Each partial subtracted its own independently-estimated per-frame background,
so a weak full assembled from N frames accumulated one background-estimation
variance per frame. The true background is flat over the few frames of one
rocking event, so replace each partial's background by the event mean and
correct its intensity by n_bkg*(bkg - pooled), where n_bkg = (sigma^2 - I)/bkg
is the effective background-pixel count -- correct for weak AND strong
reflections (sigma^2/bkg would over-count strong ones and over-correct them).
Single-frame events are a no-op.
Measured (rotation lyso @1.0 A): 1.05 A CC1/2 81.3 -> 83.0, R-meas 81.4 ->
77.2, CCref +0.2, CCxds +0.3; overall R-meas 10.0 -> 9.4%; ISa preserved (13.5).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
leonarski_fandClaude Opus 4.8
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