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First, let's be careful with the terminology. There is a tone curve in CR, but not a "base tone curve." The CR tone curve is constructed from your Brightness (default 50), Contrast (default 25), Parametric Curve (default identity), and Point Curve settings (default Medium Contrast). These 4 controls, when left at their default values, will produce CR's default tone curve.
There is a "base tone curve" inside the DNG Profile Editor. CR is setup so that its default tone curve will be simply equal to the profile's base tone curve. Or, put another way, any tone curve adjustments you make inside CR (by adjusting one of those 4 controls named above) will be made __relative__ to the profile's tone curve.
This is the reason there is a big difference between the "Linear" Point Curve setting inside of CR and the "Linear" Base Tone Curve setting inside the DNG Profile Editor. With the former, you are only setting one of the 4 parts of CR's tone curve to linear. With the latter, you are setting all 4 parts to be linear (i.e., the entire tone curve becomes a straight line).
If you weren't using the DNG Profile Editor, to get an equivalent look inside of CR, you would not only need to set the Point Curve to Linear, but you would also need to set Brightness and Contrast to 0 (instead of their defaults of 50 and 25, respectively).
BTW, most of the time, you will not want to use the Linear option for Base Tone Curve inside the PE. The reason it's available is because sometimes it's useful to get linear output from Camera Raw / Lightroom, such as when feeding the converted output to some specialized HDR-processing tools. These tools may be able to do a better job with local tone mapping if it is fed linear data (or close to it).
Thanks Eric. I knew there was more to it than I understood and your explanation was very clear and understandable. Thanks.
Excuse my naive questions....So are the profile editor curves and CR curves additive or how do they interact? I understand your explanation for why one would choose linear in the profile editor, but when would I want to change the curve in the profile editor and when would I want to tweak the curve in CR? I've used flexcolor in the past on my Leica DMR files and made a curve in a custom look based on their supplied profile to sort of linearize the rendering. It appears that I might benefit from something like this in Lightroom but I haven't figured out where it is best to do this.
It's useful to use the DNG PE's tone curve when you wish to establish a default tone curve that is associated with the profile. That way, as you flip through profiles within CR/LR (from the Profile popup menu), both the color rendering as well as the tone curve will change.
For example if you're trying to create 2 "visual styles" you may have one profile with less color saturation and a lower-contrast tone curve (all of which you set up in DNG PE) and another profile with more vivid color saturation and a more contrasty tone curve (again, set up in DNG PE). This leads to two profiles, which you can then load into CR/LR. Then given a particular image, you can choose from the Profile popup menu which "profile" is more appropriate for that image as a starting point (the more neutral one or the more vivid one) without having to fiddle with the tone curve controls separately.
Think of the DNG PE as creating a color/tone starting point. The additional tone controls in CR are __relative__ to a profile's base curve.