Hey all !
I’m now working on a short film (graduate movie for school
)
We have a lot of forest/trees,
we decided to use matte as possible for the background, leaves mass for the middle/back, and handmade 3d leaves for the foreground.
Now i’m testing some rendering about the masses, we would like to translate this kind of 2D look into 3D (not realistic) :

look at the background red mass of leaves, not so much details, but a bit crispy, and with translusence on the border.
So I thought about using Maya particlesClouds to get a sort of cotton/cotton candy , but not so realistic. After few test, i got a shape that i like for a beginning :

at this point there is no lights, so no question about lighting/translusency already.
So i tried to import it in a scene, with a basic direcitonnal light, i like it cause it’s kind of fluffy, and the tree can desapear trough the mass, here ine the viewport I guess you see what i mean :

Proble, when I render, i get more longer render time (because of the light i guess, and there are a lot of particles), and i also get BLACKS particles, like if they where full shadowed, it is very ugly, and seems random
:

So i tried to look for a way to disable self shadowing, but did not find, so i went to the MR flags and override for “no shadow” , so i get something closer to when it was with no lights, but stil some artifacts where the tree colide with it :

so, seems buggy…? or is it the tree shadow …? anyway it is ugly, and I don’t have shadows from the mass on the floor anymore.
Here is my particleCloud shader (simple, with a tweaked Cloud 3d texture) :
http://image.noelshack.com/fichiers/2012/46/1352731187-5.jpg
Any idea to solve this ?
Any other direction to get what i whant (translusency, leaves mass, etc…) maybe something less tricky ? I’m open to any suggestion, this topic is as much how to solve my problem as how to do what I want in another way…
thank you by advance 
PS : sorry for my bad english :s