MiniMagick

A ruby wrapper for ImageMagick or GraphicsMagick command line.

NOTE: This readme reflects the latest version – 4.0.0.rc.

gem "mini_magick", "~> 4.0.0.rc"

Why?

I was using RMagick and loving it, but it was eating up huge amounts of memory. Even a simple script would use over 100MB of RAM. On my local machine this wasn't a problem, but on my hosting server the ruby apps would crash because of their 100MB memory limit.

Solution!

Using MiniMagick the ruby processes memory remains small (it spawns ImageMagick's command line program mogrify which takes up some memory as well, but is much smaller compared to RMagick). See Thinking of switching from RMagick? below.

MiniMagick gives you access to all the command line options ImageMagick has (found here).

Requirements

ImageMagick or GraphicsMagick command-line tool has to be installed. You can check if you have it installed by running

$ convert -version
Version: ImageMagick 6.8.9-7 Q16 x86_64 2014-09-11 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2014 ImageMagick Studio LLC
Features: DPC Modules
Delegates: bzlib fftw freetype jng jpeg lcms ltdl lzma png tiff xml zlib

MiniMagick has been tested on following Rubies:

• MRI 1.9.2
• MRI 1.9.3
• MRI 2.0.0
• MRI 2.1.3
• Rubinius

JRuby

The latest version (4.0.0) doesn't work on JRuby (because of a bug in JRuby), so if you need JRuby support, use the 3.x versions.

Installation

Add the gem to your Gemfile:

gem "mini_magick"

Information

• API documentation

Usage

Let's first see a basic example of resizing an image.

image = MiniMagick::Image.open("input.jpg")
image.path #=> "/var/folders/k7/6zx6dx6x7ys3rv3srh0nyfj00000gn/T/magick20140921-75881-1yho3zc.jpg"
image.resize "100x100"
image.format "png"
image.write "output.png"

MiniMagick::Image.open makes a copy of the image, and further methods modify that copy (the original stays untouched). We then resize the image, and write it to a file. The writing part is necessary because the copy is just temporary, it gets garbage collected when we lose reference to the image.

MiniMagick::Image.open also accepts URLs.

image = MiniMagick::Image.open("http://example.com/image.jpg")
image.contrast
image.write("from_internets.jpg")

On the other hand, if we want the original image to actually get modified, we can use MiniMagick::Image.new.

image = MiniMagick::Image.new("input.jpg")
image.path #=> "input.jpg"
image.resize "100x100"
# No calling #write, because it's no a copy

Combine options

While using methods like #resize directly is convenient, if we use more methods in this way, it quickly becomes inefficient, because it calls the command on each methods call. MiniMagick::Image#combine_options takes multiple options and from them builds one single command.

image.combine_options do |b|
  b.resize "250x200>"
  b.rotate "-90"
  b.flip
end # the command gets executed

Attributes

A MiniMagick::Image has various handy attributes.

image.type        #=> "JPEG"
image.mime_type   #=> "image/jpeg"
image.width       #=> 250
image.height      #=> 300
image.dimensions  #=> [250, 300]
image.size        #=> 3451 (in bytes)
image.colorspace  #=> "DirectClass sRGB"
image.exif        #=> {"DateTimeOriginal" => "2013:09:04 08:03:39", ...}
image.resolution  #=> [75, 75]

If you need more control, and want to access raw image attributes, you can use #[].

image["%[gamma]"] # "0.9"

Configuration

MiniMagick.configure do |config|
  config.cli = :graphicsmagick
  config.timeout = 5
end

For a complete list of configuration options, see Configuration.

Composite

MiniMagick also alows you to composite images:

first_image  = MiniMagick::Image.new("first.jpg")
second_image = MiniMagick::Image.new("second.jpg")
result = first_image.composite(second_image) do |c|
  c.compose "Over"    # OverCompositeOp
  c.geometry "+20+20" # copy second_image onto first_image from (20, 20)
end
result.write "output.jpg"

Layers/Frames/Pages

For multilayered images you can access its layers.

gif.frames #=> [...]
pdf.pages  #=> [...]
psd.layers #=> [...]

gif.frames.each_with_index do |frame, idx|
  frame.write("frame#{idx}.jpg")
end

Image validation

By default, MiniMagick validates images each time it's opening then. It validates them by running identify on them, and see if ImageMagick finds them valid. This adds slight overhead to the whole processing. Sometimes it's safe to assume that all input and output images are valid by default and turn off validation:

MiniMagick.configure do |config|
  configure.validate_on_create = false
  configure.validate_on_write = false
end

You can test whether an image is valid:

image.valid?
image.validate! # raises MiniMagick::Invalid if image is invalid

Debugging

When things go wrong and commands start failing, you can set the debug mode:

MiniMagick.configure do |config|
  config.debug = true
end

In this mode every command that gets executed in the shell will be written to stdout.

Switching CLIs (ImageMagick <=> GraphicsMagick)

Default CLI is ImageMagick, but if you want to use GraphicsMagick, you can specify it in configuration:

MiniMagick.configure do |config|
  config.cli = :graphicsmagick
end

If you're a real ImageMagick guru, you might want to use GraphicsMagick only for certain processing blocks (because it's more efficient), or vice versa. You can acomplish this with .with_cli:

MiniMagick.with_cli(:graphicsmagick) do
  # Some processing that GraphicsMagick is better at
end

Metal

If you want to be close to the metal, you can use ImageMagick's command-line tools directly.

MiniMagick::Tool::Mogrify.new do |mogrify|
  mogrify.resize "100x100"
  mogrify.antialias.+
  mogrify << "image.jpg"
end
# executes `mogrify -resize 100x100 +antialias image.jpg`

I would highly recommend this if you want to maximize performance of your image processing.

See MiniMagick::Tool.

Troubleshooting

Errors being raised when they shouldn't

This gem raises an error when ImageMagick returns a nonzero exit code. Sometimes, however, ImageMagick returns nonzero exit codes when the command actually went ok. In these cases, to avoid raising errors, you can pass false to MiniMagick::Tool's constructor.

MiniMagick::Tool::Identify.new(false) do |b|
  b.help
end

Thinking of switching from RMagick?

Unlike RMagick, MiniMagick is a much thinner wrapper around ImageMagick.

• To piece together MiniMagick commands refer to the Mogrify Documentation. For instance you can use the -flop option as image.flop.
• Operations on a MiniMagick image tend to happen in-place as image.trim, whereas RMagick has both copying and in-place methods like image.trim and image.trim!.
• To open files with MiniMagick you use MiniMagick::Image.open as you would Magick::Image.read. To open a file and directly edit it, use MiniMagick::Image.new.