Reflective Material Artifacts

[JPS]

Hello all:

I've been having trouble with mental ray and how it handles reflective or mirror materials. Every time I render something reflective or mirrors, I get these dark reflections or dark artifacts that occur only in the reflections. I've tried all the mirror materials; Arch&Design(chrome), Architectural (Mirror), ProMaterials: Mirror.

What can I do to eliminate this?

 

PS: I would like to keep render times as low as possible.

 

Thanks in advanced.

JPS

[Justin Hunt]

can you post your FG and or Photon settings, it looks like it could be the max reflections in the FG are too low.

 

jhv

[MrCAD]

Did you try Raytrace in the reflection slot ? I normally use it to bring down my render times and no artifacts too

 

Meher

[Justin Hunt]

Be very careful with using raytrace with mentalray, they dont talk nicely. Besides if your using the A&D shader there is no need for raytrace.

 

jhv

[JPS]

Here are my FG and Photon settings, its as if its going to render fine while processing the FG but then when it does the final "rendering" buckets I get the artifacts. I've tried using FG setting on High but get same results with different looking artifacts.

Please help, this has been bugging me for a while.

[JPS]

As you can see when I set FG on High and it takes much much longer to render and I still end up with the artifacts only in the reflection of the mirror.

[JPS]

Thanks MrCAD but Raytrace in the reflection slot of a Standar material produces the same artifacts, plus it makes the reflection a foggy white. Any more ideas would be greatly appreciated.

Thanks.

[JPS]

Here is the scene, if you guys want to play around with it and see what you can come up with.

Thanks.

[noi-pi]

It seems that FG's are absent on that certain area. I have played around with your scene and come up with with + result. Using FG only, I saved the FG map as increment, then placed a camera at the opposite side to established FG points then went back to Cam 1 again and re-render. First image rendered with artefacts. Second image rendered the opposite side. Third image re-render the first one.

[Justin Hunt]

OK dowloaded the scene, and had a little play. I played on the weekend and am writing this from memory so there may be some other things to add.

 

Basically its a combination of problems,

 

Firstly, dont use Architectural materials, they are optimised for Radiocity and use raytrace which mentalray hates. Rather use Arch&Design or Pro-materials.

 

Secondly change the lights to emit from a shape (either rectangle of sphere) rather than point. This will help sperad the photon and FG samples.

 

Third, add a shell modifier to the walls to give them some thinkness. Photons dont always play nice with single sided objects.

 

Try setting a sample radius to the Photons (I tried 2' although I must admit feet and inches confuse me)

 

I also found switching the FG Interpolation methode from Number of points to Radius cleaned all the artifacts up.

 

Here is the model with my adjustments. I have changed a few things around in the trouble shooting process.

jhv

Edited July 12, 2009 by Justin Hunt

[RevitGary]

I thought mental ray was a combination of raytrace and scanline.

[Matt McDonald]

Mental Ray uses its own raytrace engine and doesn't like it when you try and use the studio max raytrace material or raytrace map. Dial up the reflectivity in an MR A&D material and the reflections are indeed raytraced.

 

MR can use scanline rendering for some of the additonal reflections and stuff but it does so with an ify increase in speed on low poly scenes and poor memory management.