This page provides a step-by-step guide to setting up and optimizing global illumination.
In this tutorial we will take a closer look at Global Illumination in V-Ray. We are using the headphone scene from the previous tutorials, with a slight modification to make it work better for indirect illumination.
To follow this tutorial, you will need to have the V-Ray for Modo plugin installed. This tutorial is a companion to go along with the QuickStart video posted on our YouTube channel.
To download the files used in this tutorial, please click on the button below.
We start with the headphone scene we have been using previously. For this tutorial the room has been outfitted with two windows.
For comparison purposes we'll first look at the standard render from the start of QuickStart - Rendering with the four area lights.
2) Set up the scene to use indirect lighting
In order to test the GI calculations, we are going to remove the four area lights from inside the room and replace them with indirect light coming from outside the room.
Select the area lights and delete them. Then press F6 to bring up the Modo Preset Browser and navigate to the Smart IBL Environments folder under the Environments. Double-click the Barcelona Rooftops preset to add it to the scene.
3) Adjust Exposure
Start V-Ray RT.
The scene is a little dark. Open up the V-Ray Physical Camera tab and change the Shutter Speed from 25 to 2 for around 4 stops of extra light. Much better.
All of the lighting for the scene is now coming from outside the room, and our headphones are lit exclusively by indirect light. This means that the Adaptive Sampler will need to fire a lot of GI rays to result in a clean render.
Do a test render, and note the much longer render time.
2) Optimize the GI
The render time has experienced a significant increase due to removing area lights in the scene.The GI has been forced to use a much larger amount of sampling to get a clean solution. In order to speed up the render, we need to use a faster GI solution. Draw a render region and re-render without changing any settings yet, so that you have a benchmark for the render time.
Next, navigate to the V-Ray GI tab on the Render Item and change the Primary Engine from Brute Force to Irradiance Mapping. Do a test render using the Region Render that was set up in the previous step.
The resulting test render will be much faster. The main reason is the low detail areas, like the flat table, which make the scene suited for Irradiance Mapping.
To optimize the render further, select the Low preset from the list of Irradiance Mapping presets and perform another test render.
The latest test will only be very marginally faster, so in order to optimize the Irradiance Mapping further you will need to manually alter the settings. Set the Min rate to -10 and do another test.
This time the render time will improve slightly more at the expense of some of the finer shadow detail. As a final tweak, activate the Ray Distance On checkbox under the Global Illumination - advanced tab and enter a distance of 5 meters to terminate the rays early. Do a final test render.
Once again the render time will improve slightly. Disable the Region Render and render the whole scene. The final render should be considