Panasonic have confirmed that the GH4 (quite amazingly) outputs 10bit 4K 4:2:2 direct from the onboard micro HDMI port without the optional but expensive YAGH accessory box.
So that means you can record in 10 bit in an external recorder , which means that colour grading should be way better.
In my last film using the GH2 and GH3, I had real problems with some shots that had been filmed using the wrong colour balance . The 8 bit images began to really fall apart when I tried strong colour correction. So 10 bit should be fantastic.
….on the other hand I could have got the colour balance right in the first place, as we used to have to do with film 🙂
If you can afford it, the add -on base accessory box (which costs more than the camera) has even more useful facilities, though it has to have an external power supply, which is a bit of a limitation.
The YAGH accessory box for the GH4 takes video entirely from the micro HDMI port on the GH4, which is why it can offer 10bit 4:2:2 through the full sized HDMI port it offers as well as HD-SDI.
Thanks to EOSD.com for the info
Now got some more details from Panasonic about what the camera can really do.
…and another interesting hands on review with a pre-production model. Showing how it can do really nice slo mo.
Best stuff is about 10 mins in.