Fireflies with non-GPU rendering

[fabrice_barbey]

Hi
I'm rendering a tyflow object with a lot of opacity (hundreds of hair cards).
I was rendering in with Vray GPU 6 2.1 but ther's a cast shadow bug that forced me to switch to Vray 6 (non GPU).

Now dozens of fireflies suddendly appeared everywhere in the hairs!
I cant get rid of it, even lowering the noise threshold and upping the Max subdiv changes nothing (except render time!).

Any help please?

PS : the object has no reflections at all.

[vladimir_krastev]

Hi, thanks for posting. Please try to reset your render settings to default.
I can't say much without looking into your scene. Could you archive and send it for review? You can do that here or through the support contact form.

[Joelaff]

Increasing the min subdivs is usually the first step. Do you have any lights with high directionality (or Vray Sun)? However, you say no reflection, so may be unrelated.

Are there transparencies (refraction)? If so, try increasing max transparencies in the render settings, and max depth in the material.

Turn on LightMix and see which light (s) are causing the issue and troubleshoot further from there.

Try exporting to a TyCache and changing the render mode from instances to mesh. (Or set the mesh mode in the mesh operator to mesh vs. instances.)

Please let us know how you resolve it so we can all benefit. Thanks.

[^Lele^]

We'd really need a scene to be able to tell.

[fabrice_barbey]

Hi all thanks for your answers.

As I'm in a production hurry I had to find a workaround so I...simply turned off "affect specularity" for the sun.
No fireflies now.
But it's weird because the reflection of the material is set to 0 so there shouldnt be any reflection in this simple scene (1 tyflow object).

I'll definitly make a sample scene in a few day to figure this out.

[Joelaff]

In my experience the majority of fireflies are caused by directional lights. Vray sun with full directionality, or other lights with high directionality values.

I create a second VrayLight disc at the location of the sun (making sure it is decently far away, but not incredibly so because you will get the danger problem again— the sun distance does not matter, but this new light will, and it needs to be far enough away such that the decay is not visible in the scene). Set the directionality of this new light no higher than 0.3, but start with about 0.15 directionality Use this new light to affect specular and reflection, while using the sun for diffuse. Set the radius of this new light as large as you can get away with visually (again, don’t make it a point, but keep an eye on highlights).

This typically solves the problem. Usually renders faster as well.

Odd you saw it with no reflectivity. Do you have a coat turned on, or metalness?

[fabrice_barbey]

No, very simple material but with a lot of opacities (tyflow) like leaves in a tree.

[Joelaff]

No, very simple material but with a lot of opacities (tyflow) like leaves in a tree.

Interesting. I wonder if a different Opacity Mode (Normal, Stochastic, Clip) would affect it... Or if Thin Walled might affect it... Interesting.

Or Max Transparencies in the render settings...

[vladimir_krastev]

Hi, do you have your Sun as visible? This is the default state and a visible sun could produce fireflies in some cases.
Please enable this checker for a test.