FreeImage Ruby Bindings


The free-image gem provides Ruby language bindings for the FreeImage library. It is free software, released under the MIT License.

FreeImage is an light-weight, open source image manipulation library that supports many popular graphics image formats such as PNG, JPEG, GIF, BMP, and TIFF.

We think FreeImage is a great library for applications that need to read, write, create and modify images and thumbnails because:

  • Its easy to use

  • Its supports almost all popular image formats

  • Its a light-weight alternative to larger libraries such as ImageMagick, supporting basic manipulation functions but not advanced functionality

  • Its cross-platform

  • The ruby bindings are implemented using FFI, so work across all Ruby implementations and do not have to be compiled

  • Its much more comprehensive than ImageScience

  • Has comprehensive documentation

Note that FreeImage is not the right library for you if you need:

  • Advanced image processing operations such as convolution and transforms

  • Bitmap drawing

  • Vector graphics


free-image requires FreeImage version 3.10 or higher and Ruby 1.8.7 or higher. The easiest way to install free-image is via Ruby Gems. To install:

gem install free-image

Getting Started

Getting started is easy - first work through the examples in the cookbook. Once you've done that, the refer to rdocs for extensive documentation.

Memory Management

Opening and working with images consumes some memory. Generally you won't have to worry about this. When an image goes out of scope, it will be garbage collected and the underlying image memory will be freed.

Having said that, FreeImage also lets you control when the memory is freed. Any method that creates a new image also takes a block. When the block finishes, the underlying image memory is freed. This works the same way as the method. For example:'images/lena.png') do |image|
  thumbnail = image.make_thumbail do |thumbail|'images/thumbnail.png', :png)

When the inner block finishes the thumbnail image is freed and when the outer block finished the lena image is freed.

If you need even more control, you can use FreeImage::Bitmap#free which frees the underlying image. Be careful though - once the image is freed further usage of it will result in a segmentation fault.

Implementation Status

The FreeImage API is divided into multiple parts. As summarized below, the Ruby ffi bindings currently implement a subset of the available api. Patches are welcome to extend the coverage.

Bitmap functions

  • General - FreeImage::Bitmap

  • Bitmap management - FreeImage::Bitmap

  • Bitmap information - FreeImage::Information, FreeImage::Color::Palette

  • Filetype - FreeImage::File, FreeImage::IO, FreeImage::Memory

  • Pixel access - FreeImage::Pixel

  • Conversion - FreeImage::Conversions

  • Tone mapping - Not Implemented

  • ICC profile - FreeImage::ICC

  • Plugin - Not Implemented

  • Multipage - Not Implemented

  • Memory I/O streams - FreeImage::MemoryStream

  • Compression - Not Implemented

  • Helper functions - FreeImage::Helper

Metadata Functions

  • Introduction - Not Implemented

  • Tag creation and destruction - Not Implemented

  • Tag accessors - Not Implemented

  • Metadata iterator - Not Implemented

  • Metadata accessors - Not Implemented

  • Metadata helper functions - Not Implemented

Toolkit Functions

  • Rotation and flipping - FreeImage::Transforms

  • Upsampling / downsampling - FreeImage::Modify

  • Color manipulation - Not Implemented

  • Channel processing - Not Implemented

  • Copy / Paste / Composite routines - FreeImage::Modify

  • Background filling - FreeImage::Modify

  • Miscellaneous algorithms - FreeImage::Helper


Documentation is available via rdoc, and is installed automatically with the gem. Note that much of the documentation is directly copied from the FreeImage API documentation available here.

free-image's online documentation is generated using Hanna. To generate documentation from source:

gem install hanna-nouveau
rake rdoc
- or -
rdoc -o doc/rdoc -f hanna -m "README.rdoc" lib/**/*.rb README.rdoc


If you have any questions about using free-image, please ?


See LICENSE for license information.