VRAY FOR 3 DS MAX Global Illumination Introduction

V-RAY FOR 3 DS MAX Global Illumination Introduction

LESSON INTRODUCTION Orientation • This presentation discusses theory behind Global Illumination • This lesson topic is approximately 15 minutes in length • This Lesson only has a lecture part

GLOBAL ILLUMINATION Basics • Makes the image more realistic • Adds the light coming from the environment • Adds the bounced light – light that is reflected from diffuse surfaces and further illuminates the scene • Requires additional calculations which slow down the rendering

GLOBAL ILLUMINATION Color bleeding • Color bleeding happens when the color of a highly saturated object affects (bleeds onto) a more neutrally colored object near it

GLOBAL ILLUMINATION Caustics • Caustics from direct light most often appear when light travels through refractive objects like glass, water etc. and it is focused into bright spots • GI Caustics are created when bounced light or light coming from an environment is being either refracted or reflected in such a way that it creates a bright spot • Caustics from a direct light source are a calculated in a separate pass that requires the tracing of photons and is enabled separately

GLOBAL ILLUMINATION Theory • In V-Ray GI is calculated starting from the camera and tracing rays of light into the scene. • Effective approach – we only trace rays in the parts of the scene that are visible in the rendered image • Some GI calculation engines allow us to save the GI solution and reuse it • In V-Ray GI calculation is split into Primary Bounce and Secondary Bounce

GLOBAL ILLUMINATION Primary and Secondary Bounces • Primary Bounce – this is the first GI ray that we trace starting from the end of a camera ray/primary ray. • Greatly affects the illumination of the image • Needs to be calculated with high precision

GLOBAL ILLUMINATION Primary and Secondary Bounces • Secondary Bounce – these are all GI bounces traced from the end point of a Primary Bounce ray. • Contributes to the illumination in interior scenes and in other cases where light bounces around a lot • Needs to be calculated with high depth (number of bounces) but precision is not as important

GLOBAL ILLUMINATION GI Methods • Brute Force • Irradiance Map • Light Cache

GLOBAL ILLUMINATION Brute Force • Calculated on the fly for each camera ray • Can be used for both Primary and Secondary Bounce • Very precise but can be slow • Quality is controlled with a single parameter Subdivs • Depth (number of bounces after the primary bounce) can be manually set with a single parameter - Bounces

GLOBAL ILLUMINATION Brute Force • Subdivs – the number of rays traced for each shaded point – at the end of each camera ray • Smaller values improve render speeds but produce more noise • Larger values reduce the noise at the cost of render times

GLOBAL ILLUMINATION Irradiance Map • Calculated in a pre-pass and saved into a map – top image • Map is used during the actual rendering – bottom image • Can be used only for Primary Bounce • Different levels of precision: • less precise on flat surfaces where GI is not changing very much • more precise where objects are close together, there is fine detail in the geometry or in places with sharp GI shadows

GLOBAL ILLUMINATION Irradiance Map • The quality of an Irradiance Map depends on the number and distribution of samples in the map and the number of rays traced for each sample • The minimum and maximum number of samples per pixel depend on the Min rate and Max rate parameters. • The quality of each sample depends on the Subdivs parameter

GLOBAL ILLUMINATION Light Cache • Calculated in a pre-pass and saved into a map – top image • Can calculate multiple secondary light bounces very quickly and efficiently • Map is used during the actual rendering – bottom image • Most effective when used as a Secondary Bounce but can be used as Primary Bounce too

GLOBAL ILLUMINATION Light Cache • The quality of the Light Cache depends on the number of light paths traced, and the size of the generated samples • Subdivs – top image – controls the number of light paths traced. Higher values increase the quality but slow down the rendering • Sample size – controls the precision of the light cache. Higher values produce a smoother result but fine details are blurred out.

GLOBAL ILLUMINATION Light Cache • Scale – determines the meaning of the Sample size and Filter size parameters • World – the sample size is in world units. This ensures uniform sample size when the camera is moving. Prevents flickering in animations • Screen – samples are a certain fraction of the final image. Samples closer to the camera are smaller than samples far away. Useful for still images that have parts far away from the camera.

GLOBAL ILLUMINATION Light Cache • Filter – allows us to smooth out the Light Cache before we use it • Type – Nearest – the filter looks up the nearest samples to the shading point and averages their values • Type – Fixed – the filter lloks up all the samples that fall in a specified radius around the shading point and averages their values • Prefilter – the samples in the light cache are filtered before rendering (normal filtering happens during rendering) by examining each sample in turn and modifying it so it represents the average of the given number of nearby samples

GLOBAL ILLUMINATION Exterior Scenes – Primary + Secondary • Brute Force + Brute Force • Very accurate • In an exterior scene light bounces only a couple of times before going into the environment. Using Brute Force for secondary engine allows us to limit the number of bounces we calculate and improve render times • Because we use only brute force, GI is calculated on the fly for each shaded point. This means that we can affect the GI quality using the Shading Quality slider.

GLOBAL ILLUMINATION Exterior Scenes – Primary + Secondary • Irradiance Map + Brute Force • Fast combination • Irradiance map uses an approximation which makes it faster than Brute Force • Since we limit the number of secondary bounces calculations are reasonably fast • Image is rendered in two passes – first the GI is calculated (top) and then the actual rendering is performed (bottom)

GLOBAL ILLUMINATION Interior Scenes – Primary + Secondary • Brute Force + Light Cache • Very accurate • Light Cache is able to trace multiple light bounces which makes it perfect for interior scenes • Because we use Brute Force for primary bounce, GI is calculated on the fly for each shaded point. This means that we can affect the GI quality using the Shading Quality slider. • Image is rendered in passes – first we calculate the Light Cache and then we trace Camera Rays which shoot Brute Force rays to gather information from the Light Cache

GLOBAL ILLUMINATION Interior Scenes – Primary + Secondary • Irradiance Map + Light Cache • Very fast - Irradiance Map speeds up the GI calculation by spending more time in the important areas of the image and using approximation for the rest • Image is rendered in passes. Light cache is traced first. Then the Irradiance Map uses the information from the Light Cache and refines the GI by tracing more rays. Finally camera rays are traced which gather information from the Irradiance Map.