Chroma Key at Desk

[James J. Lee]

Hey guys, I've just been experimenting with Chroma Keying and I have a client request for a very specific shoot. I told him I'd need to do some testing first. Here's the scenario: Video of subject will be displayed within a 3d graphical interface primarily seated behind this virtual desk. The subject will at times lean on or pound on the desk. I'm fairly new to Chroma Key work so this seems a bit daunting. I will, of course, be covering a desk with chroma key material and shooting on a chroma key backdrop. However, I foresee serious problems with spill from the "desktop" surface on my subject. I'm thinking of lighting the background and my subject normally, then trying to mask the desk out seperately since it's values obviously will not be the same as the background. I'm using the latest Final Cut Suite. Any recommendations for the easiest way for a newby to accomplish this would be appreciated. Are there software / plug-in recommendations that may work better than Final Cut's filters? Thanks.

[Dean Sensui]

Do a lot of testing before doing this on a set.

I don't think FCP's filters are very good at keying. Take a look at what Motion has. I believe "Primatte" is included, and that's a very powerful keyer.

Here's a sample of something composited with Primatte via After Effects.

Green screen opening shot for HGF-205

Illuminate the set so your green is at IRE 50. Use your camera's zebras to help with lighting. With the zebras set at 50 you'll quickly see what's right and what's not.

To minimize green spill on your talent, have him dress in darker shades or colors complimentary to green (red, magenta, etc). Avoid wearing white.

A very flat, non-reflective material or paint works best for green screen. You may have to do some testing to find out which color works best. I use material from EEFX.com for my green screen work and the results are always good.

Have fun with it!

[James J. Lee]

Thanks Dean, I'll look into Primatte. Definately going to build a set and do some testing. I will be getting some EEFX material. Right now I've borrowed some Photoflex pop out background that seems to be working. Not having too many problems with the basic key it's working on a table top that has me concerned with spill. Maybe primatte or some other keyer is powerful enough to differentiate between spill on the subjects arms and the main material?

[Paul Hudson]

Primatte is a very good keyer DV Matte Blast is another good choice. If you are working in AE Keylight is by far the very best.

Paul Hudson
Lizarlandvideo.com
Phoenix Video Production

[Dean Sensui]

Paul...

Primatte has some very good controls to deal with spill and to refine the key. I don't know if they're all available in the version used in Motion, but it'll be far better than what you'll find in FCP.

Let us see what your results are afterward.

[James J. Lee]

Thanks for all the help. Here's a very rough test done with the Keylight demo in FCP. This was truly a "worst case scenario" test since all I had available was one Tota and one Prolight. I'll be buying/renting a proper lighting rig & greenscreen material when/if the time comes to do this work.

Chroma Key Test 3 on Vimeo

And here is the Flash Developer's rough composite using a low res 150kbs .flv encoding of the video:
green_test_150