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Custom particles and alpha channels

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Chris Poisson
Custom particles and alpha channels
on Nov 15, 2006 at 3:15:32 am

I'm fooling around with some greyscale tiff images of snowflakes, say 8 or 10 different ones, which I will put in a precomp to use as custom particles. These are pretty much white on black, my question is do I have to imbed alpha channels in the tiffs to make the snowflake's edges transparent or what? They are around an inch or so in diameter floating on about a 3" black square, right now they're 150 dpi.

Also, instead of precomping them, does it make any sense to import them into QT as a sequence and make a movie out of them? Do the number of frames of each image make a difference in how they animate?

Or would it be better to put them in a precomp so that I could make each one behave differently, say spinning or rotating?



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Mylenium
Re: Custom particles and alpha channels
on Nov 15, 2006 at 7:27:32 am

Yes, you need proper Alpha on them. There is no magic trck that can do that for you. Since you are using greyscales, simply use a duplicate of each layer as a track matte or get yourself an unmultiplying plugin such as Knoll Unmult, XMult or Walker Alpha Tool. It doesn't matter whether they are a comp or a footage item, so rendering them out wouldn't yield different results. Just animate them in your pre-comp as you need.

Mylenium

[Pour Myl


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Chris Poisson
Re: Custom particles and alpha channels
on Nov 15, 2006 at 2:06:13 pm

Mylenium,

Thanks, I was playing around with it last night and tried Unmult and it worked great, just a couple other things, does the number of frames on each snowflake impact the speed of the emitter? What else changes the speed of the emitter, I tried velocity and it didn't do much, I want the snowflakes to fall really slowly.


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Mylenium
Re: Custom particles and alpha channels
on Nov 15, 2006 at 3:43:09 pm

In your case you shouldn't use velocity at all (I know I sound like a broken record). Just use a box emitter that covers the width of your comp and have the particles fall driven by gravity. In addition animate the Wind X to and fro to get a slight swaying in your snow. Use Air resistance to balance speed against viscosity. The length of the clips does not matter that much, it's only relevant if you use the split clip methods and have all of your different flakes in one sub-comp (looking up "remote" frames that are not at the current time can take a moment, but isn't usually a problem).

Mylenium

[Pour Myl


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Chris Poisson
Re: Custom particles and alpha channels
on Nov 15, 2006 at 10:13:37 pm

Mylenium,

That all makes sense, thanks much.

As it turns out, I think I'm gonna just put one flake in each comp and have it tumble and set up several particle layers to mix with each other. But all this you've given me is great.


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