pngquant is a command-line utility and a library for lossy compression of PNG images. The conversion reduces file sizes significantly (often as much as 70%) and preserves full alpha transparency. Generated images are compatible with all web browsers and operating systems.
pngquant uses modified version of Median Cut quantization algorithm and additional techniques to mitigate deficiencies of Median Cut. Instead of splitting boxes with largest volume or number of colors, boxes are selected to minimize variance from their median value. Histogram is built with addition of a basic perception model, which gives less weight to noisy areas of the image.
High-quality palette generation using a combination of vector quantization algorithms. Unique adaptive dithering algorithm that adds less noise to images than the standard Floyd-Steinberg. Easy to integrate with shell scripts, GUIs and server-side software. Fast mode for real-time processing/large numbers of images.