Fireflies!

[eriklint]

Hi all,
This is my first post to this fabulous forum.
I have been unable to de-firefly my image, and there are a lot of them. I am hoping I can get some clues/help from the group to help me better understand the process.
I am posting a section of the rendering and some settings related.
Any pointers are appreciated.
Thanks!

[Beanzvision]

Hi there,  this could be a range of things from incorrect material or lighting setup, can you possibly share your scene with us via our private uploader? The link is in my signature below. Thx

[Ealexander]

My professional unprofessional guess would be that you have a low light, high contrast scene there and since you've limited it to 18 passes and it would probably take more time/passes to clear it up....

[eriklint]

Thank you Beanzvision and Evan.
Unfortunately the project is tied up with NDAs and it would take me some time to strip out the "secret" stuff, so I can't post the file. Thank you beanzvision for suggesting and offering.
Evan (Erik here btw), thank you for the very accurate analysis. It is indeed a low light, high contrast situation. I am going to try two things. More passes and then also adding more light and then adjusting to get the drama in the post effects. I have this file set up for Lightmix too, so I will try that too.
Oddly enough, since this isn't 100% about photorealism, the fireflies added some detail/sparkle/something in the shadows that actually helped with the final presentation rendering. That being said, my professional curiosity would like to scrub them out.
I really appreciate the generous and helpful replies.
Best,
Erik

[Konichowaa]

what is your light setup?
do you have by chance a hdri as a background (without GI/shadows)?
I once had a project where I had unexplainable fireflies in some blurry reflections, that no matter what I tried, I couldn't get rid of. The fireflies also became worse and worse the longer I rendered (kept appearing new ones).
I had a scene setup with HDRI for lighting and another HDRI for background (without GI/shadows). I spent more than a day searching... When I finally tried to put the high-res JPG version instead of the HDRI for the background the fireflies were gone ...

[eriklint]

Thank you Konichowaa!
I think your suggestion was a good one. My lighting setup was indeed mostly an HDRI with a Corona compositing tag with an illuminating skyline backplate (also with a Corona compositing tag.) I already did a quick test and it reduced the fireflies by a lot. I am slammed with a deadline at the moment and will fiddle with the jpeg option when I get some time.
Great idea, thank you!!