//图片按比例缩放 
var flag = false; 
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) { 
flag = true; 
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; 
} 
} 
}