Write "hello, world" on a PNG

gistfile1

#!/usr/bin/env ruby

require 'rubygems'
require 'mini_magick'

BLANK = 'blank.png'    # 1x1px white png
$text = 'hello, world' # text to write

img = MiniMagick::Image.from_file(BLANK)

font_size = 12                 # points
margin    = 6                  # 3px on each side
h         = font_size + margin
w         = 7 * $text.length   # 7px per letter

img.combine_options do |c|
  c.resize     "#{w}X#{h}!"
  c.gravity    'Center'
  c.font       '-*-arial-*-r-*-*-' + font_size.to_s + '-*-*-*-*-*-*-1'
  c.pointsize  font_size.to_s
  c.draw       "text 0,0 '#{$text}'"
  c.fill       '#000000'
end
img.write("out.png")
puts `identify out.png`