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XAVC green screen, was documentary cameras

Art Adams
 

>Actually, the FS7 is 10-bit 4:2:2 when recording with the 4K XAVC-I codec (same codec as the F55), and I’ve had no trouble pulling clean keys from it.

How clean? I'm shooting a project next week on an F55. For the non-green screen day I'm shooting 4K XAVC-I, but for the green screen I was going to shoot HD SStP SQ 444. I've looked at both under a digital microscope and the edges are much cleaner with SStP, but the budget is getting slashed and I'm wondering if I can get away with a lesser codec as I won't have as many cards as I'd like.

--
Art Adams
Director of Photography
San Francisco Bay Area

Doug Jensen
 

XAVC-I has been plenty clean enough for replacing backgrounds on standard interview setups, but I’ve never needed to use it for anything more complex than that.   So I don’t now whether it would be good enough for someone else’s needs or not, my main reason for posting was just to correct the misinformation that 4K on the FS7 is only 8-bit.

SStP SQ-444 on the F55 is a nice codec, but it’s only HD.  I’d rather shoot 4K XAVC-I and down-sample in post for keying. But if you really want high quality and an easy codec to work with, rent an R7 recorder for the F55 and shoot 4K XOCN-ST.  It’s an excellent lightweight RAW codec that is a really pleasure to work with in Resolve.  I’d say 90% of everything I’ve shot in the past year with my F55/R7 was XOCN-ST.   But if I didn’t have an R7, then I’d feel very confident going forward shooting green screen with 4K XAVC-I.  As someone else has pointed out already, lenses and lighting are just as , if not more, important.

Doug Jensen



From: Art Adams <art.cml.only@...>

How clean? I'm shooting a project next week on an F55. For the non-green screen day I'm shooting 4K XAVC-I, but for the green screen I was going to shoot HD SStP SQ 444. I've looked at both under a digital microscope and the edges are much cleaner with SStP, but the budget is getting slashed and I'm wondering if I can get away with a lesser codec as I won't have as many cards as I'd like.

Art Adams
 

Thanks, Doug. I’m hoping we have a VFX house signed on soon as we shoot next week, and I’ll check in with them, but my gut says go with SStP. I was hoping that XAVC-I 480 might be an option, but I’m not sure the higher bitrate will help me get around the 4:2:2 subsampling.

Years ago I shot a test for another project and wrote an article about it. This is the comparison, using diagonal lines on a Chroma Du Monde chart as a reference:


SStP is only HD but the edges are much cleaner. Still, you have to zoom in a long way to see the differences, and I don’t know at what level these details become important.

I shot this video a long time ago but didn’t capture a 4K version:


Noise makes more of a difference, but I’m very aware that it takes only slightly more effort for me to make the VFX house happier, especially on low budget projects.

Hopefully we have a VFX house signed before we shoot. I’d prefer to shoot 4K XAVC-I 480 just for flexibility, but I know SStP SQ works.

--
Art Adams
Director of Photography
San Francisco Bay Area

cml@...
 

I have personally recorded hundreds of sports people against green screen, using 4K XAVC on an F5, over the last few years. This was for use by Sky Sports in the UK, and they have always been able to pull a very clean key.  Every year, every Premiership Football (Soccer) player, every Premiership rugby player, and all the F1 drivers, amongst others, are recorded in this format.

Andrew van de Waal

DOP
Near London

Art Adams
 

Thanks, Andrew. That's great to know. 

--
Art Adams
DP
San Francisco Bay Area



On Mar 30, 2018 at 9:13 AM, <Cml> wrote:

I have personally recorded hundreds of sports people against green screen, using 4K XAVC on an F5, over the last few years. This was for use by Sky Sports in the UK, and they have always been able to pull a very clean key.  Every year, every Premiership Football (Soccer) player, every Premiership rugby player, and all the F1 drivers, amongst others, are recorded in this format.

Andrew van de Waal

DOP
Near London

Rachel Dunn
 

10-bit 4:2:2 should be enough color separation to pull a decent key - especially at 4K, since the 10 but gives you good color resolution, even though the hue/sat is effectively at half Rez.

4:2:0 is pretty much a lost cause.

A lot depends on content though, I've been presented with some RAW plates that have been tougher to pull a keys on than 10bit 4:2:2

But you will have better luck keying a bad plate from a RAW/4:4:4 file than you will from a compressed codec.



- Rachel D

310-562-5779
www.racheldunn.com


On Mar 29, 2018, at 8:40 PM, Art Adams <art.cml.only@...> wrote:

How clean? I'm shooting a project next week on an F55. For the non-green screen day I'm shooting 4K XAVC-I, but for the green screen I was going to shoot HD SStP SQ 444. I've looked at both under a digital microscope and the edges are much cleaner with SStP, but the budget is getting slashed and I'm wondering if I can get away with a lesser codec as I won't have as many cards as I'd like.

Art Adams
 

Thanks, Rachel. It's more about the edges with 4:2:2 as they tend to be a bit rougher. 4:4:4 always keys better, but on this job that limits me to HD. Not a huge deal, just trying to do more. 

