字符串与图片的Base64编码转换操作

    //图片 转为  base64编码的文本
    private void button1_Click(object sender, EventArgs e)
    {
      OpenFileDialog dlg = new OpenFileDialog();
      dlg.Title = "选择要转换的图片";
      dlg.Filter = "Image files (*.jpg;*.bmp;*.gif)|*.jpg*.jpeg;*.gif;*.bmp|AllFiles (*.*)|*.*";
      if (DialogResult.OK == dlg.ShowDialog())
      {
        ImgToBase64String(dlg.FileName);
      }
    }
    //图片 转为  base64编码的文本
    private void ImgToBase64String(string Imagefilename)
    {
      try
      {
        Bitmap bmp = new Bitmap(Imagefilename);
        this.pictureBox1.Image = bmp;
        FileStream fs = new FileStream(Imagefilename + ".txt", FileMode.Create);
        StreamWriter sw = new StreamWriter(fs);
        MemoryStream ms = new MemoryStream();
        bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
        byte[] arr = new byte[ms.Length];
        ms.Position = ;
        ms.Read(arr, , (int)ms.Length);
        ms.Close();
        String strbaser64 = Convert.ToBase64String(arr);
        sw.Write(strbaser64);
        sw.Close();
        fs.Close();
        MessageBox.Show("转换成功!");
      }
      catch (Exception ex)
      {
        MessageBox.Show("ImgToBase64String 转换失败/nException:" + ex.Message);
      }
    }

    //base64编码的文本 转为  图片
    private void button2_Click(object sender, EventArgs e)
    {
      OpenFileDialog dlg = new OpenFileDialog();
      dlg.Title = "选择要转换的base64编码的文本";
      dlg.Filter = "txt files|*.txt";
      if (DialogResult.OK == dlg.ShowDialog())
      {
        Base64StringToImage(dlg.FileName);
      }
    }
    //base64编码的文本 转为  图片
    private void Base64StringToImage(string txtFileName)
    {
      try
      {
        FileStream ifs = new FileStream(txtFileName, FileMode.Open, FileAccess.Read);
        StreamReader sr = new StreamReader(ifs);
        String inputStr = sr.ReadToEnd();
        byte[] arr = Convert.FromBase64String(inputStr);
        MemoryStream ms = new MemoryStream(arr);
        Bitmap bmp = new Bitmap(ms);
        bmp.Save(txtFileName + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
        //bmp.Save(txtFileName + ".bmp", ImageFormat.Bmp);
        //bmp.Save(txtFileName + ".gif", ImageFormat.Gif);
        //bmp.Save(txtFileName + ".png", ImageFormat.Png);
        ms.Close();
        sr.Close();
        ifs.Close();
        this.pictureBox1.Image = bmp;
        MessageBox.Show("转换成功！");
      }
      catch (Exception ex)
      {
        MessageBox.Show("Base64StringToImage 转换失败/nException："+ex.Message);
      }