Enhanced Gray-code method for three-dimensional shape measurement

Conventional Gray-code (GC) plus phase-shifting methods have been extensively utilized for three-dimensional (3D) shape measurements. Nevertheless, how to achieve fast and accurate measurement remains challenging because multiple GC patterns are necessary for absolute phase recovery. An enhanced GC method based on geometric constraint was proposed, which would decrease the number of fringe patterns. The 8-bit phase-shifting patterns could be transferred into 1-bit binary ones by using the binary dithering approach to realize high-speed projection. Specifically, a total of six binary patterns including three phase-shifting patterns and three GC patterns were employed in the proposed method. The phase-shifting patterns were adopted to compute the wrapped phase, and then the GC patterns could be utilized to unwrap the wrapped phase to obtain a pseudo unwrapped phase. In the end, the absolute phase would be reconstructed after using the geometric constraint to unwrap the pseudo unwrapped one. The experiments demonstrate that the enhanced GC method is an effective way to reconstruct the 3D shapes of measured objects.