RenderMan-tutorial-3dworld

TUTORIALS
Rendering photorealistic skin
Use RenderMan 19 to
create a productionquality
renders; create
a stylised version
of the classic Steve
Martin arrow gag
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RENDERMAN 19 | ZBRUSH | MAYA
CREATE A PHOTOREAL
MODEL IN RENDERMAN
Harsh Agrawal uses the new RIS framework in RenderMan
to render a production-quality human head
ARTIST PROFILE
Harsh Agrawal
Harsh Agrawal is a
19-year-old CG artist
interning at Pixar.
He likes to combine
aesthetics with his
technical skills to
create digital content.
www.harshagrawal.co
This tutorial will show you how
to create a photorealistic
human head using the
advanced features of RenderMan,
version 19. This version delivers a
new rendering mode called RIS,
which is designed to be fast and
easy to use, while generating
production-quality renders.
We’ll start with a raw scan
of a real person, and because
RenderMan can handle extremely
complex datasets, we can quickly
render high-quality images
straight from the original scan
without bothering with topology,
displacement maps, and so on.
We’ll explore the workflows
involved in manipulating the scan
data in ZBrush to extract texture
maps for our shaders. Then we’ll
set up our scene in Maya using
the physically based shading
and lighting tools in RenderMan
Studio. We’ll use new workflows
and traditional techniques to
render out different components
and combine them together for
our final high-quality image.
This tutorial is structured
using the familiar CG pipeline,
from sculpt to render. To fully
demonstrate how to create
photorealistic skin, I’ve included
a detailed breakdown of
RenderMan’s advanced skin
shader, which is a fully ray-traced
solution, and highlight some
important techniques for getting
the most realistic skin possible.
I have included a link to a head
scan, with a basic skin shader
attached. Download the asset
from www.bit.ly/188-renderman
and use RenderMan 19 to light and
shade your own head using the
techniques shown in this tutorial.
The raw scan data is provided by
Ten24 (www.3dscanstore.com).
Download the resources from
creativebloq.com/vault/3dw188
CLEANING UP THE DATA
It is good idea to delete
the eye from the scan
mesh and create a new
separate object for it,
because each surface
requires specialised shaders
TOPICS COVERED
Rendering photorealistic skin
with subsurface scattering
Advanced workflows
for creating hair
Managing over-modelled
scan data
Physically based
lighting and shading
1 REFINING THE SCAN DATA
First I take the scan data and clean the mesh and
add the pore details using alphas in ZBrush. Make
sure to delete the eye from the scan mesh as each
surface requires specalised shaders. For our lookdevelopment
purposes we will simply take the high
polygon model and export it from ZBrush as an
.obj file, but for a real production we could spend
more time cleaning the topology for animation and
generating displacement maps.
2 SETTING THE STAGE
The concept is to create a stylised version of the
classic Steve Martin arrow gag, so I need to simulate
the model standing on a stage. I establish this using
scene layout and set dressing. I import the head
into Maya and model a suit for him. Then I add the
high-poly details in ZBrush, auto unwrapping the UVs
based on poly-paint details. I add a microphone
and placed a drapery in the background using
Maya’s nCloth.
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TUTORIALS
Rendering photorealistic skin
EXPERT TIP
Defining details
You can sculpt details
like pores and cavities
in the skin with a
higher depth because
small details like that
get diffused out
with subsurface
scattering during
the final render.
3 CHOOSING A CAMERA LENS
The camera is placed looking up at the subject.
I match my Maya camera settings to a Canon EF
70-200mm f/2.8 L IS II USM lens. Being a zoom lens
it gets rid of convex distortions in the image. After a
few adjustments I come up with a length of 170mm
in Maya, with a wide aperture to give a shallow depth
of field that pops the head out from the background.
RenderMan provides camera controls for stylising
bokeh, which I use to achieve the final look.
4 PHYSICALLY BASED LIGHTING
I want to create modern stage lighting with saturated
colours, so I use RenderMan’s physically based spotlights
and set their colour temperatures to achieve
the warm and cool contrast I desire. I place bright
warm key lights pointing down onto the head, and
add fill lights to provide cool contrast. I use a rim light
to accentuate the stubble on his face. Progressive
re-rendering in RenderMan speeds up my process as
it allows me to light interactively.
