bmd = document.getElementById("canvas").bitmapData;

bikes = new Image();
bikes.src = "res/bikes.png";
bmd.draw(bikes);

lenna = new Image();
lenna.src = "res/lenna-300x300.png";
lennaData = new BitmapData(300, 300);
lennaData.draw(lenna);

threshold = 0x333333;
rect = new Rectangle(100, 100, 200, 200);
point = new Point(50, 50);
setInterval(function() {
	bmd.draw(bikes);
	bmd.threshold(lennaData, 
		rect, 
		point, 
		"<", 
		threshold, 
		0x00ff00, 
		null, 
		true);

	if(threshold >= 0xffffff) threshold = 0x333333;
	else threshold += 0x00eeee;
}, 10);