Skin Rendering: Triangles, Lighting, Shading, Materials, Translucency, Textures, Slides of Computer Graphics and Animation

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Skin

Rendering Review

Lighting

 We can compute the interaction of light with

surfaces to achieve realistic shading

 For lighting computations, we usually require a

position on the surface and the normal

 GL does some relatively simple local illumination

computations

 For higher quality images, we can compute

global illumination, where complete light

interaction is computed within an environment to

achieve effects like shadows, reflections,

caustics, and diffuse bounced light

Gouraud & Phong Shading

 We can use triangles to give the appearance of a smooth surface by faking the normals a little  Gouraud shading is a technique where we compute the lighting at each vertex and interpolate the resulting color across the triangle  Phong shading is more expensive and interpolates the normal across the triangle and recomputes the lighting for every pixel

Materials

 In high quality rendering, we use a function

called a BRDF (bidirectional reflectance

distribution function) to represent the scattering

of light at the surface:

f

r

(_

i

, _

i

, _

r

, _

r

, _)

 The BRDF is a 5 dimensional function of the

incoming light direction (2 dimensions), the

outgoing direction (2 dimensions), and the

wavelength

Translucency

 Skin is a translucent material. If we want to

render skin realistically, we need to account for

subsurface light scattering.

 We can extend the BRDF to a BSSRDF by

adding two more dimensions representing the

translation in surface coordinates. This way, we

can account for light that enters the surface at

one location and leaves at another.

 Learn more about these in CSE168!