Ruby, pipes and RMagick

I wanted to be able to run the following:

ls *.jpg | grep -v small | ruby thumbnailise.rb

This command lists all jpg files, excludes the ones that were already converted (thumbnailisied) and calls a Ruby script passing the files using a pipeline.
In order to do that I had to find a way of using Unix pipelines in Ruby. The solution is using STDIN.readlines:

require 'RMagick'
require 'pathname'

input = STDIN.readlines
input.each do |line|
  filename = line.strip
  image = Magick::Image.read(filename).first
  image.crop_resized!(100, 100, Magick::NorthGravity)
  path = Pathname.new(filename)
  outFile = "#{path.basename(".jpg")}_small#{path.extname}"
  image.write(outFile)
end

Do you know any nicer solutions how to do that?