Stubborn fireflies when using HDRI in Reflections Override

[Dippndots]

So I'm having this problem where using a different HDRI in the reflections override slot to the scene environment lighting slot is producing a lot of fireflies that denoising can't take care of.

The attached image is 75 passes on this region took 1:48, denoised at .6 took an additional 3:40, and really didn't make a difference, so I'm tempted to assume these over-bright pixels are messing with the denoise calculation too.

Highlight clamping was to 10 just to see if that helped, it didn't have much impact.

Both hdri's are .hdr, using the reflections override HDRI in the scene environment instead don't produce the fireflies, and using a .jpg of the HDRI in the reflection slot doesn't produce the fireflies either. This happens with a reflective override material as well, the grey metal has no reflection/gloss/bump maps that would cause speckling.

Is this some sort of conflict between HDRIs?

[romullus]

This is known bug: https://corona-renderer.com/bugs/view.php?id=1257

[Dippndots]

Good to know, haven't tested this in the dailies yet.

[Philip kelly]

Is it a polygon ,, ie not shelled?
If so shell it it will get rid of the fire flies.

Phil

[Dippndots]

Hi Phil, its a closed object.

[maru]

This is known bug: https://corona-renderer.com/bugs/view.php?id=1257

I have just checked and this is not happening in daily builds. So one solution is using them.

[Dippndots]

Uh Oh... I just tested with the latest daily and it's even worse. Let me try to setup a simplified scene to send over.

[maru]

Wow, then it must be something different. A sample scene will be appreciated.

[Dippndots]

ugh, nevermind, it was the geometry, my coworker had it auto-smoothed... as soon as I cleared the smoothing groups it looks fine. Well, at least that's solved.

[maru]

Oof. Can you double check if it's really fixed? :)

[Dippndots]

it definitely works, but if PBR mode is ticked, it breaks again

[Dippndots]

maybe move this to bugs if it hasn't already been logged?

[maru]

I will see if I can reproduce this, and then move this thread to bug reporting, or submit a Mantis report. Thanks for the involvement!

[maru]

Hmm... I wasn't able to reproduce this. Can you help? A scene with the specific HDRIs used would be great (if you can't share them publicly, you can contact us via https://coronarenderer.freshdesk.com/support/tickets/new). I am not really getting any fireflies with 1.4.1 or 1.5.

[Dippndots]

hmm, interesting. Ok, I'll simplify the scene, its a Peter Guthrie and CG Source hdri, so I should probably make a ticket.

[Dippndots]

Just submitted the ticket.

[maru]

Confirmed in the support ticket. Will create a proper report

[Ondra]

logged in mantis https://corona-renderer.com/bugs/view.php?id=2124

[Juraj]

Is this solved ?

Or just noticed ? I might have scene with issue like this.

[Ondra]

not resolved yet, but we want to minimize number of bug reports by removing duplicates

[Bormax]

Is this solved ?

Or just noticed ? I might have scene with issue like this.

Hello

I had the same problem with the scenes where I wanted to lit scene with Corona sky and reflections taken from HDRi map. For my case I found pretty simple solution: I've just saved hdr image as jpg, and then used it to override Direct visibility/Reflections/Refractions - it makes reflections to clean muuuuch faster. I like to use Vray HDRi map, I have rotation of a map it rigged to the Corona sun in my scene, so I can simply rotate corona sun (inside of day light system) and get correct rotation of environment map in Vray HDRi. Tweaking settings of Inverse gamma and Overall mult with JPG sky I've got picture pretty much the same as I get using HDRi map. Check attached pictures - tests made with VisPeople's and No Emotion's HDRis. In both cases I used Corona sky+sun for lighting and hdri/jpg for Direct visibility/Reflections/Refractions override technic. Also you can find Vray HDRi settings for both skies in hdr and jpg formats.

Hope, this solution will help you and others, who have the same problem

[Dippndots]

Thanks Bormax, unfortunately that solution doesn't work when your're looking at the sun like I am with a problem scene at the moment, there just isn't enough dynamic range in jpegs, or 16-bit TIFs :(

[Njen]

I had the same problem with the scenes where I wanted to lit scene with Corona sky and reflections taken from HDRi map. For my case I found pretty simple solution: I've just saved hdr image as jpg, and then used it to override Direct visibility/Reflections/Refractions - it makes reflections to clean muuuuch faster.

Just want to say that comparing a jpg file to a hdr file is like comparing a banana to a pumpkin seed. Sure they are both things you can eat, but they are fundamentally different types of objects. By using an LDR image file format such as jpg as an image based spherical light source, you are killing all values above 1 which makes the image way less photoreal, and you are potentially using incorrect gamma. And if you are tuning all of your shaders to react to a jpg file, you will potentially be making them too bright because you are trying to compensate for a loss of energy from bright light sources like the sun.

If you want to see if the hdr file format is broken, you should be comparing it to an exr file of the same bit depth.