Motion Fixes

We’re in the business of moving pictures. That seems like an obvious statement, but as I was working with the tracking software mocha for this month’s issue, I was reminded of when I first tried rotoscoping a scene. It was 147 frames long (yes, I remember the number), and I painstakingly worked on each frame to remove an unwanted object.

After hours of work, I finally played back the shot only to realize that I had removed the offending object, but replaced it with a mess. While the rest of the scene moved smoothly through the frame, my work jittered, chattered and did all it could to make itself obvious. The more I tried to fix it, the worse it became. I hadn’t realized that accurate motion is critical to the replacement I was trying to do. (I also realized that I should check my work after just a few frames!) If only I had access to the right tools: tracking software.

Now there’s a whole host of applications to help track motion in a scene. Sometimes the tracking function resides in another application; other times, it’s a stand-alone piece of software. Different applications use different methods to calculate motion in a scene.


As I just mentioned, if you need to replace a defect in your scene, tracking can overlay a fix. The defect might be an inappropriate phrase on a T-shirt or a reflection of the crew in a mirror.

Tracking also can be used to stabilize an image. The correction might be for a slight camera bump or some serious dolly track issues. It’s also done to affect the feel of a scene. For example, The Social Network made extensive use of image stabilization to keep small, unwanted camera movement at bay.

Tracking is involved in screen replacement. You might need to fix a scene where the image on a television, scene where the image on a television, tablet or cell phone is wrong or where the picture isn’t bright enough compared to the light level in the scene.

I worked on a project that featured an Internet-connected television. Unfortunately, at the time of the shoot, the menu system on the "smart" television was still in its beta stage so all the screens displayed debugging information. Since the scenes had camera movement, tracking was needed to mask out the extra debug info.

Another popular use for tracking is during grading. You can use tracking to create moving mattes (or windows within the grading application) that allow you to precisely apply color adjustments to your footage. I think that this use of tracking should convince anyone who’s grading their footage to look at the tools tracking provides to give them more control. Although some grading applications include tracking, dedicated tracking software offers other tools, too.