In other words HTP it is not modifying the Raw Data after it is captured, but it is modifying how the Raw data is captured (by shifting the exposure to -1EV(by means of reducing the ISO) to protect Highlights).
My guess, based on what raw files should be and on what I read (though the information is certainly confusing and contradictory) is that this is what happens.
1. With HTP activated the camera is actually underexposing by about one full stop and recording the resulting image data into a raw file unaltered.
2. The camera is also including a flag or similar that notes that the file was underexposed in this way, so that conversion software that recognizes this flag can apply a different conversion curve to the data.
3. Some conversion software (DPP for sure, apparently Adobe products, and perhaps others?) recognize this flag attached to the file and know to apply the HTP curve to bring up the luminosity of the image file except the brightest values, in line with the HTP curve. (This also explains why conversion software that doesn't know about HTP simply gives a plain raw file conversion, and it explains how we can get an unaltered conversion from Adobe products.)
What is the alternative? To think that the HTP curve is "baked in" to the file data rather than attached as flag/alert to conversion software and that all conversion software that doesn't know about HTP does know about the "reverse curve" required to compensate for it... and somehow knows (absent a flag?!) that HTP was applied. That last point makes little sense — things just aren't typically done that way.
Until I (or someone else) can test and prove otherwise, my assumption will remain that the HTP data is attached to the raw file and that it does not alter the basic data in the file.
Dan, who is certainly prepared to be proven wrong (or right!) about this.
This is the way I see it. Raw means, as the name suggests, that the info gathered by the image sensor in the camera is being recorded w/o (nearly) any alteration. As a very general rule we can say that RAW capture is only effected by the camera settings related to exposure: Aperture, Shutter and ISO settings. Any other "alteration" is tagged to the RAW and "read",generally, by the camera's proprietary Raw Converter. One exception seems to be HTP as this alteration affects directly the exposure settings by shifting the exposure to -1EV and that makes me think that HTP is applied permanently to the RAW capture. Same thing for LENR as it affects the exposure as well. Nothing scientific though and I always keep those settings off.
Socrate
