Just published
http://gimpscripts.com/2017/05/stretchrgbcolours2/A filter to implement the stretching of the colours in the input drawable.
It expands the functionality of the existing filter:
Stretch_RGB_Colours
also published some time ago under Gimp Script & Plug-in Repository.
These are the additional features:
a) it stretches also the histogram values and not only the single R,G,B
b) it uses float values for the percentages to have a more precise control
c) it works on a duplicated layer to let the user adjusting opacity
It could be useful when you have to deal with images with no values at the extremes (0 and 255).
You mat stretch diffferently the colours (R-G-B) and the absolute Value.