Thu Mar 29, 2018 5:48 pm
Jevans, lots of good advice on here. When it comes to prioritizing the things that make a good chroma keyable recording, my opinion is that first is lighting, second is the distance between the subject and the screen, third is the camera, fourth is the recording medium, and fifth is lens and focal length. That said, lighting is king, and 3-5 are not very big difference in importance. They are all pretty important to get it to work well.
Smooth, even lighting, with separate lighting for the subject and the key wall is what you want. The wall should be lit separately from the subject, and should be as evenly lit both top to bottom as well as side to side as possible, and with as low a level of lighting as is possible and still have it lit to achieve the evenness.
Distance from your subject and the wall does a few things, it makes that separate lighting mentioned above easier to do, it reduces ambient reflected colored light hitting your subject, and it adds depth of field, making the key wall more out of focus, and therefore smoother and without visible imperfections.
The quality of the camera certainly makes a difference. The higher resolution and quality of the sensor, the better the image, and thus the better the key.
The camera quality and record format quality are sometimes hard to separate, as we often record in the camera. But some cameras might record in a highly compressed format, while having an output signal that is far superior and is not compressed. External recorders that record in 10-bit video, and in a better quality, professional compression schemes, will certainly key better. An 8-bit h.264 recording will not key anywhere near as well as a 10-bit prores422. And prores 422 will not do as well as prores 444 or uncompressed. Any time you throw away data through compression or color sampling or bit depth, you are decreasing the ease and quality of the chroma key. And of course, if your camera doesn't have the quality on the chip to start with, the record format won't add it back in, so we are back to camera quality.
The last bit is the lens, and is related to the second point about distance from the screen. Depth of field makes things much easier by making the background out of focus, and you just cannot get good depth of field from a tiny lens on a phone. Actually, I am amazed that they do as well as they do, faking depth of field on some of these built in video effect apps. But in the end, good glass and a reasonably large aperture can make a big difference.
I might also add that the quality of the key wall itself, can have a big effect. A concrete wall painted green might not work well, a green colored paper roll might work better, and a nice professional keying material that has good light absorption can make things much easier. Ideally your key wall is unblemished, smooth, and has very little reflective light. Ideally, it should look green (or blue, if that is your color), but not shine or cause the rest of the room to have a colored cast.
But whatever you do to fix a chroma key, you start with lighting. And perfectly lighting a key isn't an easy task. But the camera and recording are not far behind in importance.
Scott R Smith
BMD Stuff I use: ATEM 2-M/E, 4 x ATEM PS 4K, Broadcast Videohub, 6 Hyperdeck Pros, 4 Hyperdeck Shuttles, Multidock, Smartscope Duo, Smartview, Intensity Extreme, Decklink Studio, and lots of Miniconverters and Open Gear Converters.
And using 10-bitt, 4.2.2 or higher video source will make your key Estonia pull and eliminate green casts, if the lighting is set correctly, and as Daniel said, lighting is the secret ingredient here.