Vuescan histogams

[Robert Feinman]

When scanning b&w negatives with Vuescan the histogram
display shows two overlapping curves on the "after" panels.
On is green and the other is blue. They differ slightly
in shape, but the endpoints are at about the same place.
Does anyone know what they are supposed to represent?
Thanks...

 

[Alan Smithee]

Gamma, brightness, contrast whatever you want to call it basically. There
are actually three lines, Red, Blue and Green. I suspect it's because the
gamma for each channel is being process independently and they don't quite
line up because of a rounding error. If you tweak the individual channels in
the colour tab you can see them shift around. I know for black and white the
RGB exposure time for each channel used is different than for colour. Maybe
someone else knows for sure.