Alpha Matte from Portal VFX Issues

So I am playing around with the Portal Effect for a short film I am working on but I can get the Alpha Matte to work as intended in Adobe After Effects or Premiere. Is there a guide or walkthrough I am missing that lays out these steps?

I hope your short film is going well, share it here when it’s finished so we can see your take on the portal effect. The portal effects are delivered as Prores 422 HQ files, meaning they don’t have a built in alpha channel so you should utilize both the footage and the matte file. The mattes can be applied in both AE and Premiere in very few steps, I’ll show you how I like to do it.

After Effects: Start by placing the two pieces of footage you want to use with the portal, we’ll refer to these as Inside Portal and Outside Portal. Place the Inside Portal layer above the Outside Portal layer, aka the background. Now import the portal clip you are using with the matte layer placed below the portal footage. Turn off the portal footage for now while we focus on the matte. Set the Inside Portal layer to luma matte, and this will remove everything outside of the portal from the inside layer. Turn back on the portal layer so we can composite over top of the matted layer. Since this file does not contain an alpha channel, the black background will need to be removed. This can be done with the included matte, but I think the fastest, easiest way is to use a plugin like Red Giant’s unmult (This does the best job with retaining details in my opinion) or some of the built in channel effects in AE. A blending mode like screen or add can also be used, but that gives you less control over the look of the portal. One way to do this with the native After Effects is to apply the set channels effect to the portal layer. Set the alpha source (Source Layer 4) to luminance and the black background will be removed. If you want to adjust the color, add a Hue/Saturation Effect after this and adjust it to your liking. Finally, I like to duplicate the portal layer, remove the set channels effect, and set the layer blending mode to screen to bring back in some of the edge glow.

Premiere: This is a very similar set up to After Effects, just using the effects included with Premiere. Create a sequence with your Inside Portal layer placed above the Outside Portal like I explained earlier. Place the matte layer above the Inside Portal layer. Add the Set Matte effect to the Inside Portal layer and set the “Take Matte From Layer” to the track the matte is placed on, 3 in my example. Change the “Use For Matte” option to Luminance. Add the portal clip above this and add the luma key effect to remove the background (Again I recommend Red Giant Unmult, but this works if you don’t have the plugin). Then place another copy of the portal clip on top and set it to screen to bring back the edge glow. I prefer to do this effect in AE as it provides more control, but do it in whatever you’re most comfortable in.

There are many other ways to do this, as this set up might not work for every situation. Here’s a tutorial that goes into more detail on applying mattes in a handful of programs I recommend watching if you’d like a better understanding on how mattes work. One last tip to creating a convincing portal effect is to spend some time making sure you get the lighting in the different scenes right if you have something passing through, and to create light cast from the portal on top of the environment. Hope this helps!


Ah Luma Matte, I was trying to use the Alpha Matte Mode.

That makes me feel like a Fool of a Took, after I threw myself down the well I tried the Luma Matte and it worked!

Thank you for the help @clayton1 !