How to make good keying?

[Alexey Datsenko]

Could you tell me please how in cinema make very goog keying when the object and background are look like absolutely real?
Yes everybodies knows that it is need to play with properties in Keylight 1.2. but anyway it is not enough and properties in Keylight or after that color correction is not giving the good result and we see that object and background are different and it is the fake.
I know it is necessary to put some filters to both object and background after keying.
Maybe somebody knows the algorithm of good mix the object with background?

 

[Olivier Madar]

First thing : the light
Second thing : the light
Third thing : the light

 

[Nicholas Teixeira]

this video shows some tricks that may help you... very nice to see how they do the light ..

http://vimeo.com/34365256

 

[Marc Wielage]

Read VFX master Steve Wright's excellent book:

Digital Compositing for Film and Video

Steve is a master at this, and goes into great detail all the mistakes that can happen on the set, how to improve marginal keys, and all the various compositing tools on the market.

The VES Handbook of Visual Effects is also a good general reference (but very long and expensive) that goes into even more detail as to how greenscreen material has to be shot, how post deals with the footage, rotoscoping, and all the other technical issues.

Wright also teaches several courses on the subject, and knows this area better than anybody I know personally.

 

[Alexey Datsenko]

Thank you!

 

[adrian vedder]

I completely agree with Olivier. Adding one thing: the angle. I think that's even bigger than the light.

 

[Marc Wielage]

One trick that Steve Wright mentions: a lot of people make the mistake of putting the talent much too close to the greenscreen backdrop. This creates all kinds of reflections and contamination. In a perfect world, you'd have a huge green screen and pull the people very far forward in order to minimize any green spill on the people. Getting them 20' away is not too far. This is much easy to do if you're in a very large studio, and this is one reason why the greenscreen composites on A-list Hollywood movies often looks so good: they shot in an enormous stage.

The greenscreen stage they used to have at ILM in San Rafael was massive -- you could practically land airplanes in the damned thing. And the backdrops were perfectly lit -- not a bit of shadows, shading problems, or anything, just perfect all the way across.

 

[Patrick S. Marshall]

nice distance between the background and the actors; cloth and material that absorbs light instead of reflecting it makes it also much easier; good light on the screen, on the actor and if possible light that separates background from talent also helps (descent headlight).
Also play around with gels and light temperature. you can add more substance to the background if you give the light a green or blue tint and add some weak magenta on the light for the actors. every possible light that separates the background from your actor will add to the key-ability.
last but not least get a better keyer. keylight is not bad, but there are much better ones out there, especially if there is more movement in the image.
also make sure that there is no anti aliasing of any sort to keep the edges as clear as possible.
and if you use 4k and down-convert it, key before you convert. will take much longer, but the quality will be much much better. I can highly recommend Primatte Keyer from red giant. the best keyer i have worked with yet.

 

[Steve Freebairn]

One more tip is to rotate your camera sideways if the scene is taller than it is wide. This can effectively double your resolution which as mentioned before helps hide issues when you scale your keyed image to fit your scene.

The biggest sign of a bad key is mismatched lighting though, you could have the best key in the world on an object and if the background and foreground lighting don't match, it's over.

 

[Patrick S. Marshall]

steve is absolutely right - you have to match your green screen scene color to the backplate color. so know in advance what the background will be and try to match position and effect as close as possible. if you know what you are doing, you may adjust a small amount of the green screen scene color to the background in post (correct white balance, color charts etc. help a lot), but the light strength and position should be matched as precise as possible. and the cam sideways is indeed a good trick to preserve as much image information as possible.
a small trick with motion: raise the shutter speed so that the image of the individual frames are much clearer and add some motion blur to it in post to make it look natural again. if you don't overdo it, you will get away with it and the blurry motion will look less greenish. no fine mesh, the least reflective fabrics and if you use jewelry, use a matte spray to reduce spill.

