View Full Version : Interior Scene Lighting - From Lambert to MIA - Observations + Comparisons

08 August 2007, 11:24 PM
This is kinda of a long question / observation thread, but basically i'd like to know if i'm going about this the right way. I've been doing nothing but MR the past 2 weeks for work and it been it's pretty frusturating, but ultimately very satisfying. I've been trying to read up as much as I can on these boards and elsewhere and this is my first attempt as gathering up all of that knowledge and putting it to work. I've supplied pictures and scene files in case anyone has time to take a peak. Any help would be greatly appreciated.

Scene Files :

My Goal for this is to make the room as bright and evenly illuminated as possible without it being too flat. The idea is that it's a futuristic kids room so it should feel really soft and never be too dark. The only illumination happening now is from the circular opening in the ceiling, but I would eventually like to have the two yellow lamps supply subtle illumination as well( using an omni light in the center of the shade caused some strange shadows). The first picture is a render straight out of maya with the settings supplied below. (Top of Pic 1) The second is after I brought it into photoshop and performed levels and color balance operations on it. (Bottom of Pic 1) I'm fairly happy with the results in post, but I'd like to get it as close as possible within maya. The problem is, is that it's really easy to blow out and flatten the image when trying to light a room that's bright like this.

The shaders are default lambert shaders with different colors. These were used to just get a basic test out, but I would really like to use the MIA material for all of the objects in my scene to make things more accurate, so I did another test with them exclusively.

All of my MIA shaders have a gamma correct(.455,.455,.455) node piped into the diffuse color and my camera has a mia_exposure_simple lens shader attached to it with the defaults (gamma 2.2, etc.) as far as tone mapping goes. They also have themselves piped into the photon shader slot of their shading group so that they work with GI and FG. I have two basic MIA materials so far in this scene; a more or less diffuse material with a reflectivity of .2 and a low gloss and a 'shiny' material with a reflectivity of .6 and a slightly less glossy look. My diffuse MIA shaders still seems really reflective, because even if I turn off GI and FG it appears like they're receiving way too much light from the direct light. It also appears like all color in the scene has vanished when rendered without indrect illumination.(Top of Pic 1) But as soon as I turn GI and FG back on things start to appear a better, but definitely worse than when I was using all lamberts.

Some observations w\ the MIA material test. (Bottom of Pic 2)

- While it was rendering it looked like it was going to be great. It was Nice and bright while it was chugging through the FG calculations, but as soon as it was done it wiped through all of the FG blocks and made it look as flat and dull as it does now. Is this the lens shader doing post work?

- I seem to have lost a lot of my contact shadows. Of course I could do an AO pass and get them back, but it seems strange that they were more apparent in the lambert test. Is this because I have a slight bit of reflectivity even on my diffuse shader and it's bouncing light into the contact area and brightening it up?

- Why do I have that ugly yellow splotch on my ceiling. Bother renders have this and I know it's occuring because light is bouncing off the yellow of the lamp and shooting up at the ceiling but how would I go about making it more subtle?

- it looks bad ( ha!)

Here are my scene details:

My scene scale is set to 'centimeter', but I consider each unit 1 foot.

I have one area light positioned ~4 units above the hole in the ceiling w\ a scale of 5.

The walls not visible to the camera are pulled away so that they aren't blocking the camera, but invisible bounce cards ( poly planes ) were positioned to allow the photons to add fill to the objects that needed it ( shape tower and the foreground desk ).

:::Light Settings:::

MR Area Light ( from Maya Area Light)
Intensity: 300
Decay Rate : Quadratic

Raytraced Shadows - On
Shadow Rays: 3
Ray Depth Limit: 1

Light Shape: Rectangle
High Samples: 16
High Sample Limit: 8
Low Samples: 8

Emit Photons - On
Photon Intensity: 6000
Exponent: 2
GI Photons: 100,000

I've experimented with using the physical_light, but I wasn't able to notice any advantage for this scene.

:::Render Globals:::


Reflections: 1
Refractions: 1
Max Trace Depth: 2


Accuracy: 500
Radius: 2


Accuracy: 400
Point Density: 2
Point Interpolation: 20

FG Options: Defaults

08 August 2007, 01:31 AM
Here is a test render did.
Some materials were connected in a wrong way.Also some objects were not visible to reflection/refraction.
And here is the file.

08 August 2007, 03:28 AM
wow slipknot! I didn't expect such a quick response!

I have a few questions about your setup :

- I noticed you placed a cylinder covering over the hole in the ceiling. Is this so photons don't escape and just die off and instead contribute to the light on the ceiling?

-Is there a reason why you would use physical sun in addition to an area light? How is the physical sun able to enter my room with that cylindrical cap covering the only opening?

-Your render looks really nice and clean and renders a hell of a lot faster than my crappy setup. You seemed to have used less photons and lower settings in general. Is there anything in particular that I did that could really benefit from optimization?

