js等比例压缩图片

//图片按比例缩放
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){
	    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;
	        }
	        ImgD.alt=image.width+"×"+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;
	        }
	        ImgD.alt=image.width+"×"+image.height;
	     }
    }
}