點評：以前，在web上要顯示灰度圖片的話，只有手工使用圖片軟件轉換。但是現在借助于html5的canvas可以實現這個過程，而不需要再借助圖片編輯軟件了

復制代碼

<script src="jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
// 設置 window load事件是為了等待所有圖片加載完畢之后才行運行
$(window).load(function(){
// 使圖片漸入，這樣有顏色的原圖就不會顯示出來了，然后再執行window load 事件
$(".item img").fadeIn(500);
// 復制圖片
$('.item img').each(function(){
var el = $(this);
el.css({"position":"absolute"}).wrap("<div>").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);
});
// 使圖片漸入
$('.item img').mouseover(function(){
$(this).parent().find('img:first').stop().animate({opacity:1}, 1000);
})
$('.img_grayscale').mouseout(function(){
$(this).stop().animate({opacity:0}, 1000);
});
});
// 使用canvas制作灰色圖片
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>