By all means, people should read that thread and observe Mikael 'Half The Photons' Residal's staunch defense of his explanation that the general mechanism of HTP is that the camera reduces by half the amount of light hitting the sensor, his consistent refusal to admit that his 'explanation' applies only at ISO 100, his avoidance of specific questions from several posters to describe how HTP works at any other ISO setting than 100, etc. Note how here in this thread, he reposts TheSuede's correct description of how HTP works, which matches what others in the thread were saying, but not his own flawed and incorrect explanation.
Doesn't it sort of halve the collected photons though, depending upon how you go about talking about it? If you set ISO400 HTP it uses ISO200 but exposes as if you were using ISO400 so you are shooting ISO200 but as if you were ISO400 so the camera metering does toss away a stop of light compared to what it does when you shoot ISO200 as 200 instead of 200 as ISO400 HTP. So, using the proposed tone curve, it shifts the middle gray and everything else down a full stop so you have 1 stop more room for highlights.
If you compare ISO400 to ISO400 HTP they expose the same way and collect same # of photons but the one without HTP applies one stop more gain than the other and assumes a more typical tone curve will be applied and doesn't shift all of that down 1 stop. But looking at it from the true RAW level ISO400 HTP actual corresponds to ISO200 not ISO400....
It depends how you go about talking about it in detail. I don't know if talk about photon collection is really is the best way. I didn't read that other thread of much of this yet so I don't know went on.
I think it is simplest just to say that:
1. HTP isn't anything special and isn't a real new mode and it is nothing more than software and metering games.
2. You can do the exact same thing (for RAW shots) by using ISO stop lower in regular mode than what you set in HTP mode and then setting EC -1 to all your shots (or for M mode decide simply use the ISO you want in either case and then for the times you want the 'HTP' shots you decide to set shutter speed one stop faster so as to save one stop more highlights)*.
3. All HTP is is metering at the labelled stop but applying the gain of one stop less and, in cam (or default in RAW converters), applying a special tone curve that shifts most of the data down one stop and applies different tail and especially top end curves.
*And then you shift things around with the RAW settings to give it a curve a mid-tone point that works (using some built-in profiles you may run into the twisted profiles issue and if you are not skilled at moving sliders and setting TRCs and such it might be a bit trickier with some software to work it out as well than having the software give you automatic starting point under the hood though perhaps, although since most standard starting points and exposures are not fully ETTR you might not actually hit all that must problems at all and might even hit less).
That's all you had to say, Mikael. Why did you feel in necessary instead to lead off by insulting my knowledge and intelligence?
I'm just guessing, but maybe he was just snapping after all the grief dumped on him in some other threads and stuck in fight fire with fire mode after all of that? Jrista and plenty others certainly insulted him by the bucket load (myself too in some of those threads
). Some people who were rather incorrect about a lot of things had been dumping all sorts of insults over a few members for a long time, maybe he just got sick of it and now just snaps back at the slightest hint of anything? Maybe not the best way to go about it, but you can understand a bit where it comes from (plus it is interesting that none of those bashing him now ever got on the cases of everyone who started insulting him and others way back when and they were all fine with it all in that case, why, probably because the ones insulting and bashing in those cases tended to rarely ever treat Canon as anything less than a god.).