Fine-phasing simulation results of 126-unit segmented-imaging system. (a) Differential spectral-analysis process. The initial piston distribution and modulated piston distribution are shown in (a1) and (a2). The corresponding initial aberrated PSF and modulated PSF are shown in (a3) and (a4). (a5) Differential PTF. (b) Fine-phasing results. Residual piston and corrected PSF with wavefront RMS of 32.3 nm are shown in (b1) and (b2).