Tracking background motion with foreground passersbys

[Bhoneck]

you track up to the part where the track dot is obscured and then you need to go to where it appears again and start tracking again. We do many previews to make sure that the hand tracking we do inbetween cover ups look as realistic as possible. Many times we dont do four corner pin track, insead we track each one by itself and use expressions to tie the tracks back into our cornerpinned image. this allows us to focus on getting each track nailed down one at a time, and works pretty good. Hopefully you know how to do that. We dont have very good luck with tracking when the dots are cut off at all, you really have to spend time getting the tracker to look realistic when you have footage shot the way that you do. We now try using Boujou or some other product to track random dots in the entire scene and then place a box in 3d space where the TV is so that the track looks better. Any way you slice it there is much more work this way. You can try to find other objects that are on the same plane of existance that are not blocked and then offset the track center, but once again this has no guarantees. Good luck.

[Justin Productions]

I’m a bit tired and it would be a little long to explain the solution with the Motion Tracker, but if I were you, I’d simply apply a mask on my tracked image so when people pass by, I’d simply animate the mask so your image gives the illusion that people are in front of the TV.

Nothing difficult.

Justin Productions
Tangerin01@hotmail.com
Adobe After Effects 6.0 Professional

[Mike Clasby]

Next time try taping a green screen (or more appropriate color) onto the tv screen, then you can key it out and put a layer behind your footage, then you don’t have to worry about those walking folks.

[Halmasonberg]

Thanks.

“we track each one by itself and use expressions to tie the tracks back into our cornerpinned image. this allows us to focus on getting each track nailed down one at a time, and works pretty good”.

Would love to know more about how to do this. Currently working in After Effects.

Hal

[Halmasonberg]

“if I were you, I’d simply apply a mask on my tracked image so when people pass by, I’d simply animate the mask so your image gives the illusion that people are in front of the TV.”

Not sure I get this, but definitely want to find out. Could you tell me more?

Hal

[Tony Kloiber]

You have two things to deal with here. One – the screen replacement. Two – roto of the objects (people) that are in the foreground of the the screen replacement.

On the screen replacement for the locked off shots you can corner pin the replacement layer to the screen, try to use a transfer mode that maintains the reflection on the the glass.

On the shots that move you need to track the camera motion. You can do this with the corner pinning (4 point) track but you might also be able to do with a 2 point or even a single point track, It depends on the motion of the camera in relation to the TV set. You don’t have to track the corners of the TV (but if you can it may help) you can track some other object in the frame. It works best if it is on the same plane (distance from camera) as the TV but if the motion isn’t that great it could be just about anywhere. You can relocate the track point if it becomes obscured to another point and continue the track.

Once you have the track information (and your happy with the results) apply it to a null, parent the screen replacement layer to the null and then corner pin the layer to the screen – again using a transfer mode to retain the highlights in the glass.

The next step is to roto around any objects (people) that pass in front of the screen replacement layer. Here is a link that has a great explanation of the roto process https://effectscorner.blogspot.com/
Keep in mind that you only need to roto the parts that pass over the screen and only for as long as they are in front of the screen.

P.S. Putting green on the screen during the shot can kill the reflections and cause green spill on the bezel both of which reduce the believability of the final shot.

TonyTony