Compositing solution

Palee wrote on 6/8/2004, 4:38 AM

Compositing solution, that I can't seem to find. Please help me out in this.

I have 4 tracks. All with a same, fixed camera position. The first three tracks shows three different car race on the same racetrack. Cars go by the camera. The forth track shows just the racetrack, without cars.

The goal is to render a video to show all cars passing by one group after another, as they would be in the same race. Obviously the second starts a certain (time)offset, and the third a bigger offset.

I didn't find a good way to produce it. I'd like to substract the empty racetrack from a racetrack with the cars. So only the cars would show. Then do this for the 3 event, then finally putting the racetrack under them.

Is there any way to reach this goal?

Comments

Spot|DSE wrote on 6/8/2004, 5:54 AM

Both of your desired effects are doable, but given the speed of the cars and depending on the length of the clips, I'd probably do this in Commotion, Combustion, or RED.
Vegas now has the rotoscoping tools, but you're gonna be inserting a bezier keyframe mask for every half-frame of video, or 60 keyframes per second.
THAT will be slow and hard. You could also keyframe only the track, but you've still got cars going over the track, so that single track will need to be masked as well. Without motion tracking, and the varied colors of the cars, creating a mask based on chroma will be tough, so.....
I guess it depends on the kind of time you're willing to commit to the task. But it is quite doable.

Palee wrote on 6/8/2004, 6:15 AM

Thanks Spot,
it sounds a more difficult job than I thought it would be.

I supposed the substracting composition would do that for me. But since it is hard to distinguish the cars form the background, it is hard.
Mathematically, it would be easy. When two pixels are the same, then they would neutralize each other, and leave one put, if different.

But I"m not sure about this method ever exist.