C# 文件轉Base64

  using (FileStream filestream = new FileStream("LOGO.png", FileMode.Open))
            {
                byte[] bt = new byte[filestream.Length];

                //調用read讀取方法
                filestream.Read(bt, 0, bt.Length);
               var  base64Str = Convert.ToBase64String(bt);

              return base64Str;
            }