Abstract
A three-dimensional (3D) profilometry method without phase unwrapping is proposed. The key factors of the proposed profilometry are the use of composite projection of multi-frequency and four-step phase-shift sinusoidal fringes and its geometric analysis, which enable the proposed method to extract the depth information of even largely separated discontinuous objects as well as lumped continuous objects. In particular, the geometric analysis of the multi-frequency sinusoidal fringe projection identifies the shape and position of target objects in absolute coordinate system. In the paper, the depth extraction resolution of the proposed method is analyzed and experimental results are presented.
Highlights
IntroductionProfilometry is comparable with coherent interferometry. Some coherent interferometric techniques use multi-frequency patterns synthesized with a few laser sources with different wavelengths or several different carrier frequencies in order to reduce the phase ambiguity that usually appears in single frequency interferometric techniques [5, 6]
The fringe patterns for 3D profiling of target objects are directly generated by the projector and the projected images of the fringe patterns on target objects captured by the charge-coupled device (CCD) camera are used as measurement fringe patterns
The pictures of objects illuminated by the fringe patterns with the lowest spatial frequency and the highest spatial frequency are shown in Figs. 8(a) and 8(b), respectively. 36 pictures for sinusoidal fringe patterns of nine spatial frequencies are taken
Summary
Profilometry is comparable with coherent interferometry. Some coherent interferometric techniques use multi-frequency patterns synthesized with a few laser sources with different wavelengths or several different carrier frequencies in order to reduce the phase ambiguity that usually appears in single frequency interferometric techniques [5, 6]. Conventional phase-shifting profilometry methods use a single spatial frequency fringe pattern [12, 13]. The spatial frequency is smaller than the maximum frequency that can be recorded on a CCD camera In this case, phase unwrapping is indispensable for depth extraction of target objects [14]. The key factors of the proposed profilometry method are the use of composite projection of multi-frequency and four-step phase-shift sinusoidal fringe patterns and its geometrical analysis. Without phase unwrapping process, the proposed method provides the depth and position information of target objects in the absolute coordinate system with the geometric analysis regarding the positions and field-of-views of a projector and a CCD camera. The construction of multi-frequency and four-step phase-shift sinusoidal fringe patterns and its use for practical depth extraction are addressed in detail.
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