I found ToneMapperFilm might have a bug.
I notice viewport’s look doesn’t like the buffer visulization: Final Image(Postporcessinput0), and PostTonemapHDRColor(Postporcessinput3), also Postporcessinput4,5,6 for the same result with Postporcessinput3.
But, I use r.tonmapperFilm 0. viewport’s look just like Postprocessinput0,3,4,5,6. but just have a little maybe gamma or exposure difference issue.
So I think Maybe UE4 forgot apply the ToneMapperFilm to post Postprocessinput0,3,4,5,6.
Please see these screen shots.