--
Art Adams
DP
San Francisco Bay Area



On Mar 30, 2018 at 9:32 AM, <Rachel Dunn> wrote:

10-bit 4:2:2 should be enough color separation to pull a decent key - especially at 4K, since the 10 but gives you good color resolution, even though the hue/sat is effectively at half Rez.

4:2:0 is pretty much a lost cause.

A lot depends on content though, I've been presented with some RAW plates that have been tougher to pull a keys on than 10bit 4:2:2

But you will have better luck keying a bad plate from a RAW/4:4:4 file than you will from a compressed codec.



- Rachel D

310-562-5779
www.racheldunn.com


On Mar 29, 2018, at 8:40 PM, Art Adams <art.cml.only@...> wrote:

How clean? I'm shooting a project next week on an F55. For the non-green screen day I'm shooting 4K XAVC-I, but for the green screen I was going to shoot HD SStP SQ 444. I've looked at both under a digital microscope and the edges are much cleaner with SStP, but the budget is getting slashed and I'm wondering if I can get away with a lesser codec as I won't have as many cards as I'd like.

Rachel Dunn
 

Avoid 8-bit and use as little compression as possible.

Resolution helps, but it won't be as big a factor as color depth/compression.

A lot depends on subject matter.

Fine fly-away hair is always a nightmare, but a bald guy can go together with a push-button key.

There's also a big difference between a real-time ultimatte key for sports center and a photo-real composite for a tentpole.

Also taking the time to make sure that your green screen is as evenly lit as possible will help, because you won't have to key as large of a color slice to eliminate the GS, so the edge detail will be lower contrast and higher detail.

Larger color slice means higher contrast edge detail, which bring out any noise/artifacts.

- Rachel D

310-562-5779
www.racheldunn.com


On Mar 30, 2018, at 9:50 AM, Art Adams <art.cml.only@...> wrote:

Thanks, Rachel. It's more about the edges with 4:2:2 as they tend to be a bit rougher. 4:4:4 always keys better, but on this job that limits me to HD. Not a huge deal, just trying to do more.

Art Adams
 

Thanks, Rachel. I've done tons of green screen but I'm usually able to record to better formats. Budgets are pushing me in directions I haven't had to go before, or at least in a while. I hate living on the edge when it comes to this stuff, and I've had post houses opt for SStP 444 over XAVC, so just trying to find out how low I can go--especially since I don't think this production will spend money on a real post house, which usually means I have to compensate on my end so I don't get the blame when stuff goes wrong.

No matter what I do it won't be as bad as shooting green screen on an HPX-500, so there's that.

--
Art Adams
DP
San Francisco Bay Area



On Mar 30, 2018 at 10:36 AM, <Rachel Dunn> wrote:

Avoid 8-bit and use as little compression as possible.

Resolution helps, but it won't be as big a factor as color depth/compression.

A lot depends on subject matter.

Fine fly-away hair is always a nightmare, but a bald guy can go together with a push-button key.

There's also a big difference between a real-time ultimatte key for sports center and a photo-real composite for a tentpole.

Also taking the time to make sure that your green screen is as evenly lit as possible will help, because you won't have to key as large of a color slice to eliminate the GS, so the edge detail will be lower contrast and higher detail.

Larger color slice means higher contrast edge detail, which bring out any noise/artifacts.

- Rachel D

310-562-5779
www.racheldunn.com


On Mar 30, 2018, at 9:50 AM, Art Adams <art.cml.only@...> wrote:

Thanks, Rachel. It's more about the edges with 4:2:2 as they tend to be a bit rougher. 4:4:4 always keys better, but on this job that limits me to HD. Not a huge deal, just trying to do more.

Rachel Dunn
 

I can say from experience that 8-bit 4:2:2 prorez from an a7s onto an Odyssey 7Q+ is not the way to go.

Even at 4K, the 8-bit color compression is too noisy - and not a good kind of noisy.

10-bit is much better, but not as good as RAW.

- Rachel D

310-562-5779
www.racheldunn.com


On Mar 30, 2018, at 11:23 AM, Art Adams <art.cml.only@...> wrote:

so just trying to find out how low I can go

Art Adams
 

Hi all-

Just wanted to post a follow-up... I decided to go with XAVC 480 on the green screen day as we had someone available at the stage who could rough in some test comps. It worked perfectly. I was worried that a 4:2:2 codec wouldn't give me enough edge detail, but it did just fine. Most of the shots were fairly tight so it was easy to make the screen perfectly even, which always helped. We had one super wide shot with a green wall, green cloth on the floor, and not perfectly even lighting (thanks, budget!) and it still looked pretty decent.

I'm glad I don't have to insist on raw when shooting VFX on the F55 anymore.

Thanks, all, for your help.

--
Art Adams
Director of Photography
San Francisco Bay Area

Doug Jensen
 

Art, it is good to hear XAVC met your needs, and that mirrors my own experience.  Thanks for the follow-up.


From: Art Adams <art.cml.only@...>
Reply-To: <cml-general@...>
Date: Thursday, April 5, 2018 at 5:03 PM
To: <cml-general@...>
Subject: Re: [general] XAVC green screen, was documentary cameras

Hi all-

Just wanted to post a follow-up... I decided to go with XAVC 480 on the green screen day as we had someone available at the stage who could rough in some test comps. It worked perfectly. 

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