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I've figured out a way to change the colour of the atmosphere on my Earth model, however the output node only has 1 option for "Color" and "Alpha". I need to be able to attach the blue part and the orange part to the output in the same way.

This is what it looked like before. The Extended Material node needs to attach to the output with both "color" and "alpha".

I've done the same node set up for the atmosphere as I did with the day to night textures. I've tested without attaching the alphas and it works perfectly, however the alphas MUST connect in order to be transparent. Is there a node that can send the color and alpha of both materials to the output?

enter image description here

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    $\begingroup$ just use math node to ( sum, max, min ) the two alpha outputs and plug the result to the end $\endgroup$
    – Chebhou
    Oct 3, 2015 at 17:37

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For the record, there are a few different methods to combine alpha correctly, loosely summed up as:

Correlated geometry: Use an add. Examples are where you are certain the geometry doesn't occlude each other at the subpixel level.

Uncorrelated geometry: Use a probabilistic A+B-AB. Examples include two pieces of glass overlapping, or any element where the geometry overlaps another piece.

Further reading: http://lists.openimageio.org/pipermail/oiio-dev-openimageio.org/2012-July/005642.html

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If both materials have the same input into their alpha, then just take the alpha of one of the materials because they'll be exactly the same.

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