Tip #1317: An Example of a B-spline Mask

… for Apple Motion

Tip #1317: An Example of a B-spline Mask

Larry Jordan – LarryJordan.com

The B-spline mask tool is great when you DON’T want sharp edges.

A morphing blob shape, composed of two still images of colored chalk.

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Most of the time, when we need a mask, we’ll use the Bezier tool, because it creates very flexible, highly-precise masks. So, I wondered, when should we use the B-spline mask tool?

The B-spline tool creates “blobs,” masks which have no sharp edges. It reminded me of the Blob generator in Final Cut.

So, I set out to create my own blob and discovered the very interesting effect you see in the screen shot.


  • Add Chalk 03 to a layer
  • Apply Behaviors > Spin to rotate slowly
  • Apply Filters > Blur > Gaussian Blur
  • Manually enter an Amount of 700, to make it REALLY blurry
  • Add Chalk 02 on a higher layer
  • Apply Filters > Blur > Gaussian Blur
  • Manually enter an Amount of 700
  • Use the B-spline mask tool to create a blob of this upper layer, then add as much feathering as possible
  • Finally, add keyframes to different B-spline control points so that the shape of the blob animates/morphs over time



There’s lots of other effects you can add to change the look of this effect. Feel free to play as much as you want.

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