一个缩略图的类

    public class GetThumbnailImg
    {
        /// <summary>
        /// 读取图片的缩略图
        /// </summary>
        /// <param name="PicPath">源图片的路径</param>
        /// <param name="PicTemp">生成缩略图的目录</param>
        /// <param name="Width">生成缩略图的宽</param>
        /// <param name="Height">生成缩略图的高</param>
        /// <returns>生成成功则返回路径,否则返回""</returns>
        public static string GetThumbnailPic(string PicPath, string PicTemp, int Width, int Height)
        {
            System.Drawing.Bitmap Bitmap = new System.Drawing.Bitmap(PicPath);
            if (Bitmap.Width > Width)
            {
                Height = Bitmap.Height * Width / Bitmap.Width;
            }
            else
            {
                Width = Bitmap.Width * Height / Bitmap.Height;
            }
            var img = Bitmap.GetThumbnailImage(Width, Height, () => { return false; }, IntPtr.Zero);
            try
            {
                img.Save(PicTemp);
                return PicTemp;
            }
            catch
            {
                return "";
            }
        }
    }

调用：

            string FileName = MapPath("~/img/") + Guid.NewGuid().ToString() + System.IO.Path.GetExtension(FileUpload1.FileName);    
            FileUpload1.SaveAs(FileName);
            string TempPath = FileName.Replace(@"img", @"imgTemp");
            var Path = GYFDLL.GetThumbnailImg.GetThumbnailPic(FileName, TempPath, 200, 200);
            Image img = new Image();
            img.ImageUrl = "~/img/Temp/" + System.IO.Path.GetFileName(Path);
            this.Controls.Add(img);