Join Chris Meyer for an in-depth discussion in this video Understanding alpha channels, part of After Effects Apprentice 02: Basic Animation.
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Now if you remember, earlier in this lesson, when we imported our snowstorm…title, After Effects asked us what type of alpha channel this layer had.…At the time, we clicked on Guess, and After Effects correctly guessed…that it was pre-multiplied with white.…I thought it would be useful to explain, in a little more detail, the difference…between straight and pre-multiplied.…Now you will not see this dialog, unless the alpha channel is unlabeled.…Unlabeled alpha channels may come from outside of the Creative Suite.…
Photoshop, Illustrator, and After Effects always label their alpha channels, but…if you don't ever see this dialog box, I do want to point out that there's a…preference that someone may have set…that will always get the dialog.…Click OK and I'll show you Preferences > Import. The default is to always ask…the user if After Effects comes across an unlabeled alpha.…If someone had set this preference to Guess, After Effects will always guess,…and sometimes it guesses incorrectly.…So I like to leave it set to Ask User.…
After Effects Apprentice is created by Trish and Chris Meyer and designed to be used on their own and as a companion to their book After Effects Apprentice.
- Starting a project from scratch
- Building a composition
- Arranging and transforming layers interactively and numerically
- Animating parameters including motion paths
- Applying and re-using effects
- Creating variations and rendering the final movie
- Importing layered Photoshop files
- Understanding alpha channels
- Avoiding common mistakes