[Cycles] Mix Two Images With Alpha? (World Globe)

Atom · December 28, 2012, 1:00pm

Hi All,

I am trying to mix two images together to form a single material for a world globe.

When I render them separately, they look fine and solid.

But when I try to mix them together I get a half-alpha out of each one.

I tried using the Mix and Add nodes but they both fail to combine the alpha channel correctly.

Here is my node setup.

How would I modify this node setup to “solidify” my alpha channel?

Atom · December 28, 2012, 1:50pm

I guess you have to “pre-mix” all image colors and “pre-mix” all alphas from each image keeping alpha separated from color until you get to the shader node where it is used as the final factor.

The trick seems to be that you have to enable Clamp on the final math node for the alpha channels. This seems to act kind of like a normalize, I think.

Atom · December 28, 2012, 5:38pm

Thanks for the link that helps some. But what I am running into is that when you try to stack two or more images with distinct alphas the color mix fails on my system. Partially because there still seems to be bugs in Blender’s ability to read alpha channels from certain images on my machine. I have troubles with certain RGBA PNG files I export out of Photoshop. So I end up forcing the creation of alpha, like Blender Internal’s RGB To Intensity feature for image textures, using the RGBTOBW node in Cycles.