zopflipng

Optimize PNG files with Zopfli compression

TLDR

Optimize PNG

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

In-place optimization

$ zopflipng -y [file.png] [file.png]

Lossy optimization

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

Maximum compression

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

Keep metadata

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

Quick mode

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

Set specific number of iterations

$ zopflipng --iterations=[50] [input.png] [output.png]

SYNOPSIS

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.

PARAMETERS

-m

Compress more: use more iterations (slower but better compression).

-q

Quick mode, less thorough compression.

-y

Allow overwriting the output file.

--iterations N

Number of iterations for compression (default: 15 for small files, 5 for large files).

--lossy_transparent

Lossy optimization of fully transparent pixels for smaller file size.

--keepchunks CHUNKS

Comma-separated list of metadata chunk names to preserve (e.g., iCCP,sRGB).

--keeptime

Keep the original modification time of the input file.

--filters TYPES

Filter strategies to try: 0-4, m (minimum sum), e (entropy), p (predefined), b (brute force).

--prefix PREFIX

Add prefix to output filenames (may contain a directory path).

CAVEATS

Very slow for large images due to exhaustive compression search. CPU intensive. Best suited for final-stage optimization in build pipelines rather than interactive use. Strips metadata chunks by default.

HISTORY

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