Optimizing PNG Images

Publish date: Jan 20, 2020
Tags: notes

Optimizing a bunch of images in a directory

I found these commands here coincidentally on a pull request at Github. I found them quite handy ;-)

find . -type f -name "*.png"  -print0 | xargs -0 -I {} optipng -nb -nc "{}"
find . -type f -name "*.png"  -print0 | xargs -0 -I {} advpng -z4 "{}"
find . -type f -name "*.png"  -print0 | xargs -0 -I {} pngcrush -rem gAMA -rem alla -rem cHRM -rem iCCP -rem sRGB -rem time -ow "{}"

Quickly optimizing only one image

I’ve set up a function in my .zaliases file for this to be done on a single image aswell:

function opti() {
  optipng -nb -nc "$*";
  advpng -z4 "$*";
  pngcrush -rem gAMA -rem alla -rem cHRM -rem iCCP -rem sRGB -rem time -ow "$*";
}

Update on April 17 2021:

Okay that worked with ZSH (and prezto), and this one will work on fish:

function opti --description "Optimizes .png files"
  # Author: Dominic, OE7DRT <dominic@oe7drt.com>
  # 2021-04-17
  set -e missing

  for program in optipng advpng pngcrush
    if \! command -v $program > /dev/null
      set -a missing $program
      continue
    end
  end

  if test -n "$missing"
    echo "Could not find executables: $missing"
    return 1
  end

  if test -z $argv[1]
    echo "usage: opti <files...>"
    return 1
  end

  set count (count $argv)

  for i in (seq 1 $count)
    if test ! -f $argv[$i]
      echo "Could not read file $argv[$i]..."
      continue
    end

    optipng -nb -nc "$argv[$i]";
    advpng -z4 "$argv[$i]";
    pngcrush -rem gAMA -rem alla -rem cHRM -rem iCCP -rem sRGB -rem time -ow "$argv[$i]";
  end
end

To run all three commands on a single image I just call it like that:

opti image.png

That’s all the magic it needs.

Use jpegtran for JPG images.

jpegtran -copy none -optimize -progressive -outfile output.jpg input.jpg

Install these tools on your system

On debian or ubuntu

sudo apt-get install optipng pngcrush advancecomp

On Arch based distros using pacman

sudo pacman -S optipng pngcrush advancecomp

On macOS

sudo port install optipng pngcrush advancecomp

or if you use homebrew

brew install optipng pngcrush advancecomp

You may know other package managers commands, but I only use these.

An example

By filesize

The files taken from the snapshot tool on my macbook.

 33K 00_locales.png
 61K 01_control-software.png
157K 02_mmdvmhost.png
184K 03_general.png
187K 04_dmrconfig.png
 69K 05_exp_mmdvmhost-dmrnetwork.png
212K 06_exp_dmrgw-dmrnetwork1.png
236K 07_exp_dmrgw-dmrnetwork2.png

Three to four minutes later (all three commands):

 17K 00_locales.png
 33K 01_control-software.png
 81K 02_mmdvmhost.png
 98K 03_general.png
 97K 04_dmrconfig.png
 32K 05_exp_mmdvmhost-dmrnetwork.png
127K 06_exp_dmrgw-dmrnetwork1.png
144K 07_exp_dmrgw-dmrnetwork2.png

By view

 25K opti_01.png
 13K opti_02.png

This is the unmodified image: opti_01.png

Original image

And this is the optimized image: opti_02.png

Original image

Do you see much difference?