Highly efficient three-dimensional image acquisition method based on multi-mode composite encoding and epipolar constraint

Patent metadata

Field	Value
Publication number	US-2020128180-A1
Application number	US-201816496845-A
Country	US
Kind code	A1
Filing date	Feb 26, 2018
Priority date	Mar 24, 2017
Publication date	Apr 23, 2020
Grant date	—

Abstract

A highly efficient three-dimensional image acquisition method based on multi-mode composite encoding and epipolar constraint, respectively using a fast imaging mode or a high-precision imaging mode, wherein in the fast imaging mode, two phase maps having different frequencies are obtained by four stripe gratings, and a high-frequency absolute phase is obtained by means of the epipolar constraint and a left-right consistency check, and the three-dimensional image is obtained by means of a mapping relationship between the phase and three-dimensional coordinates; and in the high precision imaging mode, two phases having different frequencies are obtained by means of N+2 stripe gratings, a low-frequency absolute phase is obtained by the epipolar constraint, and the unwrapping of a high-frequency phase is assisted by means of the low-frequency absolute phase, so as to obtain the high-frequency absolute phase, and finally, the three-dimensional image is obtained by the mapping relationship between the phase and the three-dimensional coordinates. In this way, the imaging efficiency is ensured, and the imaging precision is improved.

First claim

1 . A highly efficient three-dimensional image acquisition method based on multi-mode composite encoding and epipolar constraint is characterized in that a fast imaging mode or a high-precision imaging mode is used respectively, wherein in the fast imaging mode, two phase maps having different frequencies are obtained by four stripe gratings, and a high-frequency absolute phase is obtained by means of the epipolar constraint and a left-right consistency test, and the three-dimensional image is obtained by means of a mapping relationship between the phase and three-dimensional coordinates; and in the high precision imaging mode, two phases having different frequencies are obtained by means of N+2 stripe gratings, a low-frequency absolute phase is obtained by the epipolar constraint, and the unwrapping of a high-frequency phase is assisted by means of the low-frequency absolute phase, so as to obtain the high-frequency absolute phase, and finally, the three-dimensional image is obtained by the mapping relationship between the phase and the three-dimensional coordinates.

2 . According to claim 1 , The highly efficient three-dimensional image acquisition method based on multi-mode composite encoding and the epipolar constraint is characterized in that the specific steps of the fast imaging method are as follows:
step one, imaging system calibration; step two, generating, projecting and collecting four dual-frequency grating fringes; step three, analyzing the grating fringes collected by left camera and right camera respectively so as to obtain a set of high frequency phases and a set of low frequency phases; step four, searching for each point on the high frequency phase map of the left camera by using the epipolar constraint, that is, the corresponding points of the original point in space, and removing some error points with depth constraint; step five, projecting the remaining spatial corresponding points onto the high-frequency and low-frequency phase diagrams of the right camera, and determining the final corresponding point by the phase difference between the original points and the corresponding points, so as to obtain a high-frequency absolute phase; step six, acquiring a three-dimensional image according to the absolute phase, so as to realize efficient and precise acquisition of three-dimensional images of dynamic scenes.

3 . According to claim 2 , the highly efficient three-dimensional image acquisition method based on multi-mode composite encoding and the epipolar constraint is characterized in that the imaging system in step one comprises a computer, a left camera, a right camera, and a projector, wherein the left camera ,the right camera and the projector are respectively connected to the computer through data lines, and the projector is connected with the left camera and the right camera through trigger lines; the imaging system is calibrated so as to obtain calibration parameters of the left camera, the right camera and the projector in world coordinate system, wherein the calibration parameters comprise a scaling parameter, a translation parameter, a rotation parameter and a distortion parameter between the pixel coordinate system and the world coordinate system.

