Render Setup. Global Illumination (GI). Light Cache and Brutal Force.

GI is one of the algorithms in rendering, that calculates indirect illumination bouncing back from surfaces (Birn 2014, 343).

Where global illumination is disabled, it can be seen that the space behind the tea is very dark, because the tea blocks the direct illumination from the sun and creates very strong shadow behind it. However, in real life the direct light would bounce back from the white wall and enlighten the area behind the box. When GI is enabled, algorithm calculates the angle in which the direct light hits the wall and calculates the angle and intensity of the light bouncing back from the wall. This effect can be seen in light.jpg.

The light.jpg shows how the light bounces from the wall and the ball, which was not even visible when global illumination was disabled, lighting up the area behind the box. As seen in light.jpg, the reflecting lights are called bounces and all other light in the scene is commonly called indirect light, except the one illuminating directly from the source. (Renderstuff.com 2013.)

There are different ways to compute the indirect illumination depending on the rendering software used. However, when targeting for photorealistic results with V-Ray, the Brute force is generally used as primary engine to calculate primary bounches and as the second engine the Light cache is used to calculate secondary bounches of light. This combination produces images with very good quality and is suitable for high quality interiors (Aversis3D 2016).

When the Brute Force is selected as a primary engine in V-Ray, it determines the primary bounces by tracing the rays of direct light from the camera to the scene as gi.jpg shows (Chaos Software Ltd. 2016b). Gi.jpg. Rays being traced when The Brute Force is primary and secondary engine. (Chaos Software Ltd. 2016b)

In the GI.jpg, it can be seen how the primary bounces (red) are traced when the Brute force is selected as a primary engine. Because of the fact that the rays are traced from the camera, makes the Brute Force a view dependent leading to more accurate results. (Chaos Software Ltd. 2016b). In other words, the movement or e.t.c of the camera inside the scene doesn’t have affect to the GI in the render. In contrast, for example photon map traces particles from the light source, which might lead into different kind of global illumination results when the camera is moved from one point to another (Chaos Software Ltd. 2016c).

Additionally, in the Brute Force’s GI settings, it is possible to increase the quality of GI by increasing the number of subdivisions, which is propotional to the total number of rays which are being traced by V-Ray (Chaos Software Ltd. 2016b).

As a result, the rendering time is increased, but when aiming for photorealistic results, the quality is preferred over the rendering time. The Light Cache as a secondary engine is used to spread light around the scene while the Brute Force as a primary bounce calculator processes the details of the

scene (Mintviz 2011, Rebulic of Code 2010).

Once the Brute force’s primary rays have bounced the amount they are supposed to, the rays change into Light Cache rays which store the illumination into a 3D stucture. If this ray hits a point which is already processed by Brute Force’s ray, the tracing ends and the information already available is read and thus speeds up the rendering process. As a secondary GI engine, Light Cache processes soft and clean shadows and produces accurate results of corners and small objects to the final render. (Chaos Software Ltd. 2016d.)