12-10-2016 08:27 AM - edited 12-10-2016 08:29 AM
Are you sure about HTP Tim? My understanding is that the sensor response is altered such that the 1s and 0s are affected. Thus there is no flag and neither LR nor DPP know what was done. All they see is a data file. It's not a reversible process.
The way Highlight Tone Priority works is the ISO is shifted one stop (thus no ISO 100 when using HTP) AND a different tone curve is applied when output to JPG.
So the actual RAW data taken at HTP 200 looks the same as the RAW data taken at ISO 100 with negative one exposure compensation. However, the camera and DPP apply a different tone curve to that data, so the histogram of HTP 200 does not look the same as ISO 100 with negative one exposure compensation pushed one stop in post processing. Years ago I personally did test shots that showed that they were different.
So, the tone curve that Lightroom applies to HTP 200 is most likely very close to the tone curve that is applied to in camera JPGs or when processed in DPP, but, probably not identical. Lightroom knows the data is supposed to be processed differently, how differently it is processed really only Adobe knows.