Mental Ray - Render Troubleshooting

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  10 October 2007
weird glitch

so im not sure if i am missing a render setting somewhere. i ahve a scene and the building has glass and a top area the glass goes to spandrel glass adn has a parapet behind it. when i have the building isolated and render the spandrel glass reads perfect. when i unhide the reest of the scene the parapet that made the spandrel read correctly now renders incorrectly. anyone have any ideas?

here is when i had the building isolated


and when the whole scene with ground plane and curbs and grass and all
 
  10 October 2007
weird glitch

sorry for the double post

Last edited by alkhobarspecial : 10 October 2007 at 07:38 PM. Reason: double post
 
  10 October 2007
prefferd material for skin when using MR's FG?

have done some FG and character render previuosly and for whatever reason I've gotten some renderartifacts particularly on skin on chars(never had any probl with large "gradient areas", touch wood) when using std max materials, is there any other materials that might be more suitable? subsurf scattter mtr is not a option due to render times,


cheers,

k.
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  10 October 2007
Render artifacts - uncheck Tile and Show Map On Back

Hi there everyone!

Just a random tip:

I had a problem with render artifacts in an Arch&Design material. The artifacts showed up on the underside of an airplane, that used an Arch&Design material with a map in the Glossiness slot in the Reflection panel. It looked like some of the triangular faces in the mesh were slightly darker than their neighbours, making the underside of the airplane look harlequin-textured. Quite cool, but very unwanted. The artifacts showed when the map set the Glossiness to a low value, especially if I also had a low value for the Reflectivity. The idea was to let the airplane have weak and blurry reflections at a glancing angle, but no reflections at a "head-on" angle. Nothing strange there, I basically used a Arch&design template and dropped a map into the Glossiness slot in the Reflection panel. The artifacts did not show if I had strong and un-blurry reflections, only if I had weak and blurry reflections. And they only showed on the underside of the airplane. I tried a lot, for a long while, until I found something that helped:

I un-checked the Tile checkboxes, and then unchecked the Show Map On Back checkbox for the map I used in the Glossiness slot. That helped! (Don't know why they were checked in the first place - by default, I guess)

I think I'll make it a habit to not have anything checked if I'm not dead sure I need it, in the future...
 
  11 November 2007
Render Artifacts - Multi/Sub material with reflections

Another random problem area when rendering with MR:

Having a Multi/Sub material containing at least one Arch&Design material with reflections (Reflectivity not zero) caused problems - render artifacts.

Weirdly enough not on the object in question, but a totally different object that did not have a Multi/Sub material, but just a regular Arch&Design material with reflections. Turning the reflections down to zero for either of the objects solved the problem, which sent me on a long detour trying to find what was wrong with the object with the artifacts. Which wasn't the culprit. The Multi/Sub material was, and there were no aritfacts on that object.

So if you have any trouble with render artifacts when using MR, try getting rid of any Multi/Sub materials and see if that helps.
 
  11 November 2007
Some objects go dark when using mR Sky Sun Daylight

When using the Daylight system with the mR Sun, mR Sky as skylight, and mR Physical Sky as environment, and the Logarithmic Exposure Control, with the exterior daylight setting, some objects turned very dark. Totally unrealistically dark. And only some objects, not all.

It turned out that they used Arch&Design materials with a bitmap in the environment slot, to get more interesting reflections than the mR Physical Sky. It was as if that bitmap stole light from the diffuse component, the objects got much darker than they were without any reflections at all. Turning the reflection down to zero, or switching off this bitmap, made the objects look normal in the render.

It was way better to put that bitmap in the slot for background in the mR Physical Sky material - there is a slot called "Use Custom Background Map", where you can assign that.

Another way to get around this darkness problem was to leave the bitmap in the Environment slot in the material on the dark object, and increase the RGB output value of that map. If you for some reason would want to assign a different reflection map to one or two objects, than to the rest of the scene, this would work, as far as I have been able to test.
 
  11 November 2007
So has anyone ever figured out why when network rendering on seperate machines, you get differing results from seperate computers? I saw this was stated at the beginning of this thread but no one has figured it out. I've been having that problem a lot lately, especially when net rendering hair.
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  11 November 2007
Daylight, gamma and exposure?

Hi I'm rendering a scene with an iso container in it.



The scene start outdoors and then zooms in and go through the door. I'm going to key the shutter on the exposure control to go from outdoor exposure to in door.

