RPG Maker Sprite-Sheet extractor. It generates a separate .png file for each sprite.

convert.rb

# RPG Maker sprite-sheet extractor
require 'fileutils'

target_file = File.basename(ARGV[0], File.extname(ARGV[0]))
output_dir = "#{File.dirname(ARGV[0])}/#{target_file}"
FileUtils.mkdir_p(output_dir)

# extract each sprite
%x(convert #{ARGV[0]} -crop 24x32 #{output_dir}/sprite-%03d.png)

num_player = 0
players = 8
pos = 3

positions = ['up', 'right', 'down', 'left']
players_per_line = 4
sprite_length = 12

Dir.glob("#{output_dir}/*").each_with_index do |filename, i|
  num_pos = (i % pos)
  num_player = ((i.to_f / pos).to_i % sprite_length) % players_per_line
  line = ((i.to_f / sprite_length).to_i)
  num_player += 4 if line >= 4
  pos_name = positions[line % positions.length]

  output = "#{output_dir}/player-#{num_player}-#{pos_name}-#{num_pos}.png"
  puts "#{i} => #{num_pos} => #{num_player} => #{line} => #{pos_name} (#{filename} => #{output})"
  FileUtils.mv(filename, output)
end