RMagick

Table of Contents

• Introduction
• Prerequisites
• Installing RMagick
• Using RMagick
• Things that can go wrong
• Upgrading
• More samples
• Reporting Bugs
• Development Setup
• Credits
• License
• Releasing

Introduction

RMagick is an interface between the Ruby programming language and the ImageMagick image processing library.

Prerequisites

These prerequisites are required for the latest version of RMagick.

OS

• Linux
• *BSD
• macOS
• Windows
• Other *nix-like systems

C++ compiler

• RMagick 5.4.0 or later requires a C++ compiler.

Ruby

• Version 3.2 or later.

You can get Ruby from https://www.ruby-lang.org.

Ruby must be able to build C-Extensions (e.g. MRI, not JRuby)

ImageMagick

• Version 6.9 or later (for ImageMagick 6 users).
• Version 7.1 or later (for ImageMagick 7 users).

You can get ImageMagick from https://imagemagick.org.

Linux

Debian-based

On Debian-based, you can run:

apt install libmagickwand-dev

RHEL-compatible

On RHEL-compatible, you can run:

dnf install ImageMagick-devel

Arch Linux

On Arch Linux, you can run:

pacman -Syy imagemagick

Alpine Linux

On Alpine Linux, you can run:

apk add imagemagick imagemagick-dev imagemagick-libs

or you can run if you would like to use ImageMagick 6:

apk add imagemagick6 imagemagick6-dev imagemagick6-libs

macOS

On macOS, you can run:

brew install imagemagick

or you can run if you would like to use ImageMagick 6:

brew install imagemagick@6

Windows

1. Install latest Ruby+Devkit package which you can get from RubyInstaller for Windows.
2. Download ImageMagick-7.XXXX-Q16-x64-dll.exe (not, ImageMagick-7.XXXX-Q16-x64-static.exe) binary from Windows Binary Release, or you can download ImageMagick 6 from Windows Binary Release.
3. Install ImageMagick. You need to turn on checkboxes Add application directory to your system path and Install development headers for C and C++ in an installer for RMagick.

If you want to install ImageMagick using winget, run the following command:

winget install ImageMagick.ImageMagick --custom /TASKS=modifypath,install_Devel

If you want to install ImageMagick using Chocolatey, run the following command:

choco install imagemagick -PackageParameters InstallDevelopmentHeaders=true

Windows (via MSYS2 / RubyInstaller)

If you are using RubyInstaller for Windows, you can easily install ImageMagick using MSYS2's pacman package manager. Open your command prompt and run the appropriate command for your architecture to install ImageMagick:

For x64:

ridk exec pacman -S mingw-w64-ucrt-x86_64-imagemagick

For ARM64:

ridk exec pacman -S mingw-w64-clang-aarch64-imagemagick

Installing RMagick

[!NOTE] When you update the ImageMagick version, we have recommended you should re-install RMagick.

Installing via Bundler

Add to your Gemfile:

gem 'rmagick'

Then run:

bundle install

For Windows, you need to run using ridk tool:

ridk exec bundle install

Installing via RubyGems

Run:

gem install rmagick

For Windows, you need to run using ridk tool:

ridk exec gem install rmagick

Versioning

RMagick is versioned according to Semantic Versioning. Versions >= 7 work on Ruby >= 3.2 only. For older Ruby versions, use RMagick ~> 6.0.

Using RMagick

Require RMagick in your project as follows:

require 'rmagick'

See https://rmagick.github.io/usage.html for links to more information.

Threads, fibers and fork

RMagick releases the GVL while ImageMagick works, so calls on different images run in parallel.

• Use each image from one thread at a time. To work in parallel, give each thread its own images.
• On Ruby 4.0 and later, a Fiber scheduler with a worker pool, such as Async::Scheduler.new(worker_pool: IO::Event::WorkerPool.new), runs heavy calls on its workers, and the other fibers keep running. While such a call uses an image, using that image from another fiber, or from another Ractor that shares it frozen, raises RuntimeError ("object is in use by another fiber").
• Each call in flight holds its images in memory, so memory use grows with the number of workers. Limit the calls that run at once, for example with Async::Semaphore.
• Thread#raise, Timeout and Ctrl-C reach a thread after the ImageMagick call returns. An exception raised in a trap handler can unwind through ImageMagick instead.
• Do not fork while other threads or workers are running ImageMagick. The child can hang on a lock that they held.
• After ImageMagick has used OpenMP, a call that uses OpenMP in a forked child can hang. A process that forks after using RMagick should set MAGICK_THREAD_LIMIT=1.

