  The Cadmium Zinc Telluride (CZT) Imager on board AstroSat is a hard X-ray
imaging spectrometer operating in the energy range of 20 $-$ 100 keV. It also
acts as an open hard X-ray monitor above 100 keV capable of detecting transient
events like the Gamma-ray Bursts (GRBs). Additionally, the instrument has the
sensitivity to measure hard X-ray polarization in the energy range of 100 $-$
400 keV for bright on-axis sources like Crab and Cygnus X-1 and bright GRBs. As
hard X-ray instruments like CZTI are sensitive to cosmic rays in addition to
X-rays, it is required to identify and remove particle induced or other noise
events and select events for scientific analysis of the data. The present CZTI
data analysis pipeline includes algorithms for such event selection, but they
have certain limitations. They were primarily designed for the analysis of data
from persistent X-ray sources where the source flux is much less than the
background and thus are not best suited for sources like GRBs. Here, we
re-examine the characteristics of noise events in CZTI and present a
generalized event selection method that caters to the analysis of data for all
types of sources. The efficacy of the new method is reviewed by examining the
Poissonian behavior of the selected events and the signal to noise ratio for
GRBs.
