Hacktoberfest 2026: le issue che i maintainer hanno segnato per ottobre, aperte e adatte ai principianti. Sfoglia le issue Hacktoberfest

Saturated pixels reach ngmix unflagged: survey flag bit 8 marks only the first pixel of each saturated run

Aperta
  • Qualcosa non va?
#943 0 commenti 0 reazioni 0 assegnatari Vedi su GitHub

I maintainer di solito rispondono entro 1 giorno

Nessuno ha ancora preso questa issue.

Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
50/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
python
Ambito
computer-vision

Direzione di ricerca

Start in split_exp, tracing how per-CCD flag files are produced and how SExtractor and the vignets consume them. Review default_exp.sex for the SATUR_LEVEL setting, then use the saturation evidence in /n17data/cdaley/scratch/saturation/ to check the proposed clipping, growth, and bleed-tail masks. Done means saturated pixels and their proposed extensions are flagged consistently without masking more good pixels than expected.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Saturated pixels reach ngmix unflagged and at full weight. In the CFIS survey flag map, bit 8 marks only the first (lowest-column) pixel of each horizontal run of saturated pixels. A 1-px bleed trail therefore looks fully flagged, while wider trail sections and star cores are mostly unflagged. Nothing downstream catches the rest:

  • The v2 pipeline has no mask rule, and prepare_ngmix_weights never tests image values.
  • SExtractor's saturation flag is inert, because SATURATE = 65535 in the headers while the int16 images clip at 32760.

trail
Exposure 2086786p, CCD 23. Blue: survey flag bit 8. Red: clipped, unflagged, weight > 0. Right: the trail widens to two columns, and only the left one is flagged. Each red pixel there is about 2,400σ.

Scale (4 exposures × 40 CCDs): 80–88% of clipped pixels are unflagged, 66k–99k per exposure. In horizontal runs of clipped pixels at least 2 px wide, 76% have only the first pixel flagged. The pattern is the same on both amplifiers.

Impact on shapes, so far small:

  • Among galaxy-like epoch stamps on tile 202.301, after the neighbour mask, 0.05% contain such a pixel, and 0.02% within 8 px of the centre. Most of those are coadd detections lying on a trail.
  • PSF stars (MAG_AUTO > 18) sit below the clipping onset at mag 17.0–17.4 (inferred, not checked star by star).
  • Shear impact is not measured.

Proposed fix, in split_exp, ORed into each per-CCD flag file so that SExtractor and the vignets both see it:

  1. flag image ≥ 0.9 × 32760, which catches all of them at 0.02% of good pixels;
  2. grow the mask by 1 px (3×3) for the charge spilled into the next column, about +1.5 to 3σ on the side away from the readout amplifier;
  3. extend it ±20 rows along the column for the bleed tails, which are still +2σ at 20 px. Total cost about 0.06–0.07% of good pixels.

Dilating bit 8 instead catches at most 50%, at 0.9% of the area. Separately, set SATUR_LEVEL ≈ 29000 in default_exp.sex so that exposure FLAGS bit 4 works.

Open: why the upstream flag-map production marks only the first pixel of each run. Someone who knows the CFIS flag pipeline would know.

Evidence on candide: /n17data/cdaley/scratch/saturation/ (scripts, the 4 exposures, figures, including fig_stats.png).

— Claude Opus 5.5, on behalf of Cail

Lingua principale
Python
Stelle
18
Fork
14
Merge medio
2g 10h
PR unite (30g)
37

Preparare l'ambiente

Come iniziare

  1. Leggi tutta la issue e poi la guida ai contributi del progetto.
  2. Commenta sulla issue per dire che te ne occupi tu — evita che due persone facciano lo stesso lavoro.
  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

Altre issue di CosmoStat/shapepipe

Tutte le issue di CosmoStat/shapepipe

Issue simili

Altre issue su Python

Ricevi le nuove issue nella tua casella

Un breve riepilogo di issue GitHub adatte ai principianti.