First create a mask around the object you want tracked. This will become the tracking mask.Label them to avoid confusion when you have many.

Make sure your mask covers the entire "planar area" that you want Mocha to track for you. In this case, it is the body of the skier. The key to getting Mocha’s Planar Tracker to work flawlessly is to understand how it works. It "seeks" within the boundaries of whatever loose mask you create around the area you want tracked. It’s looking for a pattern, and it will essentially lock onto this pattern and follow it as it moves across the screen.

Notice that your first mask is not perfectly at the skier’s edge. This is because you want Mocha to recognize the adjacent non-tracked areas as well. This is how you tell Mocha what it is you want tracked. Mocha can recognize the distinct planar pattern within the area defined by the mask.

If you have Translation, Rotation + Scale, Shear and Perspective checked, it will also track 3D tilt and rotation on your area as well. Think of a person wearing a tall hat: if he tilts his head down, the relative length of the head will appear to shorten. Mocha will take this into account when tracking your area. You can already begin to see how Mocha’s Planar Tracker is orders of magnitude superior to point trackers.

If the area you are tracking is subject to rapid changes, as in this example with the skier (he speeds across the rocks and there’s a lot of white snow and brown rock rushing behind the red suit), things tend to get confusing for the system. But if you understand that it’s locked onto a distinct pattern within your mask, then you can adjust your mask to filter out these outside distractions.

Another technique I’ve used to get Mocha to track what would appear to be an untrackable sequence is to load the clip into some other program and increase Brightness and Contrast to bring out as much detail as possible. Mocha can then lock onto the image much more easily.

In most cases, Mocha will perfectly track your object/area without any additional work on your part. If your eyes can track a distinct pattern in an image Mocha can usually do it, too.

Now you can create the actual matte using the tracking data generated by Mocha. This time you’ll have to be much more careful in making the mask truly to the edge of the skier. This is the final matte creation stage. Once you have defined the matte exactly to the contours of the subject, you then assign the tracked motion generated by Mocha via the Link Splines to Track button.

This is the payoff. If your initial track mask was good, your newly created matte should follow your subject like a loyal puppy! What a relief! No more frame-by-frame roto! If you find tiny areas that need a nudge or two, go ahead and do it. Four or five quick keyframes sure beat out 310 keyframes any day!

Steven M. Blasini
Co-founder and Visual Effects Supervisor
BFX Imageworks

Founded in 2001 by husband and wife team Steven M. Blasini and BenniQue Blasini, BFX Imageworks was created to provide high-end visual effects for independent, smaller-budget studios.

BFX Imageworks has over 30 films and television projects to its credit. Its clients include the Sci-Fi Channel, Lifetime Television, Regent Entertainment, Andrew Stevens Entertainment, MTV, and NBC.

Steven says Keep in Mind….
Last fall, the producers of a new Sci-Fi Channel Original Movie, Ice Spiders, contacted us with a challenge: Bring to life a colony of blood-thirsty monster spiders that wreak havoc on a ski resort. How we created this particular shot in Ice Spiders, where one spider attacks a skier as he swooshes down a mountainside, will give you a pretty good idea of the raw power inside Imagineer’s standalone tracking tool, Mocha (the big brother to Motor). In this scene, the spider jumps out from behind a rock and wraps himself around a skier going full speed down the mountain. The original plate was a generic stock shot of a skier falling, which introduced the obvious difficulty of selling an attack when the victim is not even responding to it! While the lighting and animation of the attack was moderately complex (weight distribution and speed/inertia as the spider connects and grabs onto the skier), one of the challenges was keeping the side of the spider behind the skier hidden from view. This was a natural for Mocha. Mocha’s Planar Tracker had no problems with a red skier over white snow, and it tracked it flawlessly. At 310 frames, the shot would have been a very difficult manual roto. Instead, we kicked it out perfectly in under an hour!

BFX Imageworks
www.bfximageworks.com
7440 Sepulveda Blvd., #302
Van Nuys, CA 91405-4935
ph. 818-893-5212
steve@bfximageworks.com