ImageAlpha

Lossy PNG compression for macOS — reduce file sizes by applying lossy compression to the alpha channel.

Features

• Lossy alpha compression powered by pngquant/libimagequant
• Real-time preview — see before/after as you adjust settings
• Adjustable colors and dithering for fine-tuned control
• Side-by-side comparison — split view with draggable divider to compare original and quantized
• Copy & drag export — Cmd+C to copy, or drag the image directly to Finder or other apps
• Background previews — checkerboard, solid color, and image textures
• File size savings displayed before saving
• Open With support — right-click any PNG in Finder to open in ImageAlpha

Download

Pre-built binaries are available on the Releases page.

Build from source

Prerequisites

• Xcode 16+
• Rust toolchain (cargo) — install via rustup.rs

Clone and build

git clone --recursive https://github.com/bensquire/ImageAlpha.git
cd ImageAlpha
make pngquant   # build libimagequant (Rust)
make release     # build the app (Xcode)

The built app will be at ~/Library/Developer/Xcode/DerivedData/ImageAlpha-*/Build/Products/Release/ImageAlpha.app.

To create a distributable DMG:

brew install create-dmg
make dmg

Credits

• Kornel Lesiński — original ImageAlpha author
• pngquant and libimagequant — the quantization engine
• ManyTextures — tileable background images

License

This project is licensed under the GNU General Public License v3.0.