High-precision real-time 3D shape measurement based on a quad-camera system

Abstract

Phase-shifting profilometry (PSP) based 3D shape measurement is well established in various applications due to its high accuracy, simple implementation, and robustness to environmental illumination and surface texture. In PSP, higher depth resolution generally requires higher fringe density of projected patterns which, in turn, lead to severe phase ambiguities that must be solved with additional information from phase coding and/or geometric constraints. However, in order to guarantee the reliability of phase unwrapping, available techniques are usually accompanied by increased number of patterns, reduced amplitude of fringe, and complicated post-processing algorithms. In this work, we demonstrate that by using a quad-camera multi-view fringe projection system and carefully arranging the relative spatial positions between the cameras and the projector, it becomes possible to completely eliminate the phase ambiguities in conventional three-step PSP patterns with high-fringe-density without projecting any additional patterns or embedding any auxiliary signals. Benefiting from the position-optimized quad-camera system, stereo phase unwrapping can be efficiently and reliably performed by flexible phase consistency checks. Besides, redundant information of multiple phase consistency checks is fully used through a weighted phase difference scheme to further enhance the reliability of phase unwrapping. This paper explains the 3D measurement principle and the basic design of quad-camera system, and finally demonstrates that in a large measurement volume of 200 mm × 200 mm × 400 mm, the resultant dynamic 3D sensing system can realize real-time 3D reconstruction at 60 frames per second with a depth precision of 50 μm.

Deep learning profilometry for single-frame absolute 3D shape reconstruction

“…After the depth constraint, we project the remaining candidate points onto the Camera 2 image plane by virtue of the calibration parameters between cameras. Since a correct matching point has the most similar wrapped phase to the arbitrary point P , 43 we can reject most of the wrong candidate points based on this phase similarity check. However, the only matching point cannot be obtained in this step when using high-frequency fringes, hence the second phase similarity check is usually required from the third perspective.…”

“…That is to say, we can project the candidate points which meet the error threshold conditions onto the image plane of Camera 3 for inspection, after further consideration of the influence of ambient light and calibration error. 43 By virtue of two phase similarity checks, we can basically obtain the only correct candidate point, that is, the phase ambiguity is eliminated. Step 4 In short, as is vividly shown in Fig.…”

Deep-learning-enabled geometric constraints and phase unwrapping for single-shot absolute 3D shape measurement

“…Since these methods obtain absolute phase essentially with the aid of modulation information, they will fail when measuring objects with large surface reflectivity variations. (3) The third method is to increase the number of perspectives and eliminate the ambiguity of high frequency phase with more geometric constraints [33]. Compared with the two methods mentioned above, this method is more adaptive to the objects with complex surfaces, but at the cost of further increasing the number of cameras.…”

“…Tao et al [38] proposed an adaptive depth constraint (ADC) approach, with which the measurement volume is enlarged, and the range of the depth constraint can be automatically selected, but only if the correct absolute phase can be obtained for the first measurement. In addition, since SPU relies on the similarity of phase information between multiple perspectives to realize phase unwrapping [33], (1) on the one hand, it has high requirement for the quality of the wrapped phase. So that the wrapped phase in SPU is usually acquired by phase-shifting (PS) method [4,5], which is a multi-frame phase acquisition method and can provide high spatial resolution and high measurement accuracy phase information.…”

A novel spatial phase-unwrapping method based on single-pixel binarized line pattern for real-time 3D measurement

“…Due to the advantages of non-contact, high speed, and high precision, optical measuring techniques based on structured light [1][2][3][4][5] and interferometry [6][7][8] have developed rapidly and been widely used in various fields in the past few decades. Fringe projection profilometry is one of structured light techniques and can be divided into two categories: Fourier transform profilometry (FTP) and phase-shifting profilometry * Author to whom any correspondence should be addressed.…”