文章简介：html5和jquery的灰度图片悬浮效果.
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：
// 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("
").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();
}
在线演示：/demo/html5-grayscale/
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