Rotoscoped matte not following tracking data


#1

I have followed the offline manual starting on page 61. I have tracked all the limbs of a skier in a Giant Slalom race (including movements of the ski sticks), over a small part of the course. I then created a new spline tight around the RH ski stick and linked it to the tracking data of the looser ski stick spline tracked previously. I followed the instructions to switch off tracking for the loose spline and played back the result, but the tight spline doesn’t follow anywhere near the track of the loosely tracked spline. What can I be doing wrong? All the parts of the skier were very hard to track and I had to use a great deal of keyframes to correct drift. The idea is to eventually cut the skier from the background by the use of an exported matte for use behind the titles for my video. To this end I first created a line drawing of the skier using Boris Effects before importing into Mocha and tracking. Would it have been more accurate to produce the tracking data from the original video?

Mike.

 

 


#2

Hi Mike,

I am sorry to say that absolutely you should have tracked in mocha without converting the image to a line drawing. Because mocha is a planar tracker, it really needs the texture of the image in order to get a rock solid track. Also, you will want to track with your grid and surface tool on, so that you can see whether or not the tracking data is incorrect. Your roto shapes in mocha will only follow the tracks, so if the track is not good, your roto shape won’t be easy to manage either. Don’t trust the splines, the splines all only follow the tracks and as they animate, they do not change the tracking data.

I would suggest that you retrack/re-roto using the original footage. In general, you want to do any effects like “line drawings” or color corrections after you have done your roto and VFX work on a shot.

Please let me know if you have any more questions and I will be happy to help.

 

Cheers,
Mary


#3

Hi Mary, thanks for the reply, but I have tried again with the original footage and get the same result. the loose spines track fine but the linked spline does not. It immediately shoots off to the extreme left of the video frame. Could it be something to do with keyframes?

Mike.

 


#4

Hi Mike,

That sounds like it could have something to do with perspective. Is perspective on the original track? It sounds like a “surface going behind the camera” problem. Can you either post or email me a screenshot to take a look? maryp@imagineersystems.com

Cheers,
Mary