Background for a perfect key

[Tobias Straka]

I've recently been asked to consult on how to set up a combined photo / video studio, and one question that came up was what background to choose for pulling good keys. Personally, I've always worked with green screen settings and think that this provides the best results. Now the clients are concerned because of color spill and suggest using a reflecting grey / silver background. Me I don't think color spill is something to worry about and I haven't heard much about using a silver background. Maybe that's something more common with photography?

What is your take on this? Go with green? Or something totally different?

 

[Christian Tanner]

my two cents:

grey is no good because there's a lot of that grey in skintone as well. (well - in everything really...).
that's the reason everyone's using that particular green - its the skin tones complementary color.

silver is just a reflective grey.

spill can be minimized with the right material/set-up. for instance, there are professional green screen solutions that (like a pola) only allow rays to travel in one direction only.
plus there's a good amount of nice and reliable software out there to key even the nastiest of spills...

and finally: i can't seem to find a reason why one has to use a different approach keying stills as opposed to keying for motion.

hope that helped.

 

[Hans von Sonntag]

Hi Tobias,

That's what most film studios I worked in look like:

The background wall, with a haunch for a edge-less transition between wall and floor, is painted white.

The side walls and the back wall are painted white as well and have a black velvet curtain to cover the walls.

The ceiling is painted black and has a few solid poles mounted for hanging lights and other stuff.

The white wall with the haunch can be painted to ones liking: Ultimatte green or blue, white or even orange for certain keys.
Every project needs a different background. I've done many chroma keys and luminance keys. I never used grey or silver for that matter, nor do I see a meaningful application for keying. A black background makes sense for smoke or steam for instance (luma key) and green screen (chroma key) for most other applications.

Green or blue spill is a problem. This must be tackled with lights, flags or styros and in the end cleaned with the software's tools you key with. I can assure you that Autodesk's keyers such as the Masterkeyer in Flame, Smoke or Flint can work very well with green spill so do other packages. If the background's colour cast in the foreground object is too heavy the software assumes that these parts are part of the background and you get holes in the forground. The DP needs a trained eye for spill and should not leave all of that to post production.

Hans

 

[Eki Halkka]

What is your take on this? Go with green? Or something totally different?

I'm pretty sure your client means this or similar: http://www.datavideo.info/en/Chromakeyers/CKL-200

The system uses a ring of blue or green LEDs around the lens, and a retro-reflective fabric (which looks grey in regular light). I haven't used this setup personally, but as far as i know it does indeed work pretty well, and there's practically zero spill (the leds are weak so the green cast is overpowered by the regular lights, as long as the camera isn't very close to the talent).

This said, as far as i know, the fabric appears to the camera as if it was self-illuminating, you probably won't be able to i.e. key usable shadows from full body shots, which is essential for convincing compositions. I also have some (possibly ungrounded) doubts about how the system handles semi-transparent areas like hair, glass etc.

Further, spill really isn't a big problem with today's keyers in regular cases, the spill removal algorithms do a good job. This system is also much more expensive than a regular greenscreen (you do save in lighting though).

Personally, i went for a regular half-DIY green screen at our small studio: 4m wide plastic carpet from a hardware store that rolls as a neat "cyc" to the floor, totally wrinkle free due to being both heavy and elastic, painted with ultimatte digigreen. Works more or less perfectly.

 

[Kwan Khan]

Conventional green screen are best choice if you can handles green spill very well and working with large studio.

But, If you have very little room and NO time for setup. Within those parameters, Gray Screen (Reflecmedia) is a miracle.
It does a good job of removing some of the most fundamental problems of shooting with chromakey backgrounds.

This can be very expensive tool for occasional use, for those in the business of making instructional videos, corporate presentations, music videos or anything else using a lot of chromakey effects, This could be worth every penny.

It doens't work with a thru-the-lens teleprompter - but an over the lens prompter fixes that too
Be careful when shooting glossy or reflective subjects.
don't let your make-up people anywhere near it (Gray Screen). but you can use chromatte tape to repair any areas that become non-reflective

Please spend some time familiarize yourself with the set up, before your project starts

 

[Marc Berger]

The downside with reflecmedia is if you shoot the foreground with low light (or you are very near with the ringlight to the subject) the blue/green light from the ringlight fills up the shadows. Hard to get a good key under such circumstances.
Still a great system.
Marc

 

[Paul Lee]

yes, reflecmedia is a double edge sword. It is very quick to set up and almost instantly creates a good background, but the ringlight can do weird things (eyelight) and the edges can have odd shadows. Great for quick and dirty interviews or whatever, but not a replacement for a 'real' studio set up.

 

[Bob Gruen]

Some of the latest green screen techniques I've seen actually use the spill areas as color matching highlights. Basically after you pull your key you cut/paste/smear the background under the spilled areas to make the highlight look motivated by the background. It adds another several steps but helps disguise the key that much more.

Bob

 

[Eki Halkka]

Some of the latest green screen techniques I've seen actually use the spill areas as color matching highlights. Basically after you pull your key you cut/paste/smear the background under the spilled areas to make the highlight look motivated by the background. It adds another several steps but helps disguise the key that much more.

Bob

I think you're referring to "light wrap", where you "bleed" the colors from the background over the edges of the foreground?

It's a great technique to glue the comp together more convincingly, but it's a separate thing from spill removal, which is a procedure done using the foreground only, and not dependant on the BG image.

 

[Elsie N]

This is slightly off subject, but doesn't CS5 Adobe AE have some sort of quick and dirty tool for scratching a mask-like key? Just was wondering if anyone here has used that yet and if so, the pros and cons. I seriously doubt it is a pro solution, but maybe it would work for quick turn-a-round interviews and such.

 

[Eki Halkka]

This is slightly off subject, but doesn't CS5 Adobe AE have some sort of quick and dirty tool for scratching a mask-like key? Just was wondering if anyone here has used that yet and if so, the pros and cons. I seriously doubt it is a pro solution, but maybe it would work for quick turn-a-round interviews and such.

The tool is pretty kewl, and makes the rotoscoping jobs (hand-made mattes) much easier. It's not a proper replacement for greenscreen though.

 

[Nick Shaw]

I think you're referring to "light wrap", where you "bleed" the colors from the background over the edges of the foreground?

It's a great technique to glue the comp together more convincingly, but it's a separate thing from spill removal, which is a procedure done using the foreground only, and not dependant on the BG image.

No, I don't think he is talking about light wrap.

If you use the colour of the background in your spill suppression, you are effectively making it look as if the shadows are filled with light which bounced off something in the background when they were originally filled with light which bounced off green. Used well it can be very effective at seating the image realistically into the background.

 

[Tobias Straka]

Thanks everyone for your excellent comments. You pretty much confirm what I was thinking. And right, reflectmedia, that has to be what they mean. Well for this particular studio, I don't think this is going to work and since this will be a pretty large studio, I'm not too worried about spill. Add proper lighting and they're good. Thanks guys...

 

[Eki Halkka]

If you use the colour of the background in your spill suppression, you are effectively making it look as if the shadows are filled with light which bounced off something in the background when they were originally filled with light which bounced off green. Used well it can be very effective at seating the image realistically into the background.

***thinks a little***

So, say, when keying from green, i'd take the raw original's green channel, the spill removed green channel - and use the difference of the two as a mask to insert some of the background color into the foreground.

Ah - what a brilliant idea. Why haven't i thought of that before?

Thanks!