extract thumbnail from Paint.NET file

extract_pdn.rb

require "base64"

# check for input file parameter
puts "ruby pdn_decode.rb infile.pdn" or exit if ( ARGV.length!=1 || File.extname(ARGV[0]).downcase!='.pdn' || !File.exist?(ARGV[0]) )

# extract image type and image data
imageType, base64Data = IO.read(ARGV[0]).match(/<thumb (.+?)="(.+?)" \/>/)[1..2]

# determine new filename and check that it doesn't exist
newFile = ARGV[0][0..-5] + ".#{imageType}"
puts "#{newFile} already exists." or exit if File.exists? newFile

# save image data to new file
File.open(newFile, "w") {|f| f.write(Base64.decode64(base64Data))}

# open file -- os x specific
system `open #{newFile}` if RUBY_PLATFORM=~/darwin/