Background estimate: use the mean of the local ring, not the median. For a
right-skewed (Poisson) background the median sits below the mean, so subtracting
it under-subtracts and biases every weak intensity positive; over multiplicity
this becomes fake <I/sig> of a few in no-signal high-resolution shells. Fixed in
both PixelRefine and BraggIntegrate2D (the classical route had the same bug).
<I/sig> now tracks CC honestly and the true resolution limit is visible.
Error model: fit a global a, b (XDS form sigma'^2 = a*sigma^2 + (b*I)^2) from the
scatter of symmetry equivalents at the merge level (so both integrators benefit),
and print it with ISa = 1/b in jfjoch_process. The (b*I)^2 term uses the
reflection mean (not the per-observation I_i, which biases the weights and
collapses CC); a,b come from a relative-weighted bin regression. Replaces the
earlier per-resolution-shell variant, which was partly masking the background bias.
METHODS.md: document both (Sections 6-7), integrator-agnostic.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
leonarski_f
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