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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 auto-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 auto-tracker run, then manually delete the unwanted trackers if there are only a few. 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 three methods to control where the auto-tracker tracks: animated splines, Mask ML, and alpha channel mattes. All 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 can use Mask ML or an external compositing program to create the matte. If you’ve no idea what that last phrase said, you can skip the entire alpha channel discussion and concentrate on Mask ML and animated splines, which do not require any other programs.
Mask ML is SynthEyes’s AI-based matte generation tool, it makes many of these tasks routine and basically automatic. You can read the Mask ML Quick-Start to get going with that; this section covers more details about how to use the Roto panel, multiple layers, multiple objects, etc.
©2025 Boris FX, Inc. — UNOFFICIAL — Converted from original PDF.