Weak high-resolution still reflections were systematically over-subtracted: a
bandwidth-streaked high-res spot (or a neighbour) leaks into the r2-r3 background
annulus and biases its mean high, so the subtracted background is too large and
the merged high-resolution intensities go negative (seen as reproducibly negative
<I/sig> at 100% completeness and high multiplicity past ~1.9 A).
Add one high-outlier sigma-clip pass to the box-sum background (reject ring pixels
above mean + 3*sqrt(mean), recompute) so the contamination no longer inflates it.
A clean Poisson background is essentially unchanged (~0.1% exceed the cut). On the
HEWL serial-stills jet this de-biases the high-res band - <I/sig> 2.03 A 0.9 -> 1.6,
1.79 A -0.1 -> +0.7 - extends the usable resolution ~2.2 -> ~2.0 A and improves
overall R-meas 130 -> 124%, with CC1/2 and CC-vs-reference neutral. The rotation
crystal is unchanged (ISa 19.1), its clean backgrounds being barely clipped.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
leonarski_fandClaude Opus 4.8
76e88b0fca