Caustics - Fireflies - again

[dj_buckley]

I cannot get rid of the fireflies created by reflective caustics.  Simple scene, sunlight, pool, building.  It's a villa on a tropical island so think white walls, clear blue sky, bright sunlight.

The annoying part is the refractive pool caustics looks great, it's the reflective caustics onto the building from the pool causing the fireflies.

I've tried sun/sky, hdri, environment caustics on, environment caustics off, caustics adaptivity on, caustics adaptivity off, still frame computation, animation computation.

Fireflies always there regardless of what I do.

I can't post many screenshots due to NDA's, but I've mocked up the scene setup, the blue bubble is where I get the fireflies

 

[maru]

There was a very similar thread in the past, check out the suggested solutions in it:
https://forum.corona-renderer.com/index.php?topic=30091.msg173280#msg173280

If you are able to reproduce the issue in a simpler scene and share it here, that would be awesome.

[dj_buckley]

Thanks Maru but none of that made any difference at all I'm afraid.

It's worth noting I'm using a HDRI (I believe Recent Spaces have also never had an issue with an HDRI) - so I need to leave the 'Caustics from Environment' checked.  I'll try and set up a mini scene and upload it

[maru]

Sure, I'll be waiting for a scene. Please let me know where you've uploaded it and what's the file name.

[dj_buckley]

It's uploading now via dropbox called 'Caustic Testing' - this is the exact scene with all the heavy stuff (furniture/trees) stripped out.  Just hit the render button and you'll see the issue.

[dj_buckley]

Forget to let you know it had finished uploading.

To add a few bits - the only solution I've found is to render twice, once with caustics and once without and merge then painting the caustics back in in photoshop.

Far from ideal - especially as the notes regardarding caustics say they are problematic with region rendering.

It's really frustrating as this is the one 'setup' where I was expecting caustics to shine, really hope it's me doing something wrong :)

[dj_buckley]

Me again - so I've replicated the exact HDRI setup with Sun and Sky.

The small bright sun is the problem.  As soon as you untick 'Visible to Reflection' on the Sun, the problem completely disappears.  This still isn't a solution though as I need the sun visible to reflection for the specular of every single other element in the scene.

It's quite evident in the image which one has the sun visible in reflections - although both are really low quality renders, they were both rendered for exactly the same amount of time and the only difference was that checkbox.

On a side note - let's say render time isn't an issue - how would you have the settings set in the Experimental/Debug Caustics Rollout for maximum quality?

[dj_buckley]

And this is how it looks if you leave it rendering to "clean up"

[maru]

I will check the provided scene ASAP. I have it on my todo. Sorry for the delay.
Just to make sure - you are not using region / crop rendering here? If so, it is not supported with the caustics solver and will produce splotches that never go away.

[dj_buckley]

Great, appreciate it.

Is that the case with every single region/scene regardless?  The notes suggest just a slow down or different appearance "Caustics may render slower/differently when using render regions (this will be improved)."

Also how is it possible to test Caustics without doing a full res render if that's the case - are caustics resolution dependant?  I could test at 1000px but if it's likely to change when I blow up to 5000px then ... I ask this because some of the settings in the experimental section refer to pixels i.e. initial lookup radius etc

[dj_buckley]

Left it running last night for 500 passes.  It cleaned up to a degree.  But was still noisy to the point of being unacceptable to issue as a final image to a client.  I've ended up blending two renders together.  Is there any documentation for the correct compositing of the Caustic pass?  Also my other questions re: caustics and resolution still apply.

Another interesting point.  The render with caustics on took 8* longer than without

[dj_buckley]

Just bumping this as it's been 2 weeks without a response

[alexyork]

We really do desperately need an include/exclude caustics receive system. Perhaps a straightforward "receive caustics" checkbox in the corona material would deal with this issue so well. That and caustics adaptivity to be fixed so we can avoid these black NAN squares.

[maru]

Just bumping this as it's been 2 weeks without a response

Sorry for that. Our todo lists are super long. I am downloading the scene right now and will look into it. I will definitely have some results today.

We really do desperately need an include/exclude caustics receive system. Perhaps a straightforward "receive caustics" checkbox in the corona material would deal with this issue so well. That and caustics adaptivity to be fixed so we can avoid these black NAN squares.

I am not sure if "receive caustics" will be possible at all with Corona, which does not like fakes. But we know that many users requested this, and it's logged for the devs to review.
What "black NAN squares" do you mean? The "caustics adaptivity" thing?

[alexyork]

I am not sure if "receive caustics" will be possible at all with Corona, which does not like fakes. But we know that many users requested this, and it's logged for the devs to review.
What "black NAN squares" do you mean? The "caustics adaptivity" thing?

Yes the black squares that appear pretty much any time caustics adaptivity is left enabled.

Regarding "receive caustics" and faking, that's totally understandable. But I think this is clearly one of those cases where a balance has to be struck between usability and reality. Right now caustics work but with rather a lot of work-arounds and issues.

I mean if you think about it right now you're already "faking" things by allowing the user to control when caustics are generated - we're made to check a box that says "make this behave realistically". That's fake already. So is it such a leap to allow us to control where those caustics can be received too with a similar checkbox?

Would a different solution be more practical, such as allowing the user to limit the distance caustics can be "thrown" from a surface? The default is seemingly infinite, so you get caustics splotches thrown many meters away from a water surface. If we could limit it in the settings for that scene to something like 2m/3m then we could keep those caustics under some kind of control. Basically a more aggressive falloff.  It wouldn't deal with the issue but it would help.