Four-Step Phase-Shifting Method

The structured light four-step phase-shifting method is a fundamental technique extensively employed in computer vision, computer graphics, and 3D scanning applications. This approach captures depth information by projecting a sequence of phase-shifted sinusoidal patterns onto target objects and analyzing their deformations in captured images. The method's implementation typically involves four critical stages: pattern projection using programmable light sources, image acquisition through calibrated cameras, phase calculation using arctangent functions, and 3D coordinate reconstruction through phase-depth mapping. Algorithm implementation commonly utilizes four phase-shifted patterns with π/2 radians (90°) intervals, expressed as Iₙ(x,y) = A(x,y) + B(x,y)cos[φ(x,y) + (n-1)π/2], where n=1,2,3,4. The phase φ(x,y) is computed using φ(x,y) = arctan[(I₄-I₂)/(I₁-I₃)], resolving phase ambiguities through unwrapping algorithms. This approach achieves high accuracy through temporal phase modulation, effectively mitigating ambient light interference and surface reflectance variations. As a cornerstone technique in structured light 3D scanning, this method demonstrates exceptional precision and robustness, playing pivotal roles in industrial design automation, reverse engineering workflows, and cultural heritage digital preservation. Modern implementations often incorporate GPU acceleration for real-time phase calculation and depth mapping, with OpenCV or MATLAB providing essential functions for phase unwrapping and 3D point cloud generation.