get min and max value from spectrogram

Hello,

I would like to adapt the colormap in regard to the max and min values of intensity ( in a spectrogram). How can it be done?

here the colormap is set:

Code:

QwtValueList contourLevels;
    for ( double level = 0.5; level < 10.0; level += 1.0 )
        contourLevels += level;
    d_spectrogram->setContourLevels(contourLevels);
 
    // A color bar on the right axis
    QwtScaleWidget *rightAxis = axisWidget(QwtPlot::yRight);
    rightAxis->setTitle("Intensity");
    rightAxis->setColorBarEnabled(true);
    rightAxis->setColorMap(d_spectrogram->data().range(), d_spectrogram->colorMap());
 
    setAxisScale(QwtPlot::yRight,
        d_spectrogram->data().range().minValue(),
        d_spectrogram->data().range().maxValue() );
    enableAxis(QwtPlot::yRight);

and my QwtData is:

Code:

typedef double (*benchFunc)(double, double);	// definition of function pointer for benchmark function
 
class SpectrogramData: public QwtRasterData
{
public:
    SpectrogramData(benchFunc b, double rang1[2],  double rang2[2]):
        QwtRasterData(QwtDoubleRect(rang1[0], rang2[0], rang1[1]- rang1[0], rang2[1]- rang2[0]))
    {
    	MybenchFunc = b;
    	rangeX1[0] = rang1[0];	rangeX1[1] = rang1[1];
    	rangeX2[0] = rang1[0];	rangeX2[1] = rang2[1];
    }
 
    virtual QwtRasterData *copy() const
    {
        return new SpectrogramData(*this);
    }
 
    virtual QwtDoubleInterval range() const
    {
        return QwtDoubleInterval(-5.0, 5.0);
    }
 
    virtual double value(double x, double y) const
    {
 
    	const double result = MybenchFunc(x,y);
        return result;
    }
 
private:
 
	benchFunc MybenchFunc;	// function pointer for benchmark function
	double rangeX1[2];
	double rangeX2[2];
};

At the moment the range is set to (-5, 5), but it is fix. I want to make it dynamical.

Thanks for help.

best regards,

Vitali