PNG Optimization Tools Overview

this is an overview of PNG optimization tools. you will find here some overview and description about tools. if you want detailled results and comparisons, visit PNG Test Corpus page.

Command Line Tools

advdef by Andrea Mazzoleni (2002) — Tested: 1.23

advdef -z -2 image.png

advdef is a free, open source and lossless deflate stream recompressor by Andrea Mazzoleni, from AdvanceCOMP project. it recompresses data in PNG, but does not change any other aspects but the bitdepth, always rewritten to 8 bits per pixels. for Web usage, it does iDAT recompression and should be used after an optimizer, because it does not do any reductions.


  • default option uses libdeflate, which is a heavily optimized implementation of deflate. it should compresses faster and better than the standard zlib. results are usually close to the deflate from 7-zip and is most of the time much faster.

advpng by Andrea Mazzoleni (2002) — Tested: 1.23

advpng -z -2 image.png

advpng is a free, open source and lossless PNG recompressor by Andrea Mazzoleni, from AdvanceCOMP project. this tool is a more a snapshot compressor than an optimizer for Web: it rewrites files with none filter, does not support any reductions or some colortype. if you plan to use your files for Web, it should be more efficient to use an optimizer and advdef instead.


  • grayscale is not supported, so every image that are losslessly stored as grayscale could not be compressed by this tool. also, it does not support image reductions or filtering, and is not able to remove unnecessary chunks.


cryopng by Frédéric Kayser (2010) — Tested: 0.7.5

cryopng -o3 image.png

cryopng is a free, open source and visually lossless PNG reducer by Frédéric Kayser. it is mainly based on OptiPNG with a transformation at the filter level of RGB values that are not displayed — where alpha is 0. this could improve compression for RGBA files on some cases. some of those transformations are now included in few optimizers, but it is still good for trials.



DeflOpt by Ben Jos Walbeehm (2006) — Tested: 2.07

deflopt image.png

DeflOpt is a free, closed source and lossless deflate optimizer by Ben Jos Walbeehm. it cleans huffman symbols and does other tricks to optimize the deflate structure. however, the tool does not optimize, recompress or do trials on files. still, the process is fast and should save some bytes after zlib, KS-Flate or even zopfli compression algorithms.



defluff by Joachim Henke (2010) — Tested: 0.3.2

defluff < in.png > out.png

defluff is a free, closed source and lossless deflate optimizer by Joachim Henke. this project is very close to DeflOpt: it tries to optimize the deflate stream but with different implementations. therefore, they both can be combined to get a smaller filesize. like Deflopt, defluff does not compress or optimize file, so it should be used at the end of process.


Efficient Compression Tool

Efficient Compression Tool by Felix Hanau (2015) — Tested: 0.7 (c92a022)

ect -3 file.png

ECT is a free, open source and visually lossless JPG and PNG optimizer by Felix Hanau. it uses OptiPNG for the fast mode and ZopfliPNG for stronger compression. it uses an optimized version of the libraries used by those tools, that make ECT faster. it includes nice improvements for dirty transparency, and let the user to combine trials with order of entries in palette.

Efficient Compression Tool

  • ECT speed can be improved with multithreading, which is block based but disabled by default. when enabled, it should be able to compress faster some huge files. note that ECT is not simply using OptiPNG and ZopfliPNG, it is actually much faster than the original versions.

Median Cut PNG Posterizer

Median Cut PNG Posterizer by Kornel Lesiński (2011) — Tested: 2.1 (2015)

posterize -b -q 90 image.png lossy-filter.png

Median Cut PNG Posterizer is a free, open source and lossy PNG compressor. It has two distincts mode: the lossy blurizer, that change data to make it more compressible with the average filter, or the posterizer way, that reduces the number of colors without conversion to palette mode. in both cases, the operation is lossy but should reduce filesize significantly.

Median Cut PNG Posterizer


OptiPNG by Cosmin Truta (2001) — Tested: 0.7.6

optipng -o3 image.png 

OptiPNG is a free, open source and visually lossless PNG optimizer by Cosmin Truta. it is mainly based on PNGCrush, but it performs trials in memory and does all internals reductions automatically. that should be not necessary to perform too much trials with OptiPNG; it should be better to use a better compression algorithm in complement, such as libdeflate.



pingo by Cédric Louvrier (2016) — Tested: 0.81

pingo myfolder

pingo is an experimental, free, closed source and visually lossless or lossy JPG and PNG optimizer. it processes files or folders recursively with a multi-processing system


  • pingo does image reductions over iterations. instead of doing lot of trials, it should pick a fast solution by considering file specifications
  • default option will try to reduce filesize automatically by selecting optimal settings. it could do lossy or lossless, without any notifications or backup
  • it is an ECT fork with lot of modifications for Web usage. the code source will be open and documented with some demonstrations


pngcrush by Glenn Randers-Pehrson (1999) — Tested: 1.8.5

pngcrush -blacken -reduce image.png 

pngcrush is a free, open source and visually lossless PNG optimizer by Glenn Randers-Pehrson who also wrote parts of PNG specifications. it is probably one of the first public PNG optimizer, and most of tools are inspired from it. to be used well, you actually have to know how PNG works, because the tool do not provide profiles, but lot of options.



PngOptimizer by Hadrien Nilsson (2003) — Tested: 2.5

pngoptimizercl -file :"image.png"

PngOptimizer is a free, open source and visually lossless PNG optimizer by Hadrien Nilsson. it exists as command line or with a very simple GUI that allow drag-and-drop of files or folders, and does all of major reductions — colortype trials, basic dirty transparency support. PngOptimizer also support APNG optimization, and can convert some formats (GIF, TGA, etc.) to PNG.

PngOptimizer CL

  • PngOptimizer speed is significantly increased since version 2.5.


PNGOUT by Ken Silverman (2002) — Tested: 02/13/2015

pngout image.png

PNGOUT is a free, closed source and lossless PNG optimizer by Ken Silverman. used with right options, it compresses usually better than other tool that uses zlib, thanks to its compression algorithm ks-flate. PNGOUT is slow but offers better compression with an advanced block splitter. this tool is also great for trials, and can beat zopfli on some samples. however, it does not perform image reductions automatically; for Web usage, it should be more efficient to use an optimizer first.


  • PNGOUT uses its own heuristic filter called mixed that is not the one described in W3C specification. this let the tool to compress some samples better.
  • -c3 option always rewrites entries in palette using popularity-like sorting, unlike the default option that take into consideration the initial order.


pngquant by Kornel Lesiński (2010) — Tested: 2.8.0

pngquant image.png

pngquant is a free, open source and lossy PNG converter. it transforms RGB/A PNG to indexed-color PNG — 256 colors maximum — using a nicely modified median-cut algorithm. the filesize is usually reduce by half or more thanks to the conversion to palette type. it works fine on most of simple images, but due to the color limitation, it requires some quality control.


  • be sure to use the latest version maintened by Kornel Lesiński, not the old one. there were huge improvements since version 1.x: quality and compression are much better.


pngwolf by Björn Höhrmann (2010) — Tested: 1.1.1

pngwolf --in=image.png --out=image.png

original pngwolf is a free, open source and lossless PNG filter finder by Björn Höhrmann. this tool uses a genetic algorithm to find better filter combination and selects the one that compresses better. used well, it should be able to find a better filtering solution than most of other PNG optimizers.


  • pngwolf is using the deflate from 7-zip for data, but it exists a variant that use libdeflate or zopfli instead. this pngwolf fork is maintened by Jørgen Ibsen. it could use libdeflate for the estimator that should be faster and more precise than zlib in some cases.


TruePNG by x128 (2010) — Tested:

truepng image.png

TruePNG is a free, closed source and visually lossless or lossy PNG optimizer by x128. it does most of image reductions with trials that let the tool to perform better than other optimizers. however, data could be compressed more with other tools like advdef, by using libdeflate or zopfli. the TruePNG tutorial describes how it actually works. it is not only an optimizer and can do lossy with color quantization or lossy filter.


  • TruePNG is one of the first command line tool to use another approch for sorting entries in palette. that let the tool to reduce filesize more than others
  • TruePNG picks the best result from some trials it could run. it makes the tool slow in some situations, especially on large files when user request -a1 option.


ZopfliPNG by Lode Vandevenne, Jyrki Alakuijala (2013) — Tested: 6818a08

zopflipng --lossy_transparent image.png

ZopfliPNG is a free, open source and visually lossless PNG optimizer by Lode Vandevenne and Jyrki Alakuijala. it uses lodepng library and zopfli compression algorithm. the tool is able to do some important reductions for Web, including dirty transparency. as pure compressor, the tool is usually able to compress a bit more than KS-Flate — PNGOUT.


  • there are lot of fork from zopfli, and some of them provide better speed or results. ECT uses an heavily modified version of ZopfliPNG, and should run far faster than this original version.