4 . According to claim 2 , the highly efficient three-dimensional image acquisition method based on multi-mode composite encoding and the epipolar constraint is characterized by the second step wherein the four dual-frequency grating fringes generated by the computer through MatLab are two sinusoidal stripe gratings and two triangular wave stripe gratings, and the stripe gratings are as follows:
I 1 ( x, y ) =A ( x, y ) +B ( x, y )sin [π F H (2 x/W− 1)]
I 2 ( x,y ) =A ( x, y ) +B ( x, y )cos [π F H (2 x/W− 1)]
I 3 ( x,y ) =A ( x, y ) +B ( x, y )tri [(2 F I. x/W− 1)] I 4 ( x,y ) =A ( x, y )− B ( x, y )tri [(2 F I. x/W− 1)]
where I 1 (x, y) represents the intensity of the grating fringe at the pixel coordinates (x, y) of the generated image, i=1,2,3,4 , representing the i-th grating fringe image. A is the image DC component, B is the amplitude, and tri is the triangular wave function with threshold interval [−1, 1], F H , F I. is respectively the number of fringe periods included in I 1 , I 2 and I 3 , I 4 , W is the pixel width of the entire grating fringe image, A=B=127.5, the values for F H , F l I. are respectively 64 and 9, and the range of values for x is 0 to W−1: the gratings are synchronously captured by the left camera and the right camera after being projected by the projector, wherein the grating fringes collected by the left camera are as follows:
I 1 c ( x c , y c )=α( x c , y c )[ A ( x c , y c )+ B ( x c , y c )sin Φ H ( x c , y c )]+α( x c , y c )β 1 ( x c , y c )+β 2 ( x c , y c )

I 2 c ( x c , y c )=α( x c , y c )[ A ( x c , y c )+ B ( x c , y c )cos Φ H ( x c ,y c )]+α( x,y )β 1 ( x c , y c )+β 2 ( x c , y c )

I 3 x( c , y c )=α( x c , y c )[ A ( x c , y c )+ B ( x c , y c )Φ I. ( x c , y uc )]+α( x c , y c )β 1 ( x c , y c )+β 2 ( x c , y c )

I 4 ( x c y c )=α( x c , y c )[ A ( x c , y c )− B ( x c , y c )Φ I. ( x c , y c )]+α( x c , y c )β 1 ( x c , y c )+β 2 ( x c , y c )

where I 1 c (x c , y c ) is the grating fringe image actually captured by the left camera, i=1,2,3,4. (x) is the pixel coordinates of the image captured by the camera, and α is the surface reflectance of the measured object, β c is the reflected ambient light, β 2 is the ambient light directly into the camera, Φ H (x c , y c ) is the phase included in the grating fringe diagramI 1 c and the grating fringe diagram I 2 c , Φ l (x c , y c ) is the phase included in the grating fringe diagram I 3 c and the grating fringe diagram I 4 c ; assuming
A c =α( x c , y c ) A ( x c , y c )+α( x x , y c )β 1 ( x c , y c )+β 2 ( x c , y c ), B c =α( x c , y c ) B ( x c , y c ),

and omiting (x c , y c ) the above four equations can be rewritten as:
I 1 c =A c +B c sin Φ H

I 2 c =A c +B c cos Φ H

I 3 c =A c +B c Φ I.

I c c =A c −B c Φ I.

the acquisition process of the right camera is the same as the acquisition process of the left camera.

5 . According to claim 2 , the highly efficient three-dimensional image acquisition method based on multi-mode composite encoding and the epipolar constraint is characterized by the third step wherein the grating fringes collected by left camera and right camera respectively are analyzed so as to obtain a set of high frequency phases and a set of low frequency phases, where the phases of the left camera is as follows:

φ
H

=

tan

-
1



2


I
1
c

-

I
3
c

-

I
4
c

Assignees

• Univ Nanjing Sci & Tech

Inventors

• Chen Qian
• Zuo Chao
• Feng Shijie
• Sun Jiasong
• Zhang Yuzhen
• Gu Guohua

Classifications

• H04N13/239

  using two two-dimensional [2D] image sensors having a relative position equal to or related to the interocular distance (H04N13/243 takes precedence) · CPC title

• G01B11/2545 Primary

  with one projection direction and several detection directions, e.g. stereo · CPC title

• H04N13/246

  Calibration of cameras · CPC title

• G01B11/254

  Projection of a pattern, viewing through a pattern, e.g. moiré · CPC title

• H04N5/23245 Primary

  Electricity · mapped topic