Fig. 1. Comparison of reconstruction results of dual-frequency and triple-frequency TPU algorithms. (a) 3-step and {f_h=64, f_m=8, f_l=1}; (b) 3-step and {f_h=64, f_l=1}; (c) 3f_h+2f_m+2f_l and {f_h=64, f_m=8, f_l=1}; (d) 3f_h+2f_l and {f_h=64, f_l=1}

Fig. 2. Wrapped phase error variances for 3f_h1+2f_h2+2f_h3 algorithm

Fig. 3. 3D reconstruction results of the simulated surface. (a) Simulated surface (with magnified view); frequency combination (b) { f_h=169, f_m=13, f_l=1}; (c) { f_h=169, f_m=5, f_l=1}; (d) { f_h=169, f_m=20, f_l=1}

Fig. 4. Comparison of reconstruction results based on 3f_h1+2f_h2+2f_h3 heterodyne TPU. (a) 3f_h1+2f_h2+2f_h3 and {f_h1=153, f_h2=148, f_h3=144}; (b) 3f_h1+2f_h2+2f_h3 and {f_h1=153, f_h2=143, f_h3=134}; (c) 3f_h1+2f_h2+2f_h3 and {f_h1=153, f_h2=133, f_h3=114}; (d) 12-step and {f_h1=153, f_h2=148, f_h3=144}; (e) 12-step and {f_h1=153, f_h2=143, f_h3=134}; (f) 12-step and {f_h1=153, f_h2=133, f_h3=114}; (g) cross-sectional comparison (line 600); (h) an enlarged view of (g)

Fig. 5. Comparison of reconstruction results based on 2f_h+2f_m+3f_l hierarchical TPU. (a) 2f_h+2f_m+3f_land {f_h=181, f_m=6, f_l=1}; (b) 2f_h+2f_m+3f_l and {f_h=181, f_m=16, f_l=1}; (c) 2f_h+2f_m+3f_l and {f_h=181, f_m=30, f_l=1}; (d) 12-step and {f_h=181, f_m=6, f_l=1}; (e)12-step and {f_h=181, f_m=16, f_l=1}; (f) 12-step and {f_h=181, f_m=30, f_l=1}; (g) cross-sectional comparison (line 170); (h) an enlarged view of (g)