Realistic Shading of Human Skin in Real time

Florian Struck

University of Applied

Sciences Wedel, Germany

Christian-A. Bohn

University of Applied

Sciences Wedel , Germany

Sebastian Schmidt

Bauhaus University

Weimar , Germany

Volker Helzle

Institute of Animation

Filmakademie B-W , Germany

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Introduction – Project Background

Lecturer: Florian Struck

University of Applied Sciences Wedel, Germany

• Computer Graphic Departure

• Head: Christian-A. Bohn

• Thesis about skin shading (final exam)

Filmakademie Baden-Württemberg, Germany

• Research Project „Artificial Actors“

• Head: Volker Helzle

• Supported by Sebastian Schmidt

Motivation of the Short Paper

• Highly practical reference to skin shading

• Publishers of Computer Games want realistic environments

• Describes basic anatomy, physics with imitative approaches

• Paper‘s structure:

Basic to more complex and additional effects

Introduction – Skin Shading

Complexity of Real Skin

• Characters background as age, gender and nationality (e.g. old grandfather or young woman)

• Appearance varies over the skin‘s surface:Thickness, softness, cornea, oiliness, sweat, small hairs...

• Manifold layers with different characteristics

• Complex behaviour in interacting with light

Skin in Computer Graphics

• Complexity of a simulation is challenging Soft skin versus „harsh“ look in computer graphics Diffuse illumination mostly from subsurface scattering

• Limitations of hardware (e.g. shader profiles)

• For performance issues imitative approaches are used

Geometric Detail

Geometry

• Basic shape and distinctive furrows

• Langer‘s Lines: indicate figure of wrinkles Permanent visible folds Wrinkles only seen on some facial expressions

• Eligible construction for animation (3.500 vertices)

Detail Normal Mapping

• Smoothen geometry and refine folds

• Normal Map: Compare normals of low and high polygonal model New normals stored in color channels

• Used for illumination calculation

Bump Mapping

• Fine details as characteristically fielded structure of the dermis, pores...

• Bump Map: convert grey scaled map into normal map

• Combine with (detail) normal map

Basic Skin

Fundamental Maps• Created in coherance with normal / bump map• Color Map: diversity of skin‘s base color (no shades)• Diffusion Map: light behaviour varies over skin‘s surface

Illuminating Skin• Extended Lambertian Lighting Model • Separate: shaded and lit parts, transitions

Control light situation with color gradient Or use 2nd color map (contrast, saturation, transition)

• Backsurface Scattering: less detail in shadows, high detail in shiny areas Use 2nd normal map (with less details) Rim Lighting

Ambient Occlusion and Shadows• To indicate dimension of object, add realism• Shadow Map: prev. pass – store depth from light‘s pov• Ambient Occlusion Map: areas light hardly reaches

Specular Reflection

Specular Highlights

• Modified Blinn / Phong Lighting Model

• Depending on viewing angle / light position

• Oiliness Map: Epidermis emits fat like fluid Highlights should have a soft white / blue

• Influence of normal map is strong

Perspiration

• Overall shininess increases

• Beads of sweat are formed

• Perspiration Map: Noisiness and wet map

• Factorized by the characters sweat factor

• Environmental reflections with cube maps

Subsurface Scattering and Translucency

Subsurface Scattering• Reflections between layers of the skin• Depends on viewing angle and e.g. thickness of skin• Approximation - Softness Equation:

Directly illuminated skin / shilouette Increases softness / deepness of skin

• Subsurface Scattering Map: Modified Color Map, reddish, blurred

Translucency for Ears and Nose• Translucency: not fully transparent, dimly shining through• Example: if light is behind character - ears appear red• Ear and Nose Map:

Equation manages separation and interpolation Character‘s orientation, view and light direction

Additional Improvements• Backscattering and rim lighting• in post rendering process, next slide• There are a number of more advanced approaches

Rendering Process

Post-Process Rendering

• The already rendered image is modified

• Access to texel-neighbours

• The alpha channel is used for masks

• E.g. depth of field, shadow mapping (prev. pass)

• Based on the sss factor the rendering is blurred

Texture-Space Lighting

• Render lighting of object into texture

• Texture is modified and at last mapped to character

• Diffuse lighted texture is blured to soften skin and remove harsh edges and to soften parts based on sss factor

• Costs a minimum of 2 passes

• Visual artifacts may be visible depending on uv mapping

Demo Movies and Discussion

Thanks for your Attention!

For presentation slides, demo movies and

additional material visit

www.florian.webkoenig.net