After the existing mask is complete, a second step takes the pixels it left out that are
significantly dimmer than their ring, joins them through a 6 px bridge and across module gaps of
any width, and adds a piece whole when it holds >= 2000 dim pixels of which >= 200 are deep. The
existing mask is never touched, so a sweep with no such piece keeps its mask bit for bit.
Quick subset tests (battery --only, no model check) against the rc173 a0518abe6 full battery:
152 of 233 masks identical; 10 of 10 controls (including the sets where earlier shadow changes
regressed through marginal decisions) give byte-identical merges. On the 21 sets that gain a
piece the space group never changes, merge outlier rejections fall on 19, R_meas falls and ISa
rises on 17, and the shell-scaled model R improves on 16 of 18; a transmitting arm with an
over-subtracted background strip is recovered (R_meas 13.3 -> 12.0 %, ISa 13.4 -> 15.5).
Known costs: on one set with background bumps at ring radii the low-resolution agreement with
the model falls (CC 0.89 -> 0.85) while its internal statistics improve, and two sets cut
slightly coarser (1.50 -> 1.55 A, 1.72 -> 1.80 A) with a better model R.
Squashed from branch hq-beamstop (cfa080a59..60b6c6822), whose history records the variants
tried and dropped: a straight port of the earlier arm finder moved every mask, a two-shape
construction filled almost a whole sweep through hole filling, and a deep-fraction floor
rejected a real arm that is dim along its whole length.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D1G8gJVAy6gp1K5Dz3NE5C
leonarski_fandClaude Opus 5.5
a1816e905e