mini replacement for RMagick
Latest commit 01a6752 Mar 5, 2018
janko-m Use regular -label and -caption CLI options
These options exist on convert and mogrify in ImageMagick 7, and it
seems that they have existed for 9 years already, so we should use them
instead of the creation operators. I think they should provide
equivalent behaviour with less bugs.

Fixes #191


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A ruby wrapper for ImageMagick or GraphicsMagick command line.


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.


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).


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
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 1.9.3
  • MRI 2.0
  • MRI 2.1
  • MRI 2.2
  • MRI 2.3
  • MRI 2.4
  • JRuby 9k


Add the gem to your Gemfile:

gem "mini_magick"



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

require "mini_magick"

image ="input.jpg")
image.path #=> "/var/folders/k7/6zx6dx6x7ys3rv3srh0nyfj00000gn/T/magick20140921-75881-1yho3zc.jpg"
image.resize "100x100"
image.format "png"
image.write "output.png" 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. also accepts URLs, and options passed in will be forwarded to open-uri.

image ="")

On the other hand, if we want the original image to actually get modified, we can use

image ="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"
end # the command gets executed

As a handy shortcut, also accepts an optional block which is used to combine_options.

image ="input.jpg") do |b|
  b.resize "250x200>"
  b.rotate "-90"
end # the command gets executed

The yielded builder is an instance of MiniMagick::Tool::Mogrify. To learn more about its interface, see Metal below.


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]
image.signature   #=> "60a7848c4ca6e36b8e2c5dea632ecdc29e9637791d2c59ebf7a54c0c6a74ef7e"

If you need more control, you can also access raw image attributes:

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

To get the all information about the image, MiniMagick gives you a handy method which returns the output from identify -verbose in hash format: #=>
# {
#   "format": "JPEG",
#   "mimeType": "image/jpeg",
#   "class": "DirectClass",
#   "geometry": {
#     "width": 200,
#     "height": 276,
#     "x": 0,
#     "y": 0
#   },
#   "resolution": {
#     "x": "300",
#     "y": "300"
#   },
#   "colorspace": "sRGB",
#   "channelDepth": {
#     "red": 8,
#     "green": 8,
#     "blue": 8
#   },
#   "quality": 92,
#   "properties": {
#     "date:create": "2016-07-11T19:17:53+08:00",
#     "date:modify": "2016-07-11T19:17:53+08:00",
#     "exif:ColorSpace": "1",
#     "exif:ExifImageLength": "276",
#     "exif:ExifImageWidth": "200",
#     "exif:ExifOffset": "90",
#     "exif:Orientation": "1",
#     "exif:ResolutionUnit": "2",
#     "exif:XResolution": "300/1",
#     "exif:YResolution": "300/1",
#     "icc:copyright": "Copyright (c) 1998 Hewlett-Packard Company",
#     "icc:description": "sRGB IEC61966-2.1",
#     "icc:manufacturer": "IEC",
#     "icc:model": "IEC 61966-2.1 Default RGB colour space - sRGB",
#     "jpeg:colorspace": "2",
#     "jpeg:sampling-factor": "1x1,1x1,1x1",
#     "signature": "1b2336f023e5be4a9f357848df9803527afacd4987ecc18c4295a272403e52c1"
#   },
#   ...
# }

Note that MiniMagick::Image#data is supported only on ImageMagick 6.8.8-3 or above, for GraphicsMagick or older versions of ImageMagick use MiniMagick::Image#details.


With MiniMagick you can retrieve a matrix of image pixels, where each member of the matrix is a 3-element array of numbers between 0-255, one for each range of the RGB color channels.

image ="image.jpg")
pixels = image.get_pixels
pixels[3][2][1] # the green channel value from the 4th-row, 3rd-column pixel

It can also be called after applying transformations:

image ="image.jpg")
image.crop "20x30+10+5"
image.colorspace "Gray"
pixels = image.get_pixels

In this example, the returned pixels should now have equal R, G, and B values.


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

For a complete list of configuration options, see Configuration.


MiniMagick also allows you to composite images:

first_image  ="first.jpg")
second_image ="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)
result.write "output.jpg"


For multilayered images you can access its layers.

