I am rendering a material using opacity and would like to be able to save the render element for tweaking in photoshop. The object is the water fountain and the MaterialID grabs the entire plane. How can I save a Render Element with the opacity in the material to select it easily later in post.
Is the water dropping down a texture mapped onto a plane ?
If that is the case then the materialID is doing its job correctly. It cannot distinguish each drop of water on the texture map and create a seperate id for it. You would either need to turn the water droplets into geometry (particle system), or better still would be to just render out the plane on its own with opacity and save as a png or some other format that has the ability to produce an alpha channel with it