GH4 4K for Talking Heads, etc

Oedipax

Well-known member
Hey folks,

So I shoot a lot of video every week that is generally done in a studio environment with talent presenting towards the camera. For the past couple years, we've standardized around GH2s shooting various hacks (ultimately I settled on Sanity, for reliability, small file sizes, and the fact that it still looked great and I didn't feel like I was losing anything by not shooting the hardcore intra stuff).

I would shoot 2, sometimes 3 GH2s at once: one for a wide, one for a medium, and one for a close-up, depending on the video. Time is of the essence so getting things in one or two takes is far preferable to all involved than shooting single camera and having to get all that coverage one at a time.

When the GH4 was announced, the thought of being able to shoot perhaps just one wide in 4K and punch in for the rest really appealed to me. Simpler setups, less file management, more flexibility with framing the shots in post, and dead-on eye-lines for the talent versus having the cameras slightly staggered on a tripod with multiple mounts.

However, for the last couple weeks I've been testing this setup and I have to say, so far I am not terribly impressed with the results at 100% on a 1080p timeline. I feel like I'm seeing a lot of compression artifacts in the image and it feels like a lesser image than what I'm accustomed to from the GH2s (of course, when 4K is downscaled at 50% on a 1080p timeline, it looks great). I've experimented with varying levels of sharpening in post, but I can't shake the overall ropey quality the stuff seems to have when viewed up close.

Initially I was shooting more or less with the James Miller settings, but I've reverted back to "Natural" (I think that's what it's called on the GH4 - basically an analog of "Smooth" on the GH2) with sharpening, contrast, saturation dialed back.

Lens-wise, I'm using the Panny 12-35 f2.8, the 20mm f1.7, and the 14-140 f4-5.8. Typically the 12-35 as I feel that's the sharpest one going, but the 14-140 is great too for close-ups and the 20mm for low light (albeit not really a going concern in the studio). Aperture is usually somewhere around f5.6 to f/8, ISO typically 200 or 320. This is done to make sure the talent doesn't drift in and out of focus.

I'm wondering, is anyone else using the GH4 in a similar capacity? Should I boost some of the sharpening within the GH4 to preserve more detail prior to compression? I'm not going for "filmic" or "organic" with these settings - I'm shooting for clarity and sharpness, a clean HD video look.

Edit: Little more detail - I'm shooting in UHD 4K 100M, using .MOV and running the sensor at 24hz. I've tried C4K as well, but the image quality at a glance seemed the same to me, this stuff is intended to be 16x9, and if anything I guess since the bitrate is the same on both, the UHD might come out slightly ahead in that department. Editing in Premiere CC, 1080p timeline.
 
Last edited:
To begin, you have to know what you are cropping. According to http://www.eoshd.com/comments/topic...sonic-gh4-plus-pre-review-short-film/?p=62453 these are the facts:

The GH2 multi aspect sensor for 16:9 video is 18.8x10.6mm and has a diagonal of 21.6mm wich is half diagonal of full frame film cameras
So the GH2 crop factor for video is 2x

[T]he GH3 and GH4 uses all the horizontal pixels of the sensor to capture 1080p video:
The GH3 and GH4 sensor for 16:9 video is 17.3x9.7mm and has a diagonal of 19.85mm
So the GH3 and GH4 in 1080p has a crop factor of 2.18x (43.26 / 19.85)

[T]he GH4 sensor is 4608 pixels in horizontal and C4k is 4096 pixels in horizontal and UHD is 3840 pixels in horizontal:
The GH4 in C4k mode uses an area of 15.38x8.11mm of the sensor and has a diagonal of 17.39mm
So the GH4 in C4k mode has a crop factor of 2.49x (43.26 / 17.39)

The GH4 in UHD mode uses an area of 14.42x8.11mm of the sensor and has a diagonal of 16.54mm
So the GH4 in UHD mode has a crop factor of 2.616x (43.26 / 16.54)

Right away you can see where things are going to get ugly. If the 12-35 is like most other zooms ever made, it is softest at its widest angle. So a 12mm cropped UHD image on the GH4 is the equivalent of a 31mm uncropped image on the GH2. That's a lot to ask from the soft size of a zoom lens.

