I’m trying to ‘correct’ a couple of rolls of slides/diapositive film which were exposed in the 1960 but which appear to have been poorly developed (they all have a marked purple colour cast). They have been scanned to tiffs using Vuescan and a Nikon Coolscan V, but possibly not with the optimum settings. In darkroom mode in dt I have toggled the clipping indication on and set it to show ‘saturation only’. In the slide I am editing as I type this, about 65% of the image is the profile of a large building and is glowing bright red. The remainder of the image (mostly sky) does not show any 'over saturation…
What is confusing me is that the majority of the building is in shadow, some of it quite deep, but not clipped (setting the clipping indication to ‘luminance only’ does not show any blue or red pixels). I did not expect it to be clipped in saturation . I cannot seem to find a module to control saturation when using scene-referred modules, so I have resorted to using ‘contrast brightness saturation’ - which is display-referred. But, very strangely, if I decrease the saturation (move slider to left in that module) then more of the building and then the sky starts to glow red. This seems to be completely the reverse of what I expect. Furthermore, there appears to be no way to eliminate the clipped saturation.
What exactly are the bright red pixels showing? Is there the implication that my original scan is the cause of the problem ?