Week 2 Physical Based Rendering

Definition of PBR?

•PBR materials describe the visual properties of a surface in a physically plausible way, such that realistic results are possible under all lighting conditions.

•It uses ‘Maps’ to identify different parts that will react in certain ways on a material

7 types:

Base colour

ambient occlusion

height

metallic

normal

roughness

displacement

Normal Maps:

•A normal map uses RGB information that corresponds directly with the X, Y and Z axis in 3D space. This RGB information tells the 3D application the exact direction of the surface normals are oriented in for each polygon.

•These maps allow you to add surface detail such as bumps, grooves, and scratches to a model which catch the light as if they are represented by real geometry.

displacement maps

•Displacement maps allow texture images to morph the geometry of a mesh.

•Using height differences (Represented by Greyscale images) it will calculate the height and adjust the geometry

•The strength factor can be adjusted in order to affect the severity of the geometry morphing.

Diffusion and reflection

•Diffusion and reflection – also known as “diffuse” and “specular” light respectively – are two terms describing the most basic separation of surface/light interactions. Most people will be familiar with these ideas on a practical level, but may not know how they are physically distinct.

•When light hits a surface boundary some of it will reflect – that is, bounce off – from the surface and leave heading in a direction on the opposing side of the surface normal. This behavior is very similar to a ball thrown against the ground or a wall – it will bounce off at the opposite angle. On a smooth surface this will result in a mirror-like appearance.

subsurface scattering

specular - specularity

translucency & transparency

•in materials that have wider scattering distances for example, like skin or wax. In these cases a simple colour will usually not do, and the shading system must consider the shape and thickness of the object being lit. If they are thin enough, such objects often see light scattering out the back side and can then be called translucent. If the diffusion is even lower yet (in for example, glass) then almost no scattering is evident at all and entire images can pass through an object from one side to another intact. These behaviors are different enough from the typical “close to the surface” diffusion that unique shaders are usually needed to simulate them.

Fresnel

•In computer graphics the word Fresnel refers to differing reflectivity that occurs at different angles. Specifically, light that lands on a surface at a grazing angle will be much more likely to reflect than that which hits a surface dead-on. This means that objects rendered with a proper Fresnel effect will appear to have brighter reflections near the edges.

Light explanation: