High signals spark electric ghosts in the other quadrants of the ITL 4kx4k chips.
We used four images similar to the one above. A highly defocused image of a bright star was placed such that it covered most of area of a single quadrant. We then measured the remainder signal in all the three adjacent quadrants and solved for the matrix αij in the following equation Imeas = Σi=1...4 αij I0i. Amplifier correction is done by inversion of αij and applying it to the measured signal Imeas, retrieving the incident signal I0.