bragg integration: trimmed-mean background, on by default for rotation

The local Bragg background is the mean over the r2..r3 ring. That mean reads high because the contaminants that survive the signal-disk mask - neighbour- spot wings, tails, zingers - are one-sided (positive), so it over-subtracts. Since a weak intensity is a small difference of large numbers (I = S - nS*b), a per-pixel background bias is fractionally largest at the resolution edge, exactly where it hurts most. Replace the ring mean with a symmetric trimmed mean (sort the ring, drop the lowest and highest fraction f, average the rest), controlled by a new BraggIntegrationSettings field and the rugnux `--background-trim <f>` option (default f=0.10; 0 restores the plain mean). Default on for monochromatic (rotation) data; broadband (stills) keep their tuned high-side sigma-clip, so the base engine forces the trim to 0 there. Implemented in both the CPU engine and the GPU kernel (shared-memory bitonic sort per block, flat-mean fallback above BKG_TRIM_MAX ring pixels); the two agree. 25-crystal rotation battery (fixed SG/cell): <I/sigma> improved on every crystal (median +50%), ISa on 20/22, resolution-edge R_meas fell several-fold (e.g. lyso_ref 1.0 A 108%->43%). Last-shell CC1/2 is rescued where the plain mean had collapsed to noise (Thau_9 at ~2.0 A 3.8%->64%, ~0.5 A of resolution regained; cytC_10 0.2%->10%) at a small cost (1-3%) in already-clean shells - it flattens the CC1/2 fall-off rather than shifting it. Stills unchanged. Documented in CPU_DATA_ANALYSIS.md section 9.2. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-07-16 18:32:57 +02:00
parent 118f0833dc
commit c3e877d5ec
9 changed files with 127 additions and 5 deletions
@@ -68,6 +68,10 @@ BraggIntegrationEngine::BraggIntegrationEngine(const DiffractionExperiment &expe
    beam_y = geom.GetBeamY_pxl();
    use_ellipse = !empirical && (bw_sigma > 0.0 || c_radial > 0.0);

+    // Trimmed-mean background applies to monochromatic (rotation) data; broadband (stills) keep the tuned
+    // high-side sigma-clip, so the trim is forced off there. The fraction itself comes from the settings.
+    bkg_trim = broadband ? 0.0f : settings.GetBackgroundTrimFraction();
+
    polarization = experiment.GetPolarizationFactor();
 }