//图片按比例缩放
function DrawImage(ImgD,w,h){
	var flag=false;
	var image=new Image();
	var iwidth = w; //定义允许图片宽度，当宽度大于这个值时等比例缩小
	var iheight = h; //定义允许图片高度，当宽度大于这个值时等比例缩小
	image.src=ImgD.src;
	if(image.width>0 && image.height>0)
	{
		flag=true;
		if(image.width/image.height>= iwidth/iheight)
		{
			if(image.width>iwidth)
			{ 
			ImgD.width=iwidth;
			ImgD.height=(image.height*iwidth)/image.width;
			}
			else
			{
			ImgD.width=image.width; 
			ImgD.height=image.height;
			}
			ImgD.alt=image.width+"×"+image.height;
		}
		else
		{
			if(image.height>iheight)
			{ 
			ImgD.height=iheight;
			ImgD.width=(image.width*iheight)/image.height; 
			}
			else
			{
			ImgD.width=image.width; 
			ImgD.height=image.height;
			}
			ImgD.alt=image.width+"×"+image.height;
		}
	}
} 
//调用：<img src="图片" onload="javascript:DrawImage(this)">