mental ray stories -Final Gathering-
 

I plan to finally dive into mental ray and get a little wiser.

Please contribute with your godlike knowledge of mentalray :)

FIRST SOME ISSUES:

mentalray Beta doesnt seem to support the render-region function in maya. Which means you have to (if I'm not wrong) render whole images, every time you render with mentalray.

SO FAR... (About Final Gathering)

I have found out that you can use a materials "incandesence attribute" to act as a lightsource. BUT You need to create a light, else the default lights appear and wash the scene with light. Set the intensity of the created light to "0". You need not turn on any photon emitting with final gathering alone (it seems)

ABOUT THE RADIUS SETTING...

-I have read at several places that the MAX radius should be like 5-10 % of your scene's size in maya units.
-MIN radius should be like 10% of MAX radius. Im not sure, but it was also said that the min radius should be made smaller to take into account the smaller objects in the scene. But I dont know (at this time) what the differences will be, if MIN radius is too big for your smaller objects.

The pic below shows a final gathering rendering with one material, having some incandesence. Im sure I can figure out how to make the "light source" dissappear, but I not sure how at this point.

mental ray stories -Final Gathering- 2
 

The incadensence value was set to max.

mental ray stories -Final Gathering- 3
 

The object (with incandesence material) acting as a light source was scaled bigger.

mental ray stories -Final Gathering- 4
 

The initial light source was removed. A new poly sphere was created and scaled up, until my scene and the perspective camera were inside the sphere.
The poly-sphere is fully enclosing.
Incandesence is still set to max.

mental ray stories -Final Gathering- 5
 

Same as previous but the poly-sphere was exchanged for a 180 degree nurbs sphere.

I can't see any major change here.

edit:
hmm the diffused light seem a little brighter in the last rendering. And the light seems to be more intense from the top, and not so bright from the sides as in the former rendering.

mental ray stories -Final Gathering- 6
 

Same as previous, but the incandesence is set to 50%.

mental ray stories -Final Gathering- 7
 

Same as previous, but the incandesence is set to 25 %.

mental ray stories -Final Gathering- 8
 

I have now removed the point light (whos intensity was set to "0") and added a directional light.

Directional light intensity is set to "1".
Color: slightly yellow.
Shadows are raytraced.

? It seem that there are no shadows cast from the dir-light.

mental ray stories -Final Gathering- 9
 

I hid the sphere, and the shadows did appear after that. Why is this?

Edit: Solution See next post!

mental ray stories -Final Gathering- 10
 

Ah, I checked out some of the attributes to the nurbs sphere;

Check out BOTH of these:

CAST SHADOWS
RECIEVE SHADOWS

Dir-light intensity was set to 4.
Nurbs sphere, incandesence was set to 25%.

! If you want to make the sphere non-present in your rendering, check out also the;

PRIMARY VISIBILITY

:) Now I'm getting somewhere.

mental ray stories -Final Gathering- 11
 

Looks nice I think; I'll start with this pic, and do some changes to the FG settings and not the lights.

1000 FG rays
Min rad: 0.1
Max rad: 1.0

Min samples: 0
Max samples: 2

mental ray stories -Final Gathering- 12
 

FG rays: 200

Comment: The pic has clearly gotten more grainy.

wow, that is a great thread, keep em coming. :banana: i need learn some more about mr.

:beer:

mental ray stories -Final Gathering- 13
 

This pic:

FG rays = 4000 (!)

This setting is quite a time waste if you are just fooling around. I'll go back to 200 and try some light angle with the raytrace dir-light!

mental ray stories -Final Gathering- 14
 

FG rays set back to 200
The directional light has the light-angle set to 5 degrees with 1 shadow ray.

Thus we see the shadows as quite grainy.

mental ray stories -Final Gathering- 15
 

With FG rays still at 200, the light angle is 5 degrees, with 10 shadow rays.

The result is still not good enough.

The manual says you can reduce the light-angle to reduce graininess, but I still want to puch up the number of shadow rays.

Maximum shadow rays are 40 !

Next, I'll go for 20 shadow rays in my directional light.

aaaa.. somebody stop him!! LOL :D

nice thread undseth.. keep it up!

mental ray stories -Final Gathering- 16
 

FG rays still set to 200.

Light angle set to 5 degrees.
Shadow rays set to 20.

Well, it is better but I have to push it even further. I would have but now I want to model something. ;

A room with a sky view
 

Nothing special, just a few renderings.

The walls are white.
The sky is... well, also white.
Directional Light (as sunlight) with intensity set to "1".
A nurbs sphere 180 degrees around the small scene, with incadesence material set to about 25%.

