MergeMosaic

MergeMosaic (mmm) merges linear XISF mosaic panels — either the registered full-canvas frames produced by PixInsight's MosaicByCoordinates, or raw plate-solved panel stacks directly — into a photometrically matched, seam-blended 32-bit FITS mosaic, with the astrometric solution carried into the output. It ships as a standalone CLI and as a PixInsight process module.

Source and issue tracker: GitHub. It's free and open source, and always will be — if it saves you time, donations are welcome at Ko-fi, entirely optional.

Features

Photometric matching — a global photometric solve: robust per-overlap linear fits plus a per-panel gain/offset adjustment, per channel, absorbing panel background steps of 2× and more automatically.
Seam blending — star-avoiding seams with hard star ownership, so every star (including its diffraction spikes) comes from exactly one panel and misregistration can't pinch or double it; the star-free background blends on a Laplacian-pyramid multiband base.
Session workflow — analyze scans panels once into a session directory (reprojection, summaries, photometric solve), and blend streams the finished mosaic from that cached session, so re-blending or checking a report doesn't repeat the analysis.
32-bit FITS output — the blend is a 32-bit float FITS mosaic with planar channels, and the astrometric solution is carried into the output.
XISF input — accepts registered full-canvas panels from MosaicByCoordinates, or raw plate-solved panel stacks, which are reprojected onto a fresh mosaic frame automatically.

PixInsight module

MergeMosaic ships as MegaMergeMosaic, a process in the Mosaic category, driving the same analyze/blend pipeline as the CLI from inside PixInsight.

Open Resources → Updates → Manage Repositories.
Click Add, paste the repository URL: https://dev.astrometrical.com/pixinsight/
Accept, then run Resources → Updates → Check for Updates and apply.
Restart PixInsight; find MegaMergeMosaic under Process → Mosaic.

CLI

Analyze the panels once into a session, then blend the mosaic from that session:

mmm analyze panels/*.xisf --session mosaic.mmm-session
mmm blend --session mosaic.mmm-session -o mosaic.fits

Downloads: GitHub releases.

Beta channel

Testers can add a second repository to receive pre-release builds ahead of the stable channel:

https://dev.astrometrical.com/pixinsight/beta/

Beta builds are unpolished — expect rough edges, and stick to the stable repository above unless you're specifically testing.