Cycles Material Index Pass with Alpha Mask ?

Hi all

Does anybody know how to affect only the (pseudo-)alpha-area of a material (in this case the leaves) instead of the complete geometry ?

See here:

Or is this not possible yet with Cycles ?

Edit: Here is an examplefile: alphamap_id_pass.blend (564 KB)

Kind regards

You can mix your leaf shader with a transparent shader and use an alpha map as mix value.

Watch this tutorial by Greg Zaal

What are you trying to do with just the alpha area?

If your trying to get rid of it, I think I had a similar problem when I was playing with sapling. I kept seeing traces of the alpha in the leaf texture. I found that the alpha channel on some of the leaf textures were a little dirty. I went into gimp and there is a setting under transparency that lets you set it to all or nothing. Set it to all and you shouldn’t have those boxes around your leaves anymore.

I guess you missunderstood my question.
Read what krixxuss said, it discribes the problem.

I try to change the color of the quader behind the tree in postproductions without rerendering the hole scene, this is why I need the pseudo-alphachannel of the leafmaterial.

I guess you did that with “Blender intern” Renderer and not with Cycles right ?

In Cycles you can’t use the Alphachannel of a textureimage yet.
In my example the Transparency is defined by a Black and White Image. Tranparency is just pure White (RGB 255,255,255).

Any other solutions ?

Kind regards

I saw that Jonathan Williamson uses separate Layers to maks specific Objects.

This technic works pretty well with “Alphatextures” :slight_smile:
I updated the File: alphamap_id_pass.blend (600 KB)

Kind regards