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Before we can begin making our magic here in After Effects, we need to prepare each of the layers we're going to need in the final composition. We're going to start off with the phone. Now, this may seem like a boring step in the process, but it's really foundational. Understanding how to set up correct pre-comps and building the right pre-comps for just the right situation means that when you get into the final compositing process you're going to have all of the elements that you need right there at hand. It really is a key to sort of setting up a smooth workflow for you all the way through After Effects, so you get to the final result.
So what I'm going to do here in the file is I'm going to go into the Video folder, and in my Phone Pass folder, I've got this pre-comp, and this is the pre-comp that was imported when we imported the AEC file. Now I could just use this composition originally, but I don't like to do that. I always like to keep a copy of it on hand. So I'm going to make a copy by hitting Command+D or Ctrl+D on the keyboard, and I'm going to move that into the Pre-COMP's folder. Let's scrub down and go to the Pre-COMP's and now in the Pre-COMP's folder I'm going to change the name of this and call it Phone Pass Pre.
And I'll open up the Phone Pass pre-comp and you can see this is our pre-comp, and we've got our Phone Pass, and it's over black right now. And we don't want this black here, but this black as a result of the multi-pass compositing process. So we need to be able to eliminate this back, but we need an alpha channel for the phone to do that. And so fortunately for us, when we set up our render from CINEMA 4D, we did the RGBA Pass, which gives us the complete phone with an alpha channel. So if I go back into the Special Passes folder in the Phone subfolder, you can see there is a Phone_rgba.psd sequence here. And if I bring that in--and I will just isolate it real quick by hitting the Solo button-- and you can see that with the transparency active, I can now see that I've got an alpha channel. So what I want to do is have this alpha channel cut right down through all this black, and there is a really great feature in After Effects called Stencil Alpha.
It's one of the blending modes, and if I click on the Modes pulldown and scrub all the way down to the bottom and set this to be Stencil Alpha, when I do that, it's going to chop away all of that black stuff. Now I don't see the phone anymore. All I'm seeing is the result of the alpha channel stenciling out all of that extra information for me, and so that's a really important process. Now when I clicked on this, I just noticed something very important about the RGBA Pass, and that's in the footage summary information up here. It's showing me that it's millions of colors but pre-multiplied, and I know that for sure when I rendered it from CINEMA 4D I rendered it with a straight Alpha channel.
And this happens sometimes. You get confused about whether or not you meant to have it as pre-multiplied or straight Alpha channels. You have to really watch out for this. And so I'm going to right-click on this Phone RGBA Pass, and I'm going to go to Interpret Footage > Main, and in the main footage interpretation dialog, I'm going top change it from Pre-multiplied to Straight. And I will just hit Enter on the Keyboard, and that's going to get rid of that screen for me. And now I can see that it's set to be straight alpha, and that's going to make things a lot smoother for me down the road. Now those may seem like basic steps that we just went through, but once again, this process of building this pre-comp is foundational because we're going to be building on top of this Phone Pass from here on out to make our phone really sit in the stadium, so having this pre-comp built is going to make that process a lot easier.
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