When lighting for chroma key you have to think of lighting first for the screen itself and then for the subject. In tight situations you can combine the lighting but you could end up with shadows on your screen and that will make for a much more difficult task of pulling a good key.
Start by focusing on getting a clean and even light on your screen without your subject. Here I’m using 2 ikan IDMX1500 dual color fixtures - part of the ikan 5 piece dual color chroma key kit. These are hung in front of the screen using a truss system. These are awesome LED lights that put out a lot of soft even light which is an absolute must properly lighting a greenscreen.
Now if you’re an avid DIYer you may try to use long fluorescent tubes to light the screen. Another DIY option, is the Hollywood Dressing Room Strip lighting fixture - this one I found on a street curb being thrown out - and it made a nice shadowless screen light.
To check to see the quality of our lighting on the greenscreen, I’m using the ikan MD7’s built-in waveform monitor.
Notice the tight band.. This means that are screen is evenly lit and there’s not much variation on the screen itself. You want to get this band as tight as possible, not slanted or have spikes which are hotspots..
If you can’t get your hands on a waveform monitor, you can use your camera’s zebras settings. Zebras tell you what part of your image is overexposed, if you lit your screen properly you should see the entire screen turning into zebra stripes at once as you open your iris to over expose the screen.
Once we have a well lit screen it’s time to put our subject in place and work on the subject’s lighting. Keep in mind the final composition and try to light your subject that will match the scene you’re attempting to composite.
Here I’m using the ikan IB1000 LED lights - part of their chroma key kit. These lights can be set to 3200k which will match great with the tungsten lights I already own. Just take care when lighting your subject to avoid casting shadows on your screen.
When I first started experimenting with greenscreen, I was working with DV in standard definition. You had to be exact in order to get an acceptable key, and even then there were some funky artifacts. But I’m happy to say that with HD, getting a reasonably acceptable key is much easier because the pixels are so much smaller. But the type of compression can be a detriment to quality greenscreen.
Most consumer cameras use a 4:2:0 compression for handling color - I talk more what color compression is in the lesson on Non-Linear editing if you want a refresher. 4:2:0 throws away a lot of color data - data that can be very useful for achieving a quality key.
In this demonstration, I’m using the Blackmagic Cinema Camera decked out with ikan’s Tilta Rig. The Blackmagic Cinema Camera is capable of recording in 4:2:2 compression using ProRes or DNxHD formats or even recording 4:4:4 uncompressed 12 bit raw.
My tests have shown that the compressed 4:2:2 is pretty good for pulling a good chroma key but the RAW is simply unbeatable in terms of ease and quality. If you want the best chroma key, by all means shoot RAW - just know that it is expensive in terms of the amount of memory it eats up. I’m not saying you can’t pull a decent key using anything less than 4:2:2 color compression or RAW as in the Blackmagic Cinema Camera, but a camera like this with it’s compression or lack thereof sure makes a the key a heck of a lot easier.
Most of the basic keyers you find inside NLEs behave like hardware chroma keyers in that you’ll most likely be let down by the results. But there are a lot of professional keying software solutions available out there that can help you pull pretty good keys even out of so-so footage. My favorite. happens to be one that comes bundled inside of Adobe After Effects called “Keylight” made by The Foundry. This plugin is incredibly robust with all kinds of features like matte choking, spill removal, de-spotting- and even masks that you can apply to fix little chroma key mistakes here and there. Plus After Effects is just a good platform to be working doing your compositing in the first place. Keylight is also available for purchase for other editing platforms.
Now if you can’t pull a perfect key off the entire frame - don’t worry as there is a technique called garbage matting. Using After Effects, you can create a rough mask around your subject and throw away all the other junk in your frame thats unimportant. This is a great way to work in smaller spaces - just make sure you subject does cross into the garbage matte
Once you have a good clean key, it’s a matter of compositing the subject into your background plate adjusting the color to match, and compositing foreground elements to really sell the effect.
By considering your working space, using a quality screen, lighting it evenly, using a camera with as little compression as you can get, and finally using a good software keyer, you should be able to pull off a great key. Good chroma keying is a skill, and it will take a little practice, but the reward for your patience and experimentation can be quite liberating. - Another tool for you use in your quest to make something great.