C#读取分割多页Tif文件

System.Drawing.Image img = System.Drawing.Image.FromFile(Server.MapPath("~/images/11.tif"));
Guid guid = (Guid)img.FrameDimensionsList.GetValue(0);
FrameDimension dimension = new FrameDimension(guid);
int totalPage = img.GetFrameCount(dimension);
for (int i = 0; i < totalPage; i++)
{
     img.SelectActiveFrame(dimension, i);
     img.Save("C:\\Gif"+i+".gif", ImageFormat.Gif);
}