Resize images and convert to .jpg, deleting the original files.

resize.rb

#!/usr/bin/env ruby

require 'mini_magick'
require 'fileutils'

begin
  size = Integer(ARGV[0])
rescue ArgumentError
  puts "Size argument must be an integer."
  exit
end

image_files = Dir.glob("*.{jpg,png,gif}")

total_images = image_files.count
resized_images = 0
total_starting_size = image_files.reduce(0) { |sum, file| sum + File.size(file) }
total_ending_size = 0

image_files.each do |image_file|
  image = MiniMagick::Image.open(image_file)

  # Resize the image, retaining the aspect ratio
  if image[:width] > size
    image.resize "#{size}x"
    resized_images += 1
  end

  image.quality 85

  new_file = image_file.sub(/\.[^.]+\z/, '.jpg')
  image.format 'jpg'
  image.write new_file

  total_ending_size += File.size(new_file)

  File.delete(image_file)
end

puts "Total images processed: #{total_images}"
puts "Total images resized: #{resized_images}"
puts "Total starting size: #{(total_starting_size / 1024.0).round(2)} KB"
puts "Total ending size: #{(total_ending_size / 1024.0).round(2)} KB"
puts "Saved: #{((total_starting_size - total_ending_size) / 1024.0).round(2)} KB"