Digital Light & Color

I know that there have been posts related to this issue before, but finding that the complex behavior involved with the Brightness Transformation is still present, here are my observations and a possible suggestion.

The following illustrates the complexity. Use the Black Curve tool and make a brightness adjustment with the black slider and a brightness curve. Next select the White Curve tool and use a different brightness curve and the white slider. At this point, changes in the position of the black slider generate changes to the image appropriate to the brightness curve that is not visible, that is, the one that was used when the Black Curve tool was in play.

In summary, the complex behavior of this system would become less complex and more logical and easier for me to understand (and for writing the documentation) if, when the White Curve tool is selected, only the white slider would be present, and when the Black Curve tool is selected, only the black slider would be present. The use of tabs as in Advanced Sharpen to separate white and black might also make the interaction among mask, tool, slider, and brightness curve more logical and transparent.

While I grant there would be some simplification of the user interface, there are a couple of downsides:

1) The proposed single slider would be easy to confuse with a normal Amount slider which is similar, except that in the presence of a mask it splits into a double slider. The dual black and white sliders provide a visual cue that this is a different Amount control.

2) It would remove what I consider to be a useful feature, namely the ability to tweak the black and white slider amounts without having to flip back and forth between the black and white curves. Personally, I rarely use the Amount sliders with Brightness Curve -- mostly I just adjust the curve(s) to make the effect stronger or weaker. This is more powerful than using the sliders since you can make very specific brightness and contrast adjustments.

Other possible options include:

1) automatically switching curves when you adjust the corresponding black or white slider

2) when a mask is present, displaying two sets of controls side by side -- one for masked and one for unmasked areas -- each would then have its own slider.

Your second option sounds like it would help.
The documentation on White/Black Curve is pretty complex.
When you first start to use the Brightness transformation, say using the White Curve, it is somewhat confusing that the black slider does nothing.
For me, what is lost with the present nontransparent behavior is not compensated for by what is gained in utility.
My way around all this is simply to do only one thing to an image with the Brightness transformation, which often means I will have two or more consecutive Brightness transformations in a row in my processing of an image. This makes it easy to understand how each transformation changes the image.