How to get grainy shadows using 3D tools?

[benc53610824]

Hi, 

I'm trying to achieve a grainy shadow effect on an object I've dawn. There are lots of tutorials around for how to achieve this on flat objects using masks and textured gradients, but my objects have been built using 3D tools and lit them using a parallel light, so the shadows are acurately generated based on the geometry of the object. Does anyone know a way to add noise to these types of shadows?

Thanks,

Ben

[Mylenium]

Render the whole thing as a greyscale image in a duplicate comp, extract the shadows using Shift Channels or Channel Combiner, apply whatever effects you want such as Roughen Edges, Fractal Noise, Add Grain, overlay them on top of your other graphic on which you have toned down/ turned off the shadows.

Mylenium

[benc53610824]

Thanks  Mylenium,

Sorry, I'm still a bit of a novice at 3D in AE so this might sound like a dumb question, but will I still be able to animate this afterwards? I don't understand how this will apply the effect to the sides of the geometry. I may need to increase the extrusion or bevel radius down the line, so would be better if there was a procedural way to do it.

[Mylenium]

Of course you should set it up in a way that you have all the freedom to edit it by linking parameters across the comps with pickwhip expressions or simply manipulating the shadows once you have actually finished your main animation. The actual processing of the shadow doesn't care about the specifics since it happens in 2D, only the 3D geometry generation matters.

Mylenium

[Rick Gerard]

If you are working with extruded shapes, you'll need to separate the colors and create some mattes. You can use duplicates and lights to put some keyable colors in the shadow areas. It's going to be a bit of a pain unless you use something like C4D or Element 3D and add texture maps.

If you want regular noisy shadows, try this:

Add a white layer to the comp, make it 3D, set it to Accept Shadows Only, set the layer's blend mode to Multiply, then add Noise Alpha. 

The only effects that will affect a shadow-only layer are the ones that work on the Alpha Chanel. This will give you a noisy grainy alpha.

The only other option would be to duplicate lights, the layer casting the shadow, set that to Cast Shadows only, then pre-compose the Shadow only and cast shadows layer, then add effects to the pre-comp. You can't collapse transformations, so if you have camera movement, you'll also need to duplicate the camera. It's a bit of a mess, but it can be done.