Figure 6.

Block flow of the reconstruction procedure. Outer loop changes the size of the QU piece accompanying its value (q), large (32 pixels square as a standard case) to fine (1 pixel). Stepwise change in the q value reduces the calculation time (e.g., a few steps, 8 to 1). However, it is almost irrelevant to the convergence regarding the recovery of the structure. Inner loop changes the plural base tilt angles (Θ) (the minus and the plus maximum tilt angles, and 0° as a standard), which gives the different constraint conditions of $n_{\mathrm{\Theta }}\left(x_j^{\prime }\right)$ in Eq. (3). This is especially effective to remove artificial images (mosaic-like pattern shown in Fig. 4h) due to the square shape of QU pieces in the initial and the halfway size stage. Main part of the processing inside the loops is the calculation of the error map $E_{\mathit{map}}\left(x,z\right)$, placement of QUs updating the error map, and refinement of the current arrangement of QUs also updating the error map. QU piece placement and refinement movement depend on the current error map.