javascript控制图片等比例缩放

<SCRIPT language="JavaScript">
function DrawImage(ImgD,FitWidth,FitHeight){  
    var image=new Image();  
    image.src=ImgD.src;  
    if(image.width>0 && image.height>0){  
        if(image.width/image.height>= FitWidth/FitHeight){  
            if(image.width>FitWidth){  
                ImgD.width=FitWidth;  
                ImgD.height=(image.height*FitWidth)/image.width;  
            }  
            else{  
                ImgD.width=image.width;  
                ImgD.height=image.height;  
            }  
        }  
        else{  
            if(image.height>FitHeight){  
                ImgD.height=FitHeight;  
                ImgD.width=(image.width*FitHeight)/image.height;  
            }  
            else{  
                ImgD.width=image.width;  
                ImgD.height=image.height;  
            }  
        }  
    }  
}  

</script>