quite a newbie to Blender, I started to fiddle around with compositor and created a scene, where a material is illuminating light itself. To enhance the light effect, I moved the mesh with the emitting material to a different RenderLayer, added a blur effect and mixed back together (tried mix and alpha overlay).
However, as the blur effect is rendered separately, as soon as I mix, also parts of the scene (assigned the illuminating material) that should be rendered behind other meshes were rendered with the blur and got mixed atop.
How can I mask / restrict the blur effect to only visible parts in combined scene? is the separate RenderLayers the right approach at all?
I added a rendered output to better visualize the problem. The marked lamps are actually at the back and not visible from that angle. However, the blur of the lamp RenderLayer mixed put the “glow” on top. see http://i.stack.imgur.com/yJoue.png
You could just render the whole thing in one go and use the threshold setting to only put glow on the emitting objects.
But to composite like you are trying to do, I think you need to mask the emitters with the other object, so that only the parts that are visible in front of it will be rendered. Then just use Glow node on that render layer in the compositor, and alpha over onto the main object.
Didn’t fully understand your first sentence? Which threshold? The one on the Glow Node? I used Blur to add the glow effect in Compositor, but GlareNode looks smoother on some emitting objects.
