How: Silhouette of moving person??

kentwolf wrote on 6/24/2006, 11:15 AM

Is it possible to take a video of a person, then chage that person to simply a black silhouette and retain the motion of the person?

If so, could you please tell me how?

I am not sure if this is possible in Vegas.

If it is not possible in Vegas, how would I go about this?

Thank much!

Comments

GlennChan wrote on 6/24/2006, 11:29 AM

It depends how it was shot.

The easiest way to do things would be to shoot specifically for this effect. Either do a greenscreen, or light someone with a silhouette on a white background (and then key + clean up the footage).

If you did not shoot the footage specifically for this effect, things get a lot tricker!!! You'll likely need to do some form of rotoscoping or difference key. A difference key would be easier, if it works. You'll need to shoot the background without the subject in it, and the background with the subject in it. The camera should be 100% locked off, otherwise it's very difficult to deal with (likely need to rotoscope).

If you could be more specific on how the footage will be shot, that will help.

Stonefield wrote on 6/24/2006, 1:43 PM

THATs what a difference key is !!! Always wondered that.

I shot some greenscreen footage of people moving back and forth in front of the camera to add as a foreground element in front of the subject. She was on a greenscreen in a separate shot, slowed down and then both were composited in front of a time lapse street scene......think it's still on my site...

http://www.stonefieldmedia.com/assets/clips/RoseReiter/YouWillKnow.wmv

The foreground people walking by really added to the depth of the shot.

johnmeyer wrote on 6/24/2006, 4:54 PM

The difference key is an amazing technology. The idea is exactly the same as a green screen, except that it is done by taking a difference in luma values. You shoot the scene, on a tripod, with nothing moving. You then let your actors wander into the scene. Any place where the pixels don't match, you create a mask to let those pixels show through. Any place where the pixels DO match what you shot in the static opening scene you replace, just like with a green screen.

Here are my links for difference key threads, including a link to the excellent tutorial on the subject:

Help with difference key technique

Key difference technique-Look at the results!

Difference Key Tutorial

In answer to the original question, I would use a difference key to isolate the moving people, and then simply reduce the opacity to zero (or any number of other fX can be applied to do the same thing, or to paint them in a color). Basically, you can do the "iPod commercial" effect in all its variations, without much problem, once you have isolated the motion with the difference mask.

Jim H wrote on 6/24/2006, 9:17 PM

In one of my recent projects I used a simple bed sheet and spot light to create the effect I think you're after. Here's a link to the video and a "how to" webpage:

Video

How to