  The spatial distribution of the background events may affect the source
detection capability of IBIS at high energies (> 200 keV) for both ISGRI and
PICsIT layers. The observed background is found to be variable and spatially
structured, and in some cases its properties strongly deviate from the expected
statistical behaviour. Background correction methods are then necessary to
improve the quality of the shadowgrams obtained from sources. In order to
perform an efficient flat-fielding the response of the detector to both source
gamma-rays and background events is investigated using data from Monte Carlo
simulations and in-flight calibration observations.
