fast_sss_tutorial.pdf

mental ray fast subsurface scattering tutorial

Document version 1.2

Dec 1, 2004

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Table of Contents

1 Subsurface scattering skin shader tutorial 1

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Realistic skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Tuning scattering \on your own" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.3.1 \Subdermal" scattering - the meaty stu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.3.2 \Epidermis" - the top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.3.3 The layers in context and with textures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1.3.4 Sweet specularity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1.3.5 It's in the eyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

1.4 Advanced methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

1.4.1 Environment lighting of Globulous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

1.5 Technical considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1.5.1 Application of the shader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1.5.2 Parameters, names and useage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1.5.3 Shader declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

1.6 Inspirational Gallery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

1.6.1 Standard lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

1.6.2 Environment Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

1.6.3 Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

1.7 Thank you for listening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Chapter 1

Subsurface scattering skin shader

tutorial

1.1 Introduction

Welcome to the mental ray fast subsurface scattering skin shader tutorial!

Before we begin, we should talk a little about what subsurface scattering (\sss" for short)

actually is, and what it looks like, and how it enhances the apparent smoothness of a surface.

1 Subsurface scattering skin shader tutorial

Almost everyone knows about the most \obvious" eect of subsurface scattering - when light

passes through a thin translucent object. This eect is easy to point out and easy to see.

Example image of \translucency", just one of the eects of subsurface scattering

But for skin this eect is secondary and of marginal importance since it only shows up in thin

areas such as ears. What is of greater importance is the diusion of light within the shallow

top layer of the skin.

While the human optical subsystem is specially tuned to view other humans, the very

important eects of subsurface scattering are, paradoxically, very dicult to actually see.

Generally, these eects - unless you know what to look for - are of the variety that you do

not \see" until they are absent, when it becomes obvious that \something is missing". For

this reason it is also very easy to overdo the eect, and to put too strong sss eects in one's

renderings.

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