Using FITS n’ Finish with Siril and PixInsight
FITS n’ Finish slots into a linear-data workflow: run it on your stacked,
uncalibrated-background image before stretching, then continue in your
usual tool.
Round trip
- Stack in Siril, PixInsight (WBPP), or your capture software.
- Open the stack in FITS n’ Finish — FITS (including fpack-compressed)
and monolithic XISF both open directly; pointing, capture time, and
pixel scale are read from the header/plate solution.
- Remove gradients (⌘↩). Inspect what each stage subtracted with the
Physical / Surface view modes.
- Export (⌘E) — a 16-bit FITS with the WCS and provenance cards
preserved, so plate-solve-dependent steps downstream keep working.
Scripted alternative: fnfin process --preset mysite.json stack.fits.
- ABE (PixInsight) fits a polynomial to automatically placed samples.
At degree 4+ it can follow — and remove — broad nebulosity. FITS n’
Finish never exceeds degree 2, because the atmospheric model has already
taken out the non-linear part that forces high degrees.
- DBE (PixInsight) interpolates between hand-placed samples; excellent
control, but labor-intensive and sensitive to sample placement over
faint structure. FITS n’ Finish needs no samples: the physics fixes the
baseline’s shape, the median-cell fit handles the leftovers.
- Siril background extraction (polynomial or RBF) is fast and good;
the RBF mode in particular can conform to large structures. The same
degree-2 argument applies.
A fair comparison: run your usual tool and FITS n’ Finish on the same
stack, then blink the results over the faintest extended feature you care
about (IFN, outer halo, faint Hα). The difference shows up there, not in
the background flatness — both will be flat.
Notes
- XISF: monolithic files, UInt8/16/32 and Float32/64 samples, Gray/RGB,
planar or interleaved, zlib (optionally byte-shuffled) blocks. Embedded
FITSKeyword metadata (plate solutions included) is honored.
- Export is always FITS. PixInsight and Siril both read it back directly.