Convert a list of images (dup and crop a base image and create a thumbnail).

convert_images.rb

#!/usr/bin/env ruby

# Example (crop at 100x100):
# convert_images.rb -x 100 -y 100

require 'optparse'

# This script needs imagemagick.
if !system("which convert > /dev/null 2>&1")
  puts "Abort! Require ImageMagick."
  exit
end

# -------------------------------------------------------
# Options.
# -------------------------------------------------------

x = 0
y = 0
w = 1136
h = 640

OptionParser.new do |opts|
  opts.banner = "Usage: convert_screenshots [options]"

  opts.on("-x", "--left [VALUE]", "X (0 by default)") do |o|
    x = o
  end

  opts.on("-y", "--top [VALUE]", "Y (0 by default)") do |o|
    y = o
  end

  opts.on("-w", "--width [VALUE]", "Width (#{w} by default)") do |o|
    w = o
  end

  opts.on("-h", "--height [VALUE]", "Height (#{h} by default)") do |o|
    h = o
  end
end.parse!

# -------------------------------------------------------
# Actual code.
# -------------------------------------------------------

files = Dir[Dir.getwd + "/*.png"]

files.each_with_index do |file, i|
  puts "Process #{file}…"

  `convert -crop #{w}x#{h}+#{x}+#{y} "#{file}" "#{i}.png"`
  `convert -resize 400x225! -format jpg "#{i}.png" "preview-#{i}.jpg"`
end