You can't represent additive pixels (i.e. glowing pixels) with non-associated alpha. That's why this is used in exactly zero image processing software, internally.

E.g. an associated pixel with the 8bit/channel RGBA value 255, 0, 0, 0 (glowing red).

Because PNG can only store associated data a reader must associate before displaying. And that will give you a value of 0, 0, 0 after (black instead of additive red). See e.g. [1] why this matters.

Additionally the PNG spec does not specify if the alpha is linear. Some PNG readers/writer assume it is, some assume it has gone through/should go through an sRGB transfer curve instead. It mostly works until it doesn't.

The fact that the spec. doesn't specify which one it should be is another telltale sign that it was written by people unaware of the subtleties of image processing.

I understand that unassociated alpha gives you more precision in 8bit and since people wanted to e.g. store color ramps (with alpga) in PNG at the time (pre-SVG) and most image processing software (i.e. mainly Photoshop then) would not dither gradients for 8bit, this really mattered.

But it's 2025. And when 16bit PNG got introduced this should have definitely had associated (and explicitly linear) alpha.

[1] https://academysoftwarefdn.slack.com/archives/C05782U3806/p1...