2017 Mental ray rendering large dots rather than smooth light gradiations

[Anonymous]

Recently something has changed and mental ray now seems to represent light in my models with large circular dots (see image). There's no disco ball in the model.

The arc of light falling on the wall is from the fixture in the scene, the dark yellow horizontal below is part of the model. I think the dots are intended to represent the environmental light from the fixture?

I'm not sure when this happened unless it was when I accidentally hit the render cloud button instead of the adjacent render production. This has happened before in 2017 but I am not sure what triggered it or what made it stop. It's certainly not the image I want.

Max also seems to be defaulting to the Art Render rather than Mental Ray?

[-niels-]

I think i've seen something similar with one of my renders before...
If i recall correctly it had something to do with caustics, so maybe check the render settings to see if that's enabled.

Other than that, i wouldn't know why it's happening.

[Anonymous]

Hi Niels, Thanks for the feedback, at the very least I've now read up on caustics, but no, that isn't the problem.

It appears that the problem is how final gather is calculating indirect illumination. It appears that rather than calculate a smooth transition across the surface, it is producing clusters of overlapping flat circles of illumination. This could work OK in high illumination situations such as sunlight, but in low illumination it tends to look as if many flashlights are being shined into the space. Increasing final gather precision seems to increase the number of spots while reducing the spot sizes but doesn't get me where I want to be.

Things work better (the spots go away) if I enable Indirect Diffuse (GI) on the Render Setup > Global Illumination panel > Indirect Diffuse, however this appears to turn off final gather altogether.   If I read things correctly, this is then a radiosity solution which will not handle transparency and specteral reflections which are somewhat important to me.

Also note: the documentation related to these control rollouts does not seem to line up one to one with the actual panels, making it a bit hard to follow.

[Anonymous]

OK, still trying to make sense of this issue.... while it continues to only crop up when I use final gather, it does seem to relate to how the light fixtures are modeled.

When I remove the shade, the dots go away. Could it be that even though it is intended to be a smoothed surface, I'm getting spectral reflections off the facets? When I turn the shade to black, the dots also go away, so some sort of reflection?

I've revisited a number of light fixtures modeled in 2014 and 2015 which had worked fine in those versions but now create disconcerting dot patterns in 2017. Again, it appears to happen when the light passes through glass or bounces off a near surface. Has something changed in 2017?

It does seem somewhat related to caustics but the surfaces that are creating the dot patterns are smooth, not rippled or distorted and while I've poked about a bit, I haven't found anywhere caustics are turned on that they weren't before. Basically, I've never intentionally turned them on.

[Anonymous]

OK, I'm about to throw in the towel. A bit ago, I opened the old MAX file with the desk and added a wall and the container w/ the ceiling light, rendered it and get the following image. Everything works!

 

Thinking the problem might have to do with MR sun and exposure settings, I added a sun, set to 1AM and set exposure to EV3

This is what I get... still pretty good!

Wanting to test things to make sure they were now working, I created a new empty 2017 file, added a room, the containers containing the desk and ceiling lamp, again set the time to 1AM and the exposure to EV3 and rendered this!! The circus is back in town!

The only difference I can see is that for the last image the file was created new in 2017 where as the file containing the desk was from an older version...I can't really believe that's the issue, but am now at a complete loss.

Help!

[-niels-]

Strange issue indeed...

Here are a couple of images i did quite some time ago, which had to do with the caustics i mentioned.

Might not be exactly the same issue, but it's also light scattering when passing through a glass object.

At the time i think i fixed it by making all the objects (planes, lights, the dice object) generate and receive caustics and that ended up giving me this second image.

So maybe it has something to do with that...?

If you don't have caustics enabled in the render setup, do you have photon mapping enabled?

Because if either one of those is enabled you also get the option to set "geometry properties" to "All object generate & receive photons and caustics".

Just throwing some options in the mix, hope it helps with hunting down the problem.

[spacefrog_]

Looks like low/inappropriate Photon Mapping Settings to me.

Can you post the scene or at least a screenshot of your GI rollout/Photon Mapping render parameters (+your system unit settings) ?

Strange thing is the  - as you mention the dots  ONLY appear with Final Gather enabled. If it's the photon mapping, they should appear with FG disabled

[Anonymous]

OK, here's what I know:

Problem only happens when final gather is turned on. Doesn't happen with Art Render or with Indirect Diffuse (GI) turned on.

It has to do with the shade in the light fixture. Remove the shade - no dots, change the white part of the shade to red - red dots, make it black - no dots

Simplifying things as much as possible, see below.

The following images were done this morning. 

1 - In a new session, I added a container containing the light fixture, added floor ceiling and walls, set the wall, floor and ceiling to white paint, Set render to mental ray and final gather to medium. Result images are below:

2 - In the same session, I opened an old file (pre 2017) , deleted it's contents, ran GC(), and reconstructed the test as above. The results are below.

I can move back and forth between the two files and the results are the same. Same when I shut MAX down and restart.

Before making these tests, I renamed the ENU folder to reset the user values and have updated to the latest MAX patch.

I've attached the MAX files to this post.

[Anonymous]

here is the container

[dominique.bouthillette · Accepted solution]

Hey @Anonymous!

It seems the issue is stemming from the Noise Filtering as it is set to "Standard" in the scene working as expected and set to "None" in the scene with the speckling.

To change it back to the previous setting, you can go to Render Setup > Global Illumination > Advanced rollout > Noise Filtering (Speckle Reduction) and set this from None back to Standard.

Hope this helps! 😃

Best,

Dominique

[bstepinski]

Hello!

I had similar issue while rendering with Mental Ray + FG. I'm using 3DS Max 2018.

Fitler (speckle reduction) didn't work properly.
I uncovered that my model (which was imported from *.skp) has all polygons doubled. Each face of mesh has its counterpart with flipped normal. This resulted in ugly dots of light, as shown on attached render.

As You can suspect, after removing unnecessary elements render was smooth and clean.

Best regards, Harborn.

[dominique.bouthillette]

I'm glad to hear you were able to resolve it after deleting the extra faces! Thanks so much for letting us know @bstepinski. 

[Anonymous]

Hi

I'm trying to resolve the same problem with mental ray and 3dsmax2017,

I found a webpage and is being super helpfull. Explains the final gather. To smooth those circles of light it's necessary more information so we have to give higher values of fg/bounces… check this link

https://artasmedia.com/2014/10/29/3ds-maxmental-ray-basic-final-gather-explained/