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Thursday, November 28, 2002

Pulse Rays

How to make light ray effects even cooler.

Radial Noise

At this point, we have some animated “stretchy lines” flowing from the top to the bottom of our comp. However, light ray effects emanate outwards from a center point. To convert our linear lines to radial spokes, we applied the Distort>Polar Coordinates effect, set the Type of Conversion popup to Rect to Polar, and set the Interpolation value to 100%. The result is shown below: What was previously the top of the image is now the center, and what was previously the bottom is now spread around the circular edges. Polar Coordinates works best on square sources; we used a 1000x1000 pixel comp and solid to ensure that the resulting circular noise pattern fully covered a D1-size NTSC comp edge to edge.

To make the lines seen on the previous page radiate from the center, apply Distort > Polar Coordinates, with a Conversion Type of Rect to Polar (left). To smooth it out and add grain, apply Blur & Sharpen > Radial Blur set to Zoom with Antialiasing set to Low (right).

The resulting polar noise pattern looks a bit like the details in the iris of an eye. If you don’t like this much detail, you can experiment with reducing the Complexity parameter in the Fractal Noise effect. An alternate solution we like is applying Blur & Sharpen > Radial Blur with its Type set to Zoom (seen above). This smoothes out the detail in the lines, and if you leave the Antialiasing set to Low, adds a nice graininess to the edges of the effect.

To make the noise pattern appear to grow out from the center, we used a mask to wipe it on. A potentially confusing point is that After Effects calculates Masks before Effects - so although it may look like you should create a circular mask that grows in size to wipe on the rays, this circular shape would be further processed by the Polar Coordinates effect, resulting in something quite different than intended. The solution was to temporarily turn off Polar Coordinates, and animate a mask that wiped on from top (the center point after Polar Coordinates is turned back on) to the bottom. We added some further refinements such as animating the feather of the mask to make the leading edge seem to flow out, and animated the Opacity of the layer to fade it down after the energy pulse reached the outside edges of the circle. This progression is show below:

By animating a mask for the flowing noise matte and Opacity for the underlying light ray, you can get an “energy pulse” effect.

Polar Coordinates and Radial Blur are two of the slower plug-ins in After Effects; Fractal Noise is no speed-demon either. We dropped the comp’s Resolution down to Half while tweaking parameters to save time. Another production trick worth remembering is to render just this comp, setting the Post-Render Action popup in the Output Module to Set Proxy. This will use the resulting movie as stand-in for the comp, making any comp that uses the result much more responsive. If you need to go back and tweak this effect, turn off Proxy by clicking on the black square that appears next to this comp in the Project window, or delete it by selecting this comp in the Project window and using the menu command File > Set Proxy > None.

Final Composite

The hard work is done. To use this flowing energy effect in your own project, set up your light ray effect as normal in its own composition, and nest the flowing energy comp on top of it. Then set the Track Matte popup for the light ray layer to Luma Matte. The light ray will now be cut out by your flowing energy pattern.

This effect looks best if the energy seems to flow from the same point as the light rays. To make this happen, just line up the Position of the flowing energy precomp to be on top of the Source Point for the light ray effect. If you are animating the Source Point, consider creating a simple Expression to tie the flowing precomp’s Position to it: expose both parameters in the Timeline window, select the precomp’s Position parameter and use the menu command Animation > Add Expression, drag the pick whip that appears under the Switches panel for this precomp’s Position parameter to the light ray’s Source Point parameter, and hit Enter.

While working with the client, we decided the effect looked best when this “energy pulse” was composited on top of a normal light ray. To do this, we duplicated the light ray layer. The Track Matte popup for the layer on the bottom was set back to None. We then set the Blending Mode for the matted rays on top to Add, to get a really “hot” look. Of course, you can try other modes for different looks.

Don’t consider the approach outlined here to be the only recipe to create a more animated light ray effect. Our main goal was just to add some motion and mystery to the otherwise-solid rays. An alternate approach we liked was using drifting smoke from one of the Artbeats pyrotechnic collections - as a luma matte for the rays. Other effects that might provide useful light ray mattes include Generate > Radio Waves, Simulation > Caustics, or anything else that creates naturalistic patterns or unnatural “pulses” that can add motion to the rays. Experiment, have fun, and share what you learn with others!

Click here to download a project file for this technique.

Motion Graphics •

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Fractal Noise Tutorial

Chris and Trish Meyer | 08/04- 10:38 AM

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