/// <summary>
/// A FALSE-COLOUR VERSION OF DECIBEL SPECTROGRAM
/// Taken and adapted from Spectrogram Image 5 in the method of CLASS Audio2InputForConvCNN.cs:.
/// </summary>
/// <param name="dbSpectrogramData">the sonogram data (NOT noise reduced). </param>
public static Image <Rgb24> DrawStandardSpectrogramInFalseColour(double[,] dbSpectrogramData)
{
// Do NOISE REDUCTION
double noiseReductionParameter = 2.0;
var tuple = SNR.NoiseReduce(dbSpectrogramData, NoiseReductionType.Standard, noiseReductionParameter);
double[,] nrSpectrogramData = tuple.Item1; // store data matrix
double ridgeThreshold = 2.5;
double[,] matrix = dbSpectrogramData;
byte[,] hits = RidgeDetection.Sobel5X5RidgeDetectionExperiment(matrix, ridgeThreshold);
// ################### RESEARCH QUESTION:
// I tried different EXPERIMENTS IN NORMALISATION
//double min; double max;
//DataTools.MinMax(spectralSelection, out min, out max);
//double range = max - min;
// readjust min and max to create the effect of contrast stretching. It enhances the spectrogram a bit
//double fractionalStretching = 0.2;
//min = min + (range * fractionalStretching);
//max = max - (range * fractionalStretching);
//range = max - min;
// ULTIMATELY THE BEST APPROACH APPEARED TO BE FIXED NORMALISATION BOUNDS
double truncateMin = -95.0;
double truncateMax = -30.0;
double filterCoefficient = 0.75;
double[,] dbSpectrogramNorm = SpectrogramTools.NormaliseSpectrogramMatrix(dbSpectrogramData, truncateMin, truncateMax, filterCoefficient);
truncateMin = 0;
truncateMax = 50;
// nr = noise reduced
double[,] nrSpectrogramNorm = SpectrogramTools.NormaliseSpectrogramMatrix(nrSpectrogramData, truncateMin, truncateMax, filterCoefficient);
nrSpectrogramNorm = MatrixTools.BoundMatrix(nrSpectrogramNorm, 0.0, 0.9);
nrSpectrogramNorm = MatrixTools.SquareRootOfValues(nrSpectrogramNorm);
nrSpectrogramNorm = DataTools.normalise(nrSpectrogramNorm);
// create image from normalised data
var image = SpectrogramTools.CreateFalseColourDecibelSpectrogramForZooming(dbSpectrogramNorm, nrSpectrogramNorm, hits);
return(image);
}
