PP for Green Screen?

[Chad Nikolaus]

Anyone have any FS700 tips when it comes to picture profiles while shooting green screen?

I've been doing a lot of general shooting with Cinegamma 1 default settings, and really like the results. Before i go and shoot some green screen with Cinegamma 1, i thought i'd check here to make sure that's not a big mistake for some reason i didn't know.

Also, at 24fps, do you think shooting at 1/96 shutter speed is over kill when trying to minimize motion blur?

 

[Jusgorilla]

I cant say much for the settings, came from canon to sony, still testing, but what i can say is 1/96 shutter is definitely better for keying, if you want the slower shutter look, do it in post after keying (Reelsmart motion blur or whatever)

 

[MattDavis]

Haha! Great minds think alike. I spent yesterday playing around with PProfiles for chromakey.

Specifically, ensure your detail is negative. I didn't see much improvement with -7 vs -3, but 0 and up, you'll get a very fine black line around your key. Having negative detail does make focus a bit more tricky, but read on.

I'm going to try adding a little positive 'enrichment' on the Green channel to see if this will help with the actual green matte, but I'm a bit leery of this area of PProfiles - easy to introduce an indelible colour cast.

The other lesson learned was DoF - don't go there. Blurry edges were too pale and required quite a bit of work with Keylight in AE, a touch of erode, a touch of roll back. So, it's f8 and beyond for me.

The awful truth from yesterday was that FCP7 and DVmatte Pro (a combo that I swore by with EX1 greenscreen footage) is done. The end. The FCPX keyer is dangerous - it's very easy to get a so-so key. It's easy to leave it at that and move on, but you can tweak, and it will do a good job. Keylight in AE did a marginally better job (and once I start messing with motion blur it can be even better), but requires care - the more I compensated for the issues with DoF and spill, the key quickly fell apart, requiring internal mattes to fix.

Of course, for an FX shoot, this is to be expected - my use of Chromakey is for a quick and dirty solution to rubbish backgrounds - Talking Head interview in nondescript environment? Greenscreen it. No motion tracking, not enough time/budget for roto, just bang it out.

WARNING: Unfinished video alert...

I may take this down as it's not good enough to stand alone - needs VO and callouts to explain what we're actually looking at (not some kid with a lego plane obviously) and 'final grade' and perhaps a slightly less impatient model (he was missing the beginning of an Indiana Jones movie on TV). Keep a steely eye on the left ear, and the hair as his head bobs out of frame. I think we're about 1/150th at this point.

PS: This is raw AVCHD off the camera converted to ProRes by FCPX. We haven't even started looking at how shooting at 4:2:2 10 bit from the get-go should improve matters.

 

[Nirv]

Love the page peel! Oarsome!

Yep, keep any and every sharpening out of keyed material. If sharpening doesn't add a black halo it will add a halo of a darker green that can hang about. Keeping it soft also means your 24 Mbits are distributed better leading to less compression artefacts.

Blur on the chroma channels and an edge blur really help with 420 material finished off with a light wrap. Despite FCPX/Motion keyer being really bloody good I still find Shake/NUKE the best way to key anything. Time/cost balance has to be struck of course. Ha, who am I kidding, throw it on the timeline and do an auto key because that's all the client will pay for!

 

[MattDavis]

Thank my wife for the page peel (she couldn't see the edge artifacts). But it's telling to see a bunch of other things happening in the AE output. I swear I can see a 1080i interlacing thing going on, which means I've got to go back and do it again (my AE skills are very rusty - last one I drove was v6.0).

Nirv, any advice on DoF? I'm now happy with the edges on the plane, but the ear and hair edges drove me nuts. It seems to be an issue with the out-of-focusness of it.

Keylight is a powerful tool, but four times the work for 20% better results, even though the despill affected the yellows badly. I fear it's less to do with the Picture Profile (except the sharpness thing) and more to do with the exposure of the green screen - this one was a bit too hot at around 65-70 IRE.

Just checking up on an older job done 2 years ago with DVmatte Pro and an EX1, it's 'acceptable' for the budget, but when I use the same software setup, the EX1 stuff looks fine, the FS100 stuff looks rank...

Skip to 00:50 for a fairly standard sequence of EX1 chromakey. Yes, it has its faults (black lines! Black lines!) but it's not too bad. No Depth of Field issues (half-inch sensor and all that).

But I've done similar stuff on the FS100 and, well, it's never been easy or 'as easy' as it was with the EX1. I'll be controversial here and posit that the FS100, being slightly lower in overall resolution and, well, 'bite' - I've heard that the EX1 has an internal 14 bit processor and higher resolution whereas the FS100's processor is less powerful thus objects with subtle detail shifts (faces, and now presumably edges) will lose a bit of 'oomph' on the FS100.

We're at pixel peeping levels, the heightened sensitivity one gets after staring at a string of face closeups over a couple of days.

Maybe it's not the camera. Maybe it's lens choice. Glass is the new 'film stock' after all. I just don't feel in the same sweet spot with chromakey that I had a couple of years ago.

I think I'll have to repeat the test, but with the Pix220, and with the EX1 as a side bet, and perhaps the Nikkor 17-55/2.8 (my most trustworthy lens) and a couple more PProfiles (e.g. a Rec709 and an 'enhanced green').

This is going to cost me a lot of crisp packets.

 

[Nirv]

Matte, (see what I did there!)

DOF is a problem because it creates a fine gradient between the subject and the screen. Not necessarily a problem for an uncompressed or RAW workflow but 420 and AVCHD is best avoided IMHO.

A good edge matte/blur and light wrap will blend a sharp subject into a blurred (faux DOF) background.

The edge blur is the really effective part to get the subject to sit into the background then the light wrap rounds it out. Too many people heap loads of light wrap on and it just looks bad.

Lighting the green screen so it is separated in luminance to the subject is also good. Darker screen and light subject and vice versa. It helps the keyer separate values round the edges easier if subject and key differ in IRE levels.

 

[MattDavis]

Lighting the green screen so it is separated in luminance to the subject is also good. Darker screen and light subject and vice versa. It helps the keyer separate values round the edges easier if subject and key differ in IRE levels.

Thanks Nirv - that's great intel! In fact, it brings us back on topic.

The Picture Profiles in the FS100 and FS700 have a Colour Depth setting that, as Alister Chapman demonstrates in his excellent masterclasses, completely loony.

You can pick a colour in the colour wheel and adjust its apparent brightness without adjusting its intensity, so perhaps a PP can modulate the Colour Depth of either Green or Blue to make it darker or lighter in comparison to everything else, which may help accentuate the difference.

That means some poor schmuck is going to have to try this. Just to see what happens to the green. It could be useful.

So a FS100 PP for chromakey might not only duck detail down, it may also have options to raise/lower the green to get better 'edge detection'. I can see where a 'hybrid keyer' (rather than a straight chroma keyer') would find this exceptionally useful and explains the good work DVmatte Pro did in the past...

PS: Very good with the Matte thing! :beer: Tried to become Travelling Matt for a while, beaten to it by a bloody muppet, and of course Matthew Gormley in Australia. The trouble was, my clients have no idea what a traveling matte actually is. However, over 70% of them DO know what MDMA is. Which is interesting for a corporate production company. Well, I do like happy clients.