Creating a “halo” effect for a material in cycles?

Question

I'm trying to achieve an effect similar to this image:

However it's looking more like this:

No halo; the material ends where the mesh ends.

How can I set a material to look like the first image?

Thanks in advance.

Answer 1

This kind of effect is usually created in post processing. In Blender's compositor I found that the Filter > Blur node gives a result quite close to what you are looking for, though the Glare node may also work.

Just go the the Node Editor view, switch to compositing nodes, and drop a Blur node in between the Render Layers and Composite nodes. I found that using Fast Gaussian seems to produce the best looking effect.

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To get that even wider glow you can add a second blur node with a much larger blur and mix it with the smaller blur. Set the mix mode to Add and adjust the Fac slider to suit your tastes.

Click to enlarge.

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For the actual mesh I just used the IvyGen technique outlined here with a very strong volumetric emission shader (and no surface shader).

Answer 2

You can accomplish this in cycles. But you have to add a little bit more geometry.

The easiest way for me to imagine you starting to experiment with this method is:

1. Try adding a cube that encompasses your lightning tree.
2. Shrinkwrap the cube to your tree, make sure to add an offset.
3. Add a new material to your shrunkwrapped cube.
4. Add an Emission node.
5. Plug it into the volume of the material output.
6. Set emission color to a darker royal blue.
7. Set emission strength to 1.0

APPENDING RESULTS OF COMMENTS BELOW:

1. Create the Tree with extruded Verts.
2. Add Skin Modifier.
3. Duplicate this object (Original Object = RED, Duplicated Object = YELLOW).
4. On the YELLOW object, apply the skin modifier.
5. Then add the Solidify Modifier, and set offset to one.
6. Add a Subsurf Modifier to the RED object.
7. Apply the material setup as shown to each of the objects.

The results are obviously a starting point to tweak for the look you want. However this is a pretty decent one, considering it needs no post-processing in the compositor, unless you really need to pull off the blurred effect.

@MrZak Thanks for the input.