The useable imaging area of the OM CCD detector is 256 by 256 physical (detector) pixels. Individual photon events are centroided to one eighth of a physical CCD detector pixel by the OM electronics. The resulting OM imaging area is therefore 2048 by 2048 pixels. However, the centroiding algorithm distributes the photons unevenly within each physical CCD pixel, corresponding to 8 by 8 unbinned image pixels or a single mod-8 tile, as though the pixels are smaller near the edge of the tile.
