Keying around hair

[Steve Crawford]

I'm keying out a video that we shot on a green screen, and I'm having a lot of trouble getting a clean key around the talent's hair. The setup of the lighting is - two soft boxes at the talent from the front -- one key and one fill. A third light behind the talent to light the green screen. I already can tell how hot the light is behind her because of the rims inside her arms. Unfortunately, the studio isn't deep enough to separate her from the green screen any more, and the light doesn't have a dimmer on it.

My main problem is around her hair, though. You'll see the raw green screen footage, and the key test.

I'm doing the post work in After Effects, with most of the keying done through keylight, but following this procedure:

Advanced Green Screen Keying [After Effects Tutorial] - YouTube

(Click more info for text)

Anyhow, here are the key results and the native footage. Any input? I'm sure it has mostly to do with proper lighting. But, if anyone has any keying expertise they'd like to pass along, I'd love to hear it.

Key Test:

KeyTest on Vimeo

Green Screen:

GreenScreen on Vimeo

[Darren Levine]

first off, what format was this shot in? more compression, lower resolution, lower colorspace, all make a difference

second, you should spend more time learning about lighting green screens, it isn't as simple as put a light on it and you're all set, i typically use 2x 4 bank kino style lights with diffusion to light the screen. the idea is soft and broad and even lighting. and it looks like yours was around 1.5 stops under exposed as well for the screen

[Steve Crawford]

It was shot on a Canon XF105 - 1920x1080, 30f (29.97p).

The green screen was a last second add by the talent, so I wasn't able to spend as much time on the lighting as I would have liked, and the room was pretty shallow, so I wasn't able to diffuse as much, either. I don't have a permanent studio solution (yet, we're working towards that), so all the lights were portable ones, and hadn't been used or tested in this situation before, so it was really just light it and pray.

Definitely going to be researching GS lighting and equipment, if this is a direction that we're wanting to go.

[James Huenergardt]

Hey Steve,

To get a really good key, your green screen MUST be evenly lit. The more variations in green, the tougher your job will be at pulling a good key.

Also, for her hair, you might approach this from a 2-part perspective.
What you can do is mask out just her hair, and key that separately from the rest.
That way, you can fine tune it. Then combine them back together.

For keying, there really isn't a 'single' way to solve your problems.
Sometimes, you need to key certain portions of the shot differently.

A great book on this is Mark Christiansen's Studio Techniques for After Effects.
Also, some more great info on green screen stuff is from Hollywood Camera Work. They have a green screen intensive series for directors and you'll learn a lot.

Hope this helps.

[Jeff Pulera]

I've had excellent results keying at home, using a bright green cloth as shown in your first sample with the man. At work, we have a 5' x 7' pop-up screen and it uses the darker green shown with the female model sample, and that keys terribly! Just not a good shade of green to work with.

So go for the brighter green background with more chroma to it. Also, I found that a light from above and behind that puts some light on the head and shoulders helps give the edges some definition to keep them from blending into background. If lit only from front, those top edges fall into shadows.

The light from behind in the underarms looks weird.

If on a tight budget for lighting, get some of those clamp-on metal reflector lights from the hardware store that look like a metal bowl. And get the "GE Reveal" bulbs, as they make a very clean natural light - standard incandescent bulbs are too red. These have worked very well for me.

I hope this is helpful.

[Steve Crawford]

Thanks so much, Jeff, James and Darren. I'll definitely be looking into all of this stuff.

[Guy Caplin]

I've been shooting green screen material on location for around two years and have found that problems with keying around hair are caused by insufficient back-light and/or insufficient distance between the subject and the green screen. For a mid shot you ideally need a minimum of about 8 feet between your subject and the screen. If you don't get this sort of distance, the green cast from the screen, (which you can't always see with the naked eye) can play havoc with keying.

Our lighting set-up is two lights, one on either side, level with the camera, illuminating the subject but not shining on the screen (you must use professional lights with barn-doors).

Two lights, one either side of the subject illuminating the screen, but not the subject.

Two lights either side of the screen at a level about a foot above the subjects head illuminating the subjects body, particularly the head and the hair from the rear. These back-lights should make the hair stand out clearly against the green screen and then keying then becomes straightforward.

We normally shoot with a Canon XF 305 although we have used an XF 100 with no problem. I even did a test using my Panasonic TM 900 and the results to my surprise were really very good - difficult to tell from the pro cameras. I guess if you get the lighting right, any half decent camera will do.

[Seth Bloombaum]

Originally Posted by Guy Caplin

I've been shooting green screen material on location for around two years and have found that problems with keying around hair are caused by insufficient back-light and/or insufficient distance between the subject and the green screen. For a mid shot you ideally need a minimum of about 8 feet between your subject and the screen. If you don't get this sort of distance, the green cast from the screen, (which you can't always see with the naked eye) can play havoc with keying. ...

I've been shooting green screen for a few decades more; Guy's advice is solid.

The basics of screen to subject distance, even screen lighting, purity of screen color, and good backlighting of the subject can't be ignored. Last minute "talent said let's shoot green" is not a recipe for success. There are laws, laws I tell you, laws of physics involved that will lose you many nights of sleep if ignored. Screen to subject distance is the big one here...

If the wisps of hair are green due to spill they may not be savable. I've never used the technique James H. suggests above, of masking her hair separately, but if I were willing to sink more hours in I would try it. Then I'd shrink the matte and lose some hair...

Compositing over a greenish background plate can hide a lot of spill and rough keying...

[Dean Sensui]

I film the host of our show against greenscreen and purposely put a fan on her to make her hair move.

My goal is to match the light in the background plate and that means no backlight.

I'm using Primatte along with a few other plug-ins for After Effects. I'll make a general key. Then duplicate the layer, placing it behind the general key. A mask selects just for her head. And I'll work to get a very minimalist key to retain as much detail as possible. This adds detail to the hair.

Primatte has a lot of controls that aren't available in KeyLight. Here's an older example of using two keys to retain detail.

http://hawaiigoesfishing.com/videos/...upolu_demo.flv

[Jonathan Levin]

Hi Steve.

To my eyes, I personally think that your test looks pretty good. However, you are getting excellent advice form the posters here (and so am I).

Some of the green screen stuff I have seen from some of my clients and other web video are so bad, well, we all have stories.

I agree that the backlight under the arms is a bit much, but would work in some other situation where you were using some other image/video for the background.

And to the other who posted, thank you. I have not had the opportunity to do much keying at all, but want to prepare in some small fashion.

Jonathan