Phase-unwrapping Approach Research Based On Dual-frequency Analog Structured Light

Time-encoded structured light 3D measurement technique owns a bright future in vision non-contact 3D measurement field,which can be applied in fields like medical,industry and archaeology.Multi-period analog code structured light has the advantages of high resolution,high sampling rate,and high measuring speed.However,multi-period analog code structured light needs phase unwrapping in order to achieve the 3D measurement.Focused on this problem,we propose a new phaseunwrapping approach based on dual-frequency analog code structured light to achieve an accurate phase unwrapping process for multi-period analog code structured light.Primarily,we introduce the principle of the proposed phase unwrapping approach,and obtain the theoretical model and formula of the proposed approach through mathematical deduction.Furthermore,we implement the error analysis for the proposed approach and give the fault-tolerant range of the proposed approach in the real application.Also,through theoretical analysis,we give the proper period range of the analog code when using the proposed approach.Then,we research on the principles of two categories of multi-period analog code structured light: the phase-shifting approach and the intensity ratio approach.Besides,we research on the specific applications of the two approaches which are the cosinoidal phase-shifting approach and the trapezoid phase-shifting intensity ratio approach.Focused on the two kinds of multi-period analog code structured lights,we design the simulating experiments.With the proposed phase-unwrapping approach,we implement the phase unwrapping experiments on the two multi-period analog code structured lights,and the experimental results verify the validity and the universality of the proposed approach.Finally,we set up the structured light 3D measurement system,and implement the actual experiments for the proposed phase unwrapping approach.First of all,we achieve the calibration of the camera and the projector of the system.Then,we take the standard plane as the measured object.At 15 different positions,we measure thestandard plane with both the traditional dual-frequency heterodyne approach and the proposed phase unwrapping approach.Experimental results show that with the dualfrequency heterodyne approach,the average RMS error at 15 different positions is1.08 mm,and that with the proposed approach is 0.62 mm,which proves that the proposed phase unwrapping approach owns a better accuracy.Moreover,we take experiments on standard shapes and complicated surfaces.With the proposed approach,the reconstructed objects have vivid and smooth surfaces.Also,the details of the complicated surfaces are well reconstructed,which verifies that the proposed approach is suitable for complicated surfaces.Finally,aiming at the practical application,we implement 3D reconstruction experiments on the ceramic plate and human face.Reconstruction results show that the ceramic plate and human face are well reconstructed,which prove that the proposed approach has a good prospect in practical application.