Issues with new caustics in Corona 4

[Sacifair]

Hello!

I have some problem with new caustics, in interior scenes!
I tested it first in some "Object scene" and everything was great, awesome! new caustics!! but, happiness didn't last long :(

And then, I opened a scene (interior).. that I built a few days ago, and wanted to RErendered it (cause a new caustics, new filter) so..

I got some "white fireflies" or "white dots" and this problem was in all interiors I checked (HDRI or CoronaSky+Sun doesn't matter)
I did all of that I could do :(

Here are renders with this problem:

Parameters where the interior with materials: HDRI, all glass of windows have thin+CoronaRaySwitchMtl, and all windows have CoronaPortals of course!
I rendered the full image for 4 hours! and nothing, fireflies continue to stay (Core i9 7980X) I rendered before this the same image on Corona 3 for 30 minutes "facepalm"

Parameters in another picture I sent: Just a grey box with grey material on the walls with reflections 0.65, CoronaPortal and there is not any glass and windows. The same issue! but, I noticed that this issue can be fixed here by decrease "Reflections" on material of walls!

And the last one, the first scene but without any materials (only windows and the door have it) here the same problem


Please any help with a decision! Thank you



(Sorry for my English)

[maru]

We will soon release a build with improved caustics, so please re-test your scenes once it's out. If the issues will persist, we will definitely look closer into your report.
Thanks!

[Sacifair]

Good news!

It would be great.
Thank you for the reply! Sure, I will take a look :)

[evalery]

I had the same issues with caustics 3dsmax/corona4, same fireflies. I don't know if I should post my image here but it's the same issue basically, although my system is a bit old, I left this render going for 27 hours and it's just a test 2000/2500px), playing with particles and displacement.

thanks,
cheers

[romullus]

When your renderings takes so long, that you have to include calendar in the screenshot :]

[evalery]

LOL I'm really happy with Corona usually but this time I'm doing test and experiments and stuff so yes hell

[Sacifair]

My apologies, but it still has fireflies! Even worst than it was :( but...

I noticed that there is the problem when I use HDR as main light. When I enable a simple light "Corona custom white" the problem disappears!
And one more moment, the scene with gray material has no these issues anymore (as you remember there were the issues even without any glass or portals there)

Thank you for improve this, and maybe you can check HDR lights in the next fix? It's so sad cause C4D users can work with caustics, we can't.


Thanks again!

[TomG]

The caustics are the same in C4D and Max, should be no difference, so not sure what you mean by "C4D users can work with caustics, we can't".

It would usually be best to disable caustics from HDRIs anyway - the general light of a scene in reality doesn't create much in the way of caustics, as it is too diffuse and not intense enough. It's single directional lights that generate caustics, things like the sun (and that would overwhelm any minor caustics from the environment). Indeed, the environment would be very hard to calculate and take a long time to clean up, at least as far as it seem to my thinking - with a directional light like the sun, you can sample efficiently to get the caustics. With an environment, you have to sample EVERYWHERE.

If you have an HDRI with a bright sun in it, I would suggest turning off caustics for the HDRI and placing a sun in the scene for the caustics calculations. Can't say if HDRI sampling for caustics can be improved, but my feeling is it would always be slower to clean up than caustics from a directional light, because you have to sample in every direction.

[Sacifair]

Well, ok :)

It is logical, I understand but, how about this?

I disabled caustics from HDR map.. and turned on Corona sun..
Still the issue :(

This is not about of only HDR map, this is real problem.. and I can't use these improve caustics.


What about C4D users, you showed how caustics works in some scene:

[TomG]

And it would work in the same scene in Max :) Best thing to do is send us your particular scene so we can take a look at your scene in particular, see https://corona-renderer.com/upload.

[Sacifair]

This is a commercial scene :( I can't

But, you know ..  I need to do some "experiments" maybe you were right then I should build a new scene and check this issue again :)
If this won't work anyway, I will try to get agree from my client and share this scene with you!


Anyway, thanks for the reply :)

[TomG]

Ah ok :( If you do ask client permission for any scene, you can inform them that it is is kept purely internal within the company, we never share scenes, or images from them, or use the scenes (or images) for any purpose other than fixing the bug / informing you of a scene change that would resolve the issue. We take such confidentiality very seriously!

Other thoughts on how to test the scene - you could disable caustics for materials and then enable one by one to see which materials generate the refractive caustics and if those are the source of the fireflies; you could do the same for lights (often, best to have just one light having caustics enabled); if many objects have the same material applied, or if the fireflies turn out to be from reflective caustics rather than refractive, you could disable all those objects and bring them back in one by one. That way you could pin down what is responsible for the fireflies.

Just as an aside, be sure to be using the latest release, the Hotfix 1.

[Sacifair]

Yeah, good point!

I will check them as you described as first.
Thanks

[Correntes]

The caustics are the same in C4D and Max, should be no difference, so not sure what you mean by "C4D users can work with caustics, we can't".

It would usually be best to disable caustics from HDRIs anyway - the general light of a scene in reality doesn't create much in the way of caustics, as it is too diffuse and not intense enough. It's single directional lights that generate caustics, things like the sun (and that would overwhelm any minor caustics from the environment). Indeed, the environment would be very hard to calculate and take a long time to clean up, at least as far as it seem to my thinking - with a directional light like the sun, you can sample efficiently to get the caustics. With an environment, you have to sample EVERYWHERE.

If you have an HDRI with a bright sun in it, I would suggest turning off caustics for the HDRI and placing a sun in the scene for the caustics calculations. Can't say if HDRI sampling for caustics can be improved, but my feeling is it would always be slower to clean up than caustics from a directional light, because you have to sample in every direction.

Thats a big bummer if we cant use caustics directly from hdri efficiently. (I'm also having the bright spots problem in an exterior)