Fine-phasing-simulation results of JWST-like 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. The residual piston and corrected PSF with wavefront RMS of 21.4 nm are shown in (b1) and (b2).