js获取图片的base64编码并压缩

获取图片的base64编码

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									<!DOCTYPE html>

									<html>

									  <head>

									    <meta charset="gbk">

									    <title></title>

									  </head>

									  <body>

									    <input accept="image/*" name="upimage" id="upload_file" type="file" onchange="gen_base64()">

									　　　　　<br/>

									    <textarea id="base64_output" name="Word" style=" width:820px"></textarea>

									　　　　 <br/>

									　　　　　<img src="" id="myImg" />

									    <script type="text/javascript">

									      function $_(id) {

									          return document.getElementById(id);

									      }

									      function gen_base64() {

									        var file = $_('upload_file').files[0];

									        r = new FileReader(); //本地预览

									        r.onload = function(){

									          $_('base64_output').value = r.result;

									　　　　　　　　　　　　 $_('myImg').src= r.result;

									        }

									        r.readAsDataURL(file);  //Base64

									      }

									    </script>

									  </body>

									</html>

案例2：js压缩图片

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									<html>

									 <body>

									 <script>

									 function getUrl(fil) {

									      var Cnv = document.getElementById('myCanvas');

									      var Cntx = Cnv.getContext('2d');//获取2d编辑容器

									      var imgss =  new Image();//创建一个图片

									      var agoimg=document.getElementById("ago");

									      for (var intI = 0; intI < fil.length; intI++) {//图片回显

									        var tmpFile = fil[intI];

									        var reader = new FileReader();

									        reader.readAsDataURL(tmpFile);

									        reader.onload = function (e) {

									          url = e.target.result;

									          imgss.src = url;

									          agoimg.src=url;

									          agoimg.onload = function () {

									            //等比缩放

									            var m = imgss.height / imgss.width;

									             Cnv.width = 300 ;//该值影响缩放后图片的大小

									             Cnv.height =300*m;

									            //img放入画布中

									            Cntx.drawImage(agoimg, 0, 0,300,300*m);

									                     　　　　//把画布中的数据，写出到某img的src里

									            var Pic = document.getElementById("myCanvas").toDataURL("image/png");

									            var imgs =document.getElementById("press");

									            imgs.src =Pic ;

									          }

									        }

									      }

									    }

									</script>

									<input type="file" id="fileId" name="fileId" value="上传图片" hidefocus="true" onchange="getUrl(this.files);"/>   <br/>

									<canvas id="myCanvas"   style="display: block" ></canvas>

									old img::<img src="" alt="" id="ago" style="width: 500px;"/>

									new img::<img src="" alt="" id="press"/>

									</body>

									</html>