alias maya tutorials- quick start mental ray in maya

7/29/2019 Alias Maya Tutorials- Quick Start Mental Ray in Maya

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Quick Start Mental Ray for Maya with focus on Caustics, Final

Gather, Global Illumination, Shadows, and settings for memory

management. Tutorial by Robert Cole,

http://www.texturelighting.com

Caustics

Global Illum (radiance)

Final gather ( diffuse lighting)

Shadows

Setup and Tuning Mental Ray

Misc tips and resources.

Setting up MR in Maya:Make sure the plugin is loaded:

Window>Settings/Preferences>Plugin Manager.

1.Click on Render>Render using>Mental Ray2.Create 1 each sphere, plane, spotlight.


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3. Render>Render Current Frame.

4. In the Render View window, select Options>Render

Globals>(mental ray)


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At the Format and Resolution box change it to NTSC.

At the Quality tab change it to Production

When you click on these tabs and change settings, new tabs will

appear behind the main Render Globals window. Clicking on the

symbol will bring you to the tab to adjust those settings,

but note that if you have previously made changes to that tab,

the settings in that window are re-set. I suggest that you maywant to select the window(s) from the tabs at the top of the

Global window.


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At Frame Extension make padding/name/extension changes

when you wish to render an animation, but for this tutorial leave

at defaults.

At the Memory and Performance tab, choose BSP, leave atdefaults for this tutorial.

Geek Stuff about BSP and tuning the renders for better

performance:

Binary Space Partition Parameters ..what the heck is that?

BSP is the way MR partitions a scene in memory to grab chunks

of the scene geometry, break it down into useable pieces,

process it, and go to the next chunk. So, the BSP SIZE is the

number of triangles per scene voxel MR will process, and the

BSP DEPTH is the maximum number of times MR will subdivideto get to this depth. So, I have found over the years that a setting

of 4,5,or 6 works best for the SIZE, and for the DEPTH, a setting

of 25 for light geometry scenes, 40 for medium, and as high as 55

for heavy scenes works best. Do not go over a setting of 60 or

performance will take a hit. See the excellent book

Rendering With Mental Ray by Th. Driemeyer for more

information. I understand the 2nd edition has a cd with a demo of

MR V2.1 on it.!

In the Memory and Performance box you can also select Grid

This is a setting that you may only want to choose if memory

management is a problem with very heavy scenes, but with RAM

being so cheap these days, and use of the imf-copy utility, you

may never need Grid. (more on imf copy later).

Ok, back at the Render Globals main screen, leave the rest of the

settings at their defaults, (MR will manage Virtual and Physical

Memory at the default settings just fine) next choose the

NTSC tab to view the settings, you may leave at the defaults

for this tutorial, but here is where you would choose one of the

28 output formats and 16 data flavors MR is capable of.


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Next choose the Production tab, this is where you will be

coming back to make changes when tuning you final renders. If

by chance you were to choose Preview or other tabs at theQuality box at the Render Globals main tab, a different tab

would be in this position and you can make the necessary

changes to parameters there.

Set-up the Production tab as follows: (Continue to next page)


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In the Rendering box you will want ray tracing, but at these low

values for this simple scene.


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Scanline will do just what it says (like Maya) it will scanline

parts of the scene that dont need raytracing.

Faces will tell MR to render back or front or all faces. A very

useful option.

Shadows for this release of MR for Maya, choose segments.This method is similar to Ray Marching algorithms, a topic I will

cover in a later tutorial.

Check rebuild shadow maps. One of the great aspects of MR is

that you can do simple shadows with hardware if your video card

supports at least a 24 bit Z-buffer. The drawback is that there

will be no oversampling or motion blur.

Caustics.. leave at defaults.

Global Illumination.. leave off for now.

Volume Caustics not fully implemented yet in this release.Reflection/Refraction Photons.. set to same values as raytracing

for now.

Photon Map File: the photon map, which is an addition to the

diffuse output of the final render, needs to be rebuilt each time

you make adjustments. The map can be stored anywhere you

like on your drive(s) with the extension .pmap. Sizes range from

1 Mb on up, and no, there is no viewer for them except in a MR

render.

Final Gather leave off for now.

