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Filed under: Lighting •Motion Graphics •Visual Effects •

Lurking in the Shadows

The second stop in our overview of 3D lighting in After Effects is the subject of shadows. In the Dark Ages (before version 5, when After Effects got 3D), in order to fake the all-important perspective clue of one layer darkening another layer behind it, we needed to use plug-ins such as the stock Drop Shadow effect, Real Shadows from Red Giant Software’s Image Lounge, and CC Radial Shadow (formerly part of Cycore Cult FX; now included with After Effects). With the introduction of 3D space in After Effects back in version 5, the correct casting of shadows between layers became somewhat “automatic” – as long as you know how to set it up.

One of the main points we drilled home last month was that the way lights interact with layers relies on the settings for both the light and the layer. This is also the case with shadows. Several items need to be set up properly to see a shadow:

• The Cast Shadows option must be enabled in the Light Settings (the default is the last setting you used).
• The layer receiving the shadow must have its 3D Layer switch on, and have Accepts Shadows set On in its Material Options. The default is On, but it will be Off if you duplicated a layer that had Accepts Shadows set to Off.
• The layer casting shadows must also have its 3D Layer switch on, and have Cast Shadows set to On or Only in its Material Options. The default is Off, which is probably the first “gotcha” most encounter when trying to set up shadows.
• The light and layers must be positioned in a way so that one layer is between the light and the second layer, and there is some distance between the two layers. This is the second gotcha most encounter, as new layers default to being the same distance from the viewer in Z space – and if there is no gap between the layers, you won’t see a shadow.

One other point: The light must have its Type set to anything but Ambient, as ambient lights are everyone, and by definition cannot cast a shadow from one layer onto another. If you are new to experimenting with shadows, start with the Light Type set to Point , as you don’t have to worry about aiming it – it shoots rays in all directions.

Shadow Size

Two conditions determine how large a shadows appears to the viewer: the Light Type, and the relative positions of the light, camera, and layers.

Spot and Point lights shoot light rays out at angles from a central point. The further away you are from a Spot or Point light, the more spread out its rays are. When using these Light Types, if the light is closer to the layers than the camera is, the resulting shadow will appear larger than the layer casting the shadow. For really exaggerated shadows, cozy the light right up to the layer casting the shadows.

On the other hand, if the light is further away from the layers than the camera, the resulting shadow will appear smaller than the layer casting the shadow. Depending on how the layers are positioned, the layer casting the shadow might then completely obscure the shadow itself. This is another reason why shadows can seem to be “broken.”

Parallel lights shoot their rays all in the same direction – they don’t spread out over distance. This means that the shadow received by a layer is exactly the same size as the layer casting the shadow. But – and this is a big one – the shadow appears smaller when viewed by the camera. This is because the layer receiving the shadow is some distance from the camera, and the further away that layer is, the smaller the shadow will be scaled down through the natural effects of perspective distortion. As a result, parallel lights can’t cast shadows that appear larger than the layer casting the shadow.

Of course, shadows can be distorted into appearing larger. This happens when there is an angle between the layer casting and the layer receiving the shadow, such as in the illustration at the top of this page – think of the long shadows you cast on the sidewalk early or late in the day, when the sun is low in the sky. The bottom line is, in contrast to plug-ins where you can edit a parameter for shadow size, you have to carefully manage the positions of objects in 3D space to get the size of shadow you want.

next page: shadow detail and color

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