function DrawImage(ImgD){
  var image = new Image();
  image.src=ImgD.src;
  var width = $(ImgD).attr("width");
  var height = $(ImgD).attr("height");
  if(width >100 && height>80){
    ImgD.width=100; 
    ImgD.height=80;
    ImgD.alt=image.width+"×"+image.height;
  }else{
    if(image.width>0 && image.height>0){
      flag=true;
      if(image.width>300 || image.height>200){
        ImgD.width=image.width/2; 
        ImgD.height=image.height/2;
        ImgD.alt=image.width+"×"+image.height;
      }else{
        ImgD.width=image.width;  
        ImgD.height=image.height;
        ImgD.alt=image.width+"×"+image.height;
      }
    }
  }
}

下面分享一段關(guān)于js實(shí)現(xiàn)上傳圖片及時(shí)預(yù)覽

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>   
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />   
<title>圖片上傳本地預(yù)覽</title>   
<style type="text/css">
#preview{width:260px;height:190px;border:1px solid #000;overflow:hidden;}
#imghead {filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
</style>
<script type="text/javascript">
        //圖片上傳預(yù)覽  IE是用了濾鏡。
    function previewImage(file)
    {
     var MAXWIDTH = 260; 
     var MAXHEIGHT = 180;
     var div = document.getElementById('preview');
     if (file.files && file.files[0])
     {
       div.innerHTML ='<img id=imghead>';
       var img = document.getElementById('imghead');
       img.onload = function(){
        var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
        img.width = rect.width;
        img.height = rect.height;
//         img.style.marginLeft = rect.left+'px';
        img.style.marginTop = rect.top+'px';
       }
       var reader = new FileReader();
       reader.onload = function(evt){img.src = evt.target.result;}
       reader.readAsDataURL(file.files[0]);
     }
     else //兼容IE
     {
      var sFilter='filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';
      file.select();
      var src = document.selection.createRange().text;
      div.innerHTML = '<img id=imghead>';
      var img = document.getElementById('imghead');
      img.filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = src;
      var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
      status =('rect:'+rect.top+','+rect.left+','+rect.width+','+rect.height);
      div.innerHTML = "<div id=divhead style='width:"+rect.width+"px;height:"+rect.height+"px;margin-top:"+rect.top+"px;"+sFilter+src+"\"'></div>";
     }
    }
    function clacImgZoomParam( maxWidth, maxHeight, width, height ){
      var param = {top:0, left:0, width:width, height:height};
      if( width>maxWidth || height>maxHeight )
      {
        rateWidth = width / maxWidth;
        rateHeight = height / maxHeight;      
        if( rateWidth > rateHeight )
        {
          param.width = maxWidth;
          param.height = Math.round(height / rateWidth);
        }else
        {
          param.width = Math.round(width / rateHeight);
          param.height = maxHeight;
        }
      }     
      param.left = Math.round((maxWidth - param.width) / 2);
      param.top = Math.round((maxHeight - param.height) / 2);
      return param;
    }
</script>   
</head>   
<body>
<div id="preview">
  <img id="imghead" width=100 height=100 border=0 src='<%=request.getContextPath()%>/images/defaul.jpg'>
</div>
  <input type="file" onchange="previewImage(this)" />   
</body>   
</html>

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