#77 Color aperture control

[Robert Hedges]

I deal with data which has a limited dynamic range. It would be nice to have precise control on the color aperture of the color map in use.

For example on the spectrogram, I would like to be able to select an upper and lower dBFS valued to be used on the color map; on the default color map I could then say that orange corresponds to -50dbFS and blue/black is -75dBFS.

This would also be useful on an time-values layer when displayed in the "segmentation" scheme.

This would give finer control on the spectrogram than using log/linear mapping or changing the gain, and it would add some control to the segmentation plot.

This is also useful in the case were a signal has high dynamic range, but detail of interest in a small range.