Patent ID: 11961244
Assignee: NANJING UNIVERSITY OF SCIENCE AND TECHNOLOGY
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  H | IPC G  H

Claim 2:
3. The method according to claim 2, wherein the step 2 comprise the substeps of:
(1) projecting three three-step phase-shifting fringe patterns to the object by the projector, and simultaneously triggering the four cameras to capture the images wherein three-step phase-shifting fringes captured by the first camera is expressed as:

I1C(uC,vC)=AC(uC,vC)+BC(uC,vC)cos(ΦC(uC,vC)),

I2C(uC,vC)=AC(uC,vC)+BC(uC,vC)cos(ΦC(uC,vC)+2π/3),

I3C(uC,vC)=AC(uC,vC)+BC(uC,vC)cos(ΦC(uC,vC)+4π/3),

where (uC, vC) denotes coordinates of a pixel point on the first camera, I1C, I2C, I3C denote the three fringe images captured by the first camera, AC is an average light intensity, BC represents a modulation degree light intensity, and ΦC denotes an absolute phase of the fringe images;
(2) obtaining the wrapped phase of the object
from the three fringe images collected by the first camera according to:, ϕ
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where ϕC (uC, vC) represents the wrapped phase, wherein a relationship between the wrapped phase and the absolute phase is

ΦC(uC,vC)=ϕC(uC,vC)+2kC(uC,vC)π,kC(uC,vC)ε[9,N−1]

where kC represents a fringe order, and N represents a number of fringes;
(3) performing a phase unwrapping by obtaining the absolute phase of the object only through three three-step phase-shifting fringe images, comprising the following steps:
(a) finding N 3D candidate points corresponding to a pixel in the first camera, wherein
for any pixel point oC1 in the first camera, there are N possible absolute phases, and the N possible absolute phases are reconstructed into N 3D candidates by using the 2D to 3D mapping parameters obtained in the step_1 so that wrong 3D candidate points is excluded by ADC technology;
(b) finding the 2D candidate points in the second camera by assuming that a number of excluded 3D candidate points is_N1(0<N1<N), then projecting the 3D candidate points into the second camera through the 3D to 2D mapping parameters_N1_obtained in the step_1 to obtain the corresponding 2D candidate points_N1;
(c) finding the 2D candidate points in the third camera by assuming that a number of remaining 2D candidate points is N2 (0<N2<N1<N), then projecting the 2D candidate points to the third camera through the 2D to 2D mapping parameters obtained in the step_1 to obtain corresponding N2 2D candidates point, checking candidate points for phase consistency with point oC1 in the first camera, and reserving the candidate points with a phase difference within 0.8_rad;
(d) finding the 2D candidate points in the fourth camera, and determine the phase order of a pixel in the first camera by continuing to project the remaining 2D candidate points into the fourth camera for phase consistency check, and retaining candidate points with a phase difference within 1 rad; wherein after three rounds of phase consistency checks, the only correct candidate point is confirmed, and the phase order of point oC1 is also confirmed; and
(e) obtaining the absolute phase of the object and the 3D information under a single viewing angle
by performing the above operations on each pixel in the first camera in parallel in the computer GPU; and reconstructing the high-precision 3D topography information of the object under a single viewing angle through the calibration parameters obtained in the step_1.