Are you gays serious
Take now your camera, set the camera on P and 100iso, start to metering against a white wall, grey card what ever and se what values you get in time / f-stop , for example 1/60sec F-5,6
Start HTP The camera now changes to 200iso and at the same you now get 1 stop shorter time or F-stop.
You have now halving the in falling light /photons to the sensor compared to 100 iso by a shorter exposure time or one more f-stop or both
And Neuro and others, it is you who do not understand how basic things works and Im sorry that thou do not know basic knowledge
And please Neuro stop to make your funny on my behalf, that Im writing drivel etc - try to understand instead .
First things first ... Please don't call us "gays". I guess it just might be a typo but nevertheless this is something I have to refute as it is typed out in bold.
If you read my above post, I specifically mentioned that as per my understanding the photons could be halved only by changing the shutter speed and / or the aperture - which is what you are also implying.
Also, I can agree that in the P mode, the photons hitting the sensors would be halved - but this will happen only if you started at ISO 100 in the first place - it is also of note that the halving of the photons happens only because of the in-camera override.
I also tried this just now ... Start out at ISO 400, meter a scene ... Now enable HTP ... Nothing changes whatsoever.
Thus concluded ... HTP does not change the number of photons hitting the sensor. If you we're to start out at ISO 100 though,the camera will automatically change the ISO, aperture and/or shutter speed when you are on ISO 100.