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Leonard Hasemann
Participating Frequently
April 4, 2024
Answered

After Effects 23.6.5 Mask Opacity Not Working Properly

  • April 4, 2024
  • 2 replies
  • 402 views

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. 

Correct answer JohnColombo17100380

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

2 replies

B
brooks_0785
Participating Frequently
May 1, 2025

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.

JohnColombo17100380
Community Manager
JohnColombo17100380Community ManagerCorrect answer
Community Manager
April 8, 2024

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

T
ty_9728
Participant
May 1, 2025

Why is this a feature? Not trying to be rude, but it honestly seems so illogical to me, why would the opacity not just effect the mask? For me at least, this makes it much more difficult to achieve a simple mask opacity change which would otherwise be very simple. I cant see a single clear benifit for it staying the way it is when you could just use the transform opacity to get the same result, then again, I am by no means a professional after effects user so maybe there is just something I'm not seing, could someone explain why it is this way please.

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