possible to apply a gradient to opacity?
 

Hi I have a video of some smoke that I would like to appear to get thinner as it moves towards the sky. Is it possible to set the opacity level at the bottom of the clip to say 50% and have it diminish to 0% the nearer it gets to the top of the video?

Any help would be greatly appreciated!

David

In AE you can apply a black to white ramp to one layer and then use that as a matte layer for your smoke.

Connor,

many thanks for your prompt reply. I havent had a lot of experience in mattes but I will certainly give this a go, it seems to make sense. Would be even better if I could link numerous smoke clips to the same full screen matte.

Thanks again
David

Yep, that can be done. You can make any layer a matte for another, and one layer can matte as many layers as you want. You can also precompose all the smoke into one layer and matte just that one.

Most editors will allow you to apply a gradient as a "luma mask". This will do what you're looking for without having to go to an outside program.

i do not see the reason of doing it after the shoot.
the filter will just make all the picture darker, including the smoke, so it will not increase contrast between smoke and background, just make it darker.
you should have put a real filter while shooting (and even there, the effect is almost the same).
the correct solution would be to put a light on the smoke.

What editor, specifically, do you use for editing video? Final cut, vegas, premiere...other ;) We could get you specific directions for how to make a luma mask for this effect.

I haven`t found a way to do that in AE 7....care to enlighten?

Of course...I phrased it a little bit incorrectly though (damn memory)...

First way, really clunky - say you have three layers. Your top layer, 1, is the matte layer, your black and white ramp. layer 2 and 3 will be matted. set layer 2 to a luma track matte (the matte being layer 1). Layer 3's matte must be layer 2, the alpha channel of which has been affected by matte 1, so set the next matte (for 3) to an alpha inverted matte. Repeat. It can get really tricky to manage, as you have to flip between alpha and alpha inverted as you go down, so it's better to use the...

Second way, much better - put all your layers into the comp. Put the ramp on top and set the blending mode of that layer to stencil or silhouette luma. Do other stuff in this comp, or nest this as a layer in the next comp. This is much better because it's easier to go back and adjust.

Third way, meh, why not? - Place all your layers in a precomp, bring that into the next comp then do the above, or mask.