mental ray lighting

[alias_marks]

hey all, hope this finds you well. I've been jumping into mental ray the last couple days and am having trouble getting my lighting right. It seems like my architecture under the roof is way to dark and when I pump up my levels, GI, or Sun Intensity, it only makes the roof brighter. I've also toned down my shadow density on my daylight system with no success.

 

here's a couple sample images of what I'm talking about and a snapshot of my settings below.

 

 

 

 

 

I apologize for the small settings image - anyone know a better way to do this?, hopefully you can zoom in with your browser.

 

Thanks for looking, I appreciate any insight you may have.

[chodney]

Some people would disagree, but I never use Exposure Control with Mental Ray. I find that it counteracts a lot of the control settings I use to brighten the Global Illumination.

 

Looking at your settings, I noticed a couple things I would change...

1) Your Global Decay Setting is really high.....especially for a bright exterior. I would put it down to about 0.7 or maybe even lower and that will solve a lot of your problems.

2) Your IES Sun has 'Shadow Map' as the shadow type. I would do either Raytraced Shadows or Mental Ray Shadow Map

3) When you start adding photon shaders to your materials, you'll get a lot better GI also.

 

Could you post your material settings?

good luck

[Justin Hunt]

Also crank up the diffuse level in the Photons to 50 and also the no for bounces for FG to 10

 

Don't be afraid to crank up the Photon samples (1000) but keep the FG (20)samples low, photons are quicker to calculate than FG.

 

Its OK to use the exposure control, but not the exterior daylight setting.

 

Once you put in the road it will also give more surfecr area to bounce light back onto the model, so until then simply put in a mid grey plane.

 

JHV

[Atom]

For my setup on exteriors, I have a.

 

-skylight set to 1.0 and a light blue tint

-MR spot light change to directional light and set multiplier to .74 with light yellow tint and use raytrace shadows.

-In your enviorment menu turn ambient light to black. I noticed you have yours at a grey level. This light is not accurate in 3D max and ruins renderings I think thats why your roof is getting brighter.

-set final gathering to 100 samples leave radius alone and see what happens you should end up with a cleaner rendering then you have now.

 

The modeling looks great especially the roof tiles. Sometimes you can get away with just this setup and adding a dirtmap to make it look more real. When I use mental ray i've never tried using daylight systyems or exposure options.

 

Also to speed up FG I make a huge sphere around the whole scene and add a normals modifier and then in the sphere properties set it to not render. Doing this makes FG work faster cause it has a point to bounce off instead of shooting off into infinity and waiting for hours.

 

Let me know if this helps any. Good work mental ray is challanging but worth it i think.

[alias_marks]

Hey guys/gals, I really apprecite your comments. Wow it was a hectic day at work today! I'm still working on some of your ideas and plan on sharing once I can get some more time to work on it.

 

many thanks,

 

Michael

[Cesar R]

::subscribed::

 

quic k Q. what does the radius for the FG do? and the trace depth value under FG and GI?

[Justin Hunt]

My understanding is that Trace depth is the no of bounces a sample will make before it stops calculating. The reflect and refract settings are similar to that of Raytrace settings, how many times a ray will pass through a refraction and or reflection before it stops being calculated.

 

To tell the truth I have read and reread the manual and am still a little confused with these settings

 

In Max8 FG now has a no. of bounces setting.

 

JHV

[Cesar R]

In Max8 FG now has a no. of bounces setting.

JHV

 

yeah and this setting is right under a trace Depth value to make things more complicated... this is exacly why I ask.

[alias_marks]

Yo, so I've got some better rusults, but am interested in improving quite a bit.

 

I tried lowering shadow decay and ended up with a brilliant yellow image espically bright around the reflective surfaces.

 

I did move over to a daylight and mr spot instead of a daylight system and I think this made the biggest difference. However, I did have to set my light multipliers fairly high ---- 30 for the daylight and 35 for the spot.

