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View Full Version : Tracking moving subjects with moving camera (suggestions?)


fr3drik
01-24-2004, 06:02 PM
Hi all,

I am kind of new to the whole tracking thing but I am learning. Now I am going to try and track my friends' heads in this clip (http://www.averpil.com/temp/dallas.mov) where the camera is also moving. Please note that the quality of the movie is low just to be able to keep filesize down for you to be able to download it and see what I mean...

The idea is to put a pair of horns in the forhead of my friends (or something like that). Now my problem is... tracking the scene itself is no big deal, but how do I track the heads?

Any suggestions are very much apreciated!

Tuqui-tuqui
01-24-2004, 09:03 PM
Sounds like a great tracking exercise. Not only do your friends' heads move a lot in all directions, but the camera movement also adds to your list of tasks. Thank God you mentioned that this video is compressed for the sake of showing it via web.

Best thing to do, IMO, would be to create spheres in a 3D app and attach the horn models to them. Track them (camera movement) and then animate them (head movement). Then render the horns in a layer and apply it in post to your footage.

I would separate the footage into 5 different parts
1) Friend w/ sweater and scratches head
2) Friend w/ black shirt
3) Back to Friend w/sweater
4) Back to Friend w/ black shirt in a quick pan
5) Last (third) friend
That way you can check your work one part at a time and not feel overwhelmed by the entire thing.

Lucky for you also these 2 things happened:
1) Your friend scratching his head is only for a few frames and only moves his hand very little, so you can duplicate the footage layer and mask the hand on top for those frames while they cover the horns.
2) You're only adding horns (which would be on the side of the foreheads, right?). If that's the case, then you lucked out because there is no secondary movement to take into account like muscles moving (lips, eyes, etc) or long hair!

My .02 cents

Hope it helps!!!!

fr3drik
01-25-2004, 02:04 PM
Cool!
Those are great suggestions. I'm going to start tracking my friends' heads today and I'll post my progress here. *edit* The actual footage is unfortunately miniDV quality (and as you can see lighting is pretty non-existent) but I'm hoping it will work somewhat OK.

fr3drik
01-26-2004, 09:36 AM
It was really hard to keep track points in the face of person #1 (head scratch). I think I might be better off with some new footage with better lighting.

I tried increasing the contrast in the image to easier find track points, but this resulted in huge amounts of grain.

Any tricks I could try before shooting some new footage?

Natto
01-26-2004, 11:42 AM
maybe you could try:
1. attaching little coloured points on your pals' heads where the horns will be..that might make it easier to track.
2. use a tripod for your camera, so that it will only be panned, and not moved..will make it easier to track

greetings, natto

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