Writing Alpha Mattes from Roto Splines

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‌Writing Alpha Mattes from Roto Splines ‌

If you have carefully constructed some roto splines, you can export them to other compositing programs using Save Sequence on the Shot menu or in the image

preprocessor . Select an output format that supports alpha channels and turn on the alpha channel output. If the source does not contain an alpha channel, the roto spline data will be rendered as alpha instead. The green-screen key will be combined in as well, if one is configured.

Important: Only those splines assigned to the current active tracker host are included in the output, so that you can write splines individually or in groups as separate file sequences, by manipulating the object assignments.

You can also output an RGB version of the roto information, even for formats that don’t support alpha channels, by turning off the RGB checkbox in the save-sequence settings, then turn on the alpha channel output checkbox. The data will automatically be converted from an alpha channel to RGB.

Note: the roto-spline system is intended for determining where to track and thus produces binary yes or no output; it does not produce gray-scale data with smooth edges for compositing. The truly determined might write masks at 4x resolution then filter down in an external app (or even SynthEyes).

Note : OpenEXR is currently the only format where you can write a true alpha- only sequence.

Note : Current formats supporting written alpha channels: BMP, DPX, OpenEXR, PNG, ProRes™ 4444, SGI, Targa, TIFF.

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