Part I - Photorealism 1 Why? Achieve more photorealistic images All images are from MentalRay s website 2 Computer Science Dept. Technion Page 1
3 4 Computer Science Dept. Technion Page 2
5 From Alexander 6 Computer Science Dept. Technion Page 3
From The Day After Tomorrow 7 From Crysis 8 Computer Science Dept. Technion Page 4
From Attack of The Clones 9 From Attack of The Clones 10 Computer Science Dept. Technion Page 5
From Assassin s creed 11 Photorealism (As much as possible) physically accurate simulation of illumination in a scene. Main missions: Glossy and mirror-like Reflection Translucency & transparency Shadows Diffuse inter-reflection Caustics (sub)surface scattering Refraction & Dispersion Textures..and many more 12 Computer Science Dept. Technion Page 6
Translucency Transparency is the material property of allowing light to pass through. Translucent materials allow light to pass through them only diffusely: they cannot be seen through. The light scatters inside the material before leaving the object. Also Called Subsurface Scattering Requires a more realistic Diffuse model 13 Soft Shadows Hard shadows are created as a result of discrete (aliased) illumination. In reality, shadows are softer due to light transport from other lighted materials in the scene. 14 Computer Science Dept. Technion Page 7
Diffuse Inter-reflection Light scattered from a non-specular object illuminates (bleeds unto) other objects in the scene. Diffuse models: Lambertian (CG Course model) - uniform in all directions Oren-Nayar Model for rough surfaces. Torrance-Sparrow, Schlick and more. 15 Caustics A caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. 16 Computer Science Dept. Technion Page 8
Texture mapping The art (and science) of applying realistic textures to geometric images Important issues: Parameterization Bump mapping (As usual) Antialiasing Multiresolution 3D textures (from Beowulf ) 17 Theory of Light The physics of light treated by these models: Ray Optics Geometric rays traveling in optic media. Electromagnetic optics polarization, dispersion. Wave optics interference and diffraction. Photon optics Interaction of light and matter. In computer graphics, we mostly apply ray optics. 18 Computer Science Dept. Technion Page 9
Terminology Radiometry the description of physical light (most of our work). Photometry Including the description of light perception. (Tone mapping, HDR lighting). From Half-life 2 19 Light Scattering When light encounters an obstacle, it is either absorbed or scattered. The local illumination part of lighting a scene. Common models: BRSSDF Light enters the material and scatters around before leaving the surface in another point. BRDF All light is reflected at the same location at which it hits the surface. Most rendering works apply the simpler BRDF. 20 Computer Science Dept. Technion Page 10
Light Transport (Heckbert Notation) In order to generalize the reference to the path the light goes, we use a regular expression defined thus: L Light source(s) E The eye(s) S A specular reflection D A diffuse reflection (n)+ - one or more events of n (n)* - zero or more events of n (n)? zero or one n event (n m) - either m or n event For instance L (S D)+ D E means a light from a light source, with one or more specular or diffuse reflections, finally reflected as a diffuse into the eye. A full global illumination solution L (S D)* E 21 Simple Illumination Model Light Object Eye (L (S D) E) Diffuse Specular/Glossy - cos n (θ) 22 Computer Science Dept. Technion Page 11
Ray Tracing Illumination Model Light Object Specular Specular Eye (LD?S*E) Specular reflection Specular refraction 23 Radiosity Illumination Model Light Diffuse Diffuse Diffuse Eye (L D+ E) Color bleeding 24 Computer Science Dept. Technion Page 12
Caustics Light Specular Specular Diffuse Eye (L S+ D E) Real world Rendered 25 Computer Science Dept. Technion Page 13