Edit: I think my biggest issue was due to some clamp settings I’d forgotten about. Adding r+g+b isn’t exactly the same as using white, but it approaches it as samples increase.
I’ve been experimenting with some chromatic aberration materials and have gotten stymied by some strange behavior. I’m hoping that somebody can explain it, so I can figure out a work around.
So the basis of my CA effects has been separating R, G and B channels, running those through a BSDF of some sort, and then using add shader nodes to add them back together.
But I’ve had some weird behavior when it comes to refraction and transparency. Adding three primary colored shaders looks nothing like using one white shader.
So I’m adding three primary colored transparency shaders over a diffuse plane and an HDRI world. I’m applying the material to a cube in the foreground and a plane in the background. As you can, where there are layers of multiple transparency, adding three primary transparents leads to less transparency than a single white transparent.
Oddly, the color of the layered transparent section, even though not black, doesn’t seem to respond to additional layers of add shaders-- even though it’s not black, layering this shader on top of each other doesn’t brighten the areas of multiple transparency:
Note that the first pic was in default color management, but I’m using raw color here to avoid any issues with tone mapping. Notice how the add shader multiplies the brightness of the single-surface shader, but doesn’t seem to have any effect on the multiple transparent layers.
I’m running into these issues with working on CA in a refraction shader, and I think it’s connected. Because my ultimate goal is refraction, I can’t just mix with white transparency on the basis of transparent depth; I need to divide my refaction into components to treat each differently, even on backfaces.
Any ideas what’s going on? Any suggested workarounds?