 

Atom - I did try and set my ambient down to black but just getting very dark images. Also, I set my samples down to 100 but which helped with test rendering but I found at larger scales, I started to see lots of shadow lines.

 

Justin - Thanks for the tip on the gray plane, I think it helped to reflect a lot of light back up in to the building. I couldn't really find what you were talking about regarding the diffuse level in the photon section

 

I know the materials need some work, any ideas. I'll also post some of my materials settings. Great help here! Thanks.

 

 

 

 

 

 

 

Thanks for looking.

 

Michael

[Justin Hunt]

sorry I meant Max Depth.

 

Is it possible to upgrade to Max8 ? There are some significant changes to MR in the way of samples can be lower, speed increased and there is a No. of bounces setting in FG. I can get much better results with 8 than I could with 7.

 

An other thing to try is instead of increasing the Photons samples, increase the no of Average GI Photons per light, 10000 is default but this can go up to 100000 or more. This will increase calculation time , but will improve the soothness. Increase the shadow density as the shadows are being washed out.

 

Its getting much better and looking good

 

JHV

[Cesar R]

Hey All,

Just one thing to be aware of, if you are using GI

AND FG then there is no point setting FG bounces

above 1 as they are ignored after that point and

the Photons are used to generate all the bounced

lighting.

Bri

 

 

are you sure? I thought my scene was gettin brighter when using higher values for FG bounce

[Justin Hunt]

I agree, the extra bounces are calculated, it is more evident when there are deep areas that are only light by bounced light. Besides it is better to let the photons do the hard work and FG to do the cleaning up. It is possing to us only photons, but I find with a little FG there is more detail in the shadows.

 

JHV

[Justin Hunt]

Sure, I have just the model, I will set something up and post results later.

 

I know that with the scene I am working on now, with bounces set to 1 there is no to little detail in the shadow areas, but when I crank them up to 5 (I did go to 10 with little improvment) I am now getting the shadow detail.

 

JHV

[Justin Hunt]

This is my little test.

 

Photons 1000 sampls, with 50000 average photons/light.

FG 50 samples

 

There seems to be little to no difference between Max depth of 25 and that of 5 as well as the no of bounces of 25 and 1.

 

The last image in just Photons. The average photons/light hadto cranked up to 5000000 before it got to the same level of Phtons and FG. The calculation time was quicker than Photons and FG but the render time was slower. Overall it still rendered quicker than the FG.

 

I will rerun the test using just FG. I think there will be a more noticable difference with colour bleed though.

 

JHV

[Cesar R]

great, well as i mentioned the bounces do make a difference. but the Max dpth for FG doesn not which is why I am wondering what is really does.

 

so far I think the built-in C4D radiosity engine is the easiest to work with from playing with the demo version and reading some papers.

[Cesar R]

I went to the actual mentalray website and under their FAQ section I found this:

 

Does mental ray support radiosity?

mental ray supports full physically correct global illumination. This includes radiosity as a special case, but additionally simulates all light transport modes possible in nature.

 

can someone tell me what that mean? Isnt MR and Vray and modo and C4D radiosity engine?

[Justin Hunt]

Had a little reread and think about Max depth, from what I know understand Max depth is the no of times a sample will pass through transparent surfaces before it stop calculating. the Max reflections is how many times a sample will seen in a reflection of a reflection (think two mirrors opposit each other) and the refractions is how many time a sample will refract before it stops calculation.

 

Am I correct in this?

 

JHV

[Cesar R]

Had a little reread and think about Max depth, from what I know understand Max depth is the no of times a sample will pass through transparent surfaces before it stop calculating. the Max reflections is how many times a sample will seen in a reflection of a reflection (think two mirrors opposit each other) and the refractions is how many time a sample will refract before it stops calculation.

Am I correct in this?

