FS7: FS7 Green Screen Shoot

thefilmaddict

thefilmaddict

Veteran
We have a client that wants to shoot green screen in 4k.
What settings would you recommend using?
What's the difference between XAVC I and L?
 
Cool. Thanks. It sounds like I is the way to go. A lot of compression I am sure will hurt the green screen key.

We just got the FS7. We've owned the EX1 and F3. Does this camera have picture profiles or this completely different?

24p 180 degrees sound ok for green screen or different frame rate and shutter?
 
I would go for the least compression as you can, and suggest overexposing by 1-2 stops which later when adjusted in post to correct levels will give you better noise levels.

In all honestly I would consider hypergamma. Depending on who's doing post and their experience, slog and green screen can be a bad combo.
 
The client that is editing the footage (we are not) does not know slog. Other than keying in adobe premiere and a little bit of three way color correction, that's probably as much as they will do. So is hypergamma still the best way to go knowing this info?
 
Definitely don't give them slog if they haven't worked for it. It will probably leave a bad taste in their mouth. :huh:

if for whatever reason you shoot in slog you can always transcode the footage using Davinci Resolve (free) or Sony Catalyst Browse (free) first and then give them the footage "corrected" and ready for keying.
 
I just wonder if shooting in any type of log and then color correcting or adding a lut adds noise and this noise will make chroma key harder? I think I want to give them the cleanest ready to go image I can give them that will key nicely.
 
starcentral said:
I would go for the least compression as you can, and suggest overexposing by 1-2 stops which later when adjusted in post to correct levels will give you better noise levels.

In all honestly I would consider hypergamma. Depending on who's doing post and their experience, slog and green screen can be a bad combo.
Click to expand...

"suggest overexposing by 1-2 stops"

What? Please explain.
 
If you shoot in cineEI mode, with slog3 and sgamut3.cine set as your color space, it can be easily graded by hand without any LUTs. But even if you did use a LUT, a LUT doesn't really add noise it just adjusts the gamma curve and transforms color. Surely if you boost certain tonal areas within your image you can actually increase noise but normally a "proper" grade doesn't add noise.

Regarding overexposing by 1 to 2 stops: if you overexpose your footage by 1-2 stops, later in post you reduce the levels by 1-2 stops so that the levels look normal again. When ever you lower your exposure (darken) your footage in post the signal-to-noise ratio is effectively INCREASED which means your noise gets DECREASED. Same thing if you shoot something dark or underexposed and later in post you try to raise the exposure, the noise becomes way more apparent. This technique from the film days is called "pushing" and "pulling" your exposure in post. In digital its the same thing. But obviously if you overexpose your footage too much then you start eating into your highlight latitude. So its bit of a trade off, usually 1-2 stops won't kill anyone.
 
FYI:

It's not well documented, but XAVC-L is an 8bit variation of XAVC (in UHD only), whereas XAVC-I is 10bit and holds much more information
for further postprocessing. I'd say avoid XAVC-L wherever you can when you are recording in UHD, it reduces the image quality more than you'll like...
 
Erik - is it 8 bit? I didnt know that.

I ask because I have been wondering if 4kXAVC-L would be a better 'daily codec' than 1080xavc-I- at 8bit probably not.

S
 
I have been to a Sony camera workshop lately where they said that
XAVC-L is limited to 8bit in UHD. It's different in HD, where both XAVC
codecs deliver 10bit.

I have not tested this myself, but you can read about this here and there.

XAVC-I is my go-to codec at the moment.
 
Xavc-I-hd is 100mbs, xavc-L-uhd is 200mbs, xavc-I-uhd is 600mbs,

It would be interesting to see which of the 'smaller' codecs made better HD - 600bms is going to be a PITA for me to handle on most jobs. Also you get the 'we shot 4k' ticket!

S
 
Typically when shooting greenscreen you use a lower EI, on FS7 I'd say 1000 EI, you get cleaner shadows. With controlled lighting there's little risk of highlight clipping (at 1000 EI you have +5 -9 dynamic range)

On Alexa vfx shoots typically 400 EI was used quite often.
 
morgan_moore said:
Xavc-I-hd is 100mbs, xavc-L-uhd is 200mbs, xavc-I-uhd is 600mbs,

It would be interesting to see which of the 'smaller' codecs made better HD - 600bms is going to be a PITA for me to handle on most jobs. Also you get the 'we shot 4k' ticket!

S
Click to expand...

I always see people quote the 600mb/s for UHD XAVC-I, but this is only for 60fps. XAVC-I in UHD is about 10megabits per frame. So at 24fps, your bitrate is about 240mb/s. And I hate to rain on peoples' parade but these bitrates aren't comparable to HD bit rates, which I don't think most people realize. UHD is basically the size of 4 HD frames, at once. So for UHD to have to same compression quality per frame as the 100mbps HD XAVC, the bit rate would have to be 4x that. It's not. It's only 2.4x that (100mbs vs 240mbps). I'm sure there are other factors at play that might have an effect on the image, the compression, etc. But just looking at the numbers, UHD XAVC is more compressed (relative to the size of the frame) than HD, even though the bit rate is higher.
 
SonyF5-F55-media-chart_zpsc9408fdf-1.png
 
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