pixen_to_gameQuery.rb

module PixenToGameQuery
  require 'RMagick'
  include Magick

  FPR = 12      # Frames per row in a sprite sheet generated by Pixen
  COLPAD = 2    # Pix between each column of images on the sprite sheet
  ROWPAD = 2    # Pix between each row of images on the sprite sheet
  LEFTPAD = 4   # Extra pix on left of sprite sheet
  RIGHTPAD = 20 # Extra pix on right of sprite sheet
  BOTTOMPAD = 2 # Extra pix on bottom of sprite sheet

  def PixenToGameQuery.convert_sprite(image_path, width, height, frames, new_image_path)
  
    original = ImageList.new(image_path)
    img = Image.new((width + COLPAD) * frames, height)
    sprite_rows = (frames.to_f / FPR).ceil
  
    0.upto(sprite_rows - 1) do |rownum|
      rowframes = (rownum == sprite_rows - 1) ? frames % FPR : FPR
      row_width = rowframes * (width + COLPAD)
      pix = original.get_pixels(LEFTPAD,
                                ROWPAD + (height + ROWPAD) * rownum,
                                row_width,
                                height)
      img.store_pixels(rownum * FPR * (width + COLPAD),
                       0,
                       row_width,
                       height,
                       pix)
    end
  
    img.write(new_image_path)
  end
end

Minor changes to encapsulate the code in a Module and change filename to match module name.