NOISECHISEL(1)

📦
version 0.24 · 5 versions
, in epel 10, epel 9, nixos 26.05, nixpkgs unstable, ubuntu resolute, ubuntu stonking

💖 NOISECHISEL — bestie's guide to finding signal in a noisy mess 💖

okay so. this is the NoiseChisel manual page, from the GNU Astronomy Utilities family, section 1 (user commands). if you've ever stared at an astronomical image that was 99% static and 1% actual galaxy, this is your girl. 🫶

✨ NAME ✨

NoiseChisel — detect signal in a noisy image. that's it. that's the whole vibe. she finds the treasure in the noise dumpster. 💅

🌸 SYNOPSIS 🌸

astnoisechisel [OPTION...] ASTRdata

🦋 DESCRIPTION 🦋

so NoiseChisel is part of GNU Astronomy Utilities 0.24. what she does is detect and segment signal that is deeply buried in noise (the original says "burried", we're keeping that, we don't fix typos in here, we respect the archive 🙈). she uses a noise-based detection and segmentation method, which is the whole reason she's so resilient to the rich diversity of shapes in astronomical targets. like, galaxies can be blobs, smears, spirals, weird little tadpoles — she doesn't care, she ate. 👑

if you want more info, run any of these. especially the second one, it's the comprehensive one — it explains NoiseChisel's invocation, the expected input(s), output(s), and a full description of all the options:

All options and their values:

$ astnoisechisel -P

Inputs/Outputs and options:

$ info astnoisechisel

Full section in manual/book:

$ info NoiseChisel

Full Gnuastro manual/book:

$ info gnuastro

and if you still couldn't find your answer in the manual, you can get direct help from experienced Gnuastro users and developers. for more info, run:

$ info help-gnuastro

💜 OPTIONS 💜

🍓 Input:

  • --chdu=STR — HDU/extension of the convolved image, inside the file.
  • --convolved=FITS — hand her a convolved image file so she doesn't have to do the convolution herself.
  • -h, --hdu=STR/INT — extension name or number of the input data. (name or number, both work, she's flexible.)
  • --khdu=STR — the HDU that holds the kernel image.
  • -k, --kernel=FITS — filename of the kernel to convolve with the input.
  • --whdu=STR — the HDU that holds the wide kernel image.
  • -w, --widekernel=FITS — filename of a wider kernel, for a better qthresh.

🧚 Tessellation (tile grid):

  • --checktiles — shows tile IDs in an image, sized the same as the input.
  • -F, --remainderfrac=FLT — fraction of the remainder used to split that last tile.
  • --interpmetric=STR — interpolation metric. options are radial, manhattan.
  • --interpnumngb=INT — number of neighbors to use for interpolation.
  • --interponlyblank — only interpolate over the blank tiles. nothing else. stay in your lane bestie.
  • -L, --largetilesize=INT[,INT] — same idea as --tilesize, but for the larger tiles.
  • -M, --numchannels=INT[,..] — number of channels in dim.s (FITS order).
  • --oneelempertile — display 1 element per tile, not the full input resolution.
  • --workoverch — work (not tile) over channel edges.
  • -Z, --tilesize=INT[,INT] — regular tile size on dim.s (FITS order).

🌈 Output:

  • -D, --dontdelete — don't delete the output if it already exists.
  • --ignoreblankintiles — don't write the input's blanks into the tiled output.
  • -K, --keepinputdir — keep the input directory for the automatic output.
  • -l, --label — label/count the detected pixels that are connected to each other.
  • --outfitsnocommit — no Git commit in the 0-th HDU of the output FITS.
  • --outfitsnoconfig — no metadata in the 0-th HDU of the output FITS.
  • --outfitsnodate — no 'DATE' in the 0-th HDU of the output FITS.
  • --outfitsnoversions — no versions in the 0-th HDU of the output FITS.
  • -o, --output=STR — output file name.
  • --rawoutput — output only the detection labels & the 1-element-per-tile grid.
  • --tableformat=STR — 'txt', 'fits-ascii', 'fits-binary'.
  • --wcslinearmatrix=STR — WCS linear matrix of the output. 'pc' or 'cd'.

