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Old January 9th, 2014, 20:41   #1
Janus
 
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Chromakey

Anyone have any experience with this? Anyone know (or can make an educated guess on) if a 6mm sphere flying at about 400fps would show up at all on chromakey from varying distances (5m to 50m)? Camera of decent to excellent quality to be used.
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Old January 9th, 2014, 20:48   #2
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Define "excellent quality".

For chromakey to work well, you need a good base footage. You'll need a lot of light for the image to be devoid of noise (light compensation creates noise) and you'll also need an image devoid of blur. The biggest problem is usually motion blur, which will occur *a lot* when shooting high velocity projectiles. A high speed camera will solve that problem, but cost way more than anyone wants to spend here.

Another factor is the quality of the background color. It needs to be uniform, without spots that are too light or dark compared to the rest. A good/flat color that is evenly lighted will make a world of difference.

I've never tried that particular case, but a camera that can shoot 60 or 120 fps (thinking the Canon DSLR line) with *a lot* of light and a super fast shutter speed will make this possible (without that light, the fast shutter speed will make the image really dark anyway). However, a fast shutter speed will make the motion feel a bit unnatural, but if you need chromakey, you'll be able to add some blur afterwards

Mind sharing the footage you need?
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Old January 9th, 2014, 21:52   #3
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I doubt you'll have enough of a signature to isolate the key from your footage... If it's bright enough you can track something to it and your compositing software might get enough to get a good tracker on it.

What are you keying out or tracking to the BB path?

If you have a high enough res camera you might catch a trace of it. But like k3vx said, it all depends on the color of your projectile and the contrast vs the backdrop it's flying past.

The process is essentially an automated magic wand with a feather on the selection applied to every frame... So ask yourself this: If you are able to take any one still shot from this camera and magic wand select the lens smear that is the flying BB (faster shutter will result in less smear and probably less chance you'll have of tracking or keying, but cleaner keying if it shows up).

My live action keying experience is rather limited. I have done it at work, but most of my compositing skill is in the 2d animation field.
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Old January 9th, 2014, 22:16   #4
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Running a simulation in 3dsMax, you'll see the BB around 4 frames at 120fps.

This is what you'll see on a 1080P screen, with NO blur: [Note, this image is using a 35mm lens to simulate roughly what a human would see]



As you can see, it doesn't make for the most exciting footage. On a standard camera, you'll see it one frame, if you're lucky.
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Old January 9th, 2014, 23:09   #5
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Ideally, I'm just wondering if it would be possible to have a BB that was the key where the projected image would be high intensity light of some sort. Almost like putting the glowy thing around the hockey puck.

The idea would be to be able to video an airsoft game where each BB in flight shows up like a bright motherfucker...

...then again, this might be better accomplished by slightly dimming lights in an indoor facility and using tracer rounds. I'm just trying to think of a really effective way to film airsoft that picks up BBs in flight.
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Old January 9th, 2014, 23:25   #6
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Sadly, what you describe cannot work. Tracer would be the best choice, and will save you a lot of headache on the editing process. In post, making a tracer round brighter would be doable, and a whole lot easier than trying to key out a BB.
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Old January 9th, 2014, 23:42   #7
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you'd be able to do it indoors with tracers if you wanted to enhance the tracers... outdoors.. you might have limited success. You'd have to run tests... From the perspective of the shooter you probably could light it up.. the streaming is quite clear especially with higher rof guns and the perspective is easily tracked... if you're taking a side shot of the action, you may not catch it at all.

Look at scout the doggie's YT vids..those are shot with HD cameras, probably as nice or maybe nicer than that you might be able to scrounge up.. seeing that he's a YT partner and getting enough hits to send his kids through college with ad revenue. It's safe to say he has some nice filming rigs. Anyways, in his videos, it's quite rare to see BBs leaving the guns or flying sideways through shots... you'll only see impacts and BBs flying towards the camera or away in the rare cases you see them.

There's a reason why it's called green screening... one flat color that's lit uniformly is easy to key out... a constantly changing color and luma means you would have to hand paint every frame of that key if you wanted a consistently sized key to pull. Even in the most ideal circumstances any little bit of blur in a shot can be a pain in the ass to key. I think I was working with still images at 15 megapixels and some single frame keys still took like an hour to pull a person out of a green screen.
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Old January 9th, 2014, 23:57   #8
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Now that I'm thinking about it, you'd still see the expended BBs on the floor. Tracers would fade as their charge ended.

Should be a neat idea, though.
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Old January 10th, 2014, 10:33   #9
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it's not a simple matter of just pushing a button and the key will work... there's a lot of fine adjustment.. on top of masking out the junk you don't want like expended rounds on the floor. The key will do part of the work but you may have to go in and rotoscope the garbage out of the key or go in and manually add more info in. It's quite a bit of tedious work that takes time.
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