-Is there some kind of logic to the relationship between High samples, High Sample Limit, and Low samples in an area light? I've seen so many conflicting responses on this topic that I usually just set the High Samples really high.. and then set the other two attributes to half of that. You had 64,6,3 which I don't get but the render is very clean.

-I'm going to have look into the settings of the mia_exposure_simple. I've been keeping it at default for too long. Your settings are way different than mine.

Thanks for your help!


08 August 2007, 05:23 PM
Hey drossxyu, well, the cilynder was just to prevent the sun light to enter the room, as the idea was to create an artificial light.I created the sun/sky because if you decided to change the design of the room and put a window for example, you could have the sun light coming from that window.I used low values because with mental ray 3.5, you dont need to use high values for FG anymore, specially when combining with GI.

About the area lights sample values, here from the Maya help files:

High Samples
This represents the number of sample points emitted from the light (X and Y). The default is 8. Values greater than 8 increase the quality by reducing graininess, but may increase rendering cost.

High Sample Limit
To reduce rendering cost and time, it is not necessary to use a high number of sample points after a light ray has been reflected or refracted several times. This attribute represents the number of bounces that the light ray should go through before it uses the Low Samples values instead. "
I did some tests and those values seemed to work better.
About the mia_exposure_simple, was the same thing, lots and lots of test renders until i got something that worked the way i wanted.
About the connectins, well i usually just middle mouse drag and drop over the SG and it creates all the connections.
I hope that helps you, btw i saw your demo reel, WOW! really cool :)

08 August 2007, 07:33 PM

drossxyu, i found Mia material a little buggy ...

you know when i switch to uv texture editor and toggle view picture on
the objects with Mia material suddenly turns black no matter what its color is
... ( however it renders o.k , just the view )

did you have such issue..??

thank you

Thats a bad mr implementation, not a bug.
It should render fine.

08 August 2007, 09:40 PM
Is it also necessary to pipe in the MIA material into it's own 'shadow shader' slot in its shading group?

08 August 2007, 11:40 PM
bad mr implementation ??!

you mean i did something wrong with MIa material or Mental Ray treats mia material like this ...?

I meant it is not well integrated in Maya, but thats Autodesk fault, not mental images :)
But if you connect a simple texture to the diffuse slot of the mia material you will have a correct viewport display, i only had problems when combining the gamma node and the texture map.

09 September 2007, 12:06 AM

drossxyu, i found Mia material a little buggy ...

you know when i switch to uv texture editor and toggle view picture on
the objects with Mia material suddenly turns black no matter what its color is
... ( however it renders o.k , just the view )

did you have such issue..??

thank you

09 September 2007, 01:41 AM
Thats a bad mr implementation, not a bug.
It should render fine.

bad mr implementation ??!

you mean i did something wrong with MIa material or Mental Ray treats mia material like this ...?

09 September 2007, 08:20 PM
bad mr implementation ??!

you mean i did something wrong with MIa material or Mental Ray treats mia material like this ...?

You didnt't do anything. It's just like this. it's a MR ba implementation.
I have this to.. so you can't really see a 'preview' of your texture unless you render it.

But one strange thing I noticed is in the presets , evertying renders ok except for the "satin and glossy vanished wood". Everytime I pick this preset, I can see it in the viewport but when I render, the object with that material is just plain grey... strange. So now I have to manually set all settings instead of just choosing the preset... annoying.

And slipknot, your old kitcken scene has led me to read about IBL and now I found it very interesting and was able to get fairly good result on the first try; also, it avoids me of using physical Env. cause I don't really like it.
As for tonemapping, I still haven;t got the point of this. Do I have to plug a gamme correct to ALL textures, then render as EXR and tonemap in PS ?
btw, how do I tonemap EXR in PS... everything is blocked with this format : can't create new layer, can't do image adujstment... every buttons are greyed-out

@drossxyu, may I ask how your outer box work ? I mean the black box that contains the room ? What's its purpose ?
And about the mia_materials, sometime mines also have problem during render so what I do is just using normal Maya materials and try to tweak setting so it looks realistic. And I get pretty nice results. I only mia_material when Maya ones really can't get it right


09 September 2007, 10:33 PM
The oute_wall was originally extruded from the inner_wall to give it thickness, but in the end I decided to seperate each wall and extrude them seperately. The outer_wall is just an old attempt to thicken the walls but currently serves no purpose. I just never deleted it..

09 September 2007, 10:57 PM
I got your scene and hit render button... my render was so sloow, it was never going to finish
So I re-created new lights and just wanted to do some test render. I left all materials untouched.

One MayaAreaLight converted to MR Area. No light emittion. Only GI.
All settings default, except the number of photons increased to 50 000.

