View Full Version : Alpha Texture?

11-03-2005, 04:52 PM
Anyone know if there is a way to use a texture to cut the alpha.

I have a paper on a desk and I want it to become transparent, showing the video behind it (to be composited later).

I can think of a few ways to cheat this, chroma key for example, but I was wondering if there was better way to do it so the alpha is already part of the image. Something like a plug in and apply it to a particular texture in the scene and everything in the scene with that texture cuts the alpha.

11-03-2005, 08:30 PM
There are a few different ways to do this. You could use an envelope on the transparency channel. You could use an envelope on the object dissolve. You could add a clip map to the object which would give a wipe effect.
Try each of these and see what they do.
Areas of the user manual to read the surface editor and object properties.
A clip map does not have to be solid black and white, it can be grayscale.
Hope this helps

11-03-2005, 08:53 PM
Thanks for the suggestions Silkrooster, but I'm not trying to make the paper transparent within the scene. I am trying to cut a hole through the entire scene. As if I did a boolean throught the entire scene where the page is, so that the only thing that showed where the page is would be the background of the scene.

I am rendering out a TGA32 sequence and want to load it up in premier, select alpha key, and then be able to key the video layer below through the page.

But since there are things behind the page, like the table, the ground etc, simply making the page transparent won't do the trick.

I suppose I could do a boolean through the whole scene. But I was hoping there was a way that lightwave could look at the texture and say: oh make that texture part of the alpha.

The obvious answer is to turn everything in the scene black except the page and re-render that as the alpha. But then I would have a more complicated composite.

The element I am trying to make will be used as a bumper in a TV show, which will need to be reused alot. So I want to make it as easy as possible on the post end.

11-03-2005, 09:34 PM
Ok I think I got you. What about rendering only the page save the alpha and load the alpha into premeir. I haven't used premeir for awhile so I don't know how it handles layers or alphas any more. But I would assume placing the alpha onto the entire image that was already rendered would give you the hole you need.

11-03-2005, 11:16 PM
You can set the object alpha channel for the object to "constant black" under object properties / render tab. Then use object dissolve to fade in and out the alpha effect. You could place a poly over the page if you want the effect windowed.

11-04-2005, 12:27 AM
Rendering in Layers, takes some extra time but it works always