exif图片方向处理

iphone对拍摄的照片有自动处理

//修复ios
if (navigator.userAgent.match(/iphone/i)) {
   image.src = reader.result;
   image.onload=function(){
      var degree=0,drawWidth,drawHeight,width,height;
      drawWidth=this.naturalWidth;
      drawHeight=this.naturalHeight;

      var canvas=document.createElement('canvas');
      canvas.width=width=drawWidth;
      canvas.height=height=drawHeight;
      var context=canvas.getContext('2d');
      //判断图片方向，重置canvas大小，确定旋转角度，iphone默认的是home键在右方的横屏拍摄方式
switch(Orientation){
         //iphone横屏拍摄，此时home键在左侧
case 3:
            degree=180;
            drawWidth=-width;
            drawHeight=-height;
            break;
         //iphone竖屏拍摄，此时home键在下方(正常拿手机的方向)
case 6:
            canvas.width=height;
            canvas.height=width;
            degree=90;
            drawWidth=width;
            drawHeight=-height;
            break;
         //iphone竖屏拍摄，此时home键在上方
case 8:
            canvas.width=height;
            canvas.height=width;
            degree=270;
            drawWidth=-width;
            drawHeight=height;
            break;
      }
      //使用canvas旋转校正
context.rotate(degree*Math.PI/180);
      context.drawImage(this,0,0,drawWidth,drawHeight);
      var url=canvas.toDataURL("image/jpeg",1);
      $image.attr("src", url);
      $image.cropper('replace', url);
   }