Corona Renderer Forum

Corona Renderer for 3ds Max => [Max] Bug Reporting => Topic started by: XYZ_wanderer on 2019-12-04, 13:52:26

Title: Caustics solver causes eye-bleeding fireflies
Post by: XYZ_wanderer on 2019-12-04, 13:52:26
So I've done a quick render with a poll water material having caustics enabled. Everything went good.
Then after client asked to replace people with a more summer attire, i rendered scene and noticed that caustics cause disgusting firefly stains
What is happening? There are no other light sources in scene. I've tried resetting corona settings, converted scene, nothing seems to work.
Any idea what is the problem?

Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: rowmanns on 2019-12-04, 14:51:36
Hi,

Does this also happen when not using regions?

Using caustics with render regions doesn't behave very well at the moment and can lead to these kind of results.

We are working on improving this, but currently we advise to not use caustics with render regions.

Thanks,

Rowan
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: XYZ_wanderer on 2019-12-04, 14:55:20
Unfortunately, fireflies appear even when rendering full scene at once.
I've just done some testing enabling "caustics solver" but not checking "Caustics" itself in the material tab, the fireflies are still present
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: rowmanns on 2019-12-04, 15:10:45
Hi,

How long did you leave the render to run for, and at what resolution are you outputting the final image to?

Thanks,

Rowan
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: XYZ_wanderer on 2019-12-04, 15:40:20
It renders for around 1 hour, till noise drops to 5%, final resolution 4000x2250 (16.9)
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: maru on 2019-12-04, 15:59:46
What was the difference between your scene where it used to work fine and where it stopped working? What exactly did you change?
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: XYZ_wanderer on 2019-12-04, 16:35:40
apart from different people, extra bushes in the front and added curtains, everything is the same
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: arqrenderz on 2019-12-04, 19:05:54
You can solve it by selecting animation instead of still frame
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: XYZ_wanderer on 2019-12-05, 12:45:51
At any rate this mildly helps, Anyway maybe there is a way to have caustics overriden to refractions only? I don't really need reflective caustics, i only want the caustics that are visible in pool through water
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: TomG on 2019-12-05, 13:04:31
No way to do that at present - might be possible with some fairly involved workaround, e.g. having two water objects, slightly offset. Top one would be as it is at present, and that object can be added to the Exclude list from the light creating the reflective caustics, that way it won't create reflective caustics (or refractive caustics, or indeed be affected by that light at all). The second water object would have its reflectivity modified to zero, and would not be excluded - with reflectivity 0 it won't create reflective caustics, just refractive.

Don't know if that would work. Gets even more tricky if the reflective water has to catch the light source, e.g. sun glinting on the water, as then you'd need to add some geometry with non-emitting Light Material to let that be captured in reflections without generating reflective caustics. Or have two Suns, with one set to not generate caustics and only illuminate the reflective water (an Include list for that).
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: XYZ_wanderer on 2019-12-07, 19:51:46
So, after I've done some searching, i found that my HDR is very concentrated on just a few pixels in the center of the sun. This caused some of those firefies to vanish once i adjusted it in Photoshop.
And since using environment to cast caustics already is double edged sword, note to others: do not use HDR with a very concentrated luminosity/radiance levels. In fact, dont use HDR for caustics at all. :)
Title: Re: Caustics solver causes eye-bleeding fireflies
Post by: alexyork on 2019-12-10, 17:36:56
In fact, dont use HDR for caustics at all. :)

We've not had any HDRI-specific issues with caustics.