在这个教程中，作者使用HTML5的canvas将针对网站图片做不同的灰度处理。这个演示中使用HTML5和jQuery的黄金组合来动态的克隆颜色来实现灰度效果。整个显示非常炫。是学习HTML5 canvas的不错实战教程。

jQuery 代码：

<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>

在线演示：http://webdesignerwall.com/demo/html5-grayscale/