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This issues question is tackled by Adam Watkins, the

Director of Computer Graphic Arts at the University of the

Incarnate Word (www.cgauiw.com) in San Antonio, Texas

G

etting skin to look right is tricky. It might seem as

though it should be an easy task its just a bit of

orange, tan, olive or brown together with some

good lighting, right? Well, not quite. The problem

with most materials built into Cinema 4Dis that they act as opaquesurfaces that provide highlights that are not based upon reflection,

but on the often fake-looking Specular channel. The results as can

be seen in left-hand image above have a dead look to them.

True, the various parts of the face have good surface colour

(the lips are coloured differently to the cheeks, for example) and the

lighting helps to define the form. But the result still looks as if the

colour was spray painted on, or as if the model has too much make-

up on, obliterating the glow that makes skin look alive.

There are two main features of Cinema 4Dthat will enable you

to create good skin materials. The first is its capacity to layer

materials effectively. The plan here is to work with multiple

Luminance channels for a single surface. Alt hough C4Ds materials

system currently allows for Fusion and other inner-material layering

techniques, being able to layer Luminance channels via two

materials provides much a quicker way to refine the effect.

The second feature is subsurface scattering (SSS). Subsurface

scattering is the phenomenon in the real world where light is able to

penetrate a surface and scatter beneath it. This provides an inner

glow to such diverse materials as marble, milk and skin. Although

there are some limitations to C4Ds SSS implementation (it doesnt

work with global illumination, for example), its still a pretty snazzytool to use and gives skin a visual volume and depth. Because you

pay a rendering price for activating SSS, however, you may choose

to go without (we will also look at ways to do this); but if you have

the processing power, the results are worth it.

Flat skin is a problem with most 3D applications and a challenge

for animators who have moved beyond the got-the-shape-and-

colour-right stage. Even a lot of high-end 3D produced for film has

this base-heavy look. Effective channel manipulation and material

layering can bring skin tones to life, and make your renders appear

to have more depth. For the illustration above, weve applied the

technique to a simplified, cartoon-style model. This is not supplied

on the CD, you should substitute your own.

072 | 3D WORLD3D WORLD September 2006

Q&A | Realistic skin shading

FOR

Cinema 4D

DIFFICULTY

Intermediate

TIME TAKEN

One hour

ON THE CD

Full-size screenshots

Completed skin shader

Final animations

QTVR of finished

scene

ALSO REQUIRED

N/A

FACTFILE

Q&ASOLUTIONS / FIXES / ADVICE

SubmittedbyMartinDonaldson,viatheforums

QUESTIONOFTHEMONTH

CINEMA

CINEMA 4D

How do you create a believable

skin shader in Cinema 4D?

TDW81.qa_lead 072TDW81.qa_lead 072 3/7/06 11:21:073/7/06 11:21:07


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September 2006 3D WORLD3D WORLD | 073

Import your head model. Remember to make good

use of C4Ds HyperNURBS capabilities and do not

use any more polygons than are needed. The more

polys you have, the more UVs you will need to fight with

later; and although this is about constructing materials,

having a good UV map to begin with goes a long way. Be sure

to name your objects effectively.

01

Because we are going to be using SSS, C4Dwill work

best with surfaces that it sees as closed. In this

screenshot, we are looking at the bottom of the

neck an open neck. To close areas like this off, select the

edges around the opening and use Structure > Close Polygon

Hole. Watch for spots you could miss such as the bottom of

the neck and the nostrils.

02

Establish several rings of fill lights (illustrated here

with white circles). Keep the intensities low. You

could also do this with global illumination but with

slower rendering results. You can use alternate lighting

schemes that match your scene as well; this is just one good

soft layout set-up. Create one more key light called Highlight

Light. This will be the hottest light source.

03

STAGE ONE |Scene set-up

Create a new material (named Skin Highlight on the

sample file). Activate Luminance and Bump and turn

off all the other channels. Later, the Luminance

channel of Skin Base will use the SSS capabilities. The

Luminance of Skin Highlight will enable us to make specific

adjustments to how the highlight of the surface will work.

07

Open the Material Editor for Skin Base. Click the

Bump channel and click the triangle button next to

Texture input. Choose Copy Channel. Select Skin

Highlight in the Material Manager, and in the Material Editor,

choose Bump, click the Texture triangle and choose Paste

Channel. This ensures both materials share the same bump.

08

Back in the Skin Highlight material, go to the

Luminance channel and click on the Texture triangle

button. Choose Sketch > Cel from the drop-down

menu. You wont be creating a cel-shaded look here, but this

will allow you to have control over how the luminance of the

surface moves across that surface as the lighting changes.

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Realistic skin shading | Q&A

Laying out well-spaced UVs can be tricky, but it is

absolutely necessary to create clean textures that

do not stretch or pinch across the surface. How to do

so in BodyPaint 3D(C4Ds sister application) is beyond the

scope of this tutorial, but you might try the UV Unwrap in the

demo version of modo, or various other UV modification tools

(many are available free to download on the internet).

04

Using either BodyPaint 3Dor Photoshop, paint the

colour on your UV layout. Do not worry about

painting in highlights, or simulating any sort of

SSS just do the basic colour. Remember to vary the skin

colour across the face for best results skin is never

monochromatic. Import this image into the Color channel of a

new material (labelled Skin Base in the scene file on the CD).

