In the current OSA you have background maps provided by the ISGRI team. These maps are created on the base of observations containing only faint sources in their fields of view.
Background subtraction can be tuned with the help of the SCW1_BKG_I_isgrBkgDol parameter. If it is left empty then the background map is taken automatically from the IC files. You can, in principle, provide your own background map (which is e.g. specially calculated for the time period of the analyzed observation). As a general guideline, for short time scale (e.g. 1 Science Window), the background features should be less than the statistical uncertainties so that background removal is not expected to change the result by much. On longer time scales (mosaic image), things can be different, especially in the case of a Staring observation in which background features can accumulate and become important. To have no background subtraction, set SCW1_BKG_I_isgrBkgDol=``-''.
If a bright source is present in the IBIS field of view, then it can change the relative normalization factor for the background maps. To avoid this you should provide to the script a list of bright sources in the FOV. This can be done with the parameter brSrcDOL. By default all sources previously detected by ISGRI (ISGRI_FLAG2==5) with catalog flux in the 20-60 keV energy band brighter than 100 count/s ( 600 mCrab) (ISGR_FLUX_1>100) are taken into account (cf. [1]). You can check if addition of other bright sources (e.g. the ones seen in the mosaic of your observation) to the bright source catalog improves the quality of the background subtraction in your particular observation. Apart from the persitent bright sources, it is also recommended to include in the bright source catalog bright transients which are visible in the FOV and which were active during the period of observation. Addition of a source XX to the bright source catalog can be done by changing the filtering of the ISDC reference catalog: brSrcDOL="$ISDC_REF_CAT[ISGRI_FLAG2==5&&ISGR_FLUX_1>100||NAME=='XX']"
The number of bright sources which could affect the overall normalization of the detector background count rate can be very large in a crowded field, like e.g. the Galactic Center region, considered above. In this case the number of detector pixels ingored during the calculation of the background normalization can become very large. This can result in a worsening of the quality of background subtraction. To avoid this, one can try two options. First possibility is to leave the bright source catalog empty, brSrcDOL="", so that the entire ``collective'' contribution of all the bright sources, which is almost the same in all detector modules, will be taken into account. Next, one can specify if the normalization of the background is calculated using the entire detector, or on module-by-module basis. This can be done by changing the value of parameter SCW1_BKG_I_method_cor between 1 (default, the entire detector) and 2 (on module-by-module basis). In addition, one can try a combination of these two options (both give the empty bright source catalog and force the calculation of the normalization of background using the entire detector).