var flag=false;   //控制图片大小
function DrawImage(ImgD,maxwidth,maxheight){  
   var image=new Image(); 
   image.src=ImgD.src;  
   if(image.width>0 && image.height>0){  
    flag=true;  
    if(image.width/image.height>=maxwidth/maxheight){  
     if(image.width>maxwidth){    
     ImgD.width=maxwidth;  
     ImgD.height=(image.height*maxwidth)/image.width;  
     }else{  
     ImgD.width=image.width;    
     ImgD.height=image.height;  
     }  
     }  
    else{  
     if(image.height>maxheight){    
     ImgD.height=maxheight;  
     ImgD.width=(image.width*maxheight)/image.height;       
     }else{  
     ImgD.width=image.width;    
     ImgD.height=image.height;  
     }  
     }  
    }  
   }