//图片生成缩略图
function resizeimg(ImgD,iwidth,iheight) {
     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;
           }
        }else{
           if(image.height>iheight){
                ImgD.height=iheight;
                ImgD.width=(image.width*iheight)/image.height;
           }else{
                ImgD.width=image.width;
                ImgD.height=image.height;
           }
       }
    }
}