Realistic Shading of Human Skin in Real time

1. Realistic Shading of Human Skin in Real time

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. Demo Movies and Discussion • Thanks for your Attention! • For presentation slides, demo movies and • additional material visit • www.florian.webkoenig.net