Can you write "unassociated", "non-premultiplied" or "straight" Alpha


#1

Hi,
Is it possible to write an unpremultiplied alpha for a png? (aka unassociated or straight alpha)
I can see how to set the input premult. But I really need to write/export an image with a straight alpha.
A lot of applications expect straight alpha from png images as per the png specifications.

https://www.w3.org/TR/PNG-Rationale.html#R.Non-premultiplied-alpha

So it’s really causing me problems not to be able to write a png with straight alpha. Am I missing something?

In Blackmagic Fusion you simply set the output node to “pre-divide by alpha”. Is there an equivalent in Natron.
I hope so because I think the look of the filters I get from Natron are way better than Fusion, but if Natron doesn’t respect the proper png standards, it’s going to really limit what I can do in it.

Thanks in advance


#2

You could just put an ‘Unpremult’ node before your write node.