The image qualify of an image frame from a CMOS image sensor array operated in global shutter mode may be enhanced by dispersing or randomizing the noise introduced by leakage currents from floating drains among the rows of the image frame. Further, the image quality may be improved by accounting for time dependent changes in the output of dark pixels in dark pixel rows or dark pixel columns. In addition, voltage and time dependent changes in the output of dark pixels may also be measured to provide an accurate estimate of the noise introduced to the charge held in the floating drains. Such methods may be employed individually or in combination to improve the quality of the image.