Pre-Comp with Transparent Background?

[T0x1cNugget]

I have tried animating a pre-composition with the magnification effect, so far I have had to use the screen effect to take away the black background originally there although that also makes the rest of the pre-comp slightly transparent. I discovered the checkbox at the side of the layers (which looks a bit like a sun?) that takes away the black background. However, when adding an effect to animate the black background comes straight back. Can someone help me get rid of this while being able to animate?

[Dave_LaRonde]

You can mask the background, key out the background, roto out the background... it all depends on the nature of the shot.

But you CAN'T get rid of the background with a blend mode.  That won't work with a precomp.  It will work ONLY on the right kind of footage layer.

[Roei Tzoref]

However, when adding an effect to animate the black background comes straight back. Can someone help me get rid of this while being able to animate?

if you click on the sun (collapse) to preserve the precomps blending mode, you can't add an effect.

it's written here: Precomposing, nesting, and pre-rendering After Effects compositions "When a closed mask (with mask mode other than None), a layer style, or an effect is applied to a nested composition with collapsed transformations, the layers in the nested composition are first rendered on their own, then masks and effects are applied, and then the result is composited into the main composition. This rendering order means that the blending modes of the nested layers are not applied to any underlying layers in the main composition, and that 3D layers above and below the collapsed layer cannot intersect or cast shadows on each other."

show us the exact setup you have there (screenshots/video capture). there are many ways to achieve and effect and if we know more, we could offer the proper workflow.

[T0x1cNugget]

Hi, so i put this comp together which is identical to the problem I am having, I have an image that originally had a black background, I tampered around with some effects, used the screen blending mode to take it away and make them transparent around the outside. After that, I pre-comped them which brought me to the black box around the pictures, here is a test comp:

How do you think I should get rid of the black without using a blend mode?

[Dave_LaRonde · Accepted solution]

I repeat: DO NOT try to do this with a blend mode. 

Probably the easiest way to do this would be to use AE's Extract or Luma Key effects.  A blend mode will not work.

[T0x1cNugget]

Thanks, I tried using Luma Key and that got me exactly what I wanted!

Thanks again!

[Roei Tzoref]

How do you think I should get rid of the black without using a blend mode?

just don't click on the sun icon and set your blend mode for the precomp

of course this means that all the elements inside that precomp will be treated as one composite with the screen applied. if you want to not be limited by all of this, just remove the background in Photoshop using color range or other extraction process and save as a PNG file that supports transparency. and there's always effects right in Ae that can extract based on contrast. one is called extract

[T0x1cNugget]

I couldn't import it into Photoshop because my actual composition consisted of two pictures with spectrums and stuff, although in the end the Luma Key effect got me exactly what I want

Thanks for your help Roei!