Sampling Quality.. do not go under 0.050! 0.10 is fine also.

Guass Filter is very nice, do not go below 2.0

Jitterreduces banding problems, I always have it on.

Done with the MR render Globals, minimize the render view and

select the sphere and go to the spheres Transform node and in

its attribute editor, set : (continue to next page)


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You will need to un-check Derive from Maya to access thesesettings. (These settings only apply to how MR will handle the

geometry)

Select the plane and in the Transform node of its attribute

Editor, set:


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Select the Light, and set:


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If you will want complete physical accuracy for your light and

Photons, you will have to change the light to Quadratic decay

and check the Physical box under the Photons. The Exponent

box refers to the decay rate of the energy of the photons, which

for complete physical accuracy should be set to 2, which is

quadratic decay. Setting to a lower value increases the decay

rate, which is a bit counter-intuitive.


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Notice the Global Illumination box is not active: You must turn

this process on in the MR Render Globals>Production> Caustics

tab to make it active.

Now assign shaders to the geometry.

Create two (2) Blinn shaders, assign one each to the Plane and

the Sphere. Even though you may want a Lambert type look

to the plane, you need a reflectance attribute in the shader so

it can participate in Globillum.

Set the shader for the Plane:


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Set the shader for the sphere: (see next page)


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Go to your render window, ( it may still be minimized, if not bring

it back with Render>Render Current Frame) and in the Render

View window click Render>Render Current. Make sure you have

framed up the sphere and plane in the perspective window.

Viola! Caustics!

Now, if you want to improve/alter the caustic quality, play with

the accuracy settings in the Production tab before adding

more Photons from the light attribute editor. If nothing is

showing up also try adjusting the energy boxes upwards.

The energy settings refer to RGB values, so for example an

energy setting of 5, 5, 10000 will give a nice bright blue caustic.

Note: Also, if the image is still at 320 x 240, go to Maya Render

Globals and set to 061/NTSC, and this should give you the 720 x

486 format.


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Next open up the MR Render Globals tab again and enable Global

Illumination, turn off Caustics, give the shader for the Plane

a strong color (red, perhaps), turn off the transparency of theSphere shader, turn the eccentricity values in both shaders

to 0, rolloff to 1. Duplicate the sphere, move it next to the

first sphere, and duplicate the shading network and assign it to

the new sphere, change the color and reflected colors.

Check your light to make sure it will be emitting GI Photons,

increase the energy(s) to 50000, Photons

to 30000, check the physical box, and render.

You should get:

NextFinal Gathering


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In MR Render Globals, turn off Caustics, turn on Global

Illumination, turn on Final Gathering, Turn spotlight intensityto 0, turn on physical add Photons and increase the energy

until you begin to get an nice(?)image.

In larger scenes, it will not be unusual to increase Photon count

to 1000000 and energy levels to same or more. Increasing energy

will not increase render times, but adding Photons will. Again, it

is always better to adjust Accuracy and Energy before addingPhotons.

Photons are emitted from a light even with 0 intensity, and unlike

3D/CG light they trace a path from the Light to the objects in

the scene. 3D/CG light is actually traced from the camera to


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the geometry and then to the light source. Understanding that

Photons are not Illumination is essential.

Next: IMF Copy

the imf-copy (see your documentation for use) will greatlyreduce render times with scenes that use file textures. It is

similar to creating BOT files, in that only the parts of the

texture file that are visible in the render are called. There are

some nifty options (elliptical filtering, etc.) with imf-copy that

will pre-filter the file.

I will be doing a HDRI tutorial later, as it is all the rage now, but

for now here are some resources for HDRI and MR:

Mental Ray discussion at Mental ImagesDemo Version of MR 2.1 with book Rendering

Demo Version of MR 3.1 with book Programming

http://www.pixho.com

http://www.bullerin.com/

http://www.debevec.org/HDRShop/

www.edharriss.com (hdritoxsi utility)

http://www.finalgathering.com

Tips: GlobalIllum and Final Gathering will look best when you

reduce the Diffuse component of your shaders, as the Photon

map is adding to the Diffuse component.

Some samples of my recent experiments, with the reference

image displayed first.


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continue


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continue

end.

[email protected]


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