System.IO.MemoryStream.Read C# (CSharp) Method

        public override int Read(byte[] buffer, int offset, int count)
        {
            if (buffer == null)
            {
                throw new ArgumentNullException(nameof(buffer), SR.ArgumentNull_Buffer);
            }
            if (offset < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(offset), SR.ArgumentOutOfRange_NeedNonNegNum);
            }
            if (count < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(count), SR.ArgumentOutOfRange_NeedNonNegNum);
            }
            if (buffer.Length - offset < count)
            {
                throw new ArgumentException(SR.Argument_InvalidOffLen);
            }
            if (!_isOpen)
            {
                throw new ObjectDisposedException(null, SR.ObjectDisposed_StreamClosed);
            }

            int n = _length - _position;
            if (n > count)
            {
                n = count;
            }
            if (n <= 0)
            {
                return 0;
            }

            Debug.Assert(_position + n >= 0, "_position + n >= 0");  // len is less than 2^31 -1.

            if (n <= 8)
            {
                int byteCount = n;
                while (--byteCount >= 0)
                    buffer[offset + byteCount] = _buffer[_position + byteCount];
            }
            else
                Buffer.BlockCopy(_buffer, _position, buffer, offset, n);
            _position += n;

            return n;
        }

 /// <summary>
 /// Convert Image to Byte[]
 /// Image img = Image.FromFile("c:\\hcha.jpg");
 /// </summary>
 /// <param name="image"></param>
 /// <returns></returns>
 public static byte[] ImageToBytes(Image image)
 {
     ImageFormat format = image.RawFormat;
     using (MemoryStream ms = new MemoryStream())
     {
         if (format.Equals(ImageFormat.Jpeg))
         {
             image.Save(ms, ImageFormat.Jpeg);
         }
         else if (format.Equals(ImageFormat.Png))
         {
             image.Save(ms, ImageFormat.Png);
         }
         else if (format.Equals(ImageFormat.Bmp))
         {
             image.Save(ms, ImageFormat.Bmp);
         }
         else if (format.Equals(ImageFormat.Gif))
         {
             image.Save(ms, ImageFormat.Gif);
         }
         else if (format.Equals(ImageFormat.Icon))
         {
             image.Save(ms, ImageFormat.Icon);
         }
         byte[] buffer = new byte[ms.Length];
         //Image.Save()会改变MemoryStream的Position，需要重新Seek到Begin
         ms.Seek(0, SeekOrigin.Begin);
         ms.Read(buffer, 0, buffer.Length);
         return buffer;
     }
 }