05

STAGE TWO |Basic material set-up

A good bump map for the face is important and will

add visual interest to the SSS. Remember that the

texture of the face is very different across the

cheeks than it is across the nose, eyelids and ears. Import

this into the Bump channel of Skin Base and adjust the Bump

Strength to your taste. Take several quick renders at this

stage to get that bump just right.

06

STAGE THREE |Highlight material set-up



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074| 3D WORLD3D WORLD September 2006

Q&A | Realistic skin shading

Click on the Cel button (which is now located in the

Texture input field). This opens the attributes of the

Cel Shader which will eventually control your

luminance. In the lower half, deactivate Camera, and activate

Lights. Then, in the Use Lights section, choose Include and

drag your Highlight Light from the Objects Manager into the

Lights section of the Material Editor.

10

Expand the Diffuse section (of the Luminance

channel). Change the Diffuse settings to

approximate those shown in the screenshot (pink to

blue) with added colour knots. Change the Interpolation to

Linear. This will vary depending on the complexion of your

character. If you have a darker-skinned character, you could

use more brown in the olive colour palette.

11

Assuming you have already applied Skin Base to

your model, apply Skin Highlight to the same surface

(drag from the Material Manager to the object in

Objects Manager). Click on the new Texture Tag in the Objects

Manager and activate Mix Textures. This will allow the colour

of Skin Base to show through, but will mix the settings for

the Luminance and Bump maps that the two materials share.

12

Double-click Skin Base in the Material Manager.Activate Luminance, and choose Effects >

Subsurface Scattering from the Texture drop-down

menu (triangle button). This will make the skin glow as light

penetrates it. Although the settings can be a little tricky to

get right, this is what gives your skin its inner glow.

13Subsurface scattering is rendering intensive, so tohelp speed up the test renders, create a sphere and

resize it to approximately the size of your head.

Ensure you put it in the same space as your head, and then

hide the head. Apply the Skin Base material to the sphere (do

not apply the Skin Highlight for now).

14For the kind of renders were doing now, there is noneed for things like antialiased edges. Open your

Render Settings, and in the General area turn the

Antialiasing to None. Also, turn off Transparency and

Reflection. Be sure to leave Shadow set to All Types so you

dont have extra light travelling through objects.

15

Take a test render at this point to see what the

default settings do to your sphere. The settings

for SSS can be a little tricky to get the hang of, and

will vary from scene to scene, depending on the size of your

model. You will be able to tell immediately if things are

not right in the test render. From this point, you can start

making adjustments.

16

Open Skin Base and, in the Luminance channel, click

the Subsurface Scattering button. The Absorption

Filter defines the transition from the colour of the

surface (left) to the colour of the deeper layers of skin (right).

Change the tab on the right to a colour slightly more

saturated than your main skin colour. Change the colour on

the left to blue for light-skinned characters and a greener

hue for darker-skinned characters.

17

Now its time to adjust the Absorption. This will vary

according to the size of your model, as Absorption

indicates the depth at which the light is completely

absorbed. For this rendering, it was set at 10m for a sphere

that is around 450m in diameter. Adjust and tweak as

needed, and look for the start of a healthy (although maybe

slightly purplish) glow.

18

STAGE THREE (Continued) |Highlight material set-up

STAGE FOUR |Working in the SSS



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September 2006 3D WORLD3D WORLD | 075

Realistic skin shading | Q&A

Make sure that both your Skin Base and Skin

Highlight are assigned to your face (or other body

surfaces) and unhide the face. Take some small test

renderings to see how your work is shaping up. You may find

areas like the nostrils look transparent, in which case youll

need to turn down the Scattering Length. Adjust the other

settings according to your desired results.

22

Because this technique is light-dependent, you can

make all sorts of adjustments along the way to get

your final look. Remember that things like the

Absorption Filter are dependent upon the colours being

visible in the light scattered from the skin, so whiter lights

will provide more reliable colour results. You can move, adjust

and animate the lighting set-up: view the movie on the CD to

see animated lights in motion, how the SSS holds up and how

the highlight moves across the skin. If you are on a tighter

render budget, you can cut corners by leaving SSS turned off

and still get a nice highlight. You can also get quick results

using ChanLum, a free C4Dchannel shader available at

www.happyship.com/lab/chanlum/chanlum.html, but SSS is

still a great tool to make beautiful realistic skin.

24

STAGE FOUR (Continued) |Working in the SSS

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k

Time to adjust Scattering Length. This setting

defines exactly how far the dispersed light scatters

across the subsurface. Too deep, and things get too

washed out across the surface; too shallow, however, and

you dont really need SSS in the first place as you wont be

able to see the results with the naked eye. For this shot, the

Scattering Length is set to 10m.

19

Notice that with SSS, the render can quickly get

completely washed out. While you want glow, the

overexposed look should come from the Skin

Highlight material. Reducing the Strength to somewhere

around 30% will still give you the pretty effect youre after

without blasting the skin apart. Tweak this setting to taste,

based upon your lighting scheme.

20

This is where you assign Skin Highlight to the

sphere and mix the materials. Do this by dragging

Skin Highlight from the Material Manager on to the

sphere, and then click Mix Textures and render. You will want

to do some tweaking here within your materials to get the

right look. Again, performing test renders on the sphere will

speed up the process as you dial in different settings.

21

STAGE FIVE |Finishing up

Open your Render Settings again, and turn your

Antialiasing back on (probably to Geometry).

Reactivate Transparency and Reflection. This will

slow your renderings somewhat but will provide the

considerably crisper results that you will want for your final

output. Take some renderings at a smaller resolution to see if

everything still holds up.

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