图片压缩存储(图片长宽过大时影响显示美观使用)

                System.Drawing.Image tempimage = System.Drawing.Image.FromStream(imgFile.InputStream, true);
                int imagewidth = tempimage.Width;//宽
                int imageheight = tempimage.Height;//高

              DateTime now = DateTime.Now;
                //计算文件的保存文件夹下
                //用年/月/日做文件目录，这样避免一个文件夹下文件过多问题
                //用文件的MD5值做文件名，这样避免多次上传同一副图片造成磁盘浪费


                string fileName = "/Upload/" + now.Year + "/" + now.Month + "/" + now.Day + "/"
                    + CommonHelper.CalcMD5(imgFile.FileName) + fileExt;
                imgFile.InputStream.Position = 0;
                string imgFileFullPath = Server.MapPath("~" + fileName);
                System.IO.Directory.CreateDirectory(Path.GetDirectoryName(imgFileFullPath));//如果文件夹不存在，则先创建文件夹
                imageUrl = fileName;



                if (imagewidth > 500 || imageheight > 600)
                {                
                    byte[] bytes = WebHelper.CreateImg(tempimage, imageheight * 1.0 / imagewidth);

using (Stream outStream = new FileStream(Server.MapPath(imageUrl), FileMode.Create))
                    {
                        outStream.Write(bytes, 0, bytes.Length);//类似于GetString                    
                    }

                }

                else
                {
                    imgFile.SaveAs(imgFileFullPath);
                }

        /// <summary>
        /// 生成一个验证码图片
        /// </summary>
        /// <param name="validCode">生成的验证码</param>
        /// <returns>图片的JPEG格式的二进制数据</returns>
        public static byte[] CreateImg(System.Drawing.Image imgOutput, double hw)
        {
            //常用汉字
            using (Bitmap bmp = new Bitmap(500, Convert.ToInt32(500 * hw)))
            using (Graphics g = Graphics.FromImage(bmp))
            using (MemoryStream ms = new MemoryStream())
            {
                g.Clear(Color.White);
                //修改成80×80大小 
                System.Drawing.Image imgOutput2 = imgOutput.GetThumbnailImage(500, Convert.ToInt32(500 * hw), null, IntPtr.Zero);

                g.DrawImage(imgOutput2, 0, 0);
                Random rand = new Random();

                bmp.Save(ms, ImageFormat.Jpeg);
                ms.Position = 0;
                return ms.ToArray();
            }
        }