macOS GUI for pngquant, pngnq and posterizer by Kornel Lesiński. It converts 24-bit PNGs to much smaller 8-bit palette PNGs while keeping full alpha, with a live preview against different backgrounds so you can pick the lowest palette size that still looks right. Handy for UI sprites and web builds. macOS only.
At a glance
Licence
GPL-2.0
Commercial use
commercial OK
Credit
Not required
Status
active: License spot-checked at the source; the entry carries dated evidence.
Verified
2026-09-30 (14d ago)
Maintenance
archived: The source repository is archived: read-only, no fixes or updates.
Maintenance: the GitHub repository kornelski/ImageAlpha is archived, with the last push on 2019-07-04, per the GitHub API on 2026-09-30.
The GPL covers the application. PNGs you convert are your own images, and the GPL does not reach them. The bundled pngquant executable carries its own licence (current pngquant is GPL-3.0-or-later), which only matters if you redistribute the tool
The project says "GPL v2" without "only" or "or later", so no SPDX id is recorded
Unmaintained Python/PyObjC app. Compatibility with current macOS releases was not tested this session. The pngquant CLI does the same job on any OS
Evidence
Live https://pngmini.com/ (2026-09-30): "ImageAlpha is free, open-source software under terms of the GPL v2"
Live GitHub LICENSE (2026-09-30): "GNU GENERAL PUBLIC LICENSE Version 2, June 1991"
GitHub API (2026-09-30): archived true, pushed_at 2019-07-04