Image texture for alpha mapping

Hi everyone,

I’m working on a model of a planetary nebula (the remnant from a dead Sun-like star) and I’m slowly making progress on the details needed to make it look right.

I got the edge-on emission part working over the past few days, now I’ve got a problem with what I thought was a simple process.

I have a very simple barrel-shaped (not grail-shaped) model that I’ll use as the outer layer of the planetary nebula. I have “emit” at 1 and no lamps or other lights. I used this model to get the edge-on emission bit working, but the top and bottom edge of the “barrel” is very artificial looking.

So I unwrapped the barrel and UV-mapped it to a PNG with transparency made with GIMP. I used the same PNG as an image texture mapped to alpha. After two days of troubleshooting everything I can think of and running through many tuts, I cannot get it to work.

The funny thing is: If I choose a procedural texture (wood, voronoi, etc.) the alpha map works like a charm… I just can’t get the top-and-bottom effect with the procedurals.

So, questions:

  1. Is there a procedural that’ll give the same effect as the PNG mapped to alpha?

  2. Can anyone find an error in my .blend file that is causing the PNG to fail while the procedurals work?

I’ve attached both the PNG and the .blend file.

Thanks in advance!


planetarynebulatest-try2.blend (310 KB)

I believe you want your png texture to affect the alpha of your material. In that case, the png should vary between black and white with no transparency (alpha=1). Also, in the Map Input panel, set to UV Flat instead of Tube since it has already been unwrapped.

Thanks for the quick reply…

I should add that I started with a basic black-and-white PNG, but that behaved the same way. On the chance I was mis-mapping the PNG I created the current one with transparency, but I’m still getting the same result.

Thanks for the advice on the UV Flat map. Didn’t think of that…

Thanks again for the reply. I was waaaay overthinking the problem and just solved it.

I was not aware that the image texture must be black-and-white only (no transparency) for the mapping of values to other properties (such as alpha in this case). As soon as I turned “UseAlpha”, “CalcAlpha”, and “NegAlpha”, the PNG mapped to alpha!

I won’t soon forget that particular detail…