This
Document describes how to achieve
a Non photo realistic shading effect
in Maya, it also serve as a documentation
to nprs.mel
script. You can get the script here
or on www.highend3d.com via this link
(look for Non Photo Realistic Shading
v0.5)
.:[Introduction]:.
The non photo realistic shading effect
here looks like the image below, it
works in Maya by using a simple shading
network, it can be setup easily via
a script (nprs.mel) or manually. This
doc deals very much on how to use
the shading network produced by nprs
script. Its very easy to work with
and very fast to get the result, and
I hope you have fun reading this as
me writing it :)Often working with
3D graphics the real physical shading
models can be quite difficult to use
for an artist from a traditional 2D
background, say if I wish to color
kelivina's(the girl below) skin in
2D, all I need to do is chose the
correct color I have in mind and paint.
In 3D however despite the texture/color
I have chose for her skin the shading
models I use and the lights in the
scene determines very much the end
result, and often it doesn't look
like the color you had in mind, no
matter how much tweeking....it can
be very frustrating at times, to have
a skin tone I need a skin shader,
leather needs a leather shader etc.
etc. So why can't I have one shader
that describes what I what in a image,
just like how I work in 2D? Well,
nprs works very much like the 2D approach.
Some
info on the image above:
* There's no file texture involved,
99% of the image use nprs.
* Very fast to render, under 5 min on
today's average machine.
* Using standard Maya render, no raytrace.
.:[Part1
before getting started]:.
There's one important rule when working
with nprs, you'll need to have a uniform
light intensity across your scene, for
example I have 3 light set up and all
my light's intensity add up to 1.00
So if I want to add 10lights later I'll
need to adjust them so they still adds
up to 1.00, otherwise objects shaded
with nprs may appear over exposed. You
may say how do I make object appear
more bright? You adjust the colors in
the nprs via a ramp(later on this) You
can just have one light in your scene
and still very good.
.:[Part2
install and execute nprs]:.
To get nprs script work its easy, just
copy the nprs.mel file to your Maya
scripts directory (e.g.. C:\Documents
and Settings\yinako\My Documents\Maya\4.0\scripts)
yinako is my user name. To use the script
just type nprs at the Maya command line
and press Enter or run it from the script
editor. You'll get a window like below.
I'll
explain the sliders briefly here:
bright color >> the brightest
possible color on your shaded object
dark color >> darkest possible
color on your shaded object, often
you
don't want it to be black...otherwise
its not so interesting :)
color steps >> the number of
overall colors from bright color to
dark color.(Later on this)
interpolation type >> non give
a cell shaded look, Expotiential down
have softer look between color boundaries.Now
just click on create Non Photo Realistic
Shading to get a shading network created,
so every time you want a nprs you'll
need to type it on the command line.
.:[Part3
working with nprs]:.
Now go to the hypershade select the
shader you just made and view its
up down stream connections, it should
look like below.
The
script only creates a shading network
to begin with, there's much adjustment
later on. Double click the color_steps
ramp, this color ramp is at the heart
of nprs, and how you work with it. Here's
how it looks
Here
you can see there's 6 "color steps",
the brightest color are always on top
of the ramp, and the darkest color the
lowest part of the ramp, changing the
position of these give how much light
is give to a particular color. Assign
the npr_shader to a object, below I
have the default setting of nprs assigned
to Kelivina's bra. I have setup one
light in the scene below with intensity
1.00. Notice the "color steps"
form light to dark, these color steps
corresponds to the ramp, so the color
and positions on the ramp directly controls
how much color and what particular color
fall on the object. No matter how dark
your scene is you'll never get black,
but the darkest color for that object,
which is yellowish brown here. Same
applies to the brightest color too.
Also
notice the colors between the brightest
and darkest are interpolated colors
in between, this only give you a nice
smooth shading, but like fine art
you often don't want a perfect gradient,
it looks too CG-ish, so you often
adjust the color in between them.
And the positions among them on the
color ramp. A good way to adjust the
color ramp is to use IPR in Maya and
change the interpolation to non, to
give that cell shaded look, which
clearly defines where the boundary
between you colors are. Now you can
tweak a hell lot here. Of course you
can add and delete "color steps"
as you see fit to your work.
I
have deleted some of the "color
steps", and give a dark purple
for darkest color. Too much "color
steps" can look too smooth of a
shading, unless you are working on much
higher res image which more color step
can be distinguished. You'll also notice
there's a dark border around the object
if you don't want them just locate the
condition node connected to the npr_shader
and change the second term to 0.00.
If you want the outline to be more fine
you'll need to increase the mesh resolution,
its the facing ratio method, cheap and
fast, no comments there :)
.:[Part4
Tips]:.
Now
you know how to work the ramp, there's
not much to it, very simple actually.
Since now you colors appears exactly
how you wish to appear in the scene,
you can actually get colors from other
sources. Like photos or mangas(for me
:), even though these sources are already
lit, it doesn't matter to nprs, cause
light in Maya can't change the color
of your objects anymore. Here below
I detach the color picker and go get
some skin tones :)
Here
below I also have kelivina's finall
skin color ramp, the positions and color
doesn't have to be nicely interpolated.
Notice there pink, orange, browns, it
make the image look much more interesting
that way. And this is what nprs is all
about :)
.:[Conclusion]:.
So that's all, not much to say really,
simple and easy to work with. I know
there are many short comings with the
current nprs I'm working on. I have
considered future improvements and shading
this way, here's are what's for the
better:
* specular(hard ones too :)
* file textures
* paint strokes along color boundaries
I haven't got to working on them yet,
but If I ever want to improve on nprs
those will be the first thing on mind,
and of course if you know how to implement
them I'll be god damn glad to hear it
:) Oh yeah one last note nprs was originally
called manga shader :) because that
was the
original idea behind it.
