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Is there a concept of an alpha layer in AE
Hello, I’m posting this in the basics forum because I think I’m missing something basic in my interpretation of what I’m doing.
I’m using Premier and After Effects together to piece together a compilation. What I have so far is a few text layers in AE, a rotoscoped object or two and some green-screen footage assembled into a composition that has a mostly transparent background.
Now I don’t want any slack about the use of a lens flare. Don’t worry, I’m not overdoing it. 🙂
What I’m trying to add is a lens flare animation to a layer in the comp, but it will only apply to a solid layer, such as a green plate that I could create in the background. If I apply it to a text layer or other motion layer, it is only viewed where the mask is closed, of course. Since this is an overlay plate for premier, the majority of the scene is transparent.
So my problem is, in Photoshop, I can create a picture with a transparent BG, and draw on top of this layer and save as an image w/an alpha channel.
Where is this concept in AE? I don’t want to try to green screen a lens flare….. Can’t I just apply this to an adjustment or null layer? So far, I’m not having any luck with either of these methods. It would be great if I could just select a new layer and instead of picking a color, choose transparent and be done with this.
This in my mind should be possible. Am I missing something? Keylighting a light effect does not work and I don’t want to go down that path.
Also, Yes, I could do the lens flare in premier pro, but I would prefer to keep the mechanics of this scene within AE, rather than superimpose like that.
Thanks for any insight!
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5 Replies
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if you are talking about just ‘keying’ out the lens flare, then all you need is a free effect called unmult. download it and install it. then apply the lends flare to a black (must be black) solid, then apply unmult.
the flare will now be on a transparent background (click the checker board button to see). when you render, render as lossless with alpha, setting the colors to millions+, rgb+alpha and straight (unmatted). this will give you a ‘keyed’ mov to take into premiere.
Kevin Camp
Designer – KCPQ, KMYQ & KRCW -
An alternate method to this that would give you a less desirable result (so why am i mentioning it?!) is to duplicate your lens flare layer and make it a Luma Track Matte for the original lens flare (assuming they’re both on black solids).
You could also pre-comp the layer and apply Channel > Set Matte to it, then set it to take its alpha from its own luminance.
Just an exercise in thinking through the problem =) The problem with these approaches is that there would be black fringing around the flare, which would not appear with unmult as it removes the black from the image.
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA -
Thanks for the Unmult link. That is exactly what I was looking to accomplish without the plugin.
But, I’m not sure I understand the last post about alpha. If I compost a lens flare against a black background, the black background will essentially be pulled as an alpha key and when imported to, say premier, as long as it was compiled +alpha, premier should see that alpha and only display the lens flare. Is that right?
This still doesn’t solve the problem of a multi layer project that I want a lens flare on say layer 3, If I create a new black solid layer on layer 3, and change the mode to multiply, it darkens all other layers below. It sure would be nice to not have to pre-comple the lens flare (or other effect for that matter) before being able to apply them as an effect on a transparent layer in a comp. But that’s just the AF workflow, so no biggie, I’ll work around it.
Thanks for the insight!!
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[sjohnson] “But, I’m not sure I understand the last post about alpha. If I compost a lens flare against a black background, the black background will essentially be pulled as an alpha key and when imported to, say premier, as long as it was compiled +alpha, premier should see that alpha and only display the lens flare”
i believe darby was just pointing out another method to create the layer transparency needed to be able to render an alpha channel with the file (to be imported in premiere). ae will not render and alpha channel if the flare was composited (applied) on a black solid, unless you can remove the black, which you could do if you created a matte for it, or used unmult.
[sjohnson] “This still doesn’t solve the problem of a multi layer project that I want a lens flare on say layer 3, If I create a new black solid layer on layer 3, and change the mode to multiply, it darkens all other layers below. It sure would be nice to not have to pre-comple the lens flare (or other effect for that matter) before being able to apply them as an effect on a transparent layer in a comp.”
actually, you should not need to pre-comp the flare, apply the flare to a black solid, then apply unmult to the same solid (after the flare effect). now when you render to a codec that supports alpha, and select to render the alpha in the output module settings, your rendered file will maintain the transparency of your comp.
Kevin Camp
Designer – KCPQ, KMYQ & KRCW -
[sjohnson] “This still doesn’t solve the problem of a multi layer project that I want a lens flare on say layer 3, If I create a new black solid layer on layer 3, and change the mode to multiply”
Why would you set it to multiply? Here’s some quick theory in Blending Modes for AE. Firstly, RGB values are represented internally as values between 0 and 1 (working in non-HDR). Each of the blending modes uses a fairly simple function to blend RGB values together. So for a pixel on the layer you’ve applied the blending mode to (A) and the pixel ‘below’ this layer (B) you have these very simple functions (as well as slightly more complicated ones):
Add
A + BMultiply
A * BYou can read up on all of the blending modes at:
https://livedocs.adobe.com/en_US/AfterEffects/8.0/WSFB0FE760-71F3-4616-AE88-275D718E7125.htmlSo basically, if you are Adding a black pixel to a white pixel:
[0,0,0] + [1,1,1] = [1,1,1]
You get a white pixel, since adding black is adding 0 to the RGB channels it has no effect on the underlying pixels and becomes transparent. This also occurs with Screen.
On the other hand if you Multiply a black pixel and a white pixel:
[0,0,0] * [1,1,1] = [0,0,0]
Since any number * 0 = 0 it’s easy to see that black wins here. Also, any number * 1 = itself so white becomes transparent with this blending mode since the result of multiplying the underlying layer by 1 is equal to the values in the underlying layer.
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA
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