Maya render passes Part 2 – Tutorial

In the second part will look into separating the scene elements in spate passes and incorporating render layers in our work-flow.

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March 30th, 2011 by | 2 Comments »

Maya render passes Part 1 – Tutorial

Render passes were first introduced in Maya 2009. The terms “Render Layers” and “Render Passes” are sometimes used interchangeably. However, this is inaccurate.
In this tutorial we will explore how to extract the render passes out of Maya and going through all the available options.

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March 30th, 2011 by | 6 Comments »

How to fix nParticles shadow problem with mental ray

When rendering particles or nParticles with mental ray for Maya, you will notice that the option to cast shadow has no effect on the render.
For example this scene have a group of objects and you will notice that the spot light with ray trace shadow is casting particle shadow on both cubes and tea pots.

The problem appear when we want to disable the nParticles shadow on the ground.
One would go to the nParticleShape node and disable the cast shadow under the Render Stats.

Unfortunately this currently not working in Maya 2011.

Workaround 1
Disable the particles shadows entirely by going to the nParticles node itself , under mental ray > flags and disable Derive From Maya.
This will give you the opportunity to use mental ray native flags. The obvious answer is to set Shadow to No.

However this will give us another problem, what if  we want nParticles to cast shadows on a certain object but not on the other.

Workaround 2
In this scenario , we will go the object that we don’t want it to receive shadow and disable the receive shadow option under render Stats of the shape node.

This will disable the shadow from self and other objects , but yet the nParticles is not fixed.

The fix would be going to the mental ray render settings under Quality tab > shadows and change the shadow type to Segments.

Now the shadow will respect the shape node options.


March 29th, 2011 by | No Comments »

Mental ray final gather filter – Explained

From the docs

Use this to control how Final Gather uses a speckle elimination filter to prevent samples with extreme brightness from skewing the overall energy stored in a Final Gather sampling region.
Neighboring samples are filtered so that extreme values are discarded in the filter size. By default, the filter size is 1. Setting this to 0 disables speckle elimination, which can add speckles but will better converge towards the correct total image brightness for extremely low accuracy settings. Size values greater than 1 eliminate more speckles and soften sample contrasts. Sizes greater than 4 or so are not normally useful.

What does this mean is , FG will try to optimize/control the blotchiness in the scene by either merging or illuminating some of the rays that doesn’t return enough values.
Thus getting rid of the extreme different in color (blotchiness).
This will eventually lead to lower overall illumination.

The values are from 0 – 4

0 = off (Maya default)

This will give the most natural look

1 = standard

2 = High

3 = very high

4 = Extremely high

This will bring us to the million dollar question.
How to get rid of final gather blotchiness?

Final gather by itself is not the ultimate solution if for this enclosed areas. Since FG capture the illumination from the environment, once it’s used in enclosed area  it can’t see the environment anymore.
One would need to first tighten these FG rays by:
Increasing Accuracy
Reducing Point Density
Increasing Point Interpolation

“Bitter” has this nice rule General rule:
Complex lighting needs for accuracy rays
Complex geometry needs more density

Another tip would be adding a small amount of light, for example point light with very low value.
This will help eliminate the extreme difference between bright and dark

March 18th, 2011 by | 1 Comment »

How to fix misss_physical in Maya

If you would to render your old misss_physical , or trying to follow the tutorial on the lamrug page.
you would notice that the scatter is gone.

To fix this issue, do the following:
Open the AE of the misss_physical shader.
Under Extra Attributes
Change the default mode from 4 to 0

Now the render should give you the desired scatter.

January 31st, 2011 by | 1 Comment »