You separate the thing that are in front of the shirt by rotoscope. This involves duplicating the footage and some masking.
The most efficient technique for tracking depends on the shot. Most of the time Mocha will be your best tool and tracking markers are usually not necessary. It all depends on the shot.
Show us the shot and I'll try and point you to the most efficient solution.
I appreciate the super quick answer. That's exactly what I needed to hear.
And I have a very new question as well. On the shirts I put blue pieces of tape to help with motion tracking. However when I go into mocha and I use the x-spline tool and I turn on perspective because the person is moving from side to side the tracking is never accurate. And when I don't understand is that the movements not very much but the tracking system keeps drifting all the time. Now I might be doing this in correctly but I figured that they should be pretty accurate for at least this.
Do I set the tracking a little differently? Do I do a box around the whole person first and then a new layer around the marker? Do I do a layer around each marker? Or do I do a new layer and include all the markers in one? I figured that there should be a pretty accurate tracking system because you have a Contrasting marker to follow.
Thanks so much again!
The best place to learn to use Mocha is here: Online Video Tutorials « Imagineer Systems
Don't rely on amateur Mocha tutorials on YouTube. There's a lot of inefficient tutorials out there that don't really teach you how mocha's corner pin tracking works. It is important to include a little extra area around the plane you are excluding and depending on the behavior of the objects the move in front of the plane, the arms, you may need to exclude them. The best way of tracking your shot depends entirely on your shot. Sticking blue pieces of tape on the front of a t-shirt probably isn't helping you much, but again, this depends entirely on how you did it. You may want to draw a spline around the first piece of tape and then add splines to the next 3. I can't tell if that would be the best solution without seeing the shot.
Follow the link above, follow the Browse our extensive video section link and then search for Shirt and you'll find some example footage and a tutorial that should help you. The tutorial is pretty darn good.
If you are still having problems post your shot and I'll make my recommendations. It takes a while to learn how to set up VFX shots so they are easy to do in post. You'll get better at it.
I watched the first video before and that is esentialy what I am trying to do but the video had no explanation of how to do the tracking. I know how to clone out the markers, so that's no problem, but the tracking and adding the text is not really explained.
I really appreciate all all of your help. Can you message me you email address and I'll shoot you over a sample clip?
Send your clip to dropbox or some other server. I'll take a look. Did you watch the second tutorial? It shows how to do the tracking and check it in Mocha.
I took a look at your clip and there are some fairly difficult to overcome technical problems with the way you shot the clip.
The first problem is that there is not one plane to track, there are at least two, maybe 3. The problem comes when your actress turns to a nearly profile view. Her body is not flat so there is one plane extending kind of from her shoulders to her bust line, then another plane from her bust line to just above her waist, then another from her ribs to her hips. If she did not turn from facing the camera to a near profile it would be easier to handle the movement.
The only success you are going to have without reshooting will involve doing at least 2 perspective plainer tracks in Mocha and using corner pin to put one part of your artwork on the top plane and another part on the bottom. If you want the graphic to extend to her waist you'll need to do 3 corner pin tracks and then try and line up the pieces of the artwork so that it sticks to the shirt.
The tape is pretty useless and just presents a post production problem that can only be solved by careful cloning. The tape is no help in tracking the action.
My advice is to reshoot and be a lot more careful with the dance moves. If it is OK I'll post a screenshot of how I set up the tracker on the top plane. The tracking worked fairly well and only a little adjustment was required to make the surface stick to the shirt. To get things looking believable using your artwork I would probably budget about 2 or 3 hours for this shot and I've been at this for a very long time. Unless you have access to some pretty sophisticated motion tracking software putting tape markers on a shirt is pretty much a waste of time unless the chest is very flat. On a curvy girl like your actor it's gong to take more than just plainer tracking to create a believable composite.
Thanks so much for writing back (and so quickly at that )
Could you please post the image with the corner tracking?
How would you do the corner pin (in the one corner and the other in the other corner)
I have no problem reshooting as that was just a sample demo of some movement to see if I could even do something like this.
How would you accomplish a person walking from the side and then turning to face the camera? would that even be possible?
One thought... would it be better to already have something on the shirt--text and or graphic--- and then be able to track that and replace it (using the same technique for removing the tape would be) with the new/different text/graphic?
Here's the shot tracked in Mocha:
Notice that perspective is checked, that the spline includes the areas of detail that are approximately on the same plane and I have imported your graphic to add to the surface. This track worked pretty well but as you can see by the layer name this was my fifth attempt to get a good track. Because you have a curvy actor it becomes necessary to track at least two planes to get a good composite. This will take a lot of work.
Having someone walk across frame and then turn to the front requires that the plane you are trying to track is fairly flat, that you see most if not all of the surface in the shot - which eliminates a profile shot that obscures all of the back edge of the plane. It's all a matter of careful blocking.
Adding a graphic is much easier than replacing one because you don't have to generate a clean surface for the new graphic. Just blend modes can simulate the graphic distorting on folds in the fabric.
Another option is to motion stabilize your shot so the shirt does not move in the frame then add your graphic. This technique involves a TV screen but it would work just as well for a t-shirt given the right blocking.
I would practice on a few shots and experiment with Mocha's workflow so you can learn how to block the shot so the composite will work well. If you have to have the actor move in profile and then turn toward the camera it might be better to put a cut in the shot and shoot from two angles or do two separate tracks and combine the composites using multiple layers. This will give you only a few frames that need to be adjusted by hand to cover up the transition from profile to head on.