lists images in a directory, returns javascript array

gistfile1.rb

require 'pow'

class JPEG
  attr_reader :width, :height, :bits

  def initialize(file)
    if file.kind_of? IO
      examine(file)
    else
      File.open(file, 'rb') { |io| examine(io) }
    end
  end

private
  def examine(io)
    raise 'malformed JPEG' unless io.getc == 0xFF && io.getc == 0xD8 # SOI

    class << io
      def readint; (readchar << 8) + readchar; end
      def readframe; read(readint - 2); end
      def readsof; [readint, readchar, readint, readint, readchar]; end
      def next
        c = readchar while c != 0xFF
        c = readchar while c == 0xFF
        c
      end
    end

    while marker = io.next
      case marker
        when 0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF # SOF markers
          length, @bits, @height, @width, components = io.readsof
          raise 'malformed JPEG' unless length == 8 + components * 3
        when 0xD9, 0xDA:  break # EOI, SOS
        when 0xFE:        @comment = io.readframe # COM
        when 0xE1:        io.readframe # APP1, contains EXIF tag
        else              io.readframe # ignore frame
      end
    end
  end
end

class ImageList
  attr_reader :images

  def initialize
    scan
  end
  
  def scan
    basedir = "images/gallery/"
    path = Pow(basedir)
    @images = "[\n"
    path.files.each do |document|
      case document.extention
         when /png/i   then dimensions = IO.read(basedir + document.name)[0x10..0x18].unpack('NN')
         when /gif/i   then dimensions = IO.read(basedir + document.name)[6..10].unpack('SS')
         when /bmp/i   then bmp = IO.read(basedir + document.name)[14..28]
                            dimensions = bmp[0] == 40 ? bmp[4..-1].unpack('LL') : bmp[4..8].unpack('SS')
         when /jpe?g/i then dimensions = []
                               dimensions[0] = JPEG.new(basedir + document.name).height
                               dimensions[1] = JPEG.new(basedir + document.name).width
      end
      if dimensions
        @images += "[\'#{basedir}#{document.name}\', \'#{document.name(false)}\', \'#{dimensions[0]}\', \'#{dimensions[1]}\'],\n"
      end
    end
    @images.chop!.chop! unless @images == "[\n"
    @images += "\n];\n"
  end
end