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This allows the events stored by
the WFC to be restricted to those
which are detected within a restricted spatial window within the field of view
of the WFC. The window can be any rectangular region specified with
a resolution of 32
pixels (i.e. the smallest window possible corresponds to a region
in extent with ZOOM off). Events from this window
can be either included or excluded from storage, and hence eventual
transmission to the ground. The main use for electronic windowing is in
situations where the total count rate expected from the whole field of view
exceeds the normal
maximum data rate of 200 counts s 
(and would thus lead to large dead
times). This situation will occur, for example, when making observations
with the long wavelength filter (P2), since the geocoronal
background for this filter is relatively high (see § 7.8.4 
).
The appropriate window will then be selected by operational staff.
Electronic windowing can also be used to ``mask out'' detector hot-spots or other defects which would otherwise saturate the data rate; windowing of such features, which are expected to be essentially fixed, is achieved within the WFC CDHS using a similar but independent mechanism.
