ImageAlpha

ImageAlpha reduces the file size of 24‑bit PNG images, including those with alpha transparency, by applying lossy compression and converting them to a PNG‑8+alpha format. It uses the pngquant and pngnq‑s9 libraries together with an alpha‑aware posterizer to achieve smaller files while maintaining visual quality that degrades gracefully even in older browsers such as IE6. The tool supports drag‑and‑drop of individual images, offers options for Median Cut or Posterizer compression, dithered mode, and color‑count reduction, and can be run in batch from the command line.

The application is targeted at developers and designers who need to optimize PNG assets for web or mobile use, especially when transparency must be preserved. It runs on macOS (10.8‑11) and provides a simple interface for previewing results on different background colors, as well as hidden shortcuts for zoom and original‑image comparison.

ImageAlpha is released under GPL v2, is open‑source, and built with Python 2, though the project is no longer actively maintained. It can be extended or forked, and its bundled pngquant executable can be used independently via ImageOptim‑CLI.