Need an alpha from fractal noise?

[Kevin Camp]

if you are having trouble creating the transparency in the comp prior to rendering, there are a few ways to create the transparency from a layer…

track mattes are usually effective. for this you need to place one layer (or precomp) that will act as the alpha above the layer (or precomp) that you need to apply the alpha to. then in the modes panel for the lower layer, choose luma matte (above layer name) from the track matte dropdown menu.

the set matte effect should also work well here. apply set matte to your final worm hole layer (or precomp), set it to use either itself or another layer (or precomp) as the source, then set ‘use for matte’ to luminance.

not knowing how your comp is structured or exactly what you want to make transparent, its a little hard to give an exact procedure, or which method may be the better way to go for you, but the basic idea is to create your ‘fill’ and ‘matte’ then apply the matte to the fill. then render as dave discussed.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[Adam Taylor]

Thanks Chaps…good info.

Export – wrong terminology, sorry (still had my FCP head on). I always render out Animation if an alpha is needed or 10bit uncompressed if its a finished composition. Problem with this one, is that the alpha was appearing as completely white.

I have always been a little confused by track mattes, but that info does help clear up a few questions.

My aim was to use the grey scale info from the Fractal Noise effect to create the alpha channel, as well as being the basis for the coloured effect. I just could not figure out how you took the luma from an image and used it to create the same clips alpha. I will give your suggestions a try later on….but i am already confident they will do what i need.

regards
Adam

Adam Taylor
Video Editor/Audio Mixer/ Compositor/Motion GFX/Barista
Character Options Ltd
Oldham, UK

[Jack Leto]

I just could not figure out how you took the luma from an image and used it to create the same clips alpha

you can use FCP’s composite mode ‘travel matte luma’ to create an alpha channel. in fact you could do all of this in FCP, it’s pretty close to the same concept Kevin is talking about in AE. there are pros and cons to either workflow.

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MOTIONOLOGIST
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[Derek Wolfe]

Use knoll light factories unmult, you can download it free from their website, that will extract it luminance values similer to what it does with lens flairs.