How to achieve a good mask with an alpha exe chanel

Hello everyone, i'm totally new to fusion which i've tried for some days and for the first time. I'm really enjoying the nodal structure and even if there is a lot to learn, i find it really exciting.That's said, i'd like to ask my first noob question here today. I have rendered an exr (linear) 3d scene from C4D/Redshift, i've made my composition and everything is fine. It will be a still image for a client of mine. With a saver at the end, jpeg files, done. Right. Now i would like to save a png file with no background. I'm trying to use the alpha channel (luminance black and white) to achieve this but the result is really crappy. What is the good way to use alpha channels in fusion to obtain smooth results?

Thanks a lot for all your interest in this very long post.

PS : i'm looking desperately a good course to learn fusion and there is not a lot of sources in the Internet, is there something you would recommend to me please?

PNG assumes the RGB is "straight", so for grey alpha pixels, the RGB isn't darkened. You might need to divide your RGB by the alpha to get rid of the premultiplication that most 3D renderers bake in.

Thanks Chad, i think i understand your answer well (even if my alpha channel comes from an exr and not from a png) but honestly i don't know how to do that at that time. Is it the alphaDiv or a boolean node that i have to use (or something else)? I will try in a few minutes.
Cheers

Hello everyone, i'm totally new to fusion which i've tried for some days and for the first time. I'm really enjoying the nodal structure and even if there is a lot to learn, i find it really exciting.That's said, i'd like to ask my first noob question here today. I have rendered an exr (linear) 3d scene from C4D/Redshift, i've made my composition and everything is fine. It will be a still image for a client of mine. With a saver at the end, jpeg files, done. Right. Now i would like to save a png file with no background. I'm trying to use the alpha channel (luminance black and white) to achieve this but the result is really crappy. What is the good way to use alpha channels in fusion to obtain smooth results?

Thanks a lot for all your interest in this very long post.

PS : i'm looking desperately a good course to learn fusion and there is not a lot of sources in the Internet, is there something you would recommend to me please?

I have 2 course on Fusion 9 on Udemy. There are others as well if you look around but I'll post a link to my courses in case you are interested. I will also be offering a Resolve 15 Fusion course towards the middle of April.

https://www.udemy.com/learn-blackmagic-fusion-free-after-effects-altenative/?couponCode=BMDFORUM

https://www.udemy.com/blackmagic-fusion-from-novice-to-expert/?couponCode=BMDFORUM

[EDIT] i've found a way (not totally right but it's almost OK). I apply my alpha on each part of the re-composed beauty and the black fringe is quite invisible. Don't know if it's a good way of doing it though.

Well, i must be really bad at compositing, i'm not able to reproduce that and obtain a good result. Is there any tutorial i could watch to understand how to do that? Or perhaps an example?
Thank you very much
Nico