THE SKIN SHADER
RenderMan’s skin shader,
PxrSkin, was is used for
shading the skin. Any
variations in skin like
thickness, fat, veins and so
on can be shown through
colour variations in the maps
5 SHADING SKIN COLOUR
The skin shader uses a three-layer subsurface model
and gives you a lot of control over ray penetration
length and the scattering weight at each point. The
RenderMan skin shader uses a proprietary method
to calculate an accurate approximation of physically
correct subsurface scattering, and because this
solution is fully ray-traced, look dev is accelerated
with interactive rendering. I start by painting
epidermal, sub-dermal and back scatter colour maps.
RADICAL RENDERING
Re-rendering using RIS
One great benefit of RenderMan’s
RIS mode is being able to use
re-rendering or incremental
rendering to get immediate
feedback and quick interactive
render times. You can
immediately see if you have
chosen SSS parameters that are
wrong: colour or diffusion lengths
are simple to tweak and carry out
look development.
6 SHADING SKIN REFLECTIONS
To give the skin a more realistic response, I paint
a specular map based on the skin’s cavities to
remove the highlights in the cavities, giving it
more detail by modulating the specularity over
the surface. I also paint a roughness map (left)
based on specific grey values to control the wetness/
oil on the skin. Getting the specular response correct
is a key component in creating photorealistic skin.
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EXPERT TIP
Optimising options
RenderMan gives you a
stats file that contains
all the data regarding
your render, render time,
ray hits, total number of
rays and other sampling
information that can
be used to optimise
your scene.
7 SETTING PARAMETERS
The skin shader allows you to connect weight maps
to control the penetration of rays at each point.
I paint a far length map to control the amount of
subsurface scattering at different parts of the face.
Parts of the head like the ear and thin cartilage
show more subsurface scattering because they
are thin, but you also have the option to control
the weight and length of penetration to increase
scattering as desired.
RENDERMAN HAIR SHADER
The RenderMan hair shader,
RMSHair, is used to get the
hair rendered with round curve
attributes. This mode also allows
me to use the holdout shader
available in REYES (Render
Everything You’ve Ever Seen)
mode to get shadows as alpha
to comp the hair on top of the
head rendered in RIS mode
8 SHADING THE TIE
The tie is shaded using RenderMan’s General
Purpose Shader (PxrGPSurface). A high sheen
value and higher specular roughness give a diffuse
shading model for cloth. With a repeated weave
pattern in the float displacement channel, a cloth
shader is quickly created. A RenderMan Walking
Teapot repeated pattern is made in Photoshop and
used as a tiled texture for Diffuse Color.
9 THE HAIR SETUP
RenderMan contains two different rendering
modes: a modern ray-tracing mode called RIS, and
the traditional memory-efficient REYES algorithm.
I use the REYES mode to render curves as hair, as
the REYES-based hair shader in RenderMan Studio
quickly gives me the results I want. As you have
access to both REYES and RIS modes, you can render
different elements of the composition in different
modes and get benefits from both.
RENDERMAN FOR FREE
Use Pixar’s rendering tech
With the release of version
19, RenderMan is now freely
available for all non-commercial
use, without watermark or other
limitation. It’s also the very same
renderer Pixar uses on its own
projects, such as its new animated
short, Lava. So try Pixar’s
advanced rendering technology
for free and follow along
with this tutorial using Pixar’s
RenderMan for Maya. You can
learn more about non-commercial
RenderMan here:
www.renderman.pixar.com/view/
non-commercial
10 RENDERING
The RIS mode provides different integrators to
render images. This image was rendered with the
Path Tracer integrator. With this integrator, there are
various sampling options available to get a highquality
render and to do render optimisations. The
BxDF and light samples settings can be adjusted to
get rid of noise. If you see noise in specific areas of
the render, switch to Manual Sampling mode and
increase the subsurface samples on it.
CONTACT INFO
For more information on Pixar’s RenderMan
please contact Escape Technology
Tel: 0207 734 8809
Email: sales@escape-technology.com
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