And FG rays set to 200.

mental ray stories -Final Gathering- 17
 

Blah! I had a rendering here but I missed the save option from the renderview and accidentally hit the render button. I lost this one.

However it was a bit too bright I think.

Next, I'll do a super render :)

I'll go for 8000 FG rays.
Sampling: Min 1 Max 2
MinRad: 0.01
MaxRad: 0.1

edit:
Actually, when I come to think of it, the rendering wasnt lost, maya saves all my renderings automaticly in iff format.

mental ray stories -Final Gathering- 18
 

Hmmm... This super render wasnt as good as I hoped it would be. But maybe it has to do with something other than the settings I have been working on.

The pic below is compressed to jpeg, but the original has a bad/less good transition betweent the shifting hues of the light.

FG rays = 4000
MinRad= 0.01
MaxRad=0.1

DirectionalLight Intensity = 3

MinSample = 1
MaxSample = 2

FG rays = 10.000
MinRad = 0.05
MaxRad = 0.5

MinSamples = 1
MaxSamples = 2

This picture is "smoother"

It's great to see your experimentation.

Thanks

mental ray stories -Final Gathering- 19
 

A LITTLE FOOLING AROUND WITH MIN/MAX RADIUS

This scene consists of these elements:
-180 degree nurbs-sphere, with incandesence material set to about 50%. This shere is located just outside my scene. It acts as a light source, but dont ask me why I need a light in the scene to make it light my scene with its incandesence vaule.
-Scene objects, most objects are colored white, while some has the heavy metal shader on it.
-A directional light, whos intensity is set to "0"

-FinalGathering Quality is set to "PreviewFinalGather".
-FG rays = 200

The size of this scene is 10 for the centered scene, and about 20-30 for the floor.

In this first rendering I set some very high values here for fun.
-MinRad = 1
-MaxRad = 10

RESULT:
Well, the rendering is spotty, but still quite nice for a preview (I think). Wow, the diffuse here is awsome. I have read somewhere that you can map the sphere with an image to give it some varying light shining onto the scene. Maybe a hdri image would be cool here :), for both incandesence map and reflecion map.

I will do a great rendering at the end of all this to hopefully sum up my experience today.

mental ray stories -Final Gathering- 20
 

MinRad = 0.5
MaxRad = 10

RESULT:
The diffuse is still grainy after redusing minrad from 1 to 0.5.

mental ray stories -Final Gathering- 21
 

MinRad redused to 0.2.

RESULT:
The grainynes has not been recuces at all it seem. I'll reduce the minrad a bit more and then try to figure out how the max rad changes things.

mental ray stories -Final Gathering- 22
 

Ah, here's something I have discovered.

Although some of the diffuse on the floors are still the same as the first render, in this latest render, the diffuse on the colums seem to be grainy, but in a tiny way. I take that as a good omen.

MinRad was 0.01

But I suspect that maxrad has some major role to play here, I'll do another render, starting with minrad back at 1 and decrease the maxrad, like I did on the minrad setting.

mental ray stories -Final Gathering- 23
 

Came to think of it, that I probably know why there is a minrad and a maxrad setting. I recon the mentalray works best/fastest if it can treat the scene varyingly in a render. I guess.


MinRad = 1
MaxRad = 5

RESULT:
So when I reduced the maxrad from 10 to 5, the result got better. (I already knew that 10 was too high, but I had to try it out)

Im not sure how low the minrad should be. I will go a little further down with the maxrad and change the mentalray render globals "quality" to production to get a final render.

Im not sure what is concidered a good solution in "PreviewFinalGather" mode. So I'll do a final render soon with some average min-max-rad settings and then some better ones to see if the previw mode is a good way to work with if you want to fine-tune your renderings in a time-saving way.

Great work Undseth! A great thread for anyone wanting to get to know MR!

Fantastic job..

I will add 4 points to your VIP subscription in appreciation of your work :)

mental ray stories -Final Gathering- 24
 

:) Thanks Kevin! :)

In this render the minrad was at 1 and the same vaule was set to the max rad. I would probably set the minrad lower for better renderings but I'm just fooling around here.

RESULT:
The render is better and the grains are smaller all over I think.
------------------------------------------------------------------------------------
I will now take a look at the differences between the PreviewFinalGather and Production mode.

