function convertImgToBase64(url, callback, outputFormat){         var canvas = document.createElement('CANVAS');         var ctx = canvas.getContext('2d');         var img = new Image;         img.crossOrigin = 'Anonymous';         img.onload = function(){          var width = img.width;          var height = img.height;          // 按比例压缩4倍          var rate = (width
     )              console.log(base64Img);              // base64转图片不需要base64的前缀data:image/jpg;base64                         })

 转本地 图片 base64