20–100 keV count rate history recorded by the IBIS/ISGRI detector with a time resolution of 1.0 s (green histogram) and the corresponding light curve of GRB 210312B reconstructed through the mask decoding (black histogram) with the background subtracted and the dead time corrected. The vertical dotted lines show time intervals used for image and spectral reconstruction for the GRB precursor (1), intermediate (2), and primary (3) pulses.