Default MAX REFLECTION RAYS
Preview = 2
Production = 10

Default MAX REFRACTION RAYS
Preview = 2
Production = 10

Default MAX RAY DEPTH
Preview = 4
Production = 20

My FINAL GATHER RAYS
Preview = 200 set by me
Production = 1000 (default I think)

DefaultSAMPLING QUALITY
Preview = min -1 and max 1
Filter = Triangle width = 2 and height = 2
Production = min 0 and max 2
Filter = Gauss width = 3 and height = 3

I looks that these are all the parameters that is different in the defult settings, between the previewfinalgather and the producion quality.

I will do a production render now with the settings above. The production quality will have the same min- maxrad settings as the preview mode. Which is why I used the preview menues in the first place. The finalgather rays is beefed up to 1000, with a higher sampling value and a different sampling filter.

Im not sure about the filter thing, but the sampling gets rid of those jaggy edges. Most prominent in edges that arenet quite 90 degrees perpendicular(?) to the ground plane.

mental ray stories -Final Gathering- 25
 

Here we go. This rendering took about 3 hours time on my computer.

Default Production mode, with 1000 finalgather rays.
MinRad = 1 and MaxRad = 1

RESULT:
Looks good, although it is still grainy, but much better than the preview rendering.

Looking at the columns, the sampling can be improved by setting min samples to 1 or higher (warning: higher sampling takes much longer time to render if I recall correctly).

mental ray stories -Final Gathering- 26
 

hmmm I decreased the minrad to 0.1 with maxrad at 1, but it looks like it is more grainy than the minrad and maxrad 1 solution earlier.

Of course, the finalgather rays were never set higher than 200 in the previewfinalgather mode.

This lastest rendering took 35 minutes time to process.

I want to go back to my first solution with min- maxrad at 1 and 10, to see what the limits are when rendering with very high amount of finalgather rays.

I guess it would be nice to render out with these ray counts;
x4 4000 finalgather rays
x16 16000 finalgather rays
...just to see if the grainyness will go smooth out.

But I have just rented the movie Scorpion King on dvd, so I'll do the rendering later this evening. :)

just a suggestion, but maybe you can key the settings and let it batch render a whole series when you sleep.

anybody know what the difference between normal reflection and hdri reflection is?

I intend to do a render tonight while I sleep, to get that fantastic render quality. :)

I dont know much about hdri images, but I think such a file has a dynamic content that adjusts itself according to over- and under-exposure in renderings. I think hdri images keeps up the subtle contrasts when you say flood your scene with light.

mental ray stories -Final Gathering- 27
 

RESULT:
This is quite nice I think. I'm not sure how a high min- and max-radius affect the rendering of smaller objects, but I guess cranking up the finalgather rays alone gives some very decent results.

This rendering had minrad at 1 and maxrad at 10.
Finalgather rays was set to 4000.

I'll do a 16000 ray render in my next post.

i wonder what you will be able to do if you change the lighting to something more complex then a sphere, or if you let the sphere lit by global illumination and then make the final gather.

amazing stuff already - but one question:
i know you have some knowledge about architecture, did you learn lighting there as well? or do you learn it with trial and error now ??

now put all together and write a tutorial. Very nice iniciative. Keep going.

BabyDuck:
We learned something about light, by painting exercises. About sunlight and and the diffuse bluish light from the sky.

Global Illumination works with FinalGather, there may be a way to combine both, in a time saving manner. I'll try that later.

Oh, and started a renderjob before I got to sleep. I set the finalgather rays to 20000, and it only got to about 17% before I decided to abort the render. Seems like I should lower the ray count a bit :)

Rodi:
I want to make some summarizing out of all this. Just a little more experimentation and I'll get a little more wiser about all this.

mental ray stories -Final Gathering- 28
 

Oh, I just remembered that the minrad and maxrad setting can be automated. Simply set them to "0".

This pic is not the 16000 ray setting, but a 4000 with min- maxrad settings to "0".

Um, it looks nice, and renders a bit faster I think. Now I'm puzzled :).

RESULT:
The shading is different here. The diffuse is more smoothed out! Can you see it, compared to the former pic with 4000 finalgather rays?

mental ray stories -Final Gathering- 29
 

This is another rendering with automated min-maxrad settings. Which was set to "0" on both min and max.

Finalgather rays =16000

RESULT:
The small shadows beneath the big slabs in the center, has dissappeared with the automated min-maxrad function.

So I guess these are the things that has to be taken into concideration when fiddling with a speedy final gather solution.

hmmm! I wonder what Maya put into the min-maxrad here!?!

Although I raised the final gather rays from 4000 to 16000, I cannot see ANY change in quality.

Well I'll try the 16000 ray count on the earlier solution, with min- maxrad at 1 and 10.