2D transparent Silhouette in one pass?

[Streetwise]

I'm looking for a way to generate a matte for a silhouette without the silhouette actually being rendered. The goal is to create a transparent silo. Currently, it's a two-step process for me: Render a clean plate, render the 2D shape mask, merge in Photoshop. It seems the moment I turn off "visible to camera" for the silo person, all hope is lost. I've tried using a MultiMatteElement, but no luck. I've also tried using LightMtl. Still no luck. Other cool tricks?

Thanks

Dave

[dgruwier]

I don't know of a trick to do this, but I'm curious, if all you want is a transparent silhouette, why not just make a transparent material for it?

[Morne]

I don't know of a trick to do this, but I'm curious, if all you want is a transparent silhouette, why not just make a transparent material for it?

yes, I'm wondering same thing.
If you merging anyway, why not just render it in 1 go?

[super gnu]

i expect its because semi-transparent materials look awful? you see all the back faces and internal structure. i assume hes after a flat semi transparent silhouette.. a shader to do this would be great.. u could then get reflections and shadows correct. but as it is, whenever ive done this, rendering seperately is necessary.

[Streetwise]

All good thoughts. Yes, the model is a shell, so a transparent material looks really bad. I had thought about a 2-sided material as well. About as close as I've gotten is using v-ray Light material (attached in the original thread) but no way to make it transparent.

Ideally, what would be really cool, Chaos, is to create a render element where you can select hidden geometry or "invisible to camera" geometry to create a mask.

[dlparisi]

Here you go...

Diffuse: Black
Reflect: Black
Refract: however transparent you want your silhouette (usually higher values work best)
Refract IOR: 1
Self Illumination: Usually around mid gray with Compensate Exposure checked (if your on Next which makes it a little easier)

Wrap this whole thing in a VRayMtlWrapper and uncheck "Generate GI" and "Receive GI"

Lastly, uncheck "Visible to Reflection/Refraction" in Object Properties along with "Cast Shadows" depending on your needs.

I think this rough technique was posted here years ago so I can't take the credit for it.

You can also add a VRayToon to get some nice outlines if you want. Just be sure to check "Hide Inner Edges".

[Streetwise]

@diparisi you are brilliant! (even though you're not taking credit). I did a slight variation in NOT using Self Illumination, plus Refraction to pure white, so as to get a clean plate without the silo. Then assigning a material ID to the VRayMtlWrapper, I was able to use MultiMatteElement to pull a mask for the silo. This way, I can have a lot more control over masking and blend modes.
I'm going to experiment a bit more, but this for sure is headed in the right direction! A million thanks for pulling this info from the past!

Dave

[Streetwise]

Going back to my comment of blending modes: On the left is the original image where I combined two separate renders. On the right is the method that @diparisi described, with the blending mode set to black (0). The result is fantastic, but I feel like I'd like to have even more control over the blending mode. So with turning off self-illumination, I think that's going to work better for my needs Note: The image on the right have VRayToon enabled just to see what that's like.

[Streetwise]

Here's another question:

Is there a way to put VRayToon on a separate layer, or assign a material ID that could be picked up by a MultiMatte? It would be nice to render out a clean plate, but have a mask option for the outline...