Second, the 100Mbps data rate of UHD has only the equivalent of 25Mbps when using a 1080p center crop. That's still a good data rate, but nothing compared to what the GH2 can support with the high bitrate hack.

Finally, the brain is a funny thing, and if it looks at a beautiful 4K image as its reference image, and then it looks at a 2x cut-in of that image, it's going to be a lot pickier (I suspect) than if it's looking at the only one reference image it's ever seen, the full-scale uncropped 1080p image. So one thing you could do is compare the GH4 center crop at 12mm to the GH2 at 31mm, or compare the GH4 center crop at 20mm to the GH2 at 52mm. Without ever looking at the full 4K image, how do those two compare?

But really, I think the biggest factor is that 2.616x crop factor of the GH4 vs. the GH2. Lenses have very finite amounts of high-frequency MTF, and when you digitally zoom in even 50%, you're really challenging the lens. Zooming in over 100% (in this case 160%), you are likely pushing your lens well beyond its happy place.
 
Last edited:
Thanks for your reply, Michael! I think it comes down to the compression more than lens performance, because I've shot many stills on my GH2 in the past and cropping in on those (pretty aggressively at times) never yielded the yucky stuff I'm seeing from the GH4's video, regardless of the lens in question. Looking at what Sanity shoots, it's 38Mbps, which is certainly ahead of the 25Mbps 100% crop @ 1080p on the GH4. But I still think more in-camera sharpening might aid in preserving detail in places like hair, for instance. I'll do some more testing this week and if I have any a-ha moments I'll be sure to pass them along here.

Also - I'm not shooting the 12-35 at 12. What I discovered very quickly was there was no way to go from a full wide (head to toe type coverage) to a close-up within a 4K frame. So I've been shooting my wide on a GH2, and shooting the 12-35 at around 35mm for my mediums, from which I was also hoping to derive my close-ups.

It's possible that I should invert that - since the close-up has the most scrutiny, perhaps that should be a dedicated camera, and meanwhile shoot wide and derive mediums on the GH4. I could probably do that with less than 100% scaling as well. I'll keep playing around with it!
 
Last edited:
I'd agree with you Oedipax, it is a limitation of the codec. I crop in from 50% to about 75%, but even there a keen eye could see a little less detail. Before the gh1 gave me close to true 1080p resolution, I couldn't crop in hardly at all on the 1080p from my little canon hv20 even for a 720p project. The true resolution, while decent, certainly wasn't very close to true 1080p.
 
After a month of testing I used the GH4 for its first real gig today - I'm finding the opposite to you.

Job was a 3 minute 'Sorry I can't be there' message from a senator on a ipad auto-cue.
Only had the Senator for 10 minute so thought I'd use the 4K instead of my usual XDCam.
Lens was Olympus 14-35 f2 set at about 20mm and wide open for a mid shot.
We did actually get a second take which I shot at 35mm.
Profile was standard with sharp -3 and NR -2

Edited the two shots on a 1080 timeline (FCPX) and client is happy.
Have now gone and done a (silly) re-edit using only the mid shot and I'm astounded at how sharp (too sharp for my liking) both the original and the zoomed in shots are.
I will have no hesitation doing this again for clients - in fact I'll be pushing them to give it a go.

Sure, a locked off talking head shot shouldn't stress the compression at all but I'm not seeing any issues - going from a head to toe shot to a close up sounds like a lot of zooming to do in post even with 4K.
 
i posted in the pv forum. i find 100% crop not that great either. I have decided not to scale down any more than 70-75% from 4k footage. This has changed the way I frame the shot now to not rely on 100% crop anymore
 
Back
Top