[SOLVED]Remove Fireflies Caused By Geometry Light?

[Atom]

Hi All,

I have a complex model with a geometry light. In order to obtain the amount of light coverage that is artistically needed I have to crank up the Intensity and Exposure to 4.0. This gives me the broad lighting look I need but it also introduces fireflies into the final render. I have read you can use Extra Image planes to generate debug images to help isolate and track down the problem. When I turn on what I think the extra image planes I need, I still can't find the problem. Most of the extra image planes are just blank.

Does anyone have any tips on how to remove or reduce fireflies in a render?

 

What image plane contains firefly data? Can I blur it out somehow?

I know what light is causing the problem, it is my orange light. Throwing more samples at it does not solve the problem.

All materials in the scene are Mantra materials. I can greatly reduce the fireflies by turning off reflection on the main body of the model but I don't want to do that. I still need a specular look on that metallic surface.

Edited January 27, 2016 by Atom

[fathom]

you should see the fireflies in your direct_reflect if you export that separately since you say turning off reflection gets rid of them.

 

try cranking pixel samples and see if things change.

[Atom]

Ok, in my case I am seeing the fire flies in the indirect_lighting (Per Component), specifically indirect_reflect and indirect_diffuse. I tried turning up the sample count on the geometry light but I see no change.

 

Is there any way to just remove that pass from the beauty render?

Perhaps some compositing math?

Edited January 27, 2016 by Atom

[fathom]

indirect_reflect is reflected objects.  you can try removing your object from its reflection scope (* ^$OS in the reflection scope parm on your object).  indirect_diffuse is secndary bounces of diffuse lighting, so your light is hitting something and then bouncing off that to light your object.  that is typically pretty noisy.  you can try upping your diffuse quality.

 

wait.  you're not tracing "all paths" are you?  that would add brute force caustics into the equation (might show up as indirect_reflect, not sure).  you don't want that.

 

edit: and yeah, you can subtract both of those from your beauty to remove them.

Edited January 27, 2016 by fathom

[Atom]

Thanks for the tip. I don't think I am tracing all paths, how would I know?

 

I was able to solve the problem using brute force sampling. This means each frame will take over 4 hours to render, however.

 

Here is what I did...

I created an integer field and named it light_samples.

I copied the field and pasted a relative reference into the light samples field for all geometry lights (six in this scene).

Then I pasted relative reference into the Mantra node pixel samples, minimum samples and limits for diffuse, refract and reflect.

 

So now I can control all samples from a single location.

 

This image is the result of 9 samples on each light, a 9x9x9 pixel samples on the Mantra node with limits set to 9.

 

Is there any way to just instruct Mantra not to include indirect_reflect in the beauty pass? It would be nice to avoid an extra compositing task and I could lower samples for speedier renders.

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I'm still not sure what you mean by remove your object from the reflection scope? Is that a setting at the material level, render level, lighting level...?

 

What does seem to help is to add indirect_diffuse as a contribution on each geometry light. Then turn that contribution off. There really was not much more than fireflies on that contribution layer anyway. I re-rendered my image in 8 minutes with a 3x3x3 sample setting and got a fairly clean render as far as fireflies goes. It is, of course, a bit noisy because of the low sample rate.

 

And here is a 4x4x4 render which took 10 minutes.

Edited January 27, 2016 by Atom

[iamyog]

Depending on what you need to render, you might not need extra reflection bounces. On a proper beauty render this is sort of a lazy quick fix but for an utility pass this could help.

 

If you see fireflies in the indirect_reflect, you can easily remove them by setting the reflection limit on mantra to 0.

 

Obviously it will kill all secondary reflections from your lights but it sure will remove the undesampled light reflections, thus removing the fireflies.

[fathom]

"all paths" is a pbr option.  it defaults to "specular and diffuse only".

 

the reflection limit of 0 will definitely kill all reflections.  you might try 1 or 2.  the fireflies might be a reflection of a reflection.

 

are you including the geometry of the orange light in the scene?  see if removing it gets rid of the fireflies.  if you need to keep them, you can try removing them from the reflection scope of your main object.

 

the reflection scope (and refraction scope) are right next to the light mask in the render settings for the object.  that lists all the objects that can be hit by reflection (or refraction) rays from this object.  the default is all objects.  so if you remove an object from that scope, it won't appear in the reflections.

[Atom]

Ah, I found the scope fields you mention and I now see why you would use ^$OS next to the *. Basically excluding self from reflection. Thanks for all the help I feel like I have a better understanding of how all these contributions get routed to Mantra.

 

My image looks better too.

Edited January 27, 2016 by Atom