Anyway of creating a "wetmap" in AE?

[erilaz]

Well, if I understand you correctly you could just use the liquid as a separate alpha matte on top.

[thethule]

Ok. Imagine i have a very simple scene of a drop of red paint going from top to bottom. I have animated that drop and have it rendered with alpha but have not created a wetmap that will allow me to bring in a red background colour (the trail that the drop would leave).

The wetmap (or wet mask) would basically start off black and then have a white long trail appear anywhere the drop went over, in this particuar scene, it would be a white line appearing from top to bottom.

Realflow can create this mask for you, but i didnt turn that option on and dont want to have to recalculate as it is a fairly complex scene with paint splashing onto a floor. The problem is at the moment, the paint isnt leaving the floor red where the paint has flowed over.

So, im wondering if there is a way to generate a sort of "additive" mask...in the simplified case of the single drop falling down, it would be generating a straight vertical line...

Hope i explained it a bit better.... if not, ill try to get images up as examples.

cheers for the help guys...

[Mylenium]

I don't really follow. It sure would be possible to create something for a simple map, but for a complex scene? You would have to have an unwrapped UV layout of all the items being touched by the paint and then engineer your way around it. Not for the faint hearted, for sure. I also think you are trying to attack this in the wrong program. It would be much simpler to e.g. use a 3D program, pop in a light and render out some shadow maps from your simulation which then could be tweaked...

Mylenium

[thethule]

unfortunately, i did it in Realflow a few months ago and deleted the 3d meshes as they were taking a LOT of room. So i dont have anythign useful to use in 3d anymore. To explain better here are some vids:

-This is (for the sake of simplicity) what i have now, a red ball of paint going down a wall

http://uk.youtube.com/watch?v=sV5iMzvqt6k


-This is what i want to do, have it leave behind a red trail. I would basically use a b/w mask to reveal a red layer in after effects.

http://uk.youtube.com/watch?v=x5hyR5yiQng

-This is the alpha as it is now

http://uk.youtube.com/watch?v=wQfbSQBc8uI

-This is the alpha i would like:

http://uk.youtube.com/watch?v=ojo4VEdHgUo


And finally, this is the actual video that i am going to be using this technique on. As you can see the blood (paint) doesnt leave red trails on the floor. The client didnt want it too, but i think it will look a LOT better, so for my showreel, i want to amend it (if possible)

http://uk.youtube.com/watch?v=Rd5KKOGwt2E


Any ideas?


Thanks again

[Khalor]

Possibly some kind of Time Echo effect (masked to affect the floor only) to create an alpha channel that 'echoes' where the particles have been. But with the bounces and such that occur with the impact on the floor, I don't know how effective it would be.

[Mylenium]

Yes, I agree with Khalor. If you only have the 2D representation, a Echo effect or something that does pixel motion tracking (Twixtor, for instance) is pretty much your only option. I'd use Shift Channel and similar effects to isolate the red areas, then accumulate the map based on that.

Mylenium

[thethule]

Damn....i was hoping for a nice simple solution. Ill look into twixtor, i have heard of it, but never played with it. Thanks for the replies guys, ill let you know how it comes along.

Marc

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