We report on gain and offset corrections for GaAs X-ray pixel detectors, which were hybridised to silicon CMOS readout integrated circuits (ROICs). The whole detector array contains 320×240 square-shaped pixels with a pitch of 38 μm. The GaAs pixel detectors are based on semi-insulating and VPE grown substrates. The ROIC operates in the charge integration mode and provides snapshot as well as real time video images. Previously we have reported that the image quality of semi-insulating GaAs pixel detectors suffer from local variations in X-ray sensitivity. We have now developed a method to compensate for the sensitivity variations by applying suitable offset and gain corrections. The improvement in image quality is demonstrated in the measured signal-to-noise ratio of flood exposure images.