Trying to figure out the best way to add a glow effect in cycles, but only on the hexagon-sphere. I’ve assigned a glare → bloom in compositor but of course that makes everything bloom a bit. Part of the effect is behind the monkey and part is in front… ideally the glow would only be on the opaque hexagons. Is this a case for cryptomatte or view layers? Any advice or tutorial info would be great! Thanks!
If hexagons have their own material (or they are separated objects) then cryptomatte could be an easy option.
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If the emission strenght of the hexagons is higher than the rest of the scene it’s easy to separate it from the rest using a high value for the threshold on the glare node, this is how I usually setup the glow in the compositor
And yes, you can also use cryptomatte to separate just the hexagon material and add it on top of the render
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Oh, is that how it’s supposed to be done? I’ve always just multiplied the cryptomatte mask with the image before going to glare, and it has worked well in my circumstance. Any reason this way is a better one?
Btw, I also isolate a center of spotlight “disk area” and send it to a shader AOV that I use as a mask (also via multiply) for glare node in spike mode. Allows very thin “diffraction spikes”.
I wouldn’t say it’s better or correct hehe, it’s just how it made sense for me when I started to do some basic compositing in Blender before jumping into another software, coming from an After Effects background this method clicked easier for me. But your method of multiplying the cryptomatte over the image sounds like it could give you the same result in the end, I think?
This sounds pretty interesting! Thanks for the tip, I’ll try it out at work 
Multiplying the image with the matte is the exact same thing as using that Set Alpha, since the way you apply a mask to an image is by multiplying it. Same operation, different nodes. You could also use a Set Alpha Replace Alpha followed by an Alpha Convert Straight to Premultiplied—once again the same thing. There tend to be a lot of different ways to do the same thing in compositing, and it often just comes down to preference.
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Ok, thanks. I guess I was just surprised as I’ve been using Blender since 2.72’ish, and never seen that comp node before 
Learn something every day.