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Rendering with alpha channels

From: After Effects Apprentice 06: Type and Music

Video: Rendering with alpha channels

We have a text animation we are happy with, and now we'd like to render it. If you recall, I have two layers in this animation: I have the text layer, and I have a background movie with the penguins. If I was to render this as a composite, I only need to render the RGB channels. I wouldn't need an alpha channel because the movie is filling the entire frame. However, let's say your client isn't sure of what the background movie should be, so they've asked you only to render the animated title.

Rendering with alpha channels

We have a text animation we are happy with, and now we'd like to render it. If you recall, I have two layers in this animation: I have the text layer, and I have a background movie with the penguins. If I was to render this as a composite, I only need to render the RGB channels. I wouldn't need an alpha channel because the movie is filling the entire frame. However, let's say your client isn't sure of what the background movie should be, so they've asked you only to render the animated title.

In order for them to composite this animation on another background, I need to render an alpha channel. I will turn on the transparency grid so you can see exactly what's transparent and also see that this title has a nice black drop shadow. I want to make sure that the shadow is composited smoothly on whatever background they add in the editing program. If you'd like to see what the alpha channel looks like, you can set the Show Channels to Alpha Channel, and you can even RAM preview it. Wherever the alpha channel is white, the text will be fully opaque; where it's black will be fully transparent--and the drop shadow is semitransparent.

So that all looks good, I will return to the RGB channel. To render my composition, I can select Make Movie from the Composition menu, or use the shortcut Command+M on Mac, Ctrl+M on Windows. When I do that, the Render Queue will open. It will add the composition to the Render Queue using whatever default templates are set for Render Settings in the Output module. Because I have a Preference set under Output Preferences, it automatically uses the name of the composition for the file name.

If I click on the name of the file, I can decide where I would like to save it. In this case, it's the last folder I used. I can change the default name to something more useful, such as PPlayhouse_title_alpha, and then I will click Save. And before I click on the Render button, I want to make sure I have my Render Settings and Output Module set up correctly. The Render Setting default I am using is Best Settings. The only problem I see is that the Time Span is set to Work Area Only.

Now, that can be a little dangerous. If I had set the work area to preview only a small section of my comp, that's all that would be rendered. So I want to make sure I set this to Length of Composition. Even better, I should change the Best Settings template so that it always renders with the length of composition. The other settings are fine, but I did want to point out that if I was rendering the background movie-- and remember I had separated the fields earlier in the Intrepid Footage dialog--I would want to set the Field Render pop-up to Lower Field First.

That way both fields from the source movie would be output in the final movie. Since I'm not rendering the background, I do have a choice. In this case I think I would like to have a progressive movie, so I will make sure Field Render is off. I will click OK, and let's look at the Output Module. I will click on the word 'Lossless' to open the Output Module settings. In this template, it's only saving the RGB channels, and the alpha channel is being pre-multiplied to give it a nice clean look. I will cancel out of this dialog and point out that there is another option called Lossless with Alpha.

Now when I open the Output Module Settings, you can see the channels default to saving RGB plus Alpha. The other option is to only save the alpha channel and that can be useful in some cases. The only problem with this template is that the color channel is still pre-multiplied. For a professional editing system, the preferred format is actually straight. I am probably going to use the Straight (Unmatted) Alpha Channel option more often than Premultiplied, so I am going to cancel and show you how to do this change permanently.

Under the Edit menu, let's open Templates > Output Module. We will select Lossless with Alpha, and remember the default is to pre-multiply the alpha channel. Since I might want to use this sometimes, I will change this to Premultiplied, and then I will duplicate it and I'll make a second version called Straight. And of course this version I have to edit and I will change it to Straight (Unmatted). By the way, if you are not sure of the differences between Straight and Premultiplied, I cover these in detail at the end of the basic animation installment.

So this template will use the Straight (Unmatted) option. So I will click OK, and now that I have edited by templates, my pop-up will show two options for alpha: Straight or Premultiplied--and I want to pick the Straight option. Now I could click the Render button now, but I will make one more change. I am going to change the Post Render action so that the finished movie will be imported automatically into the project. That way I won't have to open it in the finder to check that everything rendered correctly. Click OK and now I will select the Render button, and this will only take a second.

