Transparent video clip...

steveh wrote on 8/10/2001, 3:07 PM

Is is possible to create a video clip with a transparent background? I know in the movies they shoot against a blue screen, and can then drop that video on top of another background.

I've managed to do this with stills using the alpha channel and targa files, but would like to try it on a video clip.

Or is this something that needs more advanced software like Video Vegas or Adobe Premier?

Thanks

Comments

discdude wrote on 8/10/2001, 5:05 PM

Typically, this is done via chroma keying where one color (like blue) is chosen to be transprent.

Video Factory does not support chroma keying but Vegas Video does.

Alpha channels can also be used in videos in addition to stills but I don't know of many video codecs that support alpha channel (Indeo and Targa are the only two that come to mind). In addition, VF 2 doesn't really have many tools beyond the cookie cutter and titler to create an alpha channel.

Vegas Video is much more robust.

However, tell me specifically what you want to do and maybe I can find a way to do it in VF. I used VF to make a pretty good ghost movie using nothing but the transparency slider (although I did have to resort to Premiere and Vegas Video for the more complicated stuff).

steveh wrote on 8/10/2001, 10:40 PM

It's a totally frivolous exercise:
Our IT department always goes way overboard when we decorate for Halloween. Two years ago we surrounded the entire department with black plastic creating a haunted department; last year we built a crashed alien space ship in our storage room, complete with about 20 monitors running funky videos and sounds.
This year we are looking at coming in at about midnite the nite before halloween and totally stripping our department - moving everything from all of our cubicles down into our storage room where we'll have some pc's set up to use. We want to make it look like the department has disappeared, and we want to 'haunt' the rest of the office through their computers.

I figure we can digitize some video of each of us with spooky lighting and create some short 5 to 10 second videos that we can remotely run on peoples pc's, as we scream to get out of the system.

That part I can handle. The effect I'm not sure about is blending two video sources, one a live feed from a camcorder, the other a prerecorded video. The camera would be showing the office in real time, and a 'ghostly' image of the employees would be wandering around.

As I write this last part I realize a possible way to do it - sort of a take off on making someone 'transport' out. Shoot the video on a tripod with the 'ghost' moving around the office. Keep the camera focused exactly the same place and combine the two images (not sure how...) - the person should appear transparent.

As I said, nothing earthshattering, but just a matter of pride for our department.

Any tips and hints are very welcome.
Thanks
Steve

discdude wrote on 8/11/2001, 12:33 AM

Ah, the ghost effect. VF can do that. I've done it successfully.

It's best to shoot everything with a tripod and don't move the camera. First, set up your shot. Take a still of the background (or a few seconds of footage) with nobody in frame. Then (using the same background, i.e., don't move the camera) shoot your people.

Put the static background footage in the "Video" track. Put the moving "ghost" employees footage in the "Overlay" track. In the timeline, click and drag the top edge of the event in the overlay track down. This will make a pretty convincing ghost effect. You do lose the freedom of camera movement, but you can overcome that with quick shots, fancy transitions (star wipe!) and lots of motion by your "ghosts." Hey, its better than rotoscoping in Viscosity.

Hope this gives you some ideas.

steveh wrote on 8/11/2001, 10:02 PM

Thanks for the tips - I'll see how it goes.
Steve