zopflipng

Optimize PNG

$ zopflipng [input.png] [output.png]

$ zopflipng -y [file.png] [file.png]

$ zopflipng --lossy_transparent [input.png] [output.png]

$ zopflipng -m [input.png] [output.png]

$ zopflipng --keepchunks=iCCP,sRGB [input.png] [output.png]

$ zopflipng -q [input.png] [output.png]

$ zopflipng --prefix=[optimized_] [input.png]

zopflipng [-m] [-q] [--lossytransparent] [options] input output_

zopflipng optimizes PNG files using the Zopfli compression algorithm, which produces deflate-compatible output that works everywhere standard PNG files do. It typically achieves 3-8% smaller files compared to standard PNG optimization tools.
The tool strips metadata chunks by default for maximum size reduction, though specific chunks can be preserved with the --keepchunks option. A lossy transparency mode (--lossy_transparent) further reduces file size by optimizing invisible fully-transparent pixels without any visible quality change.
zopflipng is intentionally slow, trading compression time for smaller output. It is designed for final-stage optimization in build pipelines rather than interactive use. The -m flag enables additional iterations for even better compression at the cost of more processing time.

-m, --more

More iterations.

Quick, less thorough.

Overwrite output.

Lossy alpha optimization.

Preserve chunks.

Block splitting.

Output prefix.

Very slow for large images. CPU intensive. Best for final builds.

Zopfli was created by Google for maximum deflate compression. zopflipng applies it to PNG images.

optipng(1), pngcrush(1), pngquant(1)