From the course: After Effects Apprentice: 02 Basic Animation
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Understanding alpha channels - After Effects Tutorial
From the course: After Effects Apprentice: 02 Basic Animation
Understanding alpha channels
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.…
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