It's a pretty simple animation. (ring) There is the happy-happy joy-joy sound. Now there is two ways to find my movie. I can either twirl down the Output Module and click on the file path and that will open it in QuickTime Player in the Finder. But since I have asked it to automatically import, I can find it in the Project panel. If I open it in CS5 by just double-clicking, it will open it in the Footage panel with the alpha channel factored in, so the edges look nice and clean--and in particular the drop shadow is nice and soft.

But look what happens if I open it in QuickTime Player. To do that, I will press the Option key on Mac or Alt key on Windows when I double-click the movie. In QuickTime Player, that nice soft drop shadow is showing up as a hard, ugly black shadow. Well, that's because QuickTime Player is not factoring in the alpha channel. It's only showing me the RGB channels. So it's not factoring in the transparency for the shadow in the RGB channels. This is actually a good thing and nothing to be worried about.

The only time this might be a problem is if you deliver a job and the client opens it in QuickTime Player; you may get a panicked phone call. Just tell them to import it into their editing program, use the alpha channel, and everything will look nice and clean. Of course if you want to email a quick proof, be sure to render with a premultiplied alpha. That way they can view it on a web site or in QuickTime Player and it will look good. Well, I hope that helps you understand how to render with an alpha channel. If you take a few minutes and edit the default templates for render settings and output modules, you will find the next time you make a movie, it will go a lot faster because you have all the templates available.

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This video is part of

Image for After Effects Apprentice 06: Type and Music
After Effects Apprentice 06: Type and Music

49 video lessons · 18022 viewers

Chris Meyer and Trish Meyer
Author

 
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  1. 3m 35s
    1. Overview
      1m 35s
    2. Using the exercise files
      2m 0s
  2. 14m 51s
    1. Setting up
      2m 20s
    2. Entering, editing, and styling type
      5m 49s
    3. Using strokes
      3m 6s
    4. Working with paragraph text
      3m 36s
  3. 23m 21s
    1. Setting a title
      2m 31s
    2. Creating a text animator
      6m 54s
    3. Selecting by character vs. percent
      3m 0s
    4. Animating position
      2m 4s
    5. Animating more properties
      3m 31s
    6. Exploring text transitions
      2m 47s
    7. Randomizing order
      2m 34s
  4. 22m 49s
    1. The Cascade recipe
      2m 15s
    2. Exploring offset plus selection shapes
      4m 16s
    3. Working with ramp selection shapes
      4m 26s
    4. Using character anchor points
      4m 40s
    5. Further refinements
      7m 12s
  5. 9m 0s
    1. Working with selections based on words
      4m 16s
    2. Anchor point grouping
      4m 44s
  6. 15m 46s
    1. Using a vertical blur treatment
      3m 58s
    2. Animated tracking
      5m 46s
    3. Working with text on a path
      6m 2s
  7. 14m 56s
    1. Per-character 3D overview
      5m 45s
    2. Enabling per-character 3D
      4m 4s
    3. Exploring per-character 3D rotation
      5m 7s
  8. 18m 37s
    1. Separating fields
      3m 48s
    2. Exploring wiggly options
      4m 28s
    3. Animating wiggles
      3m 18s
    4. Rendering with alpha channels
      7m 3s
  9. 45m 29s
    1. Adding audio
      4m 8s
    2. Audio levels
      4m 27s
    3. Spotting hit points
      5m 33s
    4. Timing to audio
      5m 25s
    5. Spotting dialogue
      7m 32s
    6. Timing dialogue to music
      6m 45s
    7. Mixing audio
      7m 53s
    8. Exploring audio refinements
      3m 46s
  10. 23m 9s
    1. Applying text presets
      5m 50s
    2. Browsing presets in Bridge
      4m 35s
    3. Editing presets
      6m 49s
    4. Saving presets
      5m 55s
  11. 16m 27s
    1. Working with Photoshop text
      4m 58s
    2. Keyframing source text
      4m 21s
    3. The Buzz Words preset
      7m 8s
  12. 20m 43s
    1. Exploring faux styling options
      7m 42s
    2. Tracking and kerning
      4m 56s
    3. Using smart quotes
      4m 8s
    4. Using hyphens and dashes
      3m 57s

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