One sub, examined properly, can tell you whether your focus plane is tilted, your optics are collimated, your flats are keeping up with vignetting, and whether that donut in the corner is dust on the sensor or the filter. The Image Analysis panel is that examination.
Loading & Star Detection #
Open Image loads a FITS/XISF/TIFF (dimensions, file type, and bit depth shown). Choose a Fit Model – Gaussian (fast) or Moffat4 (more faithful to real star profiles; adds a Min R² fit-quality slider, default 0.60, to discard poor fits) – and run Star Detection. Results: HFR, HFD, FWHM, star count, eccentricity, mean ADU, plus image scale and field of view derived from the plate solve or the header’s focal length and pixel size.
Every deeper analysis builds on this step; an Auto-run checkbox runs the entire suite the moment detection finishes.
The Eight Analyses #
| Analysis | What it measures | What the result means |
|---|---|---|
| Star Detection | HFR, FWHM, count, eccentricity | overall frame quality baseline |
| Eccentricity | star elongation across the frame | guiding, wind, flexure issues |
| Tilt | HFR compared across a 3×3 zone grid | focus-plane tilt severity (%) and its direction – which corner is worst |
| PSF (Select Region) | interactive point-spread function viewer | 3D intensity surface, directional radial profiles, HFR/FWHM rings for any star you select |
| Collimation | eccentricity patterns and optical-center shift | how far the optical center sits from the geometric center |
| Vignetting | brightness in five concentric rings | edge falloff % plus horizontal/vertical profiles |
| Dust / Reflections | circular dark and bright artifacts | each found artifact circled and labeled, with an estimated distance from the sensor – which tells you which surface to clean |
| Exposure | background statistics and saturation | clipped stars, saturated area, background level vs. ideal |
Each analysis paints its evidence onto the image: the tilt zone grid, vignetting rings, dust circles, PSF rings – you see the diagnosis, not just a number. Status dots track each analysis (gray = not run, green = done).
The Results Dashboard #
The dashboard column collects everything with progress-bar visualizations: star quality (HFR, FWHM, eccentricity, count), frame quality (tilt %, curvature, vignetting %, collimation shift, artifact count), and exposure (mean ADU, airmass when present). Hover any metric for the exact definition – e.g. tilt is (worst zone – best zone) / median HFR × 100.
Viewer & Annotation Tools #
The image viewer offers zoom (+/-, Fit, 1:1, mouse wheel; 10-500%), drag-to-pan, and a live cursor readout of pixel coordinates – plus RA/Dec once plate-solved. A Draw annotation mode lets you mark the image freehand in six colors (Yellow, Cyan, Lime, Red, Orange, White), with a clear button and label counter – handy for documenting an issue before posting it to a forum or sending it to us.
Metadata & External Tools #
The right column lists everything the header knows: filter, coordinates, date, exposure, gain/offset, binning, sensor temperature, airmass, focal length and ratio, pixel size, focus position, rotation. Below it, external integrations (configured in Settings):
- Plate Solve with ASTAP – local solve; fills RA/Dec, rotation, and plate scale, and reports ASTAP’s own HFD/FWHM/star count for comparison.
- Open in ASTAP – launches the full ASTAP GUI with the image.
- Open CCD Inspector – hands the image to CCD Inspector if you use it.