var flag=false;    
function DrawImage(ImgD,iwidth,iheight){    
    //参数(图片,允许的宽度,允许的高度)    
    var image=new Image();    
    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;  
   
        }
        }    
    }    
}