Figure 2

Flowchart of the missing-wedge correction algorithm. The iterative procedure includes the following steps: (i) use a reconstructed 3D density map to generate a mask after low-pass filtering; (ii) apply the mask to the 3D map to remove all densities outside the mask; (iii) reset the negative densities inside the mask to zero (remove imaginary parts if any exist); (iv) Fourier transform the masked/modified 3D map; (v) replace the data within the data zone with the original data (the tile series or initial data); (vi) inverse Fourier transform to the real space to obtain the first corrected 3D map; (vii) repeat the above steps from (ii) to (vi) for 1,000 iteration cycles (referred to as round 1 or Rd_1) to achieve a convergent 3D map. If the result is unsatisfactory, additional rounds are required, in which a new mask is generated from the output map of the last round.