从昨天下午开始，我们打开各种网站后都是灰色的，我们讲解一下如何用技术手段使网页变灰色。
//分析：我们网站的元素大多数都是img标签和其他文字行标签，文字我们直接使用color:#ccc就可以更改，图片不可能每张都更换成灰色背景，那非常不现实，一张一张改起来是多大的工程。所以一定是使用类似蒙层，滤镜的东西把原本的色彩遮罩。
利用css3属性 filter:
其实只需要一行代码就可以使网页变灰，我们利用css属性中的过滤器filter就可以实现
filter: grayscale(100%);
grayscale是将图像转换为灰度图像。值定义转换的比例。值为100%则完全转为灰度图像，值为0%图像无变化。值在0%到100%之间，则是效果的线性乘子。若未设置，值默认是0；
这是几年前我仿写的淘宝页，设置100%后效果对比一下
看到评论区有在问ie浏览器的兼容问题，这里回答一下
IE7~9可以使用IE自带的滤镜，在页面头部body内加入样式：
body{ filter:gray; }/*IE7-IE9，必须加在body元素上*/
IE10/11需要用grayscale.js来解决： 这个插件是模拟IE的filter:progid方法，支持IE、Safari、Chrome、Opera、Firefox等浏览器。
<script type="text/javascript" src="grayscale.js"></script>
<script>
grayscale(document.body);
</script>
有很多人不知道在哪里下载这个js库，我把它放在下面，你可以直接复制到你的项目中去
var grayscale = (function(){
var config = {
colorProps: ['color','backgroundColor','borderBottomColor','borderTopColor','borderLeftColor','borderRightColor','backgroundImage'],
externalImageHandler : {
/* Grayscaling externally hosted images does not work
- Use these functions to handle those images as you so desire */
/* Out of convenience these functions are also used for browsers
like Chrome that do not support CanvasContext.getImageData */
init : function(el, src) {
if (el.nodeName.toLowerCase() === 'img') {
// Is IMG element...
} else {
// Is background-image element:
// Default - remove background images
data(el).backgroundImageSRC = src;
el.style.backgroundImage = '';
}
},
reset : function(el) {
if (el.nodeName.toLowerCase() === 'img') {
// Is IMG element...
} else {
// Is background-image element:
el.style.backgroundImage = 'url(' + (data(el).backgroundImageSRC || '') + ')';
}
}
}
},
log = function(){
try { window.console.log.apply(console, arguments); }
catch(e) {};
},
isExternal = function(url) {
// Checks whether URL is external: 'CanvasContext.getImageData'
// only works if the image is on the current domain.
return (new RegExp('https?://(?!' + window.location.hostname + ')')).test(url);
},
data = (function(){
var cache = [0],
expando = 'data' + (+new Date());
return function(elem) {
var cacheIndex = elem[expando],
nextCacheIndex = cache.length;
if(!cacheIndex) {
cacheIndex = elem[expando] = nextCacheIndex;
cache[cacheIndex] = {};
}
return cache[cacheIndex];
};
})(),
desatIMG = function(img, prepare, realEl) {
// realEl is only set when img is temp (for BG images)
var canvas = document.createElement('canvas'),
context = canvas.getContext('2d'),
height = img.naturalHeight || img.offsetHeight || img.height,
width = img.naturalWidth || img.offsetWidth || img.width,
imgData;
canvas.height = height;
canvas.width = width;
context.drawImage(img, 0, 0);
try {
imgData = context.getImageData(0, 0, width, height);
} catch(e) {}
if (prepare) {
desatIMG.preparing = true;
// Slowly recurse through pixels for prep,
// :: only occurs on grayscale.prepare()
var y = 0;
(function(){
if (!desatIMG.preparing) { return; }
if (y === height) {
// Finished!
context.putImageData(imgData, 0, 0, 0, 0, width, height);
realEl ? (data(realEl).BGdataURL = canvas.toDataURL())
: (data(img).dataURL = canvas.toDataURL())
}
for (var x = 0; x < width; x++) {
var i = (y * width + x) * 4;
// Apply Monoschrome level across all channels:
imgData.data[i] = imgData.data[i+1] = imgData.data[i+2] =
RGBtoGRAYSCALE(imgData.data[i], imgData.data[i+1], imgData.data[i+2]);
}
y++;
setTimeout(arguments.callee, 0);
})();
return;
} else {
// If desatIMG was called without 'prepare' flag
// then cancel recursion and proceed with force! (below)
desatIMG.preparing = false;
}
for (var y = 0; y < height; y++) {
for (var x = 0; x < width; x++) {
var i = (y * width + x) * 4;
// Apply Monoschrome level across all channels:
imgData.data[i] = imgData.data[i+1] = imgData.data[i+2] =
RGBtoGRAYSCALE(imgData.data[i], imgData.data[i+1], imgData.data[i+2]);
}
}
context.putImageData(imgData, 0, 0, 0, 0, width, height);
return canvas;
},
getStyle = function(el, prop) {
var style = document.defaultView && document.defaultView.getComputedStyle ?
