DivideOutIncidentFlux was still the last fully serial pass in Ingest: a sweep
over every observation to take each frame's mean background, and another to
divide every rlp by its frame's flux. Ten gigabytes of traffic on one thread.
The per-frame means go a frame at a time rather than an observation at a time,
so each frame's running sum stays in one thread and in the order it had -
splitting by observation would cut a frame across two threads and the partial
sums would have to be recombined, which is a different sequence of roundings.
The divide is per-element and splits anywhere.
The adaptive spot finder synchronised after flagging strong pixels. The
extractor that reads those pixels runs on the same stream, so the ordering
already guaranteed the flagging had finished; the wait only idled the host,
once per image.
Measured on a crystal with 66 million partial observations: Ingest 8.5 s and
7.7 s -> 7.1 s and 6.6 s, whole crystal 1m24s -> 1m17s. Merged statistics
unchanged.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
