Gnomonworkshop Global Illumination: Exteriors 3DMax

IT IS ALL ABOUT REFLECTION
- The main concept of Global Illumination starts with reflection.
- The way the rays react after they hit the surface is the key to the difference between specular and diffuse.
- The roughness of the surface is what determines the right look.
- Blurry reflections will give you the look of a rougher surface.
- CG specular, such as the one used in a typical Blinn BRDF, is a fake reflection of a CG light source.
- Blurry reflections can be achieved via scattering rays.
- The more rays you use the longer the rendering time.
- Diffuse light reflects off of surfaces in the same way but scattered in a much larger area.
- The same principles apply to diffuse scatter, where the more rays we use the longer the rendering time.
2. METHODS OF PRODUCING DIFFUSE SCATTER
- There are two basic methods: reflecting the light throughout the entire scene and optimizing the samples for
The viewport.
- When using global illumination, we always need to pay attention to the exposure levels, in the same way that
you need to pay attention to f-stop in a camera, since GI often uses real world lighting.
- Radiosity uses the mesh to collect samples. Every vertex collects a light sample. Precise modeling is a key
to Radiosity.
- Radiosity bakes the lighting into the entire scene.
- Photon mapping shoots rays from a light source.
- Photon maps can be thought of conceptually like shadow maps. The bigger the map, the better the quality,
the longer the rendering time.
- Gathering methods, such as final gather or irradiance mapping, or QMC sampling, only look for diffuse
bounce inside the viewport.
- Quasi Monte Carlo (QMC) sampling shoot rays for every AA sample.
- Irradiance mapping will use less samples in areas that don’t need it, and shoot more in areas that do.
3. ENVIRONMENT LIGHT
- Ambient light only works when taking occlusion into account.
- When sampling the environment, if you don’t actually bounce the light around but are only checking to see if
the geometry is occluding the environment, that is called Ambient Occlusion.
- When you actually bounce the light around, then you are doing Global Illumination.
- When lighting a scene with a skylight, you can add more light by increasing the multiplier of the sky.
- Brighter shaders create brighter scenes since they reflect more light. Darker shaders absorb more light.
- Brighter skylights and brighter shaders increase the rendering time since the rendering engine can’t be as
adaptive with its samples, and more samples are needed.
- You can use bounce cards rather then CG lights as fills, in the same manner that a photographer or DP would
use on set.
4. IMAGE BASED LIGHTING
- The best type of image to use when doing image based lighting is a High Dynamic Range Image (HDRI) which
represents 360 degrees of view.
- The HDRI is the base of all the lighting in your scene.
- A large library of HDRIs can provide a large number of lighting scenarios. Keep a large collection for different