Red Photons bug

[rotem]

Hi

Glad I found this forum. We've switched to mental ray at work and are having a repeating bug with many scenes... triggered by the most random of things. It happens when we use GI, what happens is all the photons in the scene turn red, tinting the image.

This seems to be caused randomly and not really dependent of anything logical... the last case was one in which the scene rendered fine at 320*240, then when switching to a slightly higher resolution, everything went red!

Another case was fine when a certain bump map was at 0.1 amount, but when taken higher it turned everything red.

Has anyone ever encountered this? It's driving us nuts!
It's on max 9 & latest MR.

[JeffPatton]

I haven't encountered the colored spots problem in Max9. But I know colored spots have been an issue in other builds.
http://forums.cgsociety.org/showthread.php?t=303284
(see post#2 to verify if any of that info applies)

By chance were you using any materials other than the A&D material in the scene? Is it possible to post the scene or a render of it?

It also might be related to interpolated glossy reflections/refractions if you're using that on the new A&D material.

[rotem]

I can't share the scene, but here is a good render (at 320*240) and a bad render (at 960*720). Render resolution is the only different parameter.
The scene uses only A&D (no glossy interpolation) and standard materials (no raytrace maps or anything like that).
These renders are without shadows and final gather and with poor AA, just to see the photons.

Thanks for taking the time to help!
http://farm1.static.flickr.com/126/350159964_1fcce4aa4e_o.jpg
http://farm1.static.flickr.com/126/350159966_e8d8b6f8e5_o.jpg

[JeffPatton]

First, I'd check the mental ray message window after the render for any error messages that might lead you to the problem. After that:

You might want to try hiding any glass in the scene and run a test render to see if the problem goes away. If it does then it's related to your glass material or glass mesh(es).

If that's not the problem then I'd run a render using the material override with a standard material applied. That would also help narrow the problem down to a material. From there, it would be a search for the problem material. If you have materials that use falloff maps, output maps, etc, I'd start checking those first.

[Shimrod]

You might want to try hiding any glass in the scene and run a test render to see if the problem goes away. If it does then it's related to your glass material or glass mesh(es).


Please could you explain why glass materials can cause this kind of problem ? ;)

Thx

[JeffPatton]

Please could you explain why glass materials can cause this kind of problem ?
The reason I mentioned the glass was because in the link I posted above one of the spotty scenes in that discussion had a problem with single sided glass meshes & the force 2 sided option.

Now exactly why that created the spots, I can't say for certain. If I had to guess, I'd say it was difficult to calculate photons passing though a single sided mesh when force 2 sided is enabled. But that's merely a guess on my part and I'm sure someone like Master Zap could provide a much better/accurate explanation.

[rotem]

Thanks for the help Jeff

I took your advice and isolated the materials one by one (there's no glass or transparency in the scene).

The problem material was the floor material, more specifically, the fact that it had bump applied.

Why the hell is this happening? It seems that any value above 0.8-0.9 in the bump slot causes this.:mad:

I attached a picture of the result for each bump value.

http://farm1.static.flickr.com/143/352571359_b4825900ac_b.jpg

[Brian Bradley]

Hey Rotem,

Understand you cannot share your scene but can
you create a simple scene with the same material
applied to something? Maybe we can troubleshoot
the material a little and see if there is a workaround.

Regards
Bri

[rotem]

I've recreated the bug in a new simple scene, but I have no server space to upload to. Would you like me to mail it to you?

[Brian Bradley]

Yep, that would be fine.

brian@mentalboutmax.co.uk

regards
Bri

[JeffPatton]

Now that you have narrowed it down to one material, you could also simply post some info on that material here (what is it, what type of maps did you use, etc).

Also, what did your mental ray message window say about the material or the spots during or after the render? Did it not provide any info on the error?

[rotem]

The message window doesn't pop up, shows no error.

A simple way to recreate this bug is :

1) open a default A&D material (with the default reflection).
2) assign any bump map.
3) change BRDF to 'By IOR'.
4) up the bump multiplier.
5) use global illumination.

[Brian Bradley]

Hey Rotem,

Followed your instructions and this is what
I get?

Bri

[JeffPatton]

No luck in reproducing the red photons here either Brian.

While I haven't been able to reproduce the exact error, following his settings I have found that if I increase the bump map (noise map) multiplier over 1.2 then the photon map will simply not calculate (seems to lock up).

In some cases I have seen issues when using displacement wherein it made the geometry overlap into itself and cause issues...but mental ray spit out some warnings & other issues in that scenario....but I can't help but wonder if something like that is happening in his scene with the use of a strong bump map?

[Brian Bradley]

Hey Jeff,

Does seem to warrant a little further investigation. Not
sure why we are not getting Rotems photon prob??
I had a similar lock up of the Photon Map, disappeared
when I switched from mr Spot to mr Omni which seems
a little odd??

Rotem, if you reproduced this in a simple scene mail
it as mentioned, may be a few things going on at the
same time.

Regards
Br

[rotem]

Hey guys

I sent Brian the scene, though the photons are not red in it, just overburnt white. Maybe it depends on the surroundings.

Strange you couldn't reproduce the bug. Maybe it has something to do with lighting? I was using a simple omni with inverse square decay.

Jeff, whenever the bug is 'in effect' I also get photon map hangups at certain points, though after a while it does calculate it and render.

[Brian Bradley]

Rotem,

As you say, couldn't produce the 'red' photons
in this scene but there is definately some odd
stuff goes on with the bump/photons as the numbers
hit a certain point in the spinner.
Image 01 is taken with the bump amount at
1.93 image 02 is after one click up to 1.94.
Photons definately go crazy. Might want to ask
Master Zap himself to take a look at this??

Regards
Bri

[chocot]

a buggedtrick that i used to have in newest max8 version
try to save photon map before rendering , and deleting it directly, re click now on rebuild photon map, and RENDER

this module caused me bugged result when not activated at the beginning of Mr process


maybe...