The dark art of mental ray from SimplyMaya provides workflows
intended to harness the power of render layers and passes to gain
minute control over your renders. This frees you from the
time-consuming process of tweaking your lighting and materials to
absolute perfection within Maya.
The instructor starts by briefly
covering the practical implications of linear and non-linear
workflows. These topics overlap with the beginning of “PhysicallyAccurate Lighting in mental ray”. Linear lighting is an abstract
concept and difficult to get your head around. This is compounded by
the fact that there are numerous ways to tackle linear lighting (as
with all things) in Maya. The methods given are decent, but I would
have liked a bit more explanation for these, since I previously
learned yet another method that makes more sense, to me at least.
The explanations of render layers and
render passes are excellent. It can get very confusing when and where
to use either render layers or passes, and the instructor provides
helpful examples of getting results from passes, layers, and
combinations of the two. Case in point, you can get ambient occlusion
from a render pass or a render layer, but one of them gives you much
more control. Also discussed here are layer and material overrides,
accessing passes from the render viewer, selecting passes to rebuild
a beauty pass, and a few pitfalls. This is important information for
any serious Maya user to know.
As an aside, I find that rendering
tutorials often use uninspiring geometry and scenes *cough* torus
knot *cough*, and while that does get the information across, it becomes
easier to imagine how principles can apply to your own projects when
interesting and attractive examples are used, as in this tutorial.
I have never used Nuke before; this was
my first look at it. I have quite a bit of experience
learning complicated software, so it wasn't too difficult for me to
keep up in the compositing sections. However, the tutorial does
assume some knowledge of Nuke (and Maya), so I would not recommend
this for beginners in either program. Linking the separate passes in
Nuke to rebuild the rendered image shows how you can gain control
over your render in post, especially with higher bit files. This is
the main focus of the Nuke sections of the tutorial, i.e. linking
nodes together to recompose your rendered image while gaining more and
more granular control over each aspect of the image. The instructor
doesn't go into depth on what attributes you can or should tweak in
terms of color correction etc., but this isn't the aim of the
tutorial, for better or worse.
In the same vein, creating separate
render layers for each light (with associated passes) really gets to
the heart of controlling your output. The Nuke setup gets more
involved, but it is obviously worth the effort when you see the
control you have. It doesn't stop here, as contribution maps can be
built to break down the scene in terms of geometry and materials.
More control—is the theme becoming
clear? As contribution maps and light layers are dealt with
separately, I admit I am a bit unclear on how they can be used in
conjunction, for the simple reason that different types of merge nodes would
have to be used in a specific order in certain groupings. Just a
quick look at a network with both light layers and contribution maps
would clarify this for me.
Requirements for even more granular
control allow us to see how to output to custom render passes, a very
helpful technique. Learning how to properly
add ambient occlusion passes was another eye-opener. This is all
about using mental ray the right way and to maximum effect. Finally
we get to see how to create material id passes; I'm not sure how the
method described compares to another method I've used with surface shaders as
material overrides—perhaps
just passes vs. layers?
This tutorial is
all about workflows for getting more out of your renders without
endless re-rendering. It is abundantly clear that hitting batch
render does not need to be the final step before delivery. Granular
control without additional render time is a wonderful thing. But what
is the cost? The instructor did not mention it, but I suspect it is
disk space. Adding dozens and dozens of passes and layers adds up to
eyebrow-raising file sizes. Each frame can quickly become very hefty,
and even a short animation will be massive. But space is cheap and
time is expensive; you can do the math.
One final thought:
I am fairly confident all of the techniques shown in Nuke could be
applied to After Effects, though it may be less elegant or quick to
do. As I suspect more people are familiar with After Effects, I would
be interested to see an addendum or short tutorial on connecting up a
couple of light layers each with the required render passes. Plus
ambient occlusion with the proper math. Regardless, this is an
excellent tutorial that will make you think about rendering
differently. I know I will be adopting many of these workflows in my
current project, now that I've bought a couple more hard drives.