document.defaultView.getComputedStyle(el, null)[prop]
: el.currentStyle[prop];
// If format is #FFFFFF: (convert to RGB)
if (style && /^#[A-F0-9]/i.test(style)) {
var hex = style.match(/[A-F0-9]{2}/ig);
style = 'rgb(' + parseInt(hex[0], 16) + ','
+ parseInt(hex[1], 16) + ','
+ parseInt(hex[2], 16) + ')';
}
return style;
},
RGBtoGRAYSCALE = function(r,g,b) {
// Returns single monochrome figure:
return parseInt( (0.2125 * r) + (0.7154 * g) + (0.0721 * b), 10 );
},
getAllNodes = function(context) {
var all = Array.prototype.slice.call(context.getElementsByTagName('*'));
all.unshift(context);
return all;
};
var init = function(context) {
// Handle if a DOM collection is passed instead of a single el:
if (context && context[0] && context.length && context[0].nodeName) {
// Is a DOM collection:
var allContexts = Array.prototype.slice.call(context),
cIndex = -1, cLen = allContexts.length;
while (++cIndex<cLen) { init.call(this, allContexts[cIndex]); }
return;
}
context = context || document.documentElement;
if (!document.createElement('canvas').getContext) {
context.style.filter = 'progid:DXImageTransform.Microsoft.BasicImage(grayscale=1)';
context.style.zoom = 1;
return;
}
var all = getAllNodes(context),
i = -1, len = all.length;
while (++i<len) {
var cur = all[i];
if (cur.nodeName.toLowerCase() === 'img') {
var src = cur.getAttribute('src');
if(!src) { continue; }
if (isExternal(src)) {
config.externalImageHandler.init(cur, src);
} else {
data(cur).realSRC = src;
try {
// Within try statement just encase there's no support....
cur.src = data(cur).dataURL || desatIMG(cur).toDataURL();
} catch(e) { config.externalImageHandler.init(cur, src); }
}
} else {
for (var pIndex = 0, pLen = config.colorProps.length; pIndex < pLen; pIndex++) {
var prop = config.colorProps[pIndex],
style = getStyle(cur, prop);
if (!style) {continue;}
if (cur.style[prop]) {
data(cur)[prop] = style;
}
// RGB color:
if (style.substring(0,4) === 'rgb(') {
var monoRGB = RGBtoGRAYSCALE.apply(null, style.match(/\d+/g));
cur.style[prop] = style = 'rgb(' + monoRGB + ',' + monoRGB + ',' + monoRGB + ')';
continue;
}
// Background Image:
if (style.indexOf('url(') > -1) {
var urlPatt = /\(['"]?(.+?)['"]?\)/,
url = style.match(urlPatt)[1];
if (isExternal(url)) {
config.externalImageHandler.init(cur, url);
data(cur).externalBG = true;
continue;
}
// data(cur).BGdataURL refers to caches URL (from preparation)
try {
var imgSRC = data(cur).BGdataURL || (function(){
var temp = document.createElement('img');
temp.src = url;
return desatIMG(temp).toDataURL();
})();
cur.style[prop] = style.replace(urlPatt, function(_, url){
return '(' + imgSRC + ')';
});
} catch(e) { config.externalImageHandler.init(cur, url); }
}
}
}
}
};
init.reset = function(context) {
// Handle if a DOM collection is passed instead of a single el:
if (context && context[0] && context.length && context[0].nodeName) {
// Is a DOM collection:
var allContexts = Array.prototype.slice.call(context),
cIndex = -1, cLen = allContexts.length;
while (++cIndex<cLen) { init.reset.call(this, allContexts[cIndex]); }
return;
}
context = context || document.documentElement;
if (!document.createElement('canvas').getContext) {
context.style.filter = 'progid:DXImageTransform.Microsoft.BasicImage(grayscale=0)';
return;
}
var all = getAllNodes(context),
i = -1, len = all.length;
while (++i<len) {
var cur = all[i];
if (cur.nodeName.toLowerCase() === 'img') {
var src = cur.getAttribute('src');
if (isExternal(src)) {
config.externalImageHandler.reset(cur, src);
}
cur.src = data(cur).realSRC || src;
} else {
for (var pIndex = 0, pLen = config.colorProps.length; pIndex < pLen; pIndex++) {
if (data(cur).externalBG) {
config.externalImageHandler.reset(cur);
}
var prop = config.colorProps[pIndex];
cur.style[prop] = data(cur)[prop] || '';
}
}
}
};
init.prepare = function(context) {
// Handle if a DOM collection is passed instead of a single el:
if (context && context[0] && context.length && context[0].nodeName) {
// Is a DOM collection:
var allContexts = Array.prototype.slice.call(context),
cIndex = -1, cLen = allContexts.length;
while (++cIndex<cLen) { init.prepare.call(null, allContexts[cIndex]); }
return;
}
// Slowly recurses through all elements
// so as not to lock up on the user.
context = context || document.documentElement;
if (!document.createElement('canvas').getContext) { return; }
var all = getAllNodes(context),
i = -1, len = all.length;
while (++i<len) {
var cur = all[i];
if (data(cur).skip) { return; }
if (cur.nodeName.toLowerCase() === 'img') {
if (cur.getAttribute('src') && !isExternal(cur.src)) {
desatIMG(cur, true);
}
} else {
var style = getStyle(cur, 'backgroundImage');
if (style.indexOf('url(') > -1) {
var urlPatt = /\(['"]?(.+?)['"]?\)/,
url = style.match(urlPatt)[1];
if (!isExternal(url)) {
var temp = document.createElement('img');
temp.src = url;
desatIMG(temp, true, cur);
}
}
}
}
};
return init;
})();
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