White And Blackpoints

[user_deleted]

The gamma node lets me alter the midtones without changing the black and whitepoints right?
But this is, I think at least, only true when the white and black points are 1 and 0. So, if my black point is not exactly 0 it will be affected when I change the gamma to correct the midtones, right?

Is there any way to change the midpoint value without changing the white and black points? I've tried the
Lookup, LookupHLS and LookupHSV nodes (And I've read the help file for all of them) but I just cant figure out how to set the white and black point with it. The midtones should be changable by curving the line between the white and blackpoints, that's all I know, so basically, the question is, which node works like a color curve (Which I believe would be one of the lookup nodes) and how do I use it to set the black and white points of a foreground that needs to be matched to the BG-plate. Which curves do I change? (sExr, iExr, hExr etc.)

[user_deleted]

The gamma functions independent of the white/black levels, the darkest color will can that .8 or .00, but think the gamma is a mathematic operation (power) 0 is 0 and 1 multiplied for 1 is 1, always. In some cases you can use the clamp node. To match the white/black and other values between two images you can use the Color Match node. When you use the curves you can choose to modify or not the black/white points ( you can this changing the position of extreme knots). Try use the plotscanlines nodes to identify what type of adjust you make in the image (combine two ploscanlines with iADD)

[user_deleted]

Lookup is the way to go. In the following example i have raised the midtones while defining a black point greater than zero and white point less than 1 and constraining them so that they dont change.

CODE
Lookup1 = Lookup(0, HermiteV(x,1,[0,52.37,52.37]@0,[0.1115,50.25,54.18]@0.1035,[0.6942,44.88,44.88]@0.4283,[0.8831,46.95,48.72]@0.8835,[1,50.11,50.11]@1),
    HermiteV(x,1,[0,52.37,52.37]@0,[0.1115,50.25,54.18]@0.1035,[0.6942,44.88,44.88]@0.4283,[0.8831,46.95,48.72]@0.8835,[1,50.11,50.11]@1),
    HermiteV(x,1,[0,52.37,52.37]@0,[0.1115,50.25,54.18]@0.1035,[0.6942,44.88,44.88]@0.4283,[0.8831,46.95,48.72]@0.8835,[1,50.11,50.11]@1),
    JSplineV(x,1,0@0,1@1));

Using add, gama and multiply for black points white points and midtones is a valid (and very popular) way to work. even if your white point isnt white, gamma wont change it very much. You just have to do a bit of backwards and forwards to get things right.

[user_deleted]

Great! Thanks.