Rotoscoping and Alpha Channel Mattes

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‌Rotoscoping and Alpha Channel Mattes ‌

You may choose to use SynthEyes’s rotoscoping and alpha channel matte capabilities when you are using automatic tracking or planar tracking.

Rotoscoping is helpful in the following situations:

 A portion of the image contains significant image features that don’t correspond to physical objects---such as reflections, sparkling, lens flares, camera moiré patterns, burned-in timecode, etc,

 There are pesky actors walking around creating moving features,

 You want to track a moving object, but it doesn’t cover the entire frame,

 You want to track both a moving object and the background (separately).

In these situations, the automatic or planar tracker needs to be told, for each frame, which parts of the image should be used to match-move the planar tracker or camera and each object, and which portions of the image should be ignored. More specifically, as it examines a frame, SynthEyes needs to know to which object to assign any primitive feature (blip) that it finds. Any blip can only be assigned to a single object (something can’t be part of the background and a moving object!). Those blips are ultimately linked up to form trackers on the respective camera or object.

Hint : Often you can let the autotracker run, then manually delete the unwanted trackers. This can be a lot quicker than setting up roto mattes. To help find the undesirable trackers, turn on Tracker Trails on the Edit menu.

SynthEyes provides two methods to control where the autotracker tracks: animated splines and alpha channel mattes. Both can be used in one shot.

Planar trackers have four different methods: animated splines (as described here), alpha channel mattes, in-plane masks, and tracker layering. For more details specific to planar trackers, see the Planar Tracking Manual (on the SynthEyes Help menu).

To create the alpha channel mattes, you need to use an external compositing program to create the matte, typically by some variation of painting it. If you’ve no idea what that last sentence said, you can skip the entire alpha channel discussion and concentrate on animated splines, which do not require any other programs.

Overall, and Rotoscope Panel Spline Workflow Animated Splines Roto-Panel Spline Operations in the Camera View From Tracker to Control Point Seeing and Checking Roto Spline Stackups Writing Alpha Mattes from Roto Splines Using Alpha Mattes to Direct Tracking

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