DNG PE: I want to try other Tone Curve but ...

Question

In DNG PE I load a dng file, I choose a camera profile, I go in the Tone Curve panel in the Base Tone Curve I set Linear, I click on the curve and I set in 95 out 160 (only one point for this purpose) and then I save the new profile.
I go in ACR, I load an image and I switch to new camera profile: the image become very light.
I launch the DNG PE, load the previus created camera profile, click on Show Tone Base Curve: the showed curve is not parent with that I created (95 in 185 out, see below in black what I have created, in red what the profile has registered)

Answer 1

Hi Marco,
This is mostly (*) possible, but not directly via the DNG PE. The issue is the encoding space. Your RGB tone curve that you describe above is defined in a gamma 1.8 space (since ProPhoto has a gamma encoding of 1.8 ). The (black) tone curve interface in DNG PE is defined in a gamma 2.2 space.
In other words, if x is a linear signal and x' is the transformed linear signal, then the math for the former case is effectively
x' = x ^ 1/1.8
x' = ApplyToneCurve (x')
x' = x ^ 1.8
whereas the math for the latter case is the same except for the use of 2.2 instead of 1.8.
You will need to perform the appropriate transformation so that your 1.8-relative tone curve is expressed properly in a 2.2 space.
Once you have the actual numeric curve worked out, one way to make the required tone curve is to edit the .dcpr (recipe) file from the DNG PE using a text editor.
(*) The reason I say "mostly" is because another detail is that the PS RGB tone curve is a 1D curve applied separately to each channel. This is not the way the tone curve works in Camera Raw.