DetectorEfficiency needs to average over the number of detectors within each spectrum

[martyngigg]

The algorithm currently corrects each spectrum by an efficiency factor based on the detector geometry of each contributing pixel within the group. For instruments where the number of pixels per group is different across the instrument you see a different overall correction for some parts of the instrument vs others.

See image attached of MERLIN. The shortubes are hardware grouped at 8:1 per spectrum whereas the long tubes are 4:1. The final pattern shows the obvious error in the region around the beam.

[martyngigg]

This issue was originally trac ticket 4499

[martyngigg]

http://trac.mantidproject.org/mantid/raw-attachment/ticket/4499/MERLIN_ShortTubes.png

(uploaded by @martyngigg on 2012-01-13T16:22:04)

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