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July 20, 2005

the blizzard effect

by sven at 1:09 am

Well, I still need to tweak the shot where the explorers first enter the cave so that you can see the blizzard outside behind them -- but other than that, I've got blizzards everywhere else I need them.

shot 1: establishing shot

shot 2: Carl steps out of the mist

shot 3: Carl discovers the cave

Now I can start fretting about whether I should start instead with the shot of Carl stepping from the mists. And about whether the levels of blizzarding in each shot match each other. Ugh!

...But before I get into that tizzy -- let me pause and tell you about how I accomplished the blizzard effect.

The blizzard effect involves setting up a partigon emitter, and then having it spew hypervoxel sprites across the screen. Ah, but we don't simply want it to occlude everything -- now do we? The snow in the background should be thicker than the snow in the foreground.

In my trickiest blizzard shot, I want to have the lavaman step out of white-out conditions into the foreground, where he's less occluded by blowing snow. Here's what it took to do that:

Step 1: In AfterEffects, I have a background shot and the lavaman footage in two separate layers. Render out a clip where the lavaman steps forward from the background.

Step 2: Import this first movie into LightWave, and use it as a backdrop. Run the partigon emitter and render out a second movie. Now you have the whole thing partially occluded by blowing snow.

Step 3: Import this second movie back into AfterEffects. Use it as your new back ground, and put the lavaman layer on top of it. As he steps forward, fade the lavaman from 0% to 100% opacity. This will make it look like the lavaman moves from being behind the blizzard to entirely in front of it -- and outside of the blizzard entirely, in fact! Render.

Step 4: Import this third movie into LightWave, use it as the new backdrop. Tweak the emitter and hypervoxel settings to create a less dense, more flakey snow. [That in itself is something of an art!] Render. Now you have the lavaman stepping forward from dense blizzard into the lighter snow of the foreground!

...Nifty trick -- but the devil's in the details. With two layers of snow, it's easy to totally obliterate the original background. You still want it to show through enough that the audience can still interpret what's back there. Also, creating different textures of snow for the foreground and the deep field -- pretty challenging.

Worth noting: As is, the skies in my landscapes are too blue for a blizzard. I applied the blizzard effect in LightWave to create a new still, then merged this with the original in PhotoShop to create a whiter, cloudier sky. My sense is that the modified landscape image now gives an adequate sense of snow hanging in the air when the blizzard's blowing across the foreground. At least, that's what I hope.

Guh... Even if I get the process streamlined, it's probably going to take at least five hours to assemble each blizzard shot I do. And that's presuming I like my results on the first try.


posted by sven | July 20, 2005 1:09 AM | categories: let sleeping gods lie, movies