the corrections are needed in a given image.

Hole mask data
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Spatial resolution and flux calibration were performed using the hole mask (see Fig 4). These holes are all 25 microns in diameter, to an accuracy of 5%. The mask was taped close to the detector face, about 1mm from the window, and illuminated with the collimated beam. There are two points to note in this. First, the beam illumination underfills the detector window, and is not uniform. Second, the mask is a small distance from the photocathode, by the window thickness and the gap between the window flange and its outer surface, so the spots are somewhat enlarged by diffraction.

We used the first point to our advantage by the fact that the spot images cover a wide range of signal levels, thus increasing the dynamic range of the flux calibration. The response uniformity across the detector window was checked by using a range of flux levels, and by moving the detector around the collimated beam.

We calibrated the second point by using results from a different hole mask used in testing the engineering model detector. This mask had alternating hole sizes of 25, 50, and 75 microns 