Creating Alpha masks

I know there are many answers in this forum that address the issue of alpha masks. But none of them explain how to do it for a newbie (one who had trouble finding the left mouse button). I am attempting to make a non alpha channel movie play inside blender with:

  1. a clear background
  2. zero opaque foreground colors
  3. non distorted colors
 ...4. exactly which buttons to press

This is what I do know: You need two textures on the same material. (Is that right?) You need a regular color movie “Tex” and a grey scale movie “Tex” and the col button is pressed for the color movie and the alpha button is pressed for the B/W movie. I’ve done that. But my colors are still semi opaque and greatly lightened by any object located behind the movie plane. This is my problem. Could a good soul please make it go away??

For the alpha map, ensure that the image is solid black (ie 0,0,0) for the transparent bits and solid white (ie 255,255,255) for the opaque bits.
Click “Calc Alpha” and “Use Alpha” in the texturebuttons for the map.

On the material, set the Alpha (on the left) to 0, turn on Alpha mapping (on the right) for the texture and set Val (very bottom right) to 1. If the map is inverted (ie transparent bits opaque and vice-versa) click the Alpha map button again, or click “Neg” (above the texture colour)


Don’t forget to enable “ZTrans” on your material.

This is good only for the alpha channel of an RGBA image.

See this tutorial (mine):

This is good only for the alpha channel of an RGBA image.[/quote]CalcAlpha generates an alpha channel based on the RGB channels - black is 0% alpha, white is 100%

OK, you’re right in that way.
Yet, it is unnecessary : have a look at the tutorial.

Thanks you guys. You made a blind man see. :stuck_out_tongue:

Just one more question. And this is pushing it. Is there a way to have shadow-giving spotlights respect the Alpha image and not the original mesh shape?? Please say there is…

I’m trying to have leaves cast shadows on characters.

Nope. Sorry.

What you can do is to render out a view from a camera placed at the same location as your spotlight, have only the leaves visible, and then use the resulting image as a texture for the spotlight (which is then used with ‘shadows’ switched off).