Sub Inspector is where a night’s haul gets judged. Point it at a folder, analyze everything, and separate keepers from rejects – by eye, by metrics, or both – without ever deleting a file.
Loading & the Thumbnail Grid #
Open Folder (or drag a folder onto the panel) scans recursively for FITS/XISF subs. Each sub becomes a tile: an auto-stretched thumbnail with its filter and exposure, sub number, date, an accept/reject badge, and a two-row metrics strip (Score, SQM, Mean / HFR, HFD, FWHM, Stars, Eccentricity) that fills in once analysis runs. Two hover buttons on every tile: one opens the sub in the Image Analysis panel, the other opens a high-resolution preview window.
Display controls: Size (thumbnail height, 500-1000px) and Stretch (0.1x-4.0x histogram stretch – display only, never affects measurements).
Analyze: the Measurements #
The Analyze button runs star detection over every loaded sub (cancellable, with progress) and computes per-image:
- HFR / HFD – half-flux radius/diameter, the workhorse focus metric.
- FWHM – profile width, tracks seeing and focus.
- Star count – collapses when clouds pass or focus runs away.
- Eccentricity – star elongation, 0 = round; rises with guiding error, wind, differential flexure.
- Mean – background level in ADU (gradients, passing high cloud, dawn).
- Score – a composite 0-100 quality score combining the metrics.
- SQM – sky quality, when your acquisition software wrote it into the headers.
The Graph #
Show Graph opens a time-series plot of any combination of the seven metrics across the whole session – checkboxes toggle each series. This is where trends jump out: focus drifting between autofocus runs, seeing degrading after midnight, the exact frame where clouds arrived. Click a point to select that sub in the grid; Shift+click selects a range.
Auto-Select: Threshold Grading #
Next to the graph, each metric has a percentage slider (0-100%). The slider means “keep the best N% by this metric” – set HFR to 80% and the softest 20% of frames are flagged; set Stars to 90% and cloud-eaten frames drop. A sub is rejected if it fails any active threshold, and the colored filter pills above the grid show which rule caught how many. Reset returns every slider to 100% (keep all).
Rejection Is Always Reversible #
Rejecting – by slider, by clicking a tile, or Shift+click for a range – moves files into a /rejected subfolder inside the sub folder. Nothing is ever deleted. View Rejected flips the grid to show that folder’s contents, where Unreject Selected moves files back. Your stacking software simply never sees the rejects.
Sessions, Sorting, and the Blink Player #
- Sessions – a hierarchical filter by observation night and mosaic panel (tri-state checkboxes, All/None shortcuts) so a multi-night folder can be reviewed night by night.
- Sort – by Name, Date, Filter, Score, SQM, Mean, HFR, FWHM, Stars, or Eccentricity, ascending or descending. Sorting by Score puts the worst frames together for fast triage.
- Blink Player – cycles frames rapidly like a classic blink comparator; drifting focus, wandering satellites, and passing cloud become instantly obvious.