One directional.light plugged by mib.cie.d at 6000K to simulate sunlight. (no photons)
Enabled IBL node and chose a blue sky color.

Render settings:
GI accuracy : 200, radius:3. Else, default
FG rays : 100. Else, default

880x495. 8 mins. Of course, FG radius should be tweaked to control the contact shadows, and other tweaking could be done. I modeling is very nice. I would be interested to know what the few 'planes' are for... looks like they're one-sided (could you remind how to do that). I think those planes setting contributed to the ight distribution, but I would like to know how you place them and how you adjust their settings.


09 September 2007, 02:38 PM
How would I go about lighting this scene with an FG multi-bounce setup? I tried putting a white value of 25 into the background color of my scene with:

(No GI, No Lights)


Secondary Diffuse Bounces On
Reflections 12
Refractions 12
Max Trace Depth 12


FG Diffuse Bounces 12

I know this is overkill, but I don't seem to be getting any secondary bounces whatsoever. I have intense light coming through the ceiling and the surrounding areas are hot, but there is no 'multi-bounce' to be seen. Am I missing something?

09 September 2007, 02:04 AM
Does this look normal at all? The first picture is without FG. The second picture is with FG. There are no incandescent materials in the scene and there is no color in the camera's background color. The FG seems excessively bright and unnatural and this is without any multi-bounce ( I was able to get multi-bounce to work btw, it was just more subtle than i expected). I especially don't understand the bright bounce light i'm getting on the back side of that cylindrical object in foreground left as the wall behind the camera is not close to it at all.

09 September 2007, 03:18 AM
Yea it does look a touch off. What are your settings?

09 September 2007, 03:40 AM

Maya Area Light > MR Area Light ( 2 )

Intensity: 1500
Decay: Quad

Raytrace Shadows: 4,4

Area Light: Rectangle, 64,6,3

Photon Intensity: 20k

GI Photons: 500k


MIA Material: (Itself piped into material/shadow/photon)

Diffuse Weight: 1


Raytracing: 3,3,6



Accuracy: 1000
Radius: 2



Accuracy: 100
Point Density: .8
Point Interpolation: 100

Secondary Diffuse Bounces : Off




09 September 2007, 02:51 PM
Here is a test i did, secondary diffuse bounces only.
Point Desnsity=2
Point interpolation=20
Diffuse Bounces=6

Using the IBL node, texture color intensity=6
Mia_material., with a gamma node.

09 September 2007, 03:03 PM
There's a light linking problem with one of your shaders that's causing some trouble. The mia_baby_blue_diffuse's light linking mode must be set to 2. You assigned the shader to individual faces, this usually implies light linking issues.

09 September 2007, 04:19 PM

The multi-bounce technique looks solid. I didn't know you could attach a solid color to the IBL node so I had been avoiding using it exclusively. I tried it out myself and the only downside is that it took about 17 min to render w\ -2,0 anti-aliasing. Is there a way I could lessen the strength of the blown out white near the openings, but keep the indirect illumination the same?


Thanks for checking out my scene. I've been trying to look up MR light linking in the help file, but I can't seem to find anything on it. In this instance, I'd want all of the objects to be linked under the same lights, right?

09 September 2007, 04:25 PM
Well, to reduce the overexposed areas, you could increase the compression under the mia_simple_exposure, or use a low intensity under the IBL color texture and increase the number of FG diffuse bounces.But that can make the final render look washed.Thats why i dont like to use FG secondary diffuse only to light my scenes.The best way its combine both methods (FG+GI), it will also render faster this way.

09 September 2007, 04:46 PM
Thanks for checking out my scene. I've been trying to look up MR light linking in the help file, but I can't seem to find anything on it. In this instance, I'd want all of the objects to be linked under the same lights, right?
The light linking is a shader internal issue, so you wont find anything on it in the reference.

Basically this is a mayatomr translator problem I suppose. You will encounter it with any custom mental ray shader that implements the light linking this way.

Generally, avoid assigning shaders to individual faces, rather apply it to whole objects if possible.

09 September 2007, 05:19 PM
So if we refer back to my second scene, it seems like the techniques where only one indirect simulation is used (My first picture is GI only) and slipknot's (FG multi-bounce only) look the most natural. I know it's prefered to use GI and FG in conjunction, both for speed and quality, but it seems like whenever I use them together the lighting becomes completely non-discript and flat.. and way too bright ( I.E. second scene, second picture). Am I supposed to almost under-light the scene with GI knowing that my FG ( even w\ one bounce) is going to boost the brightness significantly? My prefered workflow would be use regular lights w\ GI, and have the FG smooth things out.. rather than having the FG overpower the work I put into the GI solution.

Also, how often would you actually adjust the GI and FG scale in the render globals? I suppose this could help bring down the intensity of the fg, but it doesn't seem like a commonly used attribute.

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