dimensions_bench.rb

require 'rubygems'
require 'benchmark'
require 'dimensions'

pics = Dir.glob("/Users/jyurek/Pictures/[0-9a-zA-Z]*.*")
Benchmark.bmbm do |x|
  x.report('imagemagick') do
    pics[0..1000].each{|f| `identify -format '%wx%h' "#{f}" 2>&1`.split("x") }
  end
  x.report('dimensions') do
    pics[0..1000].each{|f| Dimensions.dimensions(f) }
  end
end

output 1.9.2

Rehearsal -----------------------------------------------
imagemagick   0.160000   1.470000  13.460000 ( 14.951678)
dimensions    0.240000   0.270000   0.510000 (  0.521630)
------------------------------------- total: 13.970000sec

                  user     system      total        real
imagemagick   0.160000   1.880000  13.980000 ( 14.503369)
dimensions    0.200000   0.290000   0.490000 (  0.488729)