MiniMagick

A ruby wrapper for ImageMagick command line.

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

$ magick -version
Version: ImageMagick 7.1.1-33 Q16-HDRI aarch64 22263 https://imagemagick.org
Copyright: (C) 1999 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC HDRI Modules OpenMP(5.0)
Delegates (built-in): bzlib fontconfig freetype gslib heic jng jp2 jpeg jxl lcms lqr ltdl lzma openexr png ps raw tiff webp xml zlib zstd
Compiler: gcc (4.2)

Installation

Add the gem to your Gemfile:

$ bundle add mini_magick

Information

• API documentation

Usage

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

require "mini_magick"

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, and options passed in will be forwarded to open-uri.

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"
# Not calling #write, because it's not 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

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

image = MiniMagick::Image.new("input.jpg") do |b|
  b.resize "250x200>"
  b.rotate "-90"
  b.flip
end # the command gets executed

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

Attributes

A MiniMagick::Image has various handy attributes.

image.type        #=> "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 magick input.jpg json::

image.data #=>
# {
#   "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 http://www.iec.ch",
#     "icc:model": "IEC 61966-2.1 Default RGB colour space - sRGB",
#     "jpeg:colorspace": "2",
#     "jpeg:sampling-factor": "1x1,1x1,1x1",
#     "signature": "1b2336f023e5be4a9f357848df9803527afacd4987ecc18c4295a272403e52c1"
#   },
#   ...
# }

Pixels

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 = MiniMagick::Image.open("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 = MiniMagick::Image.open("image.jpg")
image.crop "20x30+10+5"
image.colorspace "Gray"
pixels = image.get_pixels

Pixels To Image

Sometimes when you have pixels and want to create image from pixels, you can do this to form an image:

image = MiniMagick::Image.open('/Users/rabin/input.jpg')
pixels = image.get_pixels
depth = 8
dimension = [image.width, image.height]
map = 'rgb'
image = MiniMagick::Image.get_image_from_pixels(pixels, dimension, map, depth ,'jpg')
image.write('/Users/rabin/output.jpg')

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

Configuration

Here are the available configuration options with their default values:

MiniMagick.configure do |config|
  config.timeout = nil # number of seconds IM commands may take
  config.errors = true # raise errors non nonzero exit status
  config.warnings = true # forward warnings to standard error
  config.tmpdir = Dir.tmpdir # alternative directory for tempfiles
  config.logger = Logger.new($stdout) # where to log IM commands
  config.cli_prefix = nil # add prefix to all IM commands
  config.cli_env = {} # environment variables to set for IM commands
  config.restricted_env = false # when true, block IM commands from accessing system environment variables other than those in cli_env
end

For a more information, see Configuration API documentation.

Composite

MiniMagick also allows 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

You can test whether an image is valid by running it through identify:

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

Logging

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.

Tools

If you prefer not to use the MiniMagick::Image abstraction, you can use ImageMagick's command-line tools directly:

MiniMagick.convert do |convert|
  convert << "input.jpg"
  convert.resize("100x100")
  convert.negate
  convert << "output.jpg"
end #=> `magick input.jpg -resize 100x100 -negate output.jpg`

# OR

convert = MiniMagick.convert
convert << "input.jpg"
convert.resize("100x100")
convert.negate
convert << "output.jpg"
convert.call #=> `magick input.jpg -resize 100x100 -negate output.jpg`

This way of using MiniMagick is highly recommended if you want to maximize performance of your image processing. There are class methods for each CLI tool: animate, compare, composite, conjure, convert, display, identify, import, mogrify and stream. The MiniMagick.convert method will use magick on ImageMagick 7 and convert on ImageMagick 6.

Appending

The most basic way of building a command