ruby-vips : A fast image processing extension for Ruby.

ruby-vips is a ruby extension for vips. It is fast and it can process images without requiring the entire image to be loaded into memory. For example, the benchmark at vips-benchmarks loads a large image, crops, shrinks, sharpens and saves again:

real time in seconds, fastest of three runs
benchmark       tiff    jpeg
ruby-vips.rb    0.45    0.56    
rmagick.rb      1.69    1.90    
netpbm.sh       1.74    1.63    
image-magick.sh 2.87    3.02    
image_sci.rb    3.19    2.90    

peak memory use in kilobytes
benchmark       peak RSS
ruby-vips.rb    160400
image_sci.rb    546992
rmagick.rb      1370064

See also benchmarks at the official libvips website. There's a handy blog post explaining how libvips opens files which gives some more background.

ruby-vips allows you to set up pipelines that don't get executed until you output the image to disk or to a string. This means you can create, manipulate, and pass around Image objects without incurring any memory or CPU costs. The image is not actually processed until you write the image to memory or to disk.

note: ruby-vips will work with versions of libvips as far back as 7.12, but with missing features and with reduced performance. For best results, use the latest libvips you can.

Requirements.

• OS X or Linux
• MRI 1.8.7, 1.9.3
• libvips 7.24 and later (it will work with earlier libvips, but some features may not be functional)

Installation.

Ubuntu Prerequisites.

$ apt-get install libvips-dev

OS X Prerequisites.

$ brew tap homebrew/science
$ brew install vips

This will give you a very bare-bones vips, missing things like imagemagick loading, openslide support, FFTs, and so on. To get a list of all the optional dependencies, try:

$ brew info vips

For a full-fat version, try:

$ brew install vips --with-cfitsio --with-fftw --with-imagemagick \
    --with-libexif --with-liboil --with-libtiff --with-little-cms \
    --with-openexr --with-openslide --with-pango

If you want to build things outside homebrew which depend on vips, such as ruby-vips, your pkg-config will need to be working. You need to point pkg-config at the homebrew area, and, additionally, at homebrew's libxml2 area:

In your .profile, add something like:

export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:/usr/local/opt/libxml2/lib/pkgconfig

To verify that your vips install is correct and working, try:

$ vips --version
vips-7.32.1-Mon May 20 10:01:38 BST 2013

To verrify that your pkg-config is working correctly with vips, try:

$ pkg-config vips --libs
-L/usr/local/Cellar/vips/7.32.1/lib ... a lot of stuff

TODO: Describe & test with macports.

Other platforms

See Installation on various platforms.

Installing the gem.

$ gem install ruby-vips

or include it in Gemfile:

gem 'ruby-vips'

For a debug build:

$ gem install ruby-vips -- --enable-debug

Documentation.

ruby-vips has rdoc documentation. Also see Wiki page

Small example

See also the examples directory.

require 'rubygems'
require 'vips'

include VIPS

# Create an image object. It will not actually load the pixel data until 
# needed. 
im = Image.jpeg('mypic.jpg')

# You can read all the header fields without triggering a pixel load.
puts "it's #{im.x_size} pixels across!"

# Shrink the jpeg by a factor of four when loading -- huge speed and CPU
# improvements on large images.
im = Image.jpeg('mypic.jpg', :shrink_factor => 4)
puts "but only #{im.x_size} pixels when we shrink on load"

# Add a shrink by a factor of two to the pipeline. This will not actually be
# executed yet.
im_shrink_by_two = im.shrink(2)

# Write out the shrunk image to a PNG file. This is where the image is
# actually loaded and resized. With images that allow for random access from
# the hard drive (VIPS native format, tiled OpenEXR, ppm/pbm/pgm/pfm, tiled
# tiff, and RAW images), the entire image is never read into memory.
# For other formats, the image is either decompressed to a temporary disc 
# file and then processed from there, or, if you give the :sequential hint, 
# streamed directly from the file.
im_shrink_by_two.png('out.png', :interlace => true)

# All ruby-vips image commands can be chained, so the above sequence could
# be written as:
Image.jpeg('mypic.jpg', :shrink_factor => 4).shrink(2).png('out.png')

# You hint sequential mode in the loader, so this will stream directly from
# the source image:
Image.jpeg('large.png', :sequential => true).shrink(2).png('out.png')

# The statement above will load the jpeg (pre-shrunk by a factor of four),
# shrink the image again by a factor of two, and then save as a png image.

# If you want to let vips determine file formats, you can use the generic
# reader and writer:
Image.new('mypic.jpg').shrink(2).write('out.png')

Why use ruby-vips?

• It supports over 250 low-level image and color manipulation operations.
• Operations are chainable and do not get executed until the image is sent to an output.
• Memory use is low, even for very, very large images.
• Fastest ruby library for resizing large images. See benchmarks at the official libvips website and vips-benchmarks