FITS Blaster has four main areas. You will use all of them during a typical culling session.
Thumbnail strip of all loaded frames, grouped by filter. The three pills at the bottom switch between All, Flagged, and Rejected views.
The currently selected frame, stretched for visual inspection. File name and a summary of key metrics are shown in the info bar below it.
One dot per frame, plotted in capture order. Dot colour is the filter group. Brightness shows rejection/flag state. A white dot marks your current position.
Exact metric values for the selected frame: FWHM, Eccentricity, SNR, Stars, Sky Background, PSF Signal Weight, and the composite Score, plus any quality warnings.
A slim controls bar sits below the image viewer. All three sliders are non-destructive display adjustments — they never touch the original FITS data.
Scales the image from 0.25× to 4×. Click the icon or the percentage label to jump to 1:1, or the fit button (↖↘) next to it to fit the whole image in the viewer. Pinch on the trackpad also zooms. The zoom level persists across restarts.
Sets the desired sky background brightness (0.05–0.50, default 0.25). The STF auto-stretch targets ~0.25, so the default is a no-op. Lower values (0.10–0.15) darken the background; higher values (0.25–0.40) suit images with large extended objects. Persists across restarts.
Post-stretch contrast multiplier (0.5×–3.0×, default 1.0×). Increasing it brightens mid-tones and brings out faint structure; decreasing it flattens contrast. Resets when a new session is loaded.
Press ⌘O or drag a folder onto the window. FITS Blaster starts loading and measuring quality metrics immediately — you can begin reviewing before the full set has finished loading.
If your session spans multiple subfolders (e.g. one per filter or night), turn on Include files from subfolders in the popover that appears when you click Open Folder… or press ⌘O. Each subfolder appears as a separate section in the sidebar.
No images at hand? Download the M31 sample set (255 MB, eight colour frames) to follow along.
Glance at the dot chart at the bottom. Each dot is one frame, coloured by filter group. Look for:
Runs of bad frames — a stretch of frames where the metric is clearly worse than the dashed median line (higher FWHM, Ecc, or Sky BG; lower SNR, Stars, PSF·S, or Score). This usually means clouds, wind, a focus drift, or a guiding glitch. Use the metric buttons above the chart to switch between FWHM, Ecc, SNR, Stars, Sky BG, PSF·S (PSF Signal Weight, which drops with both haze and poor seeing), and Score. The button at the end of the row switches between dots and bars.
Isolated outliers — single bad frames scattered through an otherwise good session.
Click any dot to jump to that frame in the viewer. The dot turns white to mark your position.
The Flagged view is a review queue — frames you want to inspect more closely before deciding. Nothing is moved on disk yet.
From the session chart: drag across a run of bad dots. A confirmation sheet lets you add them to the Flagged view in one step.
From the sidebar: use ⇧↑ / ⇧↓ or ⇧+click to build an orange range, then press F to flag the whole range at once.
One frame at a time: navigate with ↑ / ↓ and press F to toggle the flag on any frame.
Automatically: click Auto-Flag in the toolbar to flag all frames that fall below configurable quality thresholds. You can preview the result before applying it.
Switch to the Flagged view using the pill at the bottom of the sidebar. Now you see only your suspect frames.
Step through them with ↑ / ↓. For each frame, decide:
Reject it — press X. The frame is moved to a REJECTED/ subfolder immediately. It stays visible in the Flagged view so you can undo straight away by pressing X again (or U if toggle mode is off).
Keep it — press F to remove it from the Flagged view, or just leave it; flagged-but-not-rejected frames are not moved anywhere.
To reject a batch in one go: use ⌘A to orange-select all flagged frames, then X to reject them all. Use ⌘R to orange-select any that have already been rejected so you can undo them in bulk.
Point PixInsight, Siril, AstroPixelProcessor, or any other stacking tool at the same folder. Rejected frames are in REJECTED/ and will not appear in a normal folder scan.
Changed your mind? Reopen the folder with Include REJECTED folder turned on in the Open Folder popover, switch to the Rejected view, select the frames, and press U (or X in toggle mode) to move them back.
Want a record of the session? Click Export… to save a CSV, TSV, or text report with every frame's metrics and any FITS header values you choose (see the FAQ).
FITS Blaster has two independent selection systems. Understanding the difference makes everything else click.
The single frame shown in the viewer. Move it with ↑ / ↓ or by clicking. It never affects the Flagged view or triggers any batch operation on its own.
A group of frames used for batch operations — reject, flag, or unflag all at once. Built with ⇧↑ / ⇧↓ or ⇧+click. Cleared with ⌘D or any plain click.
Every shortcut is configurable in Settings → Interface. These are the defaults.
| ↑ / ↓ | Previous / next frame (moves cursor) |
| ⇧↑ / ⇧↓ | Extend orange range selection |
| Home / End | First / last frame |
| X | Reject the cursor or the orange range (moves frames to REJECTED/) |
| U | Undo rejection (moves frames back). In toggle mode, X does both. |
| F | Toggle flag on the cursor or orange range |
| D | Deflag all — clear the entire Flagged view |
| ⌘A | Select all visible frames (orange) |
| ⌘D | Clear the orange range |
| ⌘I | Invert the orange range |
| ⌘R | Select all rejected frames visible in the current view |
| G | Toggle Simple / Geek mode |
| C | Toggle colour / greyscale (OSC cameras) |
| R | Remove the current frame from the list (does not touch the file) |
| P | Play / pause — auto-advance through the frames |
| V | Flip the image 180° for display (does not touch the file) |
| ⌘O | Open a folder |
See the full keyboard shortcut reference for mouse shortcuts and more detail on each action.