After Effects 23.6.5 Mask Opacity Not Working Properly

Question

I have a use case of a simple Mask and would like to keyframe the Mask Opacity On and Off (0% - 100%) however, the Mask Opacity is working as if it is the "Transform Opacity".
I strongly believe this is a Bug.

JohnColombo17100380 · Accepted Answer

Hi @Leonard Hasemann,Thanks for posting about this. The behavior in the image is the correct behavior of a Mask when it is set to Subtract; the opacity of the pixels outside of the masked area is affected by the Mask Opacity. To keyframe the mask on and off, perhaps try using the Mask Expansion with Hold keyframes toggling between a very negative value, e.g. -1000, and 0.Cheers,- John, After Effects Engineering Team

brooks_0785 · Answer

One popular method is using Mask Expansion instead of opacity; by setting it to a very negative value (like -1000) and animating it to 0, you can mimic the effect of turning the mask on and off. Another fix is to precompose the layer, which can isolate the mask from any interfering effects. You could also try moving the mask to a shape layer and use the Silhouette Alpha blending mode, which often gives better control. Lastly, double-check that the mask isn’t accidentally set to “Inverted,” as that can cause confusing results.

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