I’m really interested in whether shooting 4k for HD output actually gives more colour information that shooting HD in the first place. There’s been lots of mathematical theorising about this, some of which I kind of understand, lots of which I don’t.
So to get a real world answer, I just pointed the GH4 at the sky, and this is what happened.
First off, 100Mbps at 25p. Then the same shot a few seconds later, no changes other than to switch to 4k. Then import to FCPX, optimizing footage to ProRes. Drop both shots onto a 1080p timeline. Add a Hue/Saturation filter, crank up the Saturation to 2.0. Export as 1080p.
Obviously nobody would actually add that much saturation in real life, but it exaggerates the colours in a grey Newcastle sky.
I think the difference really stands out.
Settings: Cinelike V tweaked to Mr AR’s recommendations, cloudy WB, shutter speed 1/50, iso 200, f3.5. Not sure what the colour balance difference is due to - I changed nothing on the camera between shots other than changing between HD and 4k.