The Veil Nebula: red and teal filaments across a star field

Astrophotography software · free

Stacking and processing
of deep-sky images.

COSMO brings together, in one application, the stacking of sub-exposures, colour calibration on a star catalogue, the processing of the linear then stretched image, and the measurement of the stack.

Features Images

NGC 6960 · Veil Nebula · Seestar S50 Pro · processed in COSMO

Interface

One window, from stack to export.

The image fills the whole window. The processing sequence is on the left, the settings of the selected tool on the right. Fit frames the whole image in the free area; zoomed in, it goes under the panels.

The COSMO window: M 42 at 100 % full screen, the processing sequence on the left and the settings of the Curves tool on the right, see-through over the image
M 42 at 100 % in COSMO: the image goes under the processing sequence and under the settings.

Linear domain, stretched domain

The sequence separates the steps applied to linear data (blue) from those applied after the stretch (pink). A tool placed in the wrong domain is refused, with the reason.

Preview, Apply, Go back

Preview computes the step without applying it. Apply applies it. Go back to this step returns the image to its state before a step already applied. No step is ever run automatically.

Pipelines

A sequence of steps and their settings is saved in a .cosmopipe file, reusable on another image. The Classic pipeline is loaded at startup.

The Tools panel open: tools grouped by domain, and the description of the Faint nebulosity tool
The Tools panel: tools listed in processing order, each with its function and its domain.

Stacking

Stacking sub-exposures.

The Stack tool takes a folder of sub-exposures and produces a stack. Three modes.

Stack tool

Standard stack

  • analysis of every sub and quality table;
  • choice of the reference sub and of the subs kept, to the percent;
  • alignment on the stars and outlier rejection;
  • subs whose sky background exceeds twice that of the others are left out, with the reason shown.
Stack tool

Automatic HDR stack

  • combines long and short exposures of the same target;
  • the saturation threshold of the long exposures is measured automatically;
  • above it, the short exposures take over.
Stack tool

Automatic comet stack

  • the comet is detected by its motion, without manual pointing;
  • combined image: comet and stars both sharp;
  • stack aligned on the comet;
  • animation of its motion against the fixed stars.
Automatic HDR stack

The core of M 42

With the long exposures alone, the core of the nebula is saturated. With the HDR stack, it is recovered. The rest of the image is unchanged.

Core of M 42, HDR stack: the Trapezium and the filaments are resolved Core of M 42, long exposures only: the central region is saturated long exposuresHDR stack
Core of M 42 at 100 %, same processing chain.
Automatic comet stack

Comet and stars, both sharp

The comet is found automatically. On the left, the stack aligned on the comet: the stars trail. On the right, the combined image.

With no measurable motion, the window says so and produces a standard stack.

Combined image: comet and stars both sharp Stack aligned on the comet: trailed stars aligned on the cometcombined
Animation produced by the Stack tool from the same sub-exposures.

Processing

Nineteen tools, grouped by domain.

Every tool has a preview computed on the image. The tools of the stretched image accept a mask (bright parts or dark parts).

Linear image

  • Crop crop, rotate, flip
  • Background subtraction of sky background gradients
  • Colour calibration gains of the three channels from the stars or the Gaia DR3 catalogue
  • SharpenExperimental deconvolution: stars and detail
  • DenoiseExperimental noise reduction before the stretch

Stretch

  • Stretch generalised hyperbolic stretch (GHS), arcsinh or histogram; the curve is drawn over the histogram

Stretched image

Stars

  • Reduce starsExperimental reduction of star diameter, halos included
  • Remove halo removal of the halo of a bright star picked on the image
  • Separate starsExperimental separation into two layers: nebula and stars
  • Recombine recombination of the layers, with adjustable star contribution

Adjusting on the image

  • Right-click and drag in Curves, Saturation and Stretch: the adjustment acts on the level or the hue of the region under the pointer
Faint nebulosity tool

Faint nebulosity, in one click

In one click, the tool brings out faint nebulosity region by region, without saturating the bright parts. The Neutral black setting keeps a neutral background in dark nebulae.

Example: M 42, same sub-exposures. On the right, with the Faint nebulosity tool.

M 42 after Faint nebulosity: the diffuse outer clouds are visible M 42 after the stretch alone withoutwith Faint nebulosity
Colour calibration tool

Colours calibrated on the Gaia catalogue

The tool identifies the stars of the image in the Gaia DR3 catalogue and sets the three colours from the known colour of each star. No plate-solving software is needed.

