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AE CS5 Cast Shadow Transparency

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James MehorterAE CS5 Cast Shadow Transparency
by on Jan 25, 2011 at 3:17:53 pm

Hi Everyone,

I'm creating a series of motion graphics to overlay on a video I'm building in Premiere CS5. For all my AE comps so far, I just save the .aep file, and import it into Premiere. This lets me go back and forth making adjustments, and Premiere auto updates. K, great..

My last motion graphic clip uses a 3D scene, with a spot light pointed at an object, thus casting a shadow onto a backdrop. I want to overlay this clip in Premiere, without the backdrop. I want to keep the shadows, so it looks like the motion graphic clip is sitting on top of the footage.

Exporting as Animation with RGBA only provides transparency to the negative comp space :( Is there a way to turn off visibility of the backdrop, but still allow it to accept shadows? In Maya, for example, you can just set an object to accept shadows, but have no visibility. I tried setting the backdrop to white and turning the blending mode to 'Multiply' but this has no effect :\

Any ideas? Thanks!!


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Michael SzalapskiRe: AE CS5 Cast Shadow Transparency
by on Jan 25, 2011 at 3:50:57 pm

Short answer is "no you can't do it". Long answer is, "Yes, but you may have to render out of AE and it may get a bit tricky."

There's probably more than one way to do it...lemme have a think...

Okay, You'll need a duplicate of your 3d comp. This one is intended just for the shadow so make everything white except for the shadow.
Bring that comp into your main comp and apply unmult to it (free effect from Red Giant, if you don't already have it). That should get you your shadow on a layer all nice and transparent. (You may need to mask off bits that you don't want showing up...
You would then be able to import that into Premeire as usual.
There! Done with no rendering out of AE.

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

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Tudor "Ted" JelescuRe: AE CS5 Cast Shadow Transparency
by on Jan 25, 2011 at 3:55:00 pm

Quick work around:
Set the layer on which the shadow are cast (the background/floor) to be a solid color that you can then key out. Make the size big enough to fill the frame at all times. Make sure that in Material Options the "Accepts Lights" is off. This way you will get a solid color with no gradients. Precomp and Key out the color.
My question is why don't you composite the gfx over the footage in AE and then render out the final - no editing software will do as good of a compositing job as a compositing software package.

Tudor "Ted" Jelescu
Senior VFX Artist

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James MehorterRe: AE CS5 Cast Shadow Transparency
by on Jan 27, 2011 at 1:42:58 am

Thanks for your replies everyone! I tried each method you all posted, and ended just importing the video clip to AE and building the effect there, as Ted suggested. I can still import the .aep into Premiere, and make back and forth edits. Duh! :p Thanks again!

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Kevin CampRe: AE CS5 Cast Shadow Transparency
by on Jan 25, 2011 at 4:12:05 pm

i don't know of any way to do this a a single step in after effects...

what you can try is to create a shadow comp, by duplicating your current comp, setting the 'cast shadow' property for the layers that you need to create the shadows to 'only'. then set the shadow catching layer (backdrop) to white and to not accept lights, but still to accept shadows. hide any other layers that you don't need, so you should only see the shadow on white (you may need to set the background color to white also).

in the original comp, you'll want to hid the backdrop layer and bring in the shadow only comp. to the shadow only comp, add channel combiner setting from 'luminance', to 'alpha' and check 'invert'. then add the remove color matting and set it to white. note, if you're color settings are higher than 8-bit, there is a different recipe to get the shadow alpha that can keep things 16 or 32-bit.

now you should be able to see the transparent checkerboard pattern if you toggle it in the preview window, and it should render how you want it with rgba for premiere.

Kevin Camp
Senior Designer

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