JHV

 

 

okay so if you were rending glass, you would want the Max deph value to be nice and hight (adecuate) for light to pass throught and illuminate a space? (light through a window)

[Justin Hunt]

yes, but also take into consideration and opacity mapped textures, eg many planes stacked over each other and each with a opacity map

 

JHV

[Justin Hunt]

abot the radiosity question check out these links from the resources page. I havn't gone into any of them for a while now but they are a interesting read.

 

http://www.cgarchitect.com/resources/radiosity/default.asp

 

JHV

[Cesar R]

okay this is what I found in regards to TraceDepth Values,

 

Souce: http://www.jozvex.com/tutorials/fg2.html

 

"The light (red) strikes the glass ball and some of it reflects off into the rest of the world (purple). Some of the light also refracts through the glass (green) changing direction slightly. When the refracted light then refracts again while leaving the glass, it resumes it's original direction. So for the glass ball, we had 1 reflection and 2 refractions. To allow Mental Ray to make these reflections and refractions happen, we need to have the Raytracing 'Max Reflection Rays' set to at least 1 and the 'Max Refraction Rays' set to at least 2! The last attribute, 'Max Ray Depth' sets the limit of how many total reflections plus refractions will be calculated. I usually set this value to the sum of the reflection and refraction depths. Mental Ray (and lots of other renderers) call the light that it sends out when Raytracing is turned on a Ray, and that Ray is...Traced though the scene, hence the name. So now that you get the basic idea of how the attributes work for Raytracing, lets go back to the FG attributes and why they're great."

 

"In real life if you have a skylight, the light can shine in and illuminate the room. It's the same in Maya if you're using lights outside of the room and Raytracing is turned on. The light will shine in through the glass skylight (you need Raytracing turned on so that the light can refract through the glass, like mentioned above). Unfortunately, with Maya's default 'hidden' FG trace settings, if you tried to light the room with FG instead (using the environment colour outside) you'd get this:"

 

"Extremely dark. Why? Because with FG Trace Refraction set to 1, the light can only enter the glass (with one refraction) but then it can't refract again to exit the glass and light the room inside! Up until Maya 5 with these 'hidden' settings, we were basically doomed to darkness without regular lights in a case like this. Luckily, now we can increase the FG Trace Refraction value to 2 or more to solve the problem. You also need to increase the FG Trace Depth too remember, because 1 reflection plus 2 refractions equals a possible depth of 3, not the default 2. When I'm using FG and there are objects made of glass, metal or other reflective and refractive materials in my scene, I usually set my FG Trace settings to the same values as my Raytracing Max Rays settings. In this case I'm going to use:

 

FG Trace Reflection: 3

FG Trace Refraction: 7

FG Trace Depth: 10"

 

So i guess those values apply only to RAYTRACED items in the scene while the Bounce:X applies to overall FG brightness. Therefore they was not alot or any difference in the amound of light in the renders above =) !

 

When I go back to my office tomorow I will look for my max manual.

[Justin Hunt]

That clears it up a bit, its pretty much the same in Max, he explains it better than in the max help though.

 

JHV

[alias_marks]

Alright guys, so I've been working on this project a little more and am interested if you have any tips of getting different shadow ranges on flat, planar surfaces. Similar to the effect after I do a radiaosity solution mesh in the scanline renderer.

 

First off, should I be even be using bumpmaps in mental ray to get a stucco texture, or should I use the mental ray connection rollout and use displacement maps.

 

Here's an image rendered in mental ray but I can't seem to get any variety in the shadow tones accross the plane. It's much too regular.

 

 

Thanks for looking and for any suggestions you may have.

 

Michael

[Justin Hunt]

Sorry for the delay in getting back, Been away

 

Set the max distance for the FG, What is happening is samples(Photon and FG) from far away are hitting the walls, so in effect the wall is recieving too many secondary bounces. Try setting it down to 2m (play to get the desired result)

 

As to the stucco, it depends how fine or thick it will be. If fine then bumps if thick then displacment. Things to note though, the bump will be washed out in the areas only light by GI and displacments are trick to get right.

 

JHV