4, wherein: in the gray scale image, EkijA gray matrix representing the kth gray map, k being 1,2,3,4, PijThe coordinates of the pixel of the ith row and the jth column in the rectangular coordinate system are shown,
a direction vector representing the direction from the kth light source to the pixel at the ith row and jth column in the gray-scale map, k is 1,2,3,4,
representing the surface normal vector of the corresponding point of the pixel of the ith row and the jth column in the gray scale image on the plane template in a rectangular coordinate system; according to the lambertian reflection law, when the reflected light of the planar template is diffuse reflection, the following equation exists for any point of the surface of the planar template:
solving the equation to obtain
Solving the gradient of any point on the surface of the plane template; and integrating the gradient to calculate the z coordinate of any point on the surface of the planar template, namely restoring the first planar model.
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| CN107677216A (en) * | 2017-09-06 | 2018-02-09 | 西安交通大学 | A kind of multiple abrasive particle three-dimensional appearance synchronous obtaining methods based on photometric stereo vision |
| CN207365904U (en) * | 2017-06-01 | 2018-05-15 | 深度创新科技（深圳）有限公司 | Three-dimensional reconstruction apparatus and equipment |
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| FR2822273B1 (en) * | 2001-03-13 | 2003-07-11 | Ge Med Sys Global Tech Co Llc | CALIBRATION PROCESS FOR THE RECONSTRUCTION OF THREE-DIMENSIONAL MODELS FROM IMAGES OBTAINED BY TOMOGRAPHY |
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| JP2014112043A (en) * | 2012-12-05 | 2014-06-19 | Ihi Corp | Stereoscopic shape recognition device and light source position estimation method for stereoscopic shape recognition device |
| CN107194881A (en) * | 2017-03-23 | 2017-09-22 | 南京汇川图像视觉技术有限公司 | A kind of removal image reflex reflector and method based on photometric stereo |
| CN207365904U (en) * | 2017-06-01 | 2018-05-15 | 深度创新科技（深圳）有限公司 | Three-dimensional reconstruction apparatus and equipment |
| CN107657604A (en) * | 2017-09-06 | 2018-02-02 | 西安交通大学 | A kind of polishing scratch three-dimensional appearance original position acquisition methods based near field non-standard light source |
| CN107677216A (en) * | 2017-09-06 | 2018-02-09 | 西安交通大学 | A kind of multiple abrasive particle three-dimensional appearance synchronous obtaining methods based on photometric stereo vision |
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