我正在开发响应式网站,并使用代码为不同的屏幕大小加载正确尺寸的图片。但我遇到了一个问题,我在一些移动设备上使用Retina图像,这意味着客户端下载的图像尺寸更大。现在Google Pagespeed提醒我应该优化我的图像,但问题是如果我减小图像尺寸,那么Retina显示屏将会失去图像质量。请问Google Pagespeed支持Retina图像吗?有没有一种方法告诉Google Pagespeed这些是Retina图像?或者是否有Google关于Retina图像的最佳实践?
如果您使用srcset属性,PageSpeed现在支持视网膜图像:
<img style="height: 100px"
src="rex_1x.png"
srcset="rex_1x.png 1x, rex_2x.png 2x"
alt="My dog Rex"/>
<!DOCTYPE html>
<!--[if lt IE 7 ]><html class="ie ie6" lang="en"> <![endif]-->
<!--[if IE 7 ]><html class="ie ie7" lang="en"> <![endif]-->
<!--[if IE 8 ]><html class="ie ie8" lang="en"> <![endif]-->
<!--[if (gte IE 9)|!(IE)]><!--><html lang="en"> <!--<![endif]-->
<head>
<meta charset="utf-8">
<title></title>
<meta name="description" content="" />
<meta name="keywords" content="" />
<meta name="author" content="" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<!-- Favicons -->
<link rel="shortcut icon" href="/img/icons/favicon.ico" type="image/x-icon">
<link rel="icon" href="/img/icons/favicon.ico" type="image/x-icon">
<!-- App Screen / Icons -->
<!-- Specifying a Webpage Icon for Web Clip
Ref: https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html -->
<link rel="apple-touch-icon" href="/img/icons/sptouch-icon-iphone.png">
<link rel="apple-touch-icon" sizes="76x76" href="/img/icons/touch-icon-ipad.png">
<link rel="apple-touch-icon" sizes="120x120" href="/img/icons/touch-icon-iphone-retina.png">
<link rel="apple-touch-icon" sizes="152x152" href="/img/icons/touch-icon-ipad-retina.png">
<!-- iOS web-app metas : hides Safari UI Components and Changes Status Bar Appearance -->
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<!-- Startup image for web apps -->
<link rel="apple-touch-startup-image" href="/img/icons/ipad-landscape.png" media="screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:landscape)">
<link rel="apple-touch-startup-image" href="/img/icons/ipad-portrait.png" media="screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:portrait)">
<link rel="apple-touch-startup-image" href="/img/icons/iphone.png" media="screen and (max-device-width: 320px)">
<!--
HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries.
WARNING: Respond.js doesn't work if you view the page via file://
-->
<!--[if lt IE 9]>
<script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
<script src="https://oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js"></script>
<![endif]-->
</head>
2) 将任何静态图像的Base64编码直接嵌入其img标签中,这样您仍然可以在它们上使用缩放CSS代码,并且永远不必处理诸如缺少或设置不正确的过期标头之类的问题。(当您还在Apache服务器上运行Google mod_pagespeed时,这是一个问题。)
3) 在上传之前,无论其类型如何,都要压缩所有其他图像。
4) 在页面底部使用onload JavaScript函数来加载所有CSS和JS文件,如下所示。
window.onload = function(){
function loadjscssfile(filename, filetype) {
if(filetype == "js") {
var cssNode = document.createElement('script');
cssNode.setAttribute("type", "text/javascript");
cssNode.setAttribute("src", filename);
} else if(filetype == "css") {
var cssNode = document.createElement("link");
cssNode.setAttribute("rel", "stylesheet");
cssNode.setAttribute("type", "text/css");
cssNode.setAttribute("href", filename);
}
if(typeof cssNode != "undefined") {
var h = document.getElementsByTagName("head")[0];
h.parentNode.insertBefore(cssNode, h);
}
}
loadjscssfile("//fonts.googleapis.com/css?family=Open+Sans:300&subset=latin,cyrillic-ext,latin-ext,cyrillic,greek-ext,greek,vietnamese", "css");
loadjscssfile("//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css", "css");
loadjscssfile("/css/style.css", "css");
loadjscssfile("//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js", "js");
loadjscssfile("//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js", "js");
};
除了使用雅虎的Yslow进行测试之外,不要太过纠结。你会为了达到100/100而抓狂数天,但这些工具并不完美。尽力而为,将所学应用于下一个项目。