// On window load. This waits until images have loaded which is essential
$(window).load(function () {    
    //test for canvas support
    if (!!document.createElement('canvas').getContext) {
        // clone image
        $('.image-gallery img').each(function() {
            var el = $(this);
            el.css({ "position": "absolute" }).wrap("<div class='img_wrapper' style='display: inline-block'>").clone().addClass('img_grayscale').css({ "position": "absolute", "z-index": "998", "opacity": "0" }).insertBefore(el).queue(function() {
                var el = $(this);
                el.parent().css({ "width": this.width, "height": this.height });
                el.dequeue();
            });
            this.src = grayscale(this.src);
        });        

        // Fade image 
        $('.image-gallery img').mouseover(function() {
            $(this).parent().find('img:first').stop().animate({ opacity: 1 }, 500);
        });
        $('.img_grayscale').mouseout(function() {
            $(this).stop().animate({ opacity: 0 }, 500);
        });
    }
    
    //fade images in after they are loaded
    $('.image-gallery ul').animate({ opacity: '1' }, 500);
});


// Grayscale w canvas method
function grayscale(src){
	var canvas = document.createElement('canvas');
	var ctx = canvas.getContext('2d');
	var imgObj = new Image();
	imgObj.src = src;
	canvas.width = imgObj.width;
	canvas.height = imgObj.height; 
	ctx.drawImage(imgObj, 0, 0); 
	var imgPixels = ctx.getImageData(0, 0, canvas.width, canvas.height);
	for(var y = 0; y < imgPixels.height; y++){
		for(var x = 0; x < imgPixels.width; x++){
			var i = (y * 4) * imgPixels.width + x * 4;
			var avg = (imgPixels.data[i] + imgPixels.data[i + 1] + imgPixels.data[i + 2]) / 3;
			imgPixels.data[i] = avg; 
			imgPixels.data[i + 1] = avg; 
			imgPixels.data[i + 2] = avg;
		}
	}
	ctx.putImageData(imgPixels, 0, 0, 0, 0, imgPixels.width, imgPixels.height);
	return canvas.toDataURL();
}