Emissive material - fireflies nightmare

[Correntes]

I have an outside lit by hdri on environment slot and a bunch of light bulbs scattered with an emissive material.

I'm getting allot of fireflies with the color of the light.

I tried render with a grey override material (excluding the lamps) and i confirmed that the problem is the emissive material.

I tried everything
PT+PT

PT+HD

High lights subdivs

High  PT samples

Low max sample intensity

etc


I can't get rid of the fireflies...

Some thoughts ?

[Correntes]

Should I drop emissive material and use corona lights ?

[Eian]

Hey Correntes,

After some testing I found out that using Bucket Renderer helps with noise and fireflies problems..
Under "Renderer: Bucket" settings try something like:

subdiv AA: 2-6 (Overall Quality)
adaptive steps: 2-6 (Adaptation)
apaptive thresh.: Higher values increase adaptation as opposed to lower..

You might need to experiment with the above values a bit to get optimal results but generally higher values give better results but takes longer to finish the pass..
Hope this helps.

[Correntes]

Thanks for the tip Eian.

I will try a bit more in the "progressive way" But if I can't resolve the issue i give bucket mode a try.

Meanwhile I reverted back from daily build to alpha 5 to see if i can get better results.


Apparently with 512 PT+HD  it is significantly better in the firefly department (with alpha v05).

[Eian]

You're welcome..

I believe that the HD approach yields a more biased result, while by using Bucket method the rendering is still progressive but adaptive.
I found this to be the fastest and best solution to clear out fireflies while maintaining speed.
It's a bit close to the way Arnold Renderer works..

Do some further testing and let us know of your results..
I've been using Corona for only a few days now so any info will be helpful since I'm still experimenting with it, having used many rendering engines in the past though I must say I find Corona to be very promising and ahead of the others in some aspects.. Hope it keeps getting improved and ported to Maya as well..

[Correntes]

Back to last daily build... Well I'm resuming the render now with PTs 512

1.20h and I got 1/10 bar of the initial pass. Ill guess it gonna take a long time to see if it helps on the fireflies :S

Someone ?

[maru]

Increasing Path Tracing Samples probably won't help here. Actually you can try decreasing them to get more passes. Set PTS to 4-8 and try again.

Also, please show us your render settings and material parameters. Fireflies like this are usually caused by badly prepared materials.

You can also try rendering with buckets with low PTS (like 4 or 8) and many initial samples (try 20 and increase them if you need).

And I'm not saying any of this will help. :)

[Correntes]

Well I can try decrease the PTs then.

I excluded the problem being from materials because I used a override grey mat (excluding the light bulb) and the fireflies persisted.

Using buckets is my last resort option because I don't want waste 12h render time :S (I have the render almost clean only have fireflies).


Render settings I went PT-HD standard with light sub multiplier 20 (because all the lights).


Thanks for the input maru

[Ondra]

sidenote, you should not resume rendering with different PT samples, as it produces more noise

[Correntes]

Oh ok !

But can I play with other settings?

[Correntes]

Ok I found the problem!

The emissive material it self its fine. The problem is the super complex geometry that its is illuminating (in this case the scattered grass and bouncing on trees),
That's why even with override material, the fireflies appear. Its the complex environment that is creating the fireflies.

Now, how can I make corona more precise, I guess that if I can raise the precision which the illumination is calculated, I can get rid of the fireflies of doom.

Waiting for some help of corona gurus :)

Thanks

[Ludvik Koutny]

Posting render of entire scene would help.

First thing i would try to do in troubleshooting is:

1, Create new scene with default corona settings.

2, Merge all geometry and lights from original scene into the empty one with defaults.

3, Add same environment as in original scene.

4, Set secondary GI to HDcache

5, Hide all glass objects

6, Enable material override and put in gray diffuse material.


This test will tell you if the problem really lies in the geometry complexity ;) In 90% of cases it usually is due to the irresponsible lighting and shading.

[Eian]

If you want you can send me the scene.. Maybe I could help get rid of the fireflies..

[Correntes]

Just one update.

I resolved the fireflies question.

I remade the materials and lowered allot reflection and bump.



Now I have two questions:

1. Why the fireflies appeared even with override material ? This is a very strange behaviour.

2. Does someone know if Corona will have something like subpixel mapping ? Cutting reflections that much isn't a proper solution imho.
The day version of this scene rendered fine with proper reflection. If i had to cut reflections that much I would loose allot of details.


Tomorrow I will post  the final images, gonna let corona clean a little more.

Eian thanks for you time but I can't share the scene.

[Ondra]

if you set MSI=0 and use PT+PT, you get the true unbiased solution