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

gif.frames.each_with_index do |frame, idx|

Image validation

By default, MiniMagick validates images each time it's opening them. 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|
  config.validate_on_create = false
  config.validate_on_write = false

You can test whether an image is valid:

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


You can choose to log MiniMagick commands and their execution times:

MiniMagick.logger.level = Logger::DEBUG
D, [2016-03-19T07:31:36.755338 #87191] DEBUG -- : [0.01s] identify /var/folders/k7/6zx6dx6x7ys3rv3srh0nyfj00000gn/T/mini_magick20160319-87191-1ve31n1.jpg

In Rails you'll probably want to set MiniMagick.logger = Rails.logger.

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

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 accomplish this with .with_cli:

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

WARNING: If you're building a multithreaded web application, you should change the CLI only on application startup. This is because the configuration is global, so if you change it in a controller action, other threads in the same process will also have their CLI changed, which could lead to race conditions.


If you want to be close to the metal, you can use ImageMagick's command-line tools directly. do |mogrify|
  mogrify << "image.jpg"
end #=> `mogrify -resize 100x100 -negate image.jpg`

# OR

mogrify =
mogrify << "image.jpg" #=> `mogrify -resize 100x100 -negate image.jpg`

This way of using MiniMagick is highly recommended if you want to maximize performance of your image processing. Here are some of the features.


The most basic way of building a command is appending strings: do |convert|
  convert << "input.jpg"
  convert.merge! ["-resize", "500x500", "-negate"]
  convert << "output.jpg"

Note that it is important that every command you would pass to the command line has to be separated with <<, e.g.:

convert << "-resize" << "500x500"

convert << "-resize 500x500"

Shell escaping is also handled for you. If an option has a value that has spaces inside it, just pass it as a regular string.

convert << "-distort"
convert << "Perspective"
convert << "0,0,0,0 0,45,0,45 69,0,60,10 69,45,60,35"
convert -distort Perspective '0,0,0,0 0,45,0,45 69,0,60,10 69,45,60,35'


Instead of passing in options directly, you can use Ruby methods:

convert.distort("Perspective", "0,0,0,0 0,45,0,45 69,0,60,10 69,45,60,35")

MiniMagick knows which options each tool has, so you will get an explicit NoMethodError if you happen to have mispelled an option.


Every method call returns self, so you can chain them to create logical groups. do |convert|
  convert << "input.jpg"
  convert << "output.jpg"

"Plus" options do |convert|
  convert << "input.jpg"
  convert.distort.+("Perspective", "more args")
convert input.jpg +repage +distort Perspective 'more args'

Stacks do |convert|
  convert << "wand.gif"
  convert.stack do |stack|
    stack << "wand.gif"
  convert << "images.gif"
convert wand.gif \( wand.gif -rotate 90 \) images.gif


If you want to pass something to standard input, you can pass the :stdin option to #call:

identify =
identify.stdin # alias for "-" image_content)

MiniMagick also has #stdout alias for "-" for outputing file contents to standard output:

content = do |convert|
  convert << "input.jpg"
  convert.stdout # alias for "-"

Capturing STDERR

Some MiniMagick tools such as compare output the result of the command on standard error, even if the command succeeded. The result of MiniMagick::Tool#call is always the standard output, but if you pass it a block, it will yield the stdout, stderr and exit status of the command:

compare =
# build the command do |stdout, stderr, status|
  # ...

Limiting resources

ImageMagick supports a number of environment variables for controlling its resource limits. For example, you can enforce memory or execution time limits by setting the following variables in your application's process environment:


For a full list of variables and description, see ImageMagick's resources documentation.


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 add the following configuration:

MiniMagick.configure do |config|
  config.whiny = false

If you're using the tool directly, you can pass whiny: false value to the constructor: false) do |b|


It can happen that, when dealing with very large images, the process runs out of memory, and Errno::ENOMEM is raised in your code. In that case try installing the posix-spawn gem, and tell MiniMagick to use it when executing shell commands.

MiniMagick.configure do |config|
  config.shell_api = "posix-spawn"

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 as you would To open a file and directly edit it, use