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How to NOT constrain RGB to alpha

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Medrick GreechHow to NOT constrain RGB to alpha
by on Apr 7, 2011 at 8:26:12 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


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Dave LaRondeRe: How to NOT constrain RGB to alpha
by on Apr 7, 2011 at 8:44:44 pm

[Medrick Greech] "So I created some clean plates and placed them in my alpha"

Sorry, I'm having a tough time understanding exactly what you did in AE? Can you elaborate on how you created this alpha channel in your AE comp?

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Medrick GreechRe: How to NOT constrain RGB to alpha
by on Apr 7, 2011 at 8:56:25 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.


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Walter SoykaRe: How to NOT constrain RGB to alpha
by on Apr 7, 2011 at 9:04:25 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


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Dave LaRondeRe: How to NOT constrain RGB to alpha
by on Apr 7, 2011 at 9:12:47 pm

If I understand you correctly, you now have transparent holes in your comp, made by painting. You now need to fill these holes in with other images. Do you have images to do so?

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Cassius MarquesRe: How to NOT constrain RGB to alpha
by on Apr 8, 2011 at 8:33:45 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.


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Dave LaRondeRe: How to NOT constrain RGB to alpha
by on Apr 8, 2011 at 8:37:02 pm

Hmmmm.... yeah, that could be it. Well, if you could import the image in question TWICE. Then you can interpret the first to ignore the alpha channel, and the second to guess at the alpha channel.

When it comes to alpha channels, AE always guesses right, in my experience.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Walter SoykaRe: How to NOT constrain RGB to alpha
by on Apr 8, 2011 at 8:47:23 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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