surface force

[Tomb]

Hi Ya,

I'm just playing around with spawning particles on a teapot making them flow around its surface and then adding from their movements. I'm using a b/w bitmap to control the flow. 

I'm wondering if there any way to use the same bitmap to control the spawn location (say only the black areas) and have the particles flow only on those. 
I'm using the gradient ascent and gradient trace in the surface force, and it might be working. However, because it's spawning all over, I can't tell.  

Thanks