Ruby: Split an image in two

gistfile1.rb

#!/usr/bin/env ruby

# Takes a list of images as arguments and slices them in half
# All images should be in the same directory

require 'rubygems'
require 'RMagick'
include Magick

# Check to make sure at least one file was given
raise ArgumentError, "No files given. You must supply at least one file to split" if ARGV.empty?

# Some settings
#split_dir = 'split'	# where the split files are stored, relative to where the files are located
crop_width = 0.5		# the percent to crop

i = 1	# Used to detect if currently working on the first or last image
j = 1	# Used to rename images sequentially

# Sort the files list in a more natural way
ARGV.sort_by! { |f| f.split("-")[1].to_i }

# Process the files
ARGV.each do |file|
	if File.file?(file) 	# Make sure the argument is a file
		# Gather information about the file
		path = file.split('/')
		file_name = path.pop
		path = path.join('/')
		name_parts = file_name.split('.')
		ext = name_parts.pop
		base = name_parts.join('.')
		split_dir = "#{path}/#{base.split('-').shift}"

		Dir.mkdir(split_dir) unless Dir.exists?(split_dir)
		
		if i == 1 || i == ARGV.size
			puts "#{file} was moved to #{split_dir}/#{j}.jpg"
			`mv '#{file}' '#{split_dir}/#{j}.jpg'`
			j += 1
			
		else
			left_file = "#{split_dir}/#{j}.jpg"
			j += 1
			right_file = "#{split_dir}/#{j}.jpg"
			j += 1
			
			image = ImageList.new(file);
			# Crop and save the left image
			if image.crop(0, 0, image.columns * crop_width, image.rows).write(left_file)
			   puts "#{left_file} written successfully."
			else 
				puts "FAILED: #{left_file}" 
			end
		
			# Crop and save the right image
			if image.crop(image.columns * crop_width, 0, image.columns, image.rows).write(right_file)
				puts "#{right_file} written successfully."
			else 
				puts "FAILED: #{right_file}" 
			end
		end
		i += 1
	end
end