The Witness is free on PS4 at the moment, and it's a pretty good example of HDR with its bright and super colorful palette. Basically only downloaded it to test it out since I had already finished it on PC. Unfortunately the PC version never got updated with HDR support, but it did allow me to compare SDR and HDR directly on the same TV using two properly calibrated sources (enabling/disabling HDR while watching a movie for instance is really of no use). The Witness has always looked colorful as heck to me in the past but it's funny how much duller it looks in SDR on my PC when I switch back and forth with the PS4's HDR output. The skies alone look like such a pleasant blue-ish tone in HDR it almost makes them look greyish on my PC lol.
I really wish more games supported HDR, on PC or elsewhere. I had no idea the list was so anemic. UHD Blu-rays have been around for five years and game support has been pathetic all along, and with mixed results to boot! I guess things will change with the arrival of next-gen but I still wish so many semi-recent games lacking HDR support were patched with it. Just makes everything look a good deal nicer (when done correctly).
