Transparency from shader becomes white when exporting on transparent background

Question

So first time actually posting a question here, but I just can't seem to find a solution. So I made this fire ramp shader for a project I'm working on, and I want to have a transparent background for comp purposes. However, whenever I try to export using png the albedo details of the shader turns white when there's nothing behind it. I tried exporting it using OpenEXR as well, and that seemed to work for some reason. I don't want a 32bit image though, and would preferably keep it as a png.

Below is two images, one from blenders render window, and one exported using png with a solid background for better visualization of the problem.

I'm at a complete loss, so if anyone got a solution I would be grateful!

Hello :). I'm no expert, but I'm afraid PNG doesn't support both emissive and transparent pixels. EXR is the way in compositing. — jachym michal, Jan 05 '21 at 17:48
Does this answer your question? Render semi-transparent volume with cycles, Transparent Image different in viewport than render, — jachym michal, Jan 05 '21 at 17:50
Aah, well that's annoying, guess I'll have to find a suitable solution then ^^' But thanks a lot! now i at least know what the issue is :) — Jakob Poulsgærd, Jan 05 '21 at 18:00
Also, thank you for such a quick response! I just couldn't seem to find anything on the topic, so I guess I just gotta get better at googling :) — Jakob Poulsgærd, Jan 05 '21 at 18:11
No problem :). You probably want to google "premultiplied vs. straight alpha". The Wikipedia page on Alpha compositing is also helpful. Good luck with your project. — jachym michal, Jan 05 '21 at 18:14
Just use version 2.92. the bug with associated alpha in the render viewer has been fixed. And yes, avoid using .png as a file format as it cannot handle associated alpha correctly and cannot have pixels that are emissive and transparent. EXR is the perfect format for what you want to do. Read: blender.stackexchange.com/questions/57816/… — susu, Jan 05 '21 at 20:00
@JachymMichal premultiplied and straight can be misleading terms, Associated and unassociated alpha seem more appropriate. If you want to read further read troy_s ' Hitchiker's guide to digital color https://hg2dc.com/2020/08/26/question-25/ — susu, Jan 05 '21 at 20:01
Thanks @susu ! I did manage to make a composite setup that allows me to use png with both transparent and emissive texture tho. But I might still look into the EXR format, just not a huge fan of the amount of post handling the EXR requires to get the same color look ^^' — Jakob Poulsgærd, Jan 06 '21 at 20:28

Transparency from shader becomes white when exporting on transparent background

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