Is there a simple way to get image dimensions in Ruby?

As of June 2012, FastImage which “finds the size or type of an image given its uri by fetching as little as needed” is a good option. It works with local images and those on remote servers.

An IRB example from the readme:

require 'fastimage'

FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
=> [266, 56]  # width, height

Standard array assignment in a script:

require 'fastimage'

size_array = FastImage.size("http://stephensykes.com/images/ss.com_x.gif")

puts "Width: #{size_array[0]}"
puts "Height: #{size_array[1]}"

Or, using multiple assignment in a script:

require 'fastimage'

width, height = FastImage.size("http://stephensykes.com/images/ss.com_x.gif")

puts "Width: #{width}"
puts "Height: #{height}"