🔥 Detection:

  • -a, --outliernumngb=INT — number of neighboring tiles to look at for outliers.
  • --blankasforeground — blanks count as foreground in erosion and opening.
  • -B, --minskyfrac=FLT — minimum fraction of undetected area in a tile.
  • --checkdetection — save all the detection steps to a file.
  • --checkdetsky — save the Sky value estimation for the pseudo-dets.
  • --checkqthresh — save the quantile threshold estimation to a file.
  • --checksky — final sky and its STD steps, into a file.
  • --checksn — save the pseudo-detection S/N values to a file.
  • --cleangrowndet — remove the small S/N grown detections.
  • -c, --snquant=FLT — the quantile in the pseudo-detections that defines "true".
  • --detgrowmaxholesize=INT — max area of holes to fill after growing.
  • --dopening=INT — depth of opening after dthresh.
  • --dopeningngb=INT — 4 or 8 connectivity for dthresh opening.
  • -d, --detgrowquant=FLT — minimum quantile to expand the true detections.
  • --erodengb=INT — connectivity in erosion (number of ngbs).
  • -e, --erode=INT — number of erosions after thresholding.
  • --holengb=INT — 4 or 8 connectivity for filling holes.
  • --minnumfalse=INT — minimum number for the S/N estimation.
  • -m, --snminarea=INT — minimum pseudo-detection area for the S/N dist.
  • --noerodequant=FLT — quantile for no erosion.
  • --openingngb=INT — connectivity in opening (number of ngbs).
  • --outliersclip=FLT,FLT — sigma-clip params for the qthresh outliers.
  • --outliersigma=FLT — multiple of sigma used to define outliers.
  • --pseudoconcomp=INT — 4 or 8 neighbors for labeling the pseudo-dets.
  • -p, --opening=INT — depth of opening after erosion.
  • -Q, --meanmedqdiff=FLT — max mean and median quant difference per tile.
  • -R, --dthresh=FLT — sigma threshold for pseudo-detections.
  • --skyfracnoblank — no blanks in the tile undetected frac. (that's minskyfrac).
  • --smoothwidth=INT — flat kernel width used to smooth the interpolated stuff.
  • --snthresh=FLT — manually input the pseudo-det S/N threshold.
  • -s, --sigmaclip=FLT,FLT — sigma multiple and, tolerance or number.
  • -t, --qthresh=FLT — quantile threshold on the convolved image.

👑 Operating modes:

  • -?, --help — give this help list.
  • --checkconfig — list all config files and variables that were read.
  • --cite — BibTeX citation for this program.
  • --config=STR — read configuration file STR immediately.
  • --config-prefix=STR — custom prefix of option names in config files.
  • -C, --continueaftercheck — continue processing after the checks.
  • --lastconfig — do not parse any more configuration files.
  • --minmapsize=INT — minimum bytes to avoid RAM automatically.
  • -N, --numthreads=INT — number of CPU threads to use.
  • --onlyversion=STR — only run if the program version is STR.
  • -P, --printparams — print the parameter values to be used, then abort.
  • --quietmmap — don't print the mmap'd file's name and size.
  • -q, --quiet — only report errors, stay quiet about the steps.
  • -S, --setdirconf — set default values for this directory and abort.
  • --usage — give a short usage message.
  • -U, --setusrconf — set default values for this user and abort.
  • -V, --version — print program version.
⚠️ heads up bestie: mandatory or optional arguments to long options are also mandatory or optional for any corresponding short options. like, they're a package deal. 💀

GNU Astronomy Utilities home page: http://www.gnu.org/software/gnuastro/

😭 REPORTING BUGS 😭

found a bug? report it to bug-gnuastro@gnu.org. they're nice, i promise. don't suffer in silence.

Copyright © 2015-2025 Free Software Foundation, Inc. License GPLv3+: GNU General public license version 3 or later.

This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. (like, none. zero. nada. don't come for them if your galaxy detection goes sideways. 🫶)

Written/developed by Mohammad Akhlaghi.

🌟 SEE ALSO 🌟

The full documentation for NoiseChisel is maintained as a Texinfo manual. If the info and NoiseChisel programs are properly installed at your site, the command

info NoiseChisel

should give you access to the complete manual.

and that's the whole page, periodt. 💖 this was GNU Astronomy Utilities 0.24, dated November 2025, NOISECHISEL(1). go detect something iconic. 🦋✨

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