I was testing out "picture frame" mode here is what I did:
-I turned off the radios using the "phone info" app, which is similar to airplane mode.
-Screen brightness to min.
-Turned on all power saving options.
-Used "screen on" app to keep the screen on.
-Used the gallery with a pitch black picture(I didn't want to get screen burn in)
-The radio was turned on just prior to the screen shot so that I could e-mail myself the screen shot.
Wow a pitch black screen on a samoled screen basically means the screen is off. The reason why the blacks are so black on the phone is because the pixels are not turned on when displaying blacks.