private Bitmap DrawSpectrogram(int NFFT, double[] samples, Fourier f, Color[] palette)
{
int NumSamples = samples.Length;
int Overlap = 0;
int ColIncrement = NFFT * (1 - Overlap);
int Numcols = NumSamples / ColIncrement;
// make sure we don't step beyond the end of the recording
while ((Numcols - 1) * ColIncrement + NFFT > NumSamples)
{
Numcols--;
}
double[] real = new double[NFFT];
double[] imag = new double[NFFT];
double[] magnitude = new double[NFFT / 2];
Bitmap bmp = new Bitmap(Numcols, NFFT / 2);
for (int col = 0; col <= Numcols - 1; col++)
{
// read a segment of the recorded signal
for (int c = 0; c <= NFFT - 1; c++)
{
imag[c] = 0;
real[c] = samples[col * ColIncrement + c] * Fourier.Hanning(NFFT, c);
}
// transform to the frequency domain
f.FourierTransform(real, imag);
// and compute the magnitude spectrum
f.MagnitudeSpectrum(real, imag, Fourier.W0Hanning, magnitude);
// Draw
for (int newY = 0; newY < NFFT / 2 - 1; newY++)
{
int colorIndex = MapToPixelIndex(magnitude[newY], 100, 255);
bmp.SetPixel(col, (NFFT / 2 - 1) - newY, palette[colorIndex]);
}
}
return(bmp);
}
//////////////////////////////////////// SPECTRUM ///////////////////////////////////////////////////////////
public List <Bitmap> GenerateFourierData(int NFFT, string spectrogramDirectory)
{
List <Bitmap> bitmaps = new List <Bitmap>();
// setup fourier transformation
Fourier f = new Fourier(NFFT, true);
double divider = 2.0;
for (int k = 0; k < Header.BitsPerSample - 2; k++)
{
divider *= 2;
}
// determine how to read sample values
ReadSampleDataValueDelegate readSampleDataValue = GetSampleDataRerader();
// set up one column of the spectrogram
Color[] palette = new Color[NFFT];
if (Configuration.Settings.VideoControls.SpectrogramAppearance == "Classic")
{
for (int colorIndex = 0; colorIndex < NFFT; colorIndex++)
{
palette[colorIndex] = PaletteValue(colorIndex, NFFT);
}
}
else
{
var list = SmoothColors(0, 0, 0, Configuration.Settings.VideoControls.WaveFormColor.R,
Configuration.Settings.VideoControls.WaveFormColor.G,
Configuration.Settings.VideoControls.WaveFormColor.B, NFFT);
for (int i = 0; i < NFFT; i++)
{
palette[i] = list[i];
}
}
// read sample values
DataMinValue = int.MaxValue;
DataMaxValue = int.MinValue;
var samples = new List <int>();
int index = 0;
int sampleSize = NFFT * 1024; // 1024 = bitmap width
int count = 0;
long totalSamples = 0;
// load data in smaller parts
_data = new byte[Header.BytesPerSecond];
_stream.Position = Header.DataStartPosition;
int bytesRead = _stream.Read(_data, 0, _data.Length);
while (bytesRead == Header.BytesPerSecond)
{
while (index < Header.BytesPerSecond)
{
int value = 0;
for (int channelNumber = 0; channelNumber < Header.NumberOfChannels; channelNumber++)
{
value += readSampleDataValue.Invoke(ref index);
}
value = value / Header.NumberOfChannels;
if (value < DataMinValue)
{
DataMinValue = value;
}
if (value > DataMaxValue)
{
DataMaxValue = value;
}
samples.Add(value);
totalSamples++;
if (samples.Count == sampleSize)
{
var samplesAsReal = new double[sampleSize];
for (int k = 0; k < sampleSize; k++)
{
samplesAsReal[k] = samples[k] / divider;
}
Bitmap bmp = DrawSpectrogram(NFFT, samplesAsReal, f, palette);
bmp.Save(Path.Combine(spectrogramDirectory, count + ".gif"), System.Drawing.Imaging.ImageFormat.Gif);
bitmaps.Add(bmp); // save serialized gif instead????
samples = new List <int>();
count++;
}
}
bytesRead = _stream.Read(_data, 0, _data.Length);
index = 0;
}
if (samples.Count > 0)
{
var samplesAsReal = new double[sampleSize];
for (int k = 0; k < sampleSize && k < samples.Count; k++)
{
samplesAsReal[k] = samples[k] / divider;
}
Bitmap bmp = DrawSpectrogram(NFFT, samplesAsReal, f, palette);
bmp.Save(Path.Combine(spectrogramDirectory, count + ".gif"), System.Drawing.Imaging.ImageFormat.Gif);
bitmaps.Add(bmp); // save serialized gif instead????
}
XmlDocument doc = new XmlDocument();
doc.LoadXml("<SpectrogramInfo><SampleDuration/><TotalDuration/></SpectrogramInfo>");
double sampleDuration = Header.LengthInSeconds / (totalSamples / NFFT);
double totalDuration = Header.LengthInSeconds;
doc.DocumentElement.SelectSingleNode("SampleDuration").InnerText = sampleDuration.ToString();
doc.DocumentElement.SelectSingleNode("TotalDuration").InnerText = totalDuration.ToString();
doc.Save(System.IO.Path.Combine(spectrogramDirectory, "Info.xml"));
return(bitmaps);
}