Create a DIY Green Screen / Chroma Key

Question

What are some good resources for people attempting to setup their own green/blue screen, light, record and pull a quality key from it? Particularly on a low budget, or with materials that aren't specifically designed for that purpose. Such as,

• What sorts of fabric/material give good results? Both general tips and specific examples/links are helpful.
• Is it possible to light it adequately without a full lighting kit?
• What sort of encoding is recommended when filming it? (i.e. is it possible to use a DSLR with h.264?)
• What software would you recommend for post processing the key? Does some work better with homebrewed screens than others?
• If you have one, post an example of the results you were able to achieve with your suggestions.

Answer 1

What sorts of fabric/material give good results? Both general tips and specific examples/links are helpful.

Great Resources for tips on lighting and materials: http://provideocoalition.com/index.php/alindsay/story/greenscreen_primer_part_1/ http://rebelsguide.com/forum/viewtopic.php?t=2432

Underexposure (not lighting enough) is your biggest enemy, followed closely by uneven falloff across the screen. Always keep your talent/target a good distance from the screen.

Is it possible to light it adequately without a full lighting kit?

Not easily, but don't dismay, it always takes a skilled hand to get greenscreen lit well, so in many cases, even with a full lighting kit, results will be sub-par. It's a tough thing to get right, because lighting needs vary a lot depending on your shooting situation. Your best bet for getting good, even light, is to have an on-set monitor setup (such as a computer with OnLocation), and test, test, test, before you start shooting.

What sort of encoding is recommended when filming it? (i.e. is it possible to use a DSLR with h.264?)

Great question. This is showing that you've done enough research already to be aware of the issues. "Possible" isn't the word I'd use to describe your capture options, because it's more of a spectrum from good idea, to difficult to work with, almost entirely because of chroma subsampling

Difficult: DSLR on-camera recording, consumer capture codecs (AVCHD, HDV, all of which probably will be 4:2:0)

Better: Output to an HDMI recorder at 4:2:2

Good idea: Uncompressed S-Log 4:4:4 (from something like an F3)

What software would you recommend for post processing the key? Does some work better with homebrewed screens than others?

Some ordinary options are KeyLight (in Premiere and After Effects) and Primatte (which is a real pleasure to use). Keying tools won't care how you created the screen, just how well it was exposed, and how much color separation there is between subject and background.

Finally, a more-radical-than-it-should-be thing to consider is using a neutral gray background instead of green or blue, and relying on a combination of luma keying and roto. One bad example I've always remembered was about the keying in Forrest Gump. Stu Maschwitz once explained the effects artists had to roto every single frame to take care of green spill and edges. Their lives would've been easier if they'd just gone with a neutral gray.

Green does not equal magic movie effects, it's just one of many options.

Answer 2

Here's what I used for my setup.

Fabric/Material

The main thing is to find a material that is very green. Walmart sells (at least in Maine) a very green cotton fabric that works well ($9 for 3 yards).

I've tried materials that are a lighter green, but without success. One thing you have to watch out for is large wrinkles, which will quickly ruin the key. Also, since this fabric is typically not very wide, you don't have a lot of room to move around unless you figure out a way to combine multiple pieces. Finally, you'll probably want to hem the edges so they don't unravel.

Lighting

You want to light the screen evenly, which probably means some sort of defused light. I used a desk lamp with some sheer fabric in front of it, and tried to center the screen underneath the overhead light that was in the room. You want to be far enough away from the screen so you're not casting a shadow (unless you're compositing it in a way that you want a shadow, if you were adding a nearby wall for example).

Encoding

Most places around the internet will discourage using DSLR, or anything with a highly compressed encoding format for chromakey. That's because they often use 4:2:0 encoding, which means there's less color information to pull your chromakey from.

While it's less than ideal, however, it is possible. I was surprised how usable the footage from my Canon t3i DSLR (h.264 encoding) was. There are some very good tips on this thread on Creative Cow on what settings to use when you have a less than ideal encoding situation (low ISO, etc).

Software

Mac - I've used both Final Cut Pro X ($299) and Motion 5 ($49) for pulling the key, but I'd recommend Motion. The chroma key filter has more advanced options for tweaking the key (spill suppression, etc) as well as a "light wrap" feature that seems to help with color correction on the actor after compositing.

Linux or Windows - I recommend the Blender (free) node based compositing features. Although I haven't used them with my latest green screen, they were the best solution I could find before I got Motion. They are more complicated, however, as Blender isn't primarily a compositing tool, and you have to wait for rendering.

Here's a test I did using this setup (cotton screen, defused lamp, DSLR, and Motion) over about 4 hours. Hopefully I'll be able to get even better results with more practice and some lighting improvements.

Answer 3

Me and my friend made one for a video project.

What we did is took a white bed sheet and just painted it with basic green paint. It becomes a stiff starched fabric texture, which works well for hanging it on a wall. To light it, We used just work lights (3 100watt bulbs + unknown wattage) to light it. The lights we used were like this: We just had to play around with the positioning until there were no dark shadows (omni- directional light)

We used two DSLRs (Nikon d90 and 3100), we encoded the footage into uncompressed h.264 and went right into final cut. With a little tweaking, we were able to almost completely key out the green screen. We used Final Cut Pro 7, but all major softwares have Chroma key. You just have to play around with it. The same green screen worked well in Premier Pro CS5 as well

Answer 4

There are a zillion greenscreen tutorials on YouTube. The basics are simple.

1.Pure green paint or fabric.

2.Even lighting on the green, good lighting technique on the subject. Avoid spills and shadows.

3.Use the highest quality camera, lenses and compression you have available -- but don't freak out unless you're using a lot of translucent objects like smoke or water.

4.You often need to try more than one keying product to find the best for your situation. I primarily use Spectramatte and Keylight. There are many others.

Answer 5

This won't be a full answer to your question, but LearningDSLRVideo has a few clips about DIY greenscreen--more from a shooting/software standpoint, than the physical setup standpoint, though.

• How to Key DSLR Green Screen
• DSLR Green Screen Test
• DSLR Green Screen Test with Premiere CS5

Answer 6

I've reflecmedia chromakey with good results using a DSLR for both stills and video, producing great easy to key files.

Reflecmedia Pop up screen

We plan to use this as part of our DSLR HD Video DIY Greenscreen Training course at United By Photography.

Answer 7

I've heard green table clothes from a dollar store work very well. You can stack them to make them more opaque if you like, and the lighting is more important than the material anyway.

Answer 8

For a green screen, you can use a green or blue polyurethane film, which is stretched on a frame of metal rods. The film can be found in the Home Depot.