Ruby script to scale and crop an image into overlay or map tiles for use with Google Maps API, Javascript for display custom map tiles below.

map_tile.rb

#! /usr/bin/ruby -w
require 'rubygems'
require 'rmagick'
require 'fileutils'
include Magick

ARGV.each do |file|

	puts "Processing #{file}"

	# Check file exists
	unless File::exists?( file )
		puts "Image #{file} not found"
		next
	end

	#Setup
	img_name = File.basename(file, ".jpg")
	
	# Load the source image and a little information
	img = Magick::Image.read(file).first
	w = img.columns
	h = img.rows

	puts "Image #{file} too small (<512x512)" and next unless (h > 512 || w > 512)

	FileUtils.rm_rf(img_name) if File::directory?(img_name)
	Dir.mkdir(img_name)

	  # Find the next largest multiple of 256 and the power of 2
  dim = w > h ? w : h
  pow = -1
  
  loop do
    i = 256*(2**pow+=1)
    next if i < dim
    dim = i
    break
  end

  # Resize the source image up to the larger size
  if (dim > w && dim > h)
  	puts "Resizing image to #{dim}px"
    # Determine the optimal pixel radius for sharpening

    img.change_geometry!("#{dim}x#{dim}") { |cols, rows, i|
 		 i.resize!(cols, rows)
 	  }
        sharp = ( w/dim > h/dim ? dim/w : dim/h )/2
    img = img.sharpen(sharp)
  end

  # Build a new square image with a black background, and composite the source image on top of it.
  master = Magick::Image.new(dim,dim){ self.background_color = "#E4E3DF" }
  master.composite!(img, Magick::CenterGravity, Magick::OverCompositeOp)



  img = nil

  # Create slice layers
  layer = 0
  loop do
    # Google Maps only allows 19 layers (though I doubt we'll ever reach this point).
    break if layer > 18
    width = 256*(2**layer)

    break if width > dim
    Dir.mkdir("#{img_name}/#{layer}", 0775) unless File::directory?("#{img_name}/#{layer}")

    crop_master = master.clone
    crop_master.resize!(width, width)

    max_loop = (width / 256) - 1

    (0 .. max_loop).each do |x|
      (0 .. max_loop).each do |y|
        crop = crop_master.clone
        crop.crop!( x*256, crop_master.rows - ((y + 1) * 256), 256, 256) 
        crop.write("#{img_name}/#{layer}/#{x}-#{y}.jpg")
        crop = nil
      end
    end
    
    layer+=1
    crop_master = nil
  end

  master = nil

end
 

maps.js

var map;
function loadMap(){

	var maptiler = new google.maps.ImageMapType({ 
	  getTileUrl: function(coord, zoom) { 
	  	if (coord.x < 0 || (Math.pow(2,zoom)-coord.y-1) < 0 || (Math.pow(2,zoom)-coord.y-1) >= Math.pow(2,zoom) || coord.x >= Math.pow(2,zoom))
	  		return "/system/blank.jpg";
	  	else
			return "/system/" + map_loc + "/" + zoom + "/" + coord.x + "-" + (Math.pow(2,zoom)-coord.y-1) + ".jpg";  
		}, 
	  tileSize: new google.maps.Size(256, 256), 
	  maxZoom: map_max_zoom,
	  minZoom: map_min_zoom,
	  name:'Paris'
	});

	map = new google.maps.Map(document.getElementById("map"), {streetViewControl: false, mapTypeControl: false}); 
	map.mapTypes.set('paris', maptiler);
	map.setMapTypeId('paris');
	map.setCenter(new google.maps.LatLng(map_lat, map_lon)); 
	map.setZoom(map_init_zoom);
}