Fast and high-accuracy three-dimensional shape measurement using intermediate-bit projection

Abstract

The digital light processing (DLP) projector has been widely used in fringe projection profilometry (FPP). The bit depth of the projected fringes is mostly 8-bit or 1-bit to pursue higher measuring accuracy or speed. In this paper, a bit error model is established to evaluate phase quality of the projected fringes with different bit depths. It indicates that the phase error is jointly determined by the generation method and the bit depth of the projected fringe. Thus, a well-designed generation method for the intermediate-bit projection is proposed to balance the measuring accuracy and the speed. The well-designed generation method introduces a two-dimensional (2D) error diffusion algorithm to reduce the quantization error and compensate the error caused by the intermediate-bit projection. And it can keep good sinusoidal properties through in-focus projection and achieve high-accuracy and large-depth-range three-dimensional (3D) measurement. Experimental results demonstrate the proposed optimized intermediate-bit projection method can inherit both the dominance of 8-bit fringe on high accuracy and large depth range and that of 1-bit fringe on high speed. And it is promising to upgrade the off-the-shelf FPP system from the perspective of bit utilization.