Convert wav file to bitmap or spectrogram in Windows Application

I use the following code to convert .wav audio file to bitmap or spectrogram but get white noise.

private void button1_Click(object sender, EventArgs e)
{
    System.IO.Stream load_wav = new System.IO.MemoryStream();
    openFileDialog1.Filter = "WAV|*.wav";
    openFileDialog1.ShowDialog();
    if (openFileDialog1.ShowDialog() == DialogResult.OK)
    {
        try
        {
            if ((load_wav = openFileDialog1.OpenFile()) != null)
            {
                using (load_wav)
                {
                    using (WaveFileReader reader = new WaveFileReader(load_wav))
                    { 
                        int BitsPerSample;
                        int SampleRate;
                        BitsPerSample = reader.WaveFormat.BitsPerSample;
                        SampleRate = reader.WaveFormat.SampleRate;
                        string config = SampleRate.ToString();
                        // Write sample config to .ini
                        System.IO.StreamWriter file = new System.IO.StreamWriter(".\\config.ini");
                        file.WriteLine(config);
                        file.Close();
                        if (BitsPerSample == 16) // Check 16bit
                        {
                            // Read WAV
                            byte[] in_buffer = new byte[reader.Length];
                            int read = reader.Read(in_buffer, 0, in_buffer.Length);
                            MessageBox.Show("Load OK");
 
                            // Convert byte array to stream
                            Bitmap output = new Bitmap(600, 600);
                            Rectangle rect = new Rectangle(0, 0, output.Width, output.Height);
                            BitmapData bmpData = output.LockBits(rect, ImageLockMode.ReadWrite, output.PixelFormat);
                            IntPtr ptr = bmpData.Scan0;
                            System.Runtime.InteropServices.Marshal.Copy(in_buffer, 0, ptr, in_buffer.Length);
                            output.UnlockBits(bmpData);
                            pictureBox1.Image = output;
                            output.Save(".\\output.bmp");
                        } 
                        else
                        {
                            MessageBox.Show("16 bit WAV files only :-(");
                        }