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How Not To Motion Track A Cyc Wall

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While doing a series of 3D-Video workflow motion graphics tests, our 3D artist Luke Hattemer and I decided to try to motion track the cyc wall in Studio NuLu. Or I decided to and told him. I’m not sure. Anyway, we set up our Kessler Crane Jib and mounted our 5D to it and did some passes with our telephoto lens pulled back to 24mm. After running the footage through two match moving software packages (PFHoe and Matchmover), we realized that this was not going to be as easy as it looked. Match moving is the process of rebuilding a shot in a virtual 3D environment and then exporting that information into graphics or 3D programs, such as After Effects or Maya. The software identifies objects and details within the shot and tracks those points, and then based on comparisons of the movement of a given point with the movement of other points, determines where each point lies in relation to the camera.

In our case, the software was having a really hard time distinguishing what was where. In fact, it couldn’t even tell that there was a curve in the wall. This was because the cyc wall is designed to be an infinite space to the camera, so there were no details to track. So we tried adding details. First we added bits of tape to the wall, making a grid and and black squares to the floor.

Same result.

Next, we littered the shot with light stands.

Still the same result.

We added caution tape to the light stands, taped newspapers to the walls, removed the newspapers and light stands and created a grid with the caution tape, all to no avail.

We could not get a clean track on the wall no matter what we tried.

Now, granted, we’ve never been trained in the software, so there are probably things we could have tried that might have worked. It is doable, certainly, but after a bit more research, we made motion tracking markers consisting of black triangles inside white circles and taped them to the walls and floor, and as a precautionary measure, shot in 24mm and with a 50mm prime lens. Interestingly, we had the same troubles with the 24mm lens footage, but got a good track with the 50mm.

So, what did we learn? First of all, to get a good match move, you need good parallax within the shot (foreground elements that move at a faster rate than the background elements), and if you use PFHoe, you’d best avoid the wide angle lens.

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