MiniMagick

MiniMagick runs ImageMagick commands from Ruby. ImageMagick reads each icon entry as a separate layer and writes one entry per image, so with MiniMagick you can inspect icons, export sizes and build favicons. It uses little memory in your Ruby process because the work happens in a separate ImageMagick process.

ImageMagick must be installed on the machine. It stores entries as BMP unless they’re larger than 256x256 or you set icon:png-compression-size.

Installation#

gem install mini_magick
# plus ImageMagick
sudo apt install imagemagick   # Debian / Ubuntu
brew install imagemagick       # macOS

Basic usage: list the sizes in an ICO file#

require "mini_magick"

icon = MiniMagick::Image.open("app.ico")
icon.layers.each_with_index do |layer, i|
  puts "#{i}: #{layer.width} x #{layer.height}"
end

How to convert ICO to PNG#

Export the largest entry:

require "mini_magick"

icon = MiniMagick::Image.open("app.ico")
largest = icon.layers.max_by { |l| l.width * l.height }
largest.write("app.png")

Write every layer in a loop (layer.write("icon-#{i}.png")) to export all sizes.

How to create a multi-size favicon.ico#

icon:auto-resize resizes one square image to every listed size:

require "mini_magick"

MiniMagick.convert do |convert|
  convert << "logo.png"
  convert.resize("256x256")
  convert.define("icon:auto-resize=256,64,48,32,16")
  convert.define("icon:png-compression-size=256")  # 256x256 entry as PNG
  convert << "favicon.ico"
end

How to build an ICO from hand-drawn sizes#

Each input file becomes one entry:

MiniMagick.convert do |convert|
  convert << "icon16.png" << "icon32.png" << "icon48.png" << "icon256.png"
  convert << "app.ico"
end

Tips#

• MiniMagick.convert runs magick on ImageMagick 7 and convert on ImageMagick 6.
• MiniMagick::Image.open copies the file to a temporary file first; use MiniMagick::Image.new(path) to work on the file in place.