Rotoscoping Problem

So I’m making an atom bomb explosion to go on top of a picture of Brisbane city for a short student film. So I have a plane for the background, and a plane for the ground. I have managed to make the plane invisible. However, other objects underneath are still visible. For example I have like a sound shockwave bubble that grows in size, then when it reaches the camera you’ll hear the bomb explosion.
Here from within blender:
However, in the render, the whole bubble is visible.
But I want the bottom half to be hidden under the ground (plane). Any tips?

Why can’t you go into edit mode and delete the bottom half of the sphere? I’m sure there’s something I’m missing, but that seems to be a solution to your problem.

could you not cut it in half? (cut the bottom half off)
that might work :slight_smile:

edit: lol…my answer was beaten…

Ok… in addition to cutting it in half.

Try turning off “z-transparent” or “ray-trans” and keep alpha at 0.

This should still draw the plane as invisible, but not allow anything behind the plane to be drawn(your sphere).

Yes but this is early on in my project. Later on I have to add cubes to outline the buildings so that the atom explosion doesnt overlap the buildings.
What I need is the material that will hide other objects that are behind it.

Ok, tried that, here is my result:

So I finally figured that it would impossible to make some objects disappear but not the actual plane with the image on it. So I set the image as a backbuf (is that the only way?) and I got this:

Also does anyone know what material I should use for my shockwave bubble? Its already at Alpha: 0.000 but look at it! It supposed to suttle and bearly visible. What can I do to make it invisible but still have the IOR effect?

Try turning off the reflection, or just turn it down a lot. Don’t use too much refraction either.

Good luck.

that’s odd
i’ve achieved what you wanted to do very quickly
I’ve just set the plane’s alpha to 0 and it does hide the lower part of my “sphere”(though I used a box instead)

the widget i moved was in the material editor : in the material tab (after preview before ramps) " : A under R G B has to be set to 0.0


maybe it’s my version of blender having a problem…

Alright, ugh, I hate typing, but I cant let this go unfixed.

Take your image into photoshop, cut out the buildings you want in front of it, add them on a black background in the same place they should go, make an alpha matte for it in pure black and white. Put the buildings to go behind is on another alpha matted image. Add the background as another alpha matted image.

BUild layers of planes with different layers on them so they actually have depth and will stay infront of the shockwave untill the sphere passes thier virtual space…

Too lazy to explain better…

I’ll draw you an example tonite