The result is saved for the sensor and the filter, then reused on the following images.

3 to 8 s
duration of a calibration on Gaia
262
stars identified on M 42
2 %
difference in gains between two fields, same sensor and same filter
0.2 s
with the saved profile

More examples

Four more tools, each on a real image.

with Local contrast without withoutwith Local contrast
Local contrast tool
with Remove halo without withoutwith Remove halo
Remove halo tool
Dark structures 100 % without withoutDark structures 100 %
Dark structures tool
HDR multiscale 60 % without withoutHDR multiscale 60 %
HDR multiscale tool

Measurement

Measuring the stack.

Two tools measure the stack without changing it.

Two maps of the same stack: star width and eccentricity, with contour lines

Analysis tool

Full width at half maximum (FWHM) and eccentricity of the stars, as contour maps over the whole field. A diagnosis is given when the difference exceeds 10 %: sensor tilt, field curvature, tracking. With Gaia: limiting magnitude at 5 σ and surface-brightness limit at 3 σ over 10″ × 10″.

Example: limiting magnitude G 18.2, surface-brightness limit 24.1 mag/arcsec².

False-colour signal-to-noise map of M 31, with the readout for the region under the pointer

S/N map tool

Signal-to-noise ratio of the stack in false colours. For the region under the pointer: the measured ratio and the extra exposure time needed to reach 3, 5 and 10.

Example: M 31, outer arm at S/N 2.

Design

What the software guarantees.

Traceability

Every process reports what it measured: number of stars used, subs left out and why, gains applied, motion of the comet. A setting with no effect says why.

Published methods

Generalised hyperbolic stretch, à trous wavelet transform, photometric calibration on a catalogue, HDR composition in linear light. Implementations written from the published equations.

Optional external engines

GraXpert (sky background) and the RC-Astro engines (sharpening, noise, stars) are used from the user's own installation, when present and licensed. The other tools do not depend on them.

No automatic processing

Each step is set, previewed, then applied by the user. A step already applied can be redone.

COSMO logo

Download

Download COSMO 0.3.0.

Free. Two installers; each one carries the application and the three COSMO networks (COSMOSharp, COSMODenoise, COSMOStars), which are experimental.

macOSApple Silicon (M1 or later) Download · .dmg · 823 MB WindowsWindows 10 or 11, 64-bit · runs on the processor Download · .exe · 723 MB
Getting started
First launch · macOS
The application is not signed with an Apple Developer account. The first time, right-click it in Applications, choose Open, then Open again. On recent macOS: System Settings › Privacy & Security › Open Anyway.
First launch · Windows
The installer is not signed. If SmartScreen shows “Windows protected your PC”, click More info, then Run anyway.
SHA-256 checksums

7172756cbcc9b3ac7eb4283ea347e84d843b3aaff31d26d75b7663aa59844466 COSMO-0.3.0-macos-arm64.dmg

0bec2f4c387a49a9dd208d15dc5d87be84c5c7446ed5e7cc9a633522e4a8679a COSMO-0.3.0-windows-setup.exe

By downloading, you accept the licence: free to use; no redistribution, no use of the networks outside the application.

The optional GraXpert and RC-Astro engines are not included: COSMO uses them from your own installation. RC-Astro remains subject to its publisher's licence.

Support

Support the development of COSMO.

COSMO is free and developed on personal time. An optional one-time contribution funds training compute for the networks and the purchase of test data.

Make a contribution

Handled by an external payment site; COSMO receives no card details. A contribution unlocks nothing: the software stays the same for everyone.

FAQ

Frequently asked questions.

Is the software free?

Yes: COSMO, its stacker and its tools, with no account and no subscription. The RC-Astro engines are an optional complement, subject to their publisher's licence.

What equipment does it work with?

COSMO processes any deep-sky image in FITS or TIFF. The Stack tool reads the raw sub-exposures of a colour sensor; it was developed on the subs of a Seestar S50 Pro, with which every image on this page was taken.

Which formats are read and exported?

Read: FITS, TIFF, PNG, JPEG. Export: 32-bit FITS, 16-bit TIFF, PNG, JPEG; the last three carry the sRGB profile.

Do the measurements have scientific value?

FWHM, limiting magnitude and signal-to-noise ratio serve to assess a stack. Magnitudes are referred to the Gaia G band from a colour sensor: they are estimates, not calibrated photometry.