Help understanding the zone sliders in CR parametric curve

[jljonathan]

Can someone please explain the theory/use of the zone sliders in parametric curve and how the 3 sliders relate to the 4 controls. I see that the grid divides the tones into 4 areas which can be controlled by the 4 tone sliders, but how does one set the 3 zone sliders to correspond. What would be a good starting point?
Thanks
Jonathan

[JeffKohn]

Can someone please explain the theory/use of the zone sliders in parametric curve and how the 3 sliders relate to the 4 controls. I see that the grid divides the tones into 4 areas which can be controlled by the 4 tone sliders, but how does one set the 3 zone sliders to correspond. What would be a good starting point?
Thanks
Jonathan

They control the crossover points between the 4 tone sliders. I don't know of a really good way to explain it but if you play around with them it should become more clear.

[Mark D Segal]

The default position is a good starting point (.e. 25, 50 and 75). first adjust the four luminosity zones to taste. Having done so, you will probably notice that the amount of adjustment you have applied to each zone differs between them. You then use those three zone demarcation sliders to roughly determine how much of the luminosity scale should be more influenced by the adjustment you made to a particular zone. Now let us assume for example that you have made the lights lighter and the darks darker, but you find the ligher part of the dark zone to be a bit too dark. In that case, you spread the 50 control leftward, because that expands the adjustment you made to the lights into the region of the darks. You will notice the darsks start to lighten as you move it further and further to the left. So in general, what you are doing with those markers is altering the size of the luminosity zone over which a particular zonal adjustment has been applied. There are no rules or guidelines - just "season to taste".