vis_normalize
If vis_normalize is turned on, then we find the normalization correction factors for each detector by dividing a grand average of the vis total flux by the average total flux of each detector. To compute the grand average, first we eliminate any detectors whose average visibility total flux is <= 0, and for the remaining detectors, we further eliminate any detectors whose average total flux is more than .25*average different from average total flux of those detectors. vis_det_index_mask_used (and vis_info_det_index_mask_used) - byte array dimensioned to 9 that is 1 for each detector used in the grand average. Note that all selected detectors are still used in making the image.
vis_corr_factors (and vis_info_corr_factors) - ratio of the grand average to the total flux for each detector. The obsvis, totflux, and sigamp fields in the visibility structure are multiplied by these correction factors before being used to make the image.