I do not want to stop your enthusiasm, but from my tests, they don't exists two images from one shot.
I didn't do my tests with an engineering approach, I only did some empirical test and from these I gather that:
- when you setup the Monochrome mode, the P9 activates the left camera (on the left when facing the phone back)
- with all the other modes, the P9 activates the right camera (the one between the flash and the left camera)
The P9 doesn't create 2 images, than combine them, it just shot always 1. How I came to this conclusion? You can also try it at home:
I choosen few static subject and I made my photos with the phone on tripod, than I did many photoshoots in the normal way and also by covering alternately the 2 cameras with a black scotch tape.
Even by naked eye, even by using an image comparation software (I used Beyond Compare from Scooter Software) I found no difference at all, no more brightness, no more contrast, no better image definition.
I did in a bright environment, in a dark one, I enabled and disabled the PRO mode and I tried to do a testing more complete as I could (honestly, I omitted to test the image in RAW mode, I tested only JPEGs), but my conclusion is that the 2 cameras are doing a different job, but they are definetely NOT working together.