Discussion herein seems suggest that the nearly disappearing histograms produced by GIMP (i.e., for blue and combined channels) is the result of the choice of scale for the vertical axis. The idea being that the existence of a very large number of pixels for a discreet x value depress the height of everything else on the graphic display.
However, this should mean that the histograms shown herein that display all three color channels at the same time (I.e., as in the case of RT and G’MIC) could only appear as they do if a different scale is used for each color channel. The G’MIC histograms above appear to show the vertical scale in units that I presume to be the number of pixels. This creates a definite impression that the same scale applies to all 3 color channels. If so for G’MIC why not for GIMP? What is GIMP doing differently that causes such dramatic depression of essentially all y values?