var flag=false;
function imgresize(ImgD){
	var image=new Image(); 
	var iwidth = 300;  //定义允许图片宽度 
	var iheight =3000;  //定义允许图片高度 
	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; 
			} 

		} 
		else{ 
			if(image.height>iheight){   
				ImgD.height=iheight; 
				ImgD.width=(image.width*iheight)/image.height;   
			}
			else{ 
				ImgD.width=image.width;   
				ImgD.height=image.height; 
			} 

		} 
	} 
}