Fit the reciprocal tangential-width model y(q)=a0+a1*t+a2*t^2 in a centered,
standardized variable t=(q-qbar)/qscale instead of the raw {1,q,q^2} monomials:
the raw normal matrix went near-singular when the strong spots span a narrow
q-range (small cell / sparse still), letting tiny per-frame jitter swing the
curvature into a wild over-wide profile. Adds IRLS (Huber) robustness, a ridge
on the curvature (sharp-crystal prior), and clamps the applied width to the
fitted q-range (no extrapolation). Stays strictly per-frame (no dataset pooling),
so it works online and for stills. Neutral on rotation data (cytC high-res CC1/2
win preserved 66.8 vs 65.6%).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 4.8
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