David Beckham with G2
Realistic human skin has long been one of the most difficult
goals for CG. Not only does human skin have very detailed texture with
freckles, pores, wrinkles, and even fine hairs on its surface but its
also translucent, so a large amount of light penetrate the skin and react
with all the layers underneath. These layers make light bounce and scatter
in complex ways, resulting in the soft glow of skin. Variations
in skin thickness must be taken into account as well, since these variations
can effect the skin color and the way light interacts with the layers
The latest 3D technology called Sub
Surface Scattering makes simulating skin in CG possible. G2
skin mode makes realistic skin shading possible in LW! Even better,
you can do it in G2's real-time interactive preview!
As you can see in
Figure 1, there are not many parameters in G2's skin mode. But that
doesnt mean that its lacking power! Its designed to
be as intuitive and as simple as possible, even automatically setting
some parameters that are usually annoying for artists to define. G2s
amazing real-time preview( Figure
2 )makes tweaking a pleasure, not a chore.. With G2, your LightWave
world is changed forever.
Setting the thickness of skin from texture mapping
First of all, what G2s skin mode helps us with is
shading. What is required for making realistic human skin is not only
G2s skin mode, but also good texture mapping and light setting skills
and so on.
Lets talk about parameters in G2 skin mode! Human skin varies in
thickness so the way light interacts with it different as well. So if
you don't account for the thickness of skin at every point, you won't
get very accurate shading. But G2 does this automatically if you have
a textured skin map,deriving skin thickness by reading textured color
values. If you paint a reddish color on the surface of the skin, G2 understands
that the thickness of the skin is thinner at that point.
G2 has its PhotoMap tool, which is very useful when using a photograph
to make a texture map. A photograph includes natural lighting so its
not usually convenient to use it as a texture map, but you can get rid
of much of the poor shading using G2s PhotoMap tool. (Figure
3 and Figure
Before getting started with G2, I would like to talk about modeling and
texturing, which are very important for making your character look photorealistic.
In terms of modeling, I started the face symmetrical at first, and then
worked each side of the face separately so that the character was not
unrealistically symmetrical, a common fault in CG. (Figure
5). When it came time to texture, I used David Beckhams photo
as a base and cut it into parts that were pasted and tweaked until they
formed a single skin map. I said that G2s skin mode calculates shading
based on the colors on the surface but I also assisted it with my own
6) . Next I applied G2s skin mode and tweaked the parameters.
First, I defined the main parameter, Multilayer Subsurface Diffusion.
The higher number you put, the softer the surface looks. Compare it to
the LightWave standard shading, and you can see the difference between
LW and what G2 skin mode can do (Figure
7). The edges of the ears and cheeks are brighter, and the highlights
are clearer, and over all, the contrast became softer and it adds a human
touch onto the skin. I used 100% this time. The thickness of the skin
is still equal at this point so next I increased the Epidermis Visibility
to vary the thickness. You can see the edges of the surface became extremely
bright. The best value depends on the lighting setup, I set it to 100%
here. Epidermis Scattering allows further control of the way light reacts
to the outer layer of skin. I set it to 50% (Figure
Skin color is also effected by the G2's "Blood Color" control.
When you change the blood color brighter, the outer skin color becomes
darker, and when you set very reddish blood color, the skin color becomes
blue greenish (figure
With Follow Bump Mapping, you can define how blood color reacts to bump
maps you might add, like pores and wrinkles.
G2's Rough Surface Oren/Nayar Diffusion is similar to the Diffuse Roughness
that Gaffer had. Its usually very effective on rough appearances
but I found it not so effective for creating realistic skin.
Lighting in G2
Since G2s skin mode is specialized for skin, there
is a big difference in appearances between G2 and the LWs standard
shader. The quality of skin renders will improve by using G2s skin
mode, but the contrast will decrease since Multilayer Subsurface Scattering
can make the renders become too soft, and Epidermis Visibility and Epidermis
Scattering can make the edges around objects too bright. You can fix those
problems by tweaking G2s parameters as well as scene lighting. You
can see the big differences with and without the shader, lit in front
with the same lighting ( Figure
10). My point is that you should get the hang of what the shader does
before setting the lights.
The key point for lighting is to use back light effectively (Figure
11). With the back lighting, soft-glow effects occur and the edges
become bright so the contrast becomes clearer. This effect adds depth
to the scene by separating the subject from the background. The object's
edges become especially lifelike! Please note that you should balance
the edge's brightness with lighting setting and G2s Epidermis Control.
Luckily, G2's interactive real-time preview makes this easy to do. Not
only does G2's preview show the effect of the G2 skin shader, But you
get instant feedback when you move/add lights or change their intensity.!
I usually dont use radiosity because of the long render times but
I tried an HDRI based radiosity render as a G2 test (Figure
13). I didnt use the highest quality settings since the rendering
is too time consuming but as you can see the shading becomes soft and
natural.. Im used to using my own lighting to create realistic effects
but there is something in the renders that radiosity creates that is beyond
normal lighting. I need to explore it more! But my time is up! Id
like to check more on G2 and radiosity later for my own research.
After working for Square and Imagica, he became a free-lance 3D CG artist
and founded the company "mix
core" in 2002 with his friends. Their business includes CG movies
for games, commercials, movies, illustrating, web design, and multimedia
CD-ROM. They are way too busy with a lot of job offers,
and need to find more staff!
The Japanese version of this tutorial
was printed in the Japanese Computer
Graphics World magazine in January 2003.