• Adobe After Effects

  How to NOT constrain RGB to alpha

  Posted by Medrick Greech on April 7, 2011 at 8:26 pm

  So I created some clean plates and placed them in my alpha, but I want to send my client the entire RGB not constrained by the alpha of the cleans that currently sit in my alpha channel. I would like to show the complete RGB, but have just the work I did in the alpha.

  Possible in AE CS5?

  Thanks,
  Xen

  Walter Soyka replied 15 years, 5 months ago 3 Members · 4 Replies
• 4 Replies

• 

  Medrick Greech

  April 7, 2011 at 8:56 pm

  sorry. my english not the best.

  I am creating clean plate. clean plate has alpha where i painted.
  when bringing back into composite, they want alpha of the new composite to contain ONLY the alpha from my paint work. Yet they want the full RGB of everything in the shot.

  my alpha constrains the rgb only to the area i painted? anyway to get around that?

  thank you.
• 

  Walter Soyka

  April 7, 2011 at 9:04 pm

  [Medrick Greech] “I am creating clean plate. clean plate has alpha where i painted.
  when bringing back into composite, they want alpha of the new composite to contain ONLY the alpha from my paint work. Yet they want the full RGB of everything in the shot.”

  This sounds like the definition of straight alpha [link].

  See Aharon Rabinowitz’s Understanding Straight vs. Premultiplied [link] for a detailed explanation.

  Walter Soyka
  Principal & Designer at Keen Live
  Motion Graphics, Widescreen Events, Presentation Design, and Consulting
  RenderBreak Blog – What I’m thinking when my workstation’s thinking
  Creative Cow Forum Host: Live & Stage Events
• 

  Cassius Marques

  April 8, 2011 at 8:33 pm

  I’m having a hard time understanding it too. But from what I got, let’s say he has a frame that if you look at it ignoring the alpha…you’ll see a forest, and if you interpret it as straigh, you’ll see just one of the trees.

  I get something like that when I export from 3ds max with something on the background, yet I don’t think AE can do it.
• 

  Walter Soyka

  April 8, 2011 at 8:47 pm

  [Cassius Marques] “I’m having a hard time understanding it too. But from what I got, let’s say he has a frame that if you look at it ignoring the alpha…you’ll see a forest, and if you interpret it as straigh, you’ll see just one of the trees. I get something like that when I export from 3ds max with something on the background, yet I don’t think AE can do it.”

  This is exactly what I was suggesting when I mentioned straight alpha.

  If you apply the paint effect to a layer to make your clean plate, check the “Paint on transparent” button on the Paint effect, and render with straight alpha, the RGB pixels of the untouched areas will be preserved (but masked by the alpha). Ignoring the alpha (or using one of the channel effects to alter it) will reveal the untouched RGB pixels the original poster is concerned about preserving.

  Walter Soyka
  Principal & Designer at Keen Live
  Motion Graphics, Widescreen Events, Presentation Design, and Consulting
  RenderBreak Blog – What I’m thinking when my workstation’s thinking
  Creative Cow Forum Host: Live & Stage Events

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