Firefly madness!

[thomas_bussey]

I've got some fireflys in some of the refractive materials in this scene. I've tried everything I can think of / have read about for removing them. They seem to be linked to the spotlights above. Of course I can make these invisible to specular, but the bottle looks kind of odd without any highlight reflections.

Things I've tried:

Switch GI to animation mode
Make relection and refraction less that 255/glossy:1
reduce lighting power (and increase exposure to compensate)
Make refraction 'all channels'
Temporal denoiser
increasing image filter size (changed it back, didn't work)
Turning off spotlight directionality
Incresing adaptive lights to 12
Full lights elvauation
Increase GI retrace to 16
Increase subdiv override on bottle to x4

I made these changes one at a time and none of these seem to solve the issue, it's like only a few of the spots are seem in the relections at any one time. I'm going to have to submit to render with the lights invisible to specular for now, but I'd really like to know what's going on here.

I've archived the file here:
https://drive.google.com/file/d/1wNS...ew?usp=sharing

[bardo]

Spotlights are VrayLights or mesh with VrayLightMaterial?
Are those spotlights for lighting the scene or they're are just for visual?

[^Lele^]

The location of the bottle in respect to the lights makes the results quite unavoidable: if you rendered the image bigger, you'd see the reflection of the light fixtures where now you see "fireflies", meaning V-Ray is doing the right thing, it's just too small to be perceived properly.
This said, you can certainly ameliorate the issue via shaders: switch the glass' (and wine?) BRDF to GGX (it's now as Blinn, horrible, old stuff. don't use it, ever! :P), which alone will make things a bit better.
With GGX, you can also lower glossiness a bit more (0.95, f.e. from 0.98 ) to further diffuse the incoming energies.
Of course, the reflections on the bottle will look slightly softer, but not dramatically so.

If you find the change not big enough, then perhaps you can mask the reflection glossiness on the affected shaders with a towards/away picking the spot as source, or better still with a perpendicular/parallel to the scene's Z (vertical) axis.

To remove the Blinn BRDF from the scene, you can use the script line below (run it in the listener):

for m in getclassinstances vrayMtl do m.brdf_type = 4

To mass-change all materials with reflection glossiness set to 1.0 (non-physical.) run the line below:

for m in getclassinstances vrayMtl where m.reflection_glossiness == 1 do m.reflection_glossiness = 0.95

And the same for refraction (this may end up costing you, depending on a few factors. Use as last resort.)

for m in getclassinstances vrayMtl where m.refraction_glossiness == 1 do m.refraction_glossiness = 0.95

Another thing which should be done by habit: make the sun *disk* invisible.
If that gets seen by reflections or refractions, you're in for some trouble (it's in the millions float.).
This may change in the future, mind you, but it's the safest thing to do for now (at the cost of some physicality, ofc.)

By the way, something in your scene is freezing my PC on render, repeatedly.
One of the plugins used in the scene is quite broken (that, or my PC is about to give up the ghost.).

[thomas_bussey]

Excellent, thanks for those scripts Lele, very handy.

Is GCX the recommended setting for all material types?

Odd what you say about the plugin, I can't think of much else I have installed other than fairly standard stuff: itoo/sini/tyflow. possibly the itoo coloredge one, although I've not actually used it in this scene, I know it's very old, I'll uninstall.

The location of the bottle in respect to the lights makes the results quite unavoidable: if you rendered the image bigger, you'd see the reflection of the light fixtures where now you see "fireflies", meaning V-Ray is doing the right thing, it's just too small to be perceived properly.

I thought this might be the case, but hoped increasing the subdivs override might sort it out. I need to learn more about what's happening 'under the hood' in Vray.

Spotlights are VrayLights or mesh with VrayLightMaterial?
Are those spotlights for lighting the scene or they're are just for visual?

yep, both, they light the scene and are visible, giving self illumination and Bloom & Glare.

[^Lele^]

Excellent, thanks for those scripts Lele, very handy.

You're very welcome.

Is GCX the recommended setting for all material types?

Yes, it's by far the most modern of BRDFs (by two decades or so), the most configurable (have a play with the tail falloff parameter in the material's BRDF section.), and the prettiest to boot (thanks to the different looks one can achieve with it.).
New V-Ray materials get created with GGX already, so perhaps you have some older shader brought into the scene (the script ought to fix those, anyway).

Odd what you say about the plugin, I can't think of much else I have installed other than fairly standard stuff: itoo/sini/tyflow. possibly the itoo coloredge one, although I've not actually used it in this scene, I know it's very old, I'll uninstall.

Nono, don't: so long as they work for you, you're fine.
It could really be me, and in any event i need a hardware refresh.

I thought this might be the case, but hoped increasing the subdivs override might sort it out. I need to learn more about what's happening 'under the hood' in Vray.

The best approach to try and fight these -if any other option was exhausted- is to raise min/max AA, and let V-Ray render.
Avoid trying to override subdivs per shader, as it won't make it better or quicker, and you may end up with extremely long render for no good result at all.
The tech in V-Ray has changed a lot in the past few years. so individual subdivs are not the way to go anymore (that's why they aren't present on shaders and lights anymore).

[thomas_bussey]

Another thing which should be done by habit: make the sun *disk* invisible.
If that gets seen by reflections or refractions, you're in for some trouble (it's in the millions float.).

Thanks for that. I actually only used that to orientate a Vray sky previously, so I can get rid of it now.

[thomas_bussey]

New V-Ray materials get created with GGX already, so perhaps you have some older shader brought into the scene (the script ought to fix those, anyway).

Yeah that was bought in from a downloaded asset. I'll keep an eye out and maybe just run that script on all my assets.

[bardo]

^Lele^ already gives you some nice tips.

I haven't download your scene, so I couldn't be more precise.
Anyway, if you're using VrayLight and you don't want to mess up your lighting, you could duplicate (as copy, not instance) the lights, change it as disc, make them bigger and use them just for reflection, dimming the multiplier.

It's not the most elegant way to solve your problem...but just another way.

I've attached a sample file.
TestDoubleLights.zip

[thomas_bussey]

Sure, that's not a bad shout and I actually tried similar except the making them bigger part, which from what Lele has said seems pretty important.

[^Lele^]

Yes, Bardo's very right: if you can afford the extra preparation time, split the lighting sources from the "reflection cards".
Then you'd be able to texture your reflection lights (f.e. with vraySoftbox) and control the shape and quality of the outcome for a more artistic effect.
As you'll have better control of the high intensities, you should gain back the extra setup time from the total render time for the sequence.

[bardo]

Sure, that's not a bad shout and I actually tried similar except the making them bigger part, which from what Lele has said seems pretty important.

Good to be helpful.
If you check the file I've attached take note that:
- I've added a softbox map to the reflection light to have a softer reflection.
- I've misaligned the lights and turn off the "cast shadow" option of the reflection one, otherwise the diffuse light will interfere with the reflection.