Develop Persona: Difference of applying tone curve or not

[user_0815]

In the Develop persona there is the option in the assistant to apply a tone curve or not.

After clicking on "Develop", the Shadows/Highlights slider produces different results when reducing the highlights. I'd like to understand the difference because I would expect the same results. Developing to 32bit.

(1) When not applying the tone curve in the develop persona, the highlights can be reduced with very good results. The absolute white parts (255/255/255) will remain so for quite a while (e.g. -30) while non-whites will change.

vs.

(2) When applying the tone curve, even the absolute whites (255/255/255) will immediately change as soon as the slider moves to negative values. 

Taking a 16bit tif coming from a raw converter, I get the same behaviour as when not applying the tone curve (1).

Why is this so? 

In this example the background is pure white but the subject not.

[stokerg]

Hi @user_0815,

James has done a good job of explaining what the Tone Curve does on this post  

[user_0815]

Thanks, his explanations are always valuable. After reading that, let me phrase my question this way: 

 

With the tone curve applied, the developed image has values between 0 and 1 and cuts off everything above.

Without the tone curve applied, the developed image also retains values above 1, correct?