As far as I understand this slider action, I would prefer: - Either two sliders, the left one being used to set the correspondence between the 8-bit value zero and some HDR values and the right one being used to set the correspondence between the 8-bit value 255 and some higher HDR values. - Or no slider at all, APP being able to determine the best fit, that is the setting where the largest number of HDR values in the panorama correspond to "visible values" of the [0..255] 8-bit interval.
If neither is possible, then I missed something...
What you ask is to disable HDR display for HDR data. HDR data cannot be fully displayed on screen correctly because of it's wide dynamic range. We could lower the contrast enough to display all the dynamic range on the screen, but the resulting image would look flat and dull, and you would loose the ability to check each zone with the hdr slider. This particular slider is here to adjust display, not output.
What you ask is already provided by tone mappers : convert a high dynamic range image to a low dynamic range displayable on a screen.