align op• Data kinds: images → images
• Call: import fullseye as fs; fs.ledger.align_frames(frames, reference=0, order=3, **align_kw) (to call the implementation directly, import astrostack; astrostack.align_frames(frames, reference=0, order=3, **align_kw); from the registry, opsastrostack.get("align_frames"))
• Return value through the ledger: fullseye.ledger.align_frames(...) returns only the declared out type images (the underlying function also returns auxiliary values). When you need what was dropped, use fullseye.ledger.align_frames.raw(...) or call astrostack.align_frames directly.
• Underlying return: (aligned, matrices) -> images
Register a series of frames onto one reference.
For each frame the transform is estimated with frame_align, and scipy.ndimage.affine_transform performs inverse mapping and resampling.
An honest caveat: interpolation does not preserve the image. Noise-free 64x64 / 12 stars, shifted by (0.5, 0.5) px and shifted back, measured::
order=1 (bilinear) total flux -0.016 % star peak -11.437 %
order=3 (spline) total flux -0.016 % star peak -0.312 %
Total flux is almost preserved either way, yet with bilinear the star peak drops by more than a tenth —— a 0.5 px shift is the worst phase for bilinear, since it becomes a simple mean of the 4 neighbouring pixels. The default is order=3 because of this measurement (order=3 creates a tiny negative rim around stars, but in the measurement above the minimum was -0.0000, not a visible amount).
If you want to keep both flux and peak exactly, do not interpolate: pass to drizzle_resample —— not interpolating is drizzle's very reason for existing. However,
do not pass the estimated shifts as-is: the translation of the matrices returned here points "back to the reference", the opposite sign of what drizzle needs. Pass them through drizzle_shifts::
aligned, mats = align_frames(frames)
sci, wht = drizzle_resample(frames, drizzle_shifts(mats), scale=2.0)
Returns (aligned, matrices):
• aligned —— list of length N, each (H, W) float64 (images vocabulary). The reference frame is returned as-is without transformation (even the identity transform blurs the image through interpolation, so there is no reason to pass it through).
• matrices —— list of length N, each (3, 3). The reference gets the identity matrix.
Raises ValueError: if *frames* is not a list / tuple / fewer than 2 frames / *reference* is out of range / *order* is outside 0 to 5 / frame_align fails on any 1 frame (a failure is not silently turned into the identity).
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• The canonical algorithm (author, year) and its uses are named in the family usage guide above.
• astro_stacking — py -3.11 examples/astro_stacking.py
images as input)lucky_select · sigma_clip_stack · drizzle_resample · cosmic_ray_reject_stack
align)*Provenance: astrostack.py — ASTROSTACK operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.