Cineversity

I’m not sure how to ask this because I don’t know what it’s called, some kind of culling effect maybe.

Is there a way to render part of an object as transparent? Not just transparent, but transparent where it would also cause anything behind it to become transparent including the object itself? Sort of like an object buffer just for portions of an object.

here is a photoshopped example of what i’m referring to:
https://www.dropbox.com/s/8nhdrt70x6kx9eq/test-cube.jpg?dl=0

I’m trying to do this as a means for VFX compositing. Imagine a hole being exploded in the middle of a wall where I want to see inside the hole where the damage is but the outside needs to be transparent so the original texture of the wall shows through.

Any suggestions would be great, thanks!

Hi ryanc,

Let’s start with the file you requested via the sketch. This is normally done with the Compositing Tag. Seen by Transparency and / or refraction. Please not as well that the Texture Tag is set to Front or Back. I assume it is a real wall and the CG hole, but I’m not certain, so the following answers one option and I will share another file in a follow up post.

Scene file:
https://www.amazon.com/clouddrive/share/8FwYPVXhyUVKDMxWfypeb619O8n114h6UkgCFbNmOQF

Yes this would be a way to do it, but it might introduce at one point some problems, but I don’t know the scene at all.

How about creating the hole from the start as geometry, and render it without extra steps perhaps in the compositing.
Scene file:
https://www.amazon.com/clouddrive/share/je6yb1pO0gAonR9Pqxxsw5NEEXteHQrD39w91ZWd9H3

Typically this could be done as well with the Voronoi Fracture Object, please have a look at the
scene file:
https://www.amazon.com/clouddrive/share/BFkRbWPEBBQvuG5O32QoB3MQUIlHsvQvk9Xbsi6E7SX

I assume that there are follow up questions, I’m happy to look into them.

All the best

Ryanc,

A more complex, but in my view, more workable scene for compositing would be this set up.
I have included a camera and a back-room, ir either motion tracking was used or the room behind is needed as well. Perhaps it a locked off shot, and things are less complex.

Please render it to the picture viewer and use the Layer>Single Pass view, to see all the parts given.

Scene file:
https://www.amazon.com/clouddrive/share/jwLLYePECMIFu778QcQT9HodLcRNcaKSWoDofEHpwHy

A little overview clip, so I can point out the most important parts:
Please download it for a better viewing experience
https://www.amazon.com/clouddrive/share/ua0UygJAVKYrFNbIrhnocckjvqGgV4XCHD2559J8tNR

It is best practice to focus on the main part that you need and render it with straight alpha, to prevent problems later on.

All the best

Wonderful, thanks very much for your reply. The “matte object” parameter in the compositing tag seems to be working very well for full objects. And the “seen by transparency” method looks like it’s exactly what I was looking for.

You are correct, it would be a CGI hole (and room inside hole) with a video clip of a real wall. Very much like this video at 23 seconds: https://youtu.be/nEzga4IzPZE?t=23 It shows just the hole without the surrounding bit. I was successfulyl able to replicate that with the “seen by transparency” method you posted. I’m using R14 so I don’t have the voronoi plugin. (I have used it thought, it’s awesome) So I can’t see the project you posted for that, but I am using the “Thrausi” plugin to break apart some objects.

THanks for the feedback and the additional information, ryanc.

Yes, R14 has not the Voronoi option, but to a certain degree Thrausi will help. The main part of the Voronoi was the Selection Tags, which you will get from Thrausi as well, but Voronoi provides now an option to “crumble’ the inside of the wall surface. Just to let you know what I wanted to illustrate with that scene.

The outside of the Thrausi wall could use a material that you can “key-out” quickly, like a lilac dull material, or a pure r, g or b color, which isn’t in the rest of the scene. This might accelerates the rendering perhaps. This key or to use the term matte could be inverted and used for the hole itself. The Matte Object wouldn’t work here: Since the Compositing tag has no option for Selection Tags.

Let me know if you have any other questions, I’m happy to look into it.

My best wishes

Here is an older but yet even today used technique in VFX compositing.

The idea of it is to use a normal RGB file, preferable in 16bit/channel or better 32bit/channel float (OpenEXR!). [Note that “HDR radiance” is not 32bit per channel.]

Each channel in an RGB file represents just a grayscale channel. With that, three informations can be supplied with no effort (or six with a little bit limitation and effort, RG, GB, BG, which affects the RGB single channels, hence more work.)

Here is the scene file according to the described scene above (A sketch only of course):
https://www.amazon.com/clouddrive/share/bK0GioZMCBrXrUamhVXiYfRNnGvtnxbztSo1qwJ05vJ

A short overview screen capture:
https://www.amazon.com/clouddrive/share/v33HiHa66F830POv85JVEVaSvhb1VGpceFvhT7R3RD8

The scene can be switched from normal material (check off) to Luminance. IN later relases the Take system could store that, since you said you use R14, it needs to be done manually.

As a reminder, the Fracture > Transform> Color needs to be black for this to work.

As a side note, the original footage might be in need for shadows, perhaps even camera map the footage on the wall directly.

All the best