Pathtracer + HDRI Causing Speckles/Firefly Artifacts

Hello there,
I am having an issue with the pathtracer rendering engine in Flamingo causing visual artifacts (speckles, I’ve also seen them called “fireflies”) when paired with specific HDRI’s. In particular, HDRI’s with a very bright light source, such as an unobscured solar disk cause this issue, while HDRI’s with the sun behind clouds are free from these artifacts. This issue does not appear to be resolved readily by increasing the number of passes. Attached is an image with the speckles has been allowed to run for 1025 passes.

Note the red speckles scattered throughout the water in the reflection.

This issue is not present in the default render engine, but I cannot reasonably use that engine for the real render I am trying to produce because it completes about 1 pass every 8 or so hours. Using the pathtracer, I was able to get quite decent high-resolution images after an overnight rendering (approx 12 hours).

Toward this end, I was wondering:

  • Has anyone experienced this problem before?

  • Are there any recommendations to resolve the problem that do not involve modifying the HDR itself?

I cannot post even the sample model file because it would count as “redistributing the HDR’s”, since all could download it from here. Would not object to emailing it to a rhino/flamingo rep.

Using Flamingo Build 6-Jan-2017, Rhino V5 SR13 13/09/2016.

Thanks in advance for the help, apologies for the length.

That can be a struggle with the pathtracer and one area of super bright area in the sky. You can tag the material in the reflection type from Balance to no Light source reflections. See if that helps.

Thanks for getting back to me. I made the following change to all materials in the model:

Unfortunately, no luck on getting rid of the speckles.

Just to exhaust the possibilities, I tried every different material type, to see if any of them worked, unfortunately, nothing.

I have read that for other rendering programs, this issue can sometimes be resolved by changing parameters such as the photon size or the HDRI sampling. I don’t think these controls are exposed to the end-user within Flamingo, but you can probably fiddle with them in your dev version. I’ll see if I can email the sample model through to you folks at McNeel.

Barring that, I have a few options still left on the table. I’m experimenting with using the images .jpg’s as backplates, and use the default flamingo Sun/Sky combo with environment reflecting/refracting visible background, but the water is getting really oddly colored with such settings.

Alternatively, I could try to make my real model more render-friendly in an effort to bring down render times with the standard engine.

Thanks again

I am struggling to recreate the problem. Do you have a model you can send with the HDRI file?

If you are running the sun on and the HDRI sky from a custom source. Then it the brightness balance between the Sun and HDRI can be extreme. Each time the ray hits the solar disk it could sparkle.