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Filed under: Lighting •Motion Graphics •Visual Effects •

Gobos and Gels

Gels

There are several ways to approach recreating a gel effect inside After Effects. If all you need is a simple color to be cast by the light, use the light’s Color parameter. Note that you can animate this color to change over time.

A significant feature added back in After Effects 5.5 was a new Material Option for 3D layers called Light Transmission. It defaults to 0%, which means the layer will cast a black shadow (as long as you have enabled its Casts Shadows option – remember, this defaults to being Off!). Increase this value, and the shadow takes on more of the color of the layer. In other words, this feature casts colored shadows. Place a layer where it completely “blocks” the light, and those colored shadows become colored light…to a degree. Shadows always reduce the intensity of the light, just as a physical gel in front of a light does in real life. Be prepared to increase the Intensity parameter for your lights to compensate. You can also decrease the Opacity of the gel layer, which results in a more washed-out (or less intense) effect.

An image of a woman (above left) is used as a gel by increasing its Light Transmission parameter to 100%. When cast onto a simple set of white squares placed randomly in 3D space (above), the result is a fractured image as the squares catch pieces of the gel image at different distances and angles (left). Image from Digital Vision’s Beauty CD.

To recreate a simple gel, make the gel layer a colored Solid. If you want a multicolored gel, apply the Generate > Ramp or Generate > 4-Color Gradient effect to the gel layer. Or, for the maximum in fun, use an image or movie with an interesting colored pattern as your gel layer. This becomes the same as projecting a movie or slide onto your scene, and was shown back on the top of the first page of this post.

If you use a Light Type of Spot or Point, the light’s rays – and therefore, projected image – will spread out as they travel further away from the light, meaning the resulting image will appear different sizes on layers that are different distances from the camera. (The one exception to his is if the light and the camera are both the same distance from the layers.) Move the light closer to the layers than the camera to make the projected image appear larger on layers that are farther away; move the light back to make the projected image shrink with distance. If you use a Light Type of Parallel, the projected image will always appear to shrink with distance.

Managing the relative position of gels is the same as gobos: We suggest parenting the gel layer to the light, and moving them as a group. If the gel layer becomes visible in the scene, and you don’t want it to be, set its Casts Shadows option to Only. You can even use gels as if they were gobos: If a portion of a gel layer set to 100% opacity is black, its shadow (and therefore projected light) will be black, even if its Light Transmission value is cranked up to 100%. The black areas of gels therefore act the same was as opaque areas of gobos, with more control in that you can tint the gel layer to get colored “darkness” (such as inky blue or dark sepia shadows).

2D Trickery

3D lighting in After Effects is powerful. However, this power comes at a considerable cost when it comes time to render – especially if you are using shadows (which the gobo and gel tricks described here require). If render times become an issue, ask yourself if you need exactly the effect produced by accurate 3D space, or if an approximation that hints at 3D will do.

For example, many gel and gobo-like effects can be faked by placing a 2D layer on top of a composite, and applying it using different transfer modes. If you want to give the impression of this “light” being bent by the objects it is “illuminating,” bring your final comp and the lighting layer into a new comp, and use the Displacement Map effect to warp the lighting layer based on the image from the final comp. Similar looks, as well as other shadow casting tricks, can be created using third party effects such as Composite Suite from Digital Film Tools.

Remember: In motion graphics, quite often you aren’t trying to create reality; you’re trying to create something even cooler than reality – so go ahead and experiment with all of the tools at your disposal!

The first installment in this series - an overview, with helpful information on the Material Options - can be found here. The second installment - which focused on tips and tricks for conventional shadows - can be found here.

The content contained in our books, videos, blogs, and articles for other sites are all copyright Crish Design, except where otherwise attributed.

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