HV-20 and Green Screen?

Graham Castronovo · March 7, 2009

Hey guys, I've just got done painting an entire room bright green, and it looks and works amazing.

I'm using Keylight and After Effects to chromo-key at the moment.

However, whenever I seem to move fast or moderately-fast, I get some lag in the chromo-key.

I uploaded a video in HD for you to see what im talking about:

http://www.youtube.com/watch?v=AJLDzDp2n7o&fmt=22

I'm using the Canon HV-20, and im at 500 shutter speed. If I up'd the shutter speed to 2000, would it make a difference?

Also, I just bought a concentrated 500-watt and 250-watt individual work-lights, and I'm working on setting them in the proper spots(so I dont go blind), but I definatly have a lot of light now.

However, when the video above was shot, I did not use those lights.

I want a perfect green screen, I have the lighting, and I have the solid walls, and I have a HD camera, is it possible?

Thanks if you help! :lol:

Scott Fritzshall · March 9, 2009

Consumer cameras such as the HV20 are never really that great for effects work, since they throw out so much information in order to fit it all on tape. Since you're doing it all in a single room, however, you may be able to take advantage of its HDMI-out feature, and capture directly to a computer, which would allow you to bypass the compression and some of the subsampling.

The idea of painting the walls is... honestly kind of questionable, since I can see the texture of the paint, and that's going to make it more difficult to get an even key. I think you'll want to be lighting it a bit more from the front in order to reduce that, or maybe light it from a bunch of different angles... either way the light on it is currently way too directional- you want it to be lit very flatly. The hardest thing about doing this in a room in your house is that it will probably be difficult to get enough distance between your subject and the wall, and to avoid having the lights from the subject spill onto the screen, and vice versa.

The holes in your key are because your key isn't that good. It's very, very rough. Compare how much fine hair detail is visible in the original vs. how much is left in your composite. You're either losing too much in your key, or you're running some sort of filter that's chewing into your edges pretty severely, and it leaves a very distinct "filtery" look.

Here's the first thing you need to know about keying: you will almost never use just a single key on a shot. Especially here, since your screen is so unevenly lit, you need different key settings for different areas in your frame. The biggest problem area I saw was when your fingers crossed the bottom of the frame quickly; your key just fell apart. Definitely use a unique key for that portion. What you want to do in general for any given portion of the screen is make one key that gets the edges really well and preserves the fine detail, and a second key that loses the detail, but is just very solid, to fill in the holes of the first key. Then add them together. You may need to add some rotoscoping or even some paint work at any point if you're almost getting it but not quite. It's easy to look at software demos that promise "one click keys," but in reality it's almost always a massive amount of brute-force labor to get it to look right.

Also, since you mentioned you were going to paint the entire room, if you plan on moving the camera during your shots, you'll want to put some tracking marks on the screen- use yellow or black or red gaff tape probably.

Scott Fritzshall · March 9, 2009

Oh, and as far as the shutter, I'm assuming that's 1/500th of a second? Don't bother with that, all you're doing is drastically reducing the amount of light you have. Just keep it at 1/48th of a second, or 180degrees, or however that camera labels it.