I'm having a few problems with colour bleed in the container and also what should I have the gamma set to as the exposure control said I should enable it. Also what is that blotchyness in the corner?



I after advice as I'm new to mental ray as it seems much better in Max 2008.

Thanks in advance
Mark
 
  11 November 2007
Daylight, gamma and exposure?

Sorry double post
 
  11 November 2007
Gamma is necessary in any sort of photorealism type of renders because to have physically accurate lighting in the scene that also -feels- correct for you on the monitor screen, your renderer and application needs to translate mathematical colors to colors your monitor and your eyes register better. This is a fancy way of saying that mathematical average-grey is not the same as average grey for the eyes and monitor.

That's why everything that's not gamma corrected needs to be gamma corrected. To achieve this a curve is applied to the colors, called the Gamma Curve. 3ds Max has Gamma settings under Preferences and Gamma LUT tab. You should enable gamma correction, as well as use it for input and output images. If your images (like textures) are already gamma corrected then you can adjust their gamma override when importing them.

Usually Gamma on monitors should be somewhere between 1.8 and 2.2.

It may be strange to enable it at first, you might notice that some of your older renders become too bright and pale. That's either because your tonemapper is adjusted differently or your lights are set up non-physically correct. Once you get used to working in linear workflow (as it's called, gamma and tonemapping workflow) it'll become second nature.


Now, the other issue.

Blotchyness in the corner is the result of color bleed. Make sure your objects are 'whole' or increase your Global Illumination (FG or GI) settings to reduce the effect.
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  11 November 2007
Originally Posted by nmcelmury: So has anyone ever figured out why when network rendering on seperate machines, you get differing results from seperate computers? I saw this was stated at the beginning of this thread but no one has figured it out. I've been having that problem a lot lately, especially when net rendering hair.

I've seen this when you have different setup for HDRI and/or gamma, because these settings are not saved with the file, that's really annoing.
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Last edited by 3DMadness : 11 November 2007 at 12:59 PM. Reason: mistype
 
  11 November 2007
color spots everywhere......solved

hi everyone, this is my first post and i like to share with you how i solve this problem if my bad englis allows me to do it .
i change the IOR of the arch&dis materials to 1.0, but the colour spots keep in there, so i dis-mark (i don`t know if this word exist), i turned off the reflection`s fast interpolate, and SURPRISE!!! the spots go away.
thats it, please if this does not make any sense is because i reach the solution by try and mistake... and excuse me for my tarzanglish.
 
  11 November 2007
Originally Posted by Warisnake: hi everyone, this is my first post and i like to share with you how i solve this problem if my bad englis allows me to do it .
i change the IOR of the arch&dis materials to 1.0, but the colour spots keep in there, so i dis-mark (i don`t know if this word exist), i turned off the reflection`s fast interpolate, and SURPRISE!!! the spots go away.
thats it, please if this does not make any sense is because i reach the solution by try and mistake... and excuse me for my tarzanglish.

The fast interpolate sometimes produces artifacts, maybe that was your colour spots.

If you put an imagem with the problem and the solution it would help us understand better what was happening, "images worth a thousand words".
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  11 November 2007
Quote: The fast interpolate sometimes produces artifacts, maybe that was your colour spots.

If you put an imagem with the problem and the solution it would help us understand better what was happening, "images worth a thousand words".


you`re right, turning off the fast interpolate solve the problem. i don`t know if the IOR = 1.0 makes any difference (about the color spots), because when i do it, the spots don`t vanish, but i read somewhere that it could help. i have to do some test giving back to the arch&design materials their IOR value and joust turning off the fast interpolate.
here is an image of that nasty little colour spots.
hmmmm. this is my second post, so i can not upload any image yet, but in this links you can see them:
here
and here
 
  12 December 2007
Hey guys:
I'm having a weird problem.
3ds max 9 (and even 2008), rendering float saving a.rpf, sometimes (Especially with grass), I get values of alpha beyond 1.0, I use Fusion to comb stuff and some objects or grass hairs have alpha of beyond one (2.1) sometimes even negative! so what exactly is a pixel with a 2.1 alpha? super visible?
I only ask because if color correct or touch anything that would change the RGBA values - and that basically what you do a comp- I get nasty artifacts which is natural in such state.
does anyone have a clue on this? (hopefully Zap the pre-multiplied alpha master?)
Thanks.
~sion
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