In recent years, the reliable method to obtain absolute phase has been studied more and more widely in the field of
structured light. A 3D profile measurement using heterodyne dual-frequency phase shift method is proposed in this paper.
The method has three parts: phase shift, heterodyne dual-frequency and binocular stereo vision. The four-step phase shift
technique is used to obtain wrapped phase map. The wrapped phase map is arctangent values between -π and π. To get
the absolute phase map, wrapped phase map must be unwrapped. The traditional phase unwrapping methods, such as
Gray code, produces wrong unwrapping results easily on image code boundary or break points. To solve this issue, firstly
we project two spatial frequency fringes separately onto the object and obtain two wrapped phase maps by four-step
phase shift technique. Secondly, by superimposing one wrapped phase map upon the other produces another phase map
with a lower frequency according to heterodyne dual-frequency principle. This phase map is the absolute phase map.
Finally, the binocular stereo vision accomplishes stereo matching according to the absolute phase map and 3D point
reconstruction. Experimental results show that accurate and reliable phase result can be obtained on phase map
boundaries and break points, which proves its feasibility in industry measurement.