Insane(ly slow but wicked good) PNG image optimization
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Crunch PNG file optimization Crunch PNG file optimization


Crunch is an OS X tool for PNG image file optimization. It combines selective bit depth, color type, and color palette reduction with zopfli DEFLATE compression algorithm encoding using embedded versions of the pngquant and zopflipng PNG optimization tools. This leads to a significant file size gain at the expense of longer file optimization processing times and relatively modest decrease in image quality (see example images below).

Mean percent original file size for the 21 files included in Cédric Louvrier's PNG Test Corpus files vs. other commonly used PNG optimization applications are:

Crunch ImageOptim OptiPNG PNGOUT PNGCrush
Mean 50.64% 60.91% 69.28% 75.81% 74.25%

Full benchmarks with the current version of Crunch are available here.

Initial impressions?

Crunch is doing a remarkably better job than ImageOptim for PNGs. The same file was reduced to 189k with ImageOptim and 95k with Crunch. Just wow. :)

@herrbischoff in #1


Want to kick the tires? Choose one of the methods below:

1. Install with Hombrew Cask Package Manager

$ brew cask install crunch

Following your install you can upgrade to the latest version with:

$ brew cask uninstall crunch && brew cask install crunch

2. Install with dmg Installer

Download the dmg installer, click it, and drag the Crunch icon to your Applications directory.

Upgrade by following the same instructions and allowing the new version to replace the old version on your system.



The following examples demonstrate the benefits and disadvantages of the current iteration of this aggressive space saving lossy transformation strategy. In many cases, optimization with Crunch will lead to excellent space savings and an imperceptible decrease in image quality. In some cases, it does not (see the horizon line + clouds in the prairie photo below) . Experiment with the image types that you use and please submit an issue report with examples of any images where the image quality falls short of your expectations for production ready files.

Photography Examples

Cat Image

  • Original Size: 583,398 bytes
  • Optimized Size: 193,995 bytes
  • DSSIM similarity score: 0.00093374

cat example pre optimization


cat example post optimization

Sun's Rays

  • Original Size: 138,272
  • Optimized Size: 74,426
  • DSSIM similarity score: 0.00046923

sun rays example pre optimization


sun rays example pre optimization

Prairie Image

  • Original Size: 196,794 bytes
  • Optimized Size: 73,296 bytes
  • DSSIM similarity score: 0.00175576

prarie example pre optimization


prarie example post optimization

Illustration Examples

Robot Image

  • Original Size: 197,193 bytes
  • Optimized Size: 67,989 bytes
  • DSSIM similarity score: 0.00005817

robot example pre optimization


robot example post optimization

Color Circle Image

  • Original Size: 249,251 bytes
  • Optiimized Size: 219,429 bytes
  • DSSIM similarity score: 0.00000000

colors example pre optimization


colors example post optimization

Flowers Image

  • Original Size: 440,126 bytes
  • Optimized Size: 195,972 bytes
  • DSSIM similarity score: 0.00024169




All images above were obtained from Pixabay and are dedicated to the public domain under the CC0 Public Domain Dedication.


Drag and drop your PNG images onto the Crunch window:

Crunch PNG image optimization usage

Your optimized file is saved in the same directory as the original file with the modified path [original filename]-crunch.png.


Please create a new issue report on the issue tracker if you come across any problems or have constructive criticism about the software.


Crunch is licensed under the MIT license.

Embedded Software

pngquant is licensed under the Gnu General Public License, version 3. The pngquant source code is available here.

zopflipng is licensed under the Apache License, Version 2.0. The zopflipng source code is available here.

Embedded Images

The application icon is "Audacity Icon" by Evin @xrilla and licensed under Creative Commons Attribution 3.0 license