Thanks for the reply.
My TV is Sony KD-XE8096 which has in its specs:
"Panel bit depth: 10 bits (8 bits + FRC)". What are correct Dune video settings for this panel?
My HDMI cable is that I got in my Dune's box when bought it.
First enable 'enhanced format' on the HDMI port the Dune is connected to. As here: https://www.sony.co.uk/electronics/support/articles/00141961
Then try the settings I gave initially (http://www.futeko.com/newforum/index.php?topic=3616.msg25211#msg25211). I think they should work with your TV. If they don't then change the 12-bit settings to 4:2:0. That should definitely work.
If not then, if possible, try another HDMI cable. There have been some reports of the cable Dune supply not being the best and having problems at high bandwidth.