Importons are more than a simple Final Gather variation. They fit in a significant change in the way mental ray will deal with global illumination and sampling in general.

First step, get a correct Final Gather.

The question on how to configure the Final Gather is not straightforward as the results can deeply change depending on the scene. I'm going to assume we don't want a perfect Final Gather but an "effect" of Final Gather (indirect illumination in one bounce). I invite you to look at the documentation.


It's the number of samples send through the scene for each point of Final Gather to determine the value of the illumination at this point. If there is not enough, the actual point will not be stable. We can set it to 200-500 for most cases, but sometime you need to go on values close to 1000 in really extreme cases.

If you have a high point density value, accuracy car drastically increase render times.

Point density

This is a factor of the number of Final Gather points shoot from the camera. A value of 2.0 doubles the number of Final Gather points to compute, and so, double the Final Gather generation time.

This is the first parameter that I invite you to increase before boost the accuracy. Keep in mind that accuracy has an exponent effect. Do not change one without taking care the value of the other. A value of 10 on a production render with flat surfaces of uniform color is possible. With textures, variations can be less visible and you can almost stay on the little values like 2.0-5.0.

Point interpolation

This is the number of Final Gather points that will be interpolated to return a value of indirect illumination to the projected sample. This value drastically changes the visual appearance of Final Gather. The more interpolation is, the more Final Gather is smooth but more it flick in animation if it's not bake. If your scene has high contrasted lighting, I suggest you go down this value to make the flicking generally less visible (more granular). We can put 1 if needed.

Note that you can increase this value at the same time as point density, because the more you have points, the more you can interpolate and keep flicking invisible.

For the rest...

I do the following things:

  • Secondary Diffuse Bounce: 0
  • Reflection, Refraction and Max Trace Depth (of Final Gather of course): 0

Why all of this to zero? Because beyond to increase rendering time and potential artifacts, one diffuse bounce is enough to create a convincing "effect" of indirect illumination.

  • If you are doing animation, set the multiframe mode (Optimize for Animation in Maya).
  • If you want a brute force Final Gather, switch to force (No FG Caching). For each sample, a new Final Gather point will be created. Of course, this is (very) long.

I will not spend much time on this, it was mainly a reminder. Let's talk about Importons! :hehe:

What importons are?

I could spend a lot of time trying to explain what the importons are but I think the official documentation is very clear. Just read it! :RTFM:

Basically, you guessed it, mental ray "shoot" particles from camera that bounces in the scene and determines which areas of the scene have "visual" importance in the final image. Therefore, mental ray is able to "know" which areas of the scene will be important to sample and forget the others. Until now, Final Gather was very silly, but with the importons, it is much less. :jdicajdirien:

Autodesk, again and again and...

Well, I starts to get bored to slug them all the time but you will see that, once again, we fight against Maya to run the thing... For an unknown reason, Autodesk has decided that if the user tick Final Gather, he had no interest to tick Importons (neither Irradiance Particles). This option becomes grayed out. Yes, that's stupid... I suppose choice has been made one day, without paid to much attention to the documentation and has never been change since (are they only aware of?). So, we will not speak about this too much, I invite you to use my tool enjoyMentalRayStringOptions to go through Maya's limitations.

Insofar tick Final Gather disables importons, you need to tick Final Gather in Render Settings THEN Importons from my interface... Reverse would disables Importons...

Notice that each time you restart Render Settings window, Final Gather will disable Importons... So keep it open! (Yes yes, I know... :pasClasse: )

There is also a tool that I have not tested but who aim to fully integrate with Maya and should solve this problem. It is shown here and the page of the script is here.

And the tiny tutorial!

Once you've understand the above part, you will see it's quite easy! :D


DIM Tick FG!


DAM Tick importons!

DOOM Launch the render! :grenadelauncher:


Before... (27sec)


After... (29sec)

There is a clear improvement in artifacts on the walls. Indeed, mental ray shoot it Final Gather points taking into account the importance (calculated at the beginning of the render) of these points in the final image.

I also invite you to look at the log in Progress mode to ensure Importons are well shooted through the camera



Importons are very fast to shoot through camera so don't hesitate to use them! :banaeyouhou:


I hope this little explanations will help you to improve your renders with Final Gather. :sourit:

See you!