Things that can go wrong

The RMagick installation FAQ has answers to the most commonly reported problems, though may be out of date.

Can't install RMagick. Can't find libMagickCore-XXXX.so or one of the dependent libraries. Check the mkmf.log file for more detailed information

Typically this message means that one or more of the libraries that ImageMagick depends on hasn't been installed. Examine the mkmf.log file in the ext/RMagick subdirectory of the installation directory for any error messages. These messages typically contain enough additional information for you to be able to diagnose the problem. Also see this FAQ.

Cannot open shared object file

If you get a message like this:

... /core_ext/kernel_require.rb>:136:in `require': cannot load such file -- RMagick2.so (LoadError)
  (snip)

you probably do not have the directory in which the ImageMagick library is installed in your load path. An easy way to fix this is to define the directory in the LD_LIBRARY_PATH environment variable. For example, suppose you installed the ImageMagick library libMagickCore-XXXX.so in /usr/local/lib. (By default this is where it is installed.) Create the LD_LIBRARY_PATH variable like this:

export LD_LIBRARY_PATH=/usr/local/lib

On Linux, see ld(1) and ld.so(8) for more information. On other operating systems, see the documentation for the dynamic loading facility.

This operation might not be required when you can use 4.2.5 or later.

Segmentation fault

Default stack size of your operating system might be too small. Try removing the limit with this command:

ulimit -s unlimited

Upgrading

If you upgrade to a newer release of ImageMagick, make sure you're using a release of RMagick that supports that release. It's safe to install a new release of RMagick over an earlier release.

More samples

You can find more sample RMagick programs in the /examples and /doc/ex directories. These programs are not installed in the RMagick documentation tree.

Reporting bugs

Please report bugs in RMagick, its documentation, or its installation programs via the bug tracker on the RMagick issues page.

However, We can't help with Ruby installation and configuration or ImageMagick installation and configuration. Information about reporting problems and getting help for ImageMagick is available at the ImageMagick website or the ImageMagick Discussions.

Development Setup

In order to minimize issues on your local machine, we recommend that you make use of Dev Containers. This provides a consistent, pre-configured development environment using Docker.

Steps to get up and running with a passing build are as follows:

1) Set up the prerequisites

To use Dev Containers, you will need to install the following tools on your machine:

• Docker Desktop (or Docker Engine)
• Visual Studio Code
• Dev Containers extension for VS Code

2) Clone RMagick and open the container

Clone the repository to your local machine and open it in VS Code:

git clone https://github.com/rmagick/rmagick.git # or your fork
cd rmagick
code .

Once VS Code opens, it should detect the .devcontainer configuration and prompt you to "Reopen in Container".

During this process, VS Code will ask you to select a devcontainer.json configuration. You can choose the environment you want to develop and test against:

• ImageMagick 7 (.devcontainer/devcontainer.json) - Recommended for the latest development.
• ImageMagick 6 (.devcontainer/ImageMagick6/devcontainer.json) - For testing against the legacy ImageMagick 6 API.

Select the one you need, and VS Code will automatically build the corresponding Docker image and start your isolated development environment. This may take a few minutes the first time.

3) Build RMagick

Once the container is running and the ImageMagick setup is complete, open a new terminal inside VS Code. Install the Ruby dependencies and compile the RMagick extension:

$ bundle install
$ bundle exec rake

And you're all set! The codebase on your local machine is automatically synced with the container. You can edit files using your local VS Code, and run tests seamlessly within the integrated container terminal.

Credits

Authors: Tim Hunter, Omer Bar-or, Benjamin Thomas

Thanks to ImageMagick Studio LLC for ImageMagick and for hosting the RMagick documentation.

License

MIT License

Releasing

1. Update ChangeLog
2. Edit lib/rmagick/version.rb
3. Are the tests passing? Run rake again just to be sure.
4. rake release