 

[Gavin Greenwalt]

Ummmmm I have to actually correct to a little bit of misinformation here. Distance is not key. The reason people think distance is important is because they've been taught "Brightness = 1/n^2" but that's only true of a point light. It's not true of a laser for instance which is very parallel. Similarly it's not true of greenscreens which are essentially giant softboxes. The light striking the lens is the *exact same light* that will be striking your talent. So if it's bright enough of a green screen to expose the lens it's bright enough to spill on your talent. Usually what happens is that people think they need an enormous greenscreen but then they throw 100x the light at it to bring it up to the proper exposure. So the effect is completely cancelled. A small 10' greenscreen at 10' needs 1/100th the lighting of a 100' greenscreen. Sure you moved your talent back but you also used 100x more light.

That's not to say you don't need big green screen stages. Just don't do it for the wrong reasons.

So what does make a great greenscreen? A great compositor. You aren't going to get *1* key that will deliver a feature film quality key. You're going to be keying their hands, their hair, their clothes etc and stitching together your keys. Ideally your greenscreen is also the same average luminance of your end key. If your actor is on a street at night, use a darker greenscreen as long as it isn't noisy. If your actor is on the beach, use a nice bright greenscreen. Skin is really really reflective. Most people would be surprised at how shiny skin is. If you have a big bright green screen and a dark desired background the skin is always going to be bright and look unnatural. If you need a bright beach scene and you shoot it on a dim greenscreen then the skin will always be missing that nice natural shininess from reflecting the background.

Even under the best of situations expect to spend at least a good day on a good key for a full body shot at feature film quality.

 

[Jake Bastian]

Ummmmm I have to actually correct to a little bit of misinformation here. Distance is not key. The reason people think distance is important is because they've been taught "Brightness = 1/n^2" but that's only true of a point light. It's not true of a laser for instance which is very parallel. Similarly it's not true of greenscreens which are essentially giant softboxes. The light striking the lens is the *exact same light* that will be striking your talent. So if it's bright enough of a green screen to expose the lens it's bright enough to spill on your talent. Usually what happens is that people think they need an enormous greenscreen but then they throw 100x the light at it to bring it up to the proper exposure. So the effect is completely cancelled. A small 10' greenscreen at 10' needs 1/100th the lighting of a 100' greenscreen. Sure you moved your talent back but you also used 100x more light.

That's not to say you don't need big green screen stages. Just don't do it for the wrong reasons.

So what does make a great greenscreen? A great compositor. You aren't going to get *1* key that will deliver a feature film quality key. You're going to be keying their hands, their hair, their clothes etc and stitching together your keys. Ideally your greenscreen is also the same average luminance of your end key. If your actor is on a street at night, use a darker greenscreen as long as it isn't noisy. If your actor is on the beach, use a nice bright greenscreen. Skin is really really reflective. Most people would be surprised at how shiny skin is. If you have a big bright green screen and a dark desired background the skin is always going to be bright and look unnatural. If you need a bright beach scene and you shoot it on a dim greenscreen then the skin will always be missing that nice natural shininess from reflecting the background.

Even under the best of situations expect to spend at least a good day on a good key for a full body shot at feature film quality.

The multiple key thing is a big one. It's annoying when someone expects to use one instance of keylight and be done. Sure you can get close and it might be good enough on a project with a short timeline or low-budget - but you're gonna end up knowing it's a greenscreen project at the end of the day. Multiple keys and layers of compositing effects is what will get it done (on top of good lighting on set).

 

[Enrique Blein]

What is best for the Mysterium-X sensor: blue or green screen?


Also, is a higher than 1/60 shutter good for defining edges when actors move. I usually work at /125 or more if I can.

 

[Marc Wielage]

Also play around with gels and light temperature. you can add more substance to the background if you give the light a green or blue tint and add some weak magenta on the light for the actors. every possible light that separates the background from your actor will add to the key-ability.

VFX expert Steve Wright strongly, strongly advises against using colored backlights on actors. Check out the link I provided.

So what does make a great greenscreen? A great compositor.

There's only so much a great VFX artist can do with crap footage. It's still gotta be shot right, and the references I cited emphasize this quite a bit.

Even under the best of situations expect to spend at least a good day on a good key for a full body shot at feature film quality.

Gee, I dunno. I once hung out with an acquaintance doing composites on X Men 2 at Cinesite/Hollywood, and I watched her pull a key and finish a 10-second shot in about an hour, and it was a shot of a half-dozen people, head-to-toe. Maybe she got lucky.

 

[Gavin Greenwalt]

Gee, I dunno. I once hung out with an acquaintance doing composites on X Men 2 at Cinesite/Hollywood, and I watched her pull a key a finish a 10-second shot in about an hour, and it was a shot of a half-dozen people, head-to-toe. Maybe she got lucky.

It's like the parting of the dead sea! Half dozen people is often easier than 1 since they're smaller in frame and hair etc is probably sub-pixel. You'll lose almost all of your time to roto when it becomes necessary. So like you said the better it's shot and the less roto you have to do quicker things will go.

Also +1 on colored backlights. Once you key it out you'll be left with a weird colored halo. We just got to shoot our own footage before Christmas and it was wonderful. Greenscreen was flat and the right brightness for our intended BG luminance. Camera was over exposed as much as it could without clipping to get as little noise as possible. Super easy key. Took about 10 minutes and then another 15 for spill. Perfect motion blur. Oh it was such a breath of fresh air after fighting crappy plates for months leading up to it.

What is best for the Mysterium-X sensor: blue or green screen?

Green, by a nautical mile.

 

[Donald Strubler]

What is best for the Mysterium-X sensor: blue or green screen?


Also, is a higher than 1/60 shutter good for defining edges when actors move. I usually work at /125 or more if I can.

Motion blur is not a problem for someone who knows how to key. Why abandon a full shutter on the chance that someone may suck at integrating?

 

[Uli Plank]

Green is best for any Bayer-pattern sensor, blue is worst for silicon, since all sensors have more noise in the blue channel.

 

[hans de vries]

[QUOTE

Gee, I dunno. I once hung out with an acquaintance doing composites on X Men 2 at Cinesite/Hollywood, and I watched her pull a key a finish a 10-second shot in about an hour, and it was a shot of a half-dozen people, head-to-toe. Maybe she got lucky.[/QUOTE]

I think she got lucky; keying techniques remain a hot topic for good reasons, it's not an easy thing to do. Even in Lord of the Rings you can see some strange things now and then; see the moment where the 4 hobbits were honoured during the crowning scene in part 3; it looked pretty bad; they must have had a hard time working on that.

 

[Marc Wielage]

Even in Lord of the Rings you can see some strange things now and then; see the moment where the 4 hobbits were honoured during the crowning scene in part 3; it looked pretty bad; they must have had a hard time working on that.

My impression (after a long conversation I once had with noted VFX expert Mike Fink) is that when you do see a terrible effect shot in an otherwise good movie, it's usually a shot on which they just ran out of time. Or it got farmed out to another company who just dropped the ball. The usual line -- borrowed from French poet Michael Moncur -- is: "Visual effects projects are never finished... they're abandoned."

Another tip-off (not necessarily about Lord of the Rings) is when you see an effects-heavy movie and you see a dozen or more credits for different VFX houses. Often, that means there was a lot of last-minute work and changes going on, and things just fell through the cracks. I'm always hoping to one day see "TEMP SHOT" or "EFFECT MISSING" in a theatrical film in the theater with an audience, but so far that hasn't happened.

What always shocks me is how well they can pull a key off fine hair these days. That used to be a nightmare for us, back in the old Ultimatte days of the 1980s and early 1990s. You still see some dodgy stuff with women and green screen nowadays, but it's not nearly as bad today as it was. And at least the roto work they do is much faster now, and partially automated.

 

[Mark Toia]

Sharp lens helps a lot... Especially with hair.
Good colour separation helps,
Minimize the spill onto your subject.
Touch more luminance in the screen helps too...
Motion blur can kill ya...

But mind you... I keyed a guy standing against a brink wall the other day and it worked? go figure

Keying is getting very easy these days. Practise makes perfect.