Once upon a time, grayscale image has to be manually converted in order to be displayed on the web. Now with HTML5 canvas, images can be manipulated into grayscale without having to use image editing software. I've put together a demo to show you how to use HTML5 & jQuery to dynamically clone color images into grayscale (see demo). Credits: thanks to Darcy Clarke (my Themify's partner) for the jQuery and Javascript code.

View Demo HTML5 Grayscale

The Purpose

This demo is intented to show you how to make a grayscale/color image hover effect with HTML5 and jQuery. To achieve this effect before HTML5, two images are required: a color and a grayscale version. Now HTML 5 made it easier and faster because the grayscale image is generated from the original source. I hope you will find this script useful in your design such as portfolio showcase, photo gallery, etc.

jQuery Code

The jQuery code below will look for the target images and generate a grayscale version. When hovering the image, it will fade the grayscale image into color.

<script src="jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
	
	// On window load. This waits until images have loaded which is essential
	$(window).load(function(){
		
		// Fade in images so there isn't a color "pop" document load and then on window load
		$(".item img").fadeIn(500);
		
		// clone image
		$('.item 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 
		$('.item img').mouseover(function(){
			$(this).parent().find('img:first').stop().animate({opacity:1}, 1000);
		})
		$('.img_grayscale').mouseout(function(){
			$(this).stop().animate({opacity:0}, 1000);
		});		
	});
	
	// 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();
    }
	    
</script>

How to use it

To apply this to your site:

• include a copy of jquery.js
• paste the code as shown above
• set the target image (eg: .post-img, img, .gallery img, etc.)
• you may change the animation speed (ie. 1000 = 1 second)

Compatibility

It works with any browser that support HTML5 and Javascript such as Chrome, Safari, and Firefox. If HTML5 is not supported, it will fallback to original color image. Note: if it doesn't work with Firefox and Chrome locally. You need to put the HTML file on a web server.

Credits

The Javascript & HTML 5 grayscale is coded by Darcy Clarke.