https://my.oschina.net/smartsmile/blog/814810

//Image转换Bitmap
        //1. Bitmap img = new Bitmap(imgSelect.Image);
        //2. Bitmap bmp = (Bitmap)pictureBox1.Image;

        /// <summary>
        /// 将图片Image转换成Byte[]
        /// </summary>
        /// <param name="Image">image对象</param>
        /// <param name="imageFormat">后缀名</param>
        /// <returns></returns>
        public static byte[] ImageToBytes(Image Image, System.Drawing.Imaging.ImageFormat imageFormat)
        {
            if (Image == null) { return null; }
            byte[] data = null;
            using (MemoryStream ms = new MemoryStream())
            {
                using (Bitmap Bitmap = new Bitmap(Image))
                {
                    Bitmap.Save(ms, imageFormat);
                    ms.Position = 0;
                    data = new byte[ms.Length];
                    ms.Read(data, 0, Convert.ToInt32(ms.Length));
                    ms.Flush();
                }
            }
            return data;
        }

        /// <summary>
        /// byte[]转换成Image
        /// </summary>
        /// <param name="byteArrayIn">二进制图片流</param>
        /// <returns>Image</returns>
        public static System.Drawing.Image byteArrayToImage(byte[] byteArrayIn)
        {
            if (byteArrayIn == null)
                return null;
            using (System.IO.MemoryStream ms = new System.IO.MemoryStream(byteArrayIn))
            {
                System.Drawing.Image returnImage = System.Drawing.Image.FromStream(ms);
                ms.Flush();
                return returnImage;
            }
        }

        /// <summary>
        /// byte[] 转换 Bitmap
        /// </summary>
        /// <param name="Bytes">byte[]</param>
        /// <returns></returns>
        public static Bitmap BytesToBitmap(byte[] Bytes)
        {
            MemoryStream stream = null;
            try
            {
                stream = new MemoryStream(Bytes);
                return new Bitmap((Image)new Bitmap(stream));
            }
            catch (ArgumentNullException ex)
            {
                throw ex;
            }
            catch (ArgumentException ex)
            {
                throw ex;
            }
            finally
            {
                stream.Close();
            }
        }

        /// <summary>
        /// Bitmap转byte[]  
        /// </summary>
        /// <param name="Bitmap">Bitmap</param>
        /// <returns></returns>
        public static byte[] BitmapToBytes(Bitmap Bitmap)
        {
            MemoryStream ms = null;
            try
            {
                ms = new MemoryStream();
                Bitmap.Save(ms, Bitmap.RawFormat);
                byte[] byteImage = new Byte[ms.Length];
                byteImage = ms.ToArray();
                return byteImage;
            }
            catch (ArgumentNullException ex)
            {
                throw ex;
            }
            finally
            {
                ms.Close();
            }
        }