function changeImg(mypic){ 
    var xw=90; 
    var xl=90; 
         
    var width = mypic.width; 
    var height = mypic.height; 
    var bili = width/height;         
         
    var A=xw/width; 
    var B=xl/height; 
         
    if(!(A>1&&B>1)) 
    { 
        if(A<B) 
        { 
            mypic.width=xw; 
            mypic.height=xw/bili; 
        } 
        if(A>B) 
        { 
            mypic.width=xl*bili; 
            mypic.height=xl; 
        } 
    } 
}