Modify Histogram to show channel values less than 0.0f and greater than 1.0f
The much-needed option to show "out of display range" channel values in GIMP Histograms was discussed at length on IRC a long time ago. PhotoFlow has implemented such a histogram, which might serve as an example interface for GIMP. See this pixls.us post: https://discuss.pixls.us/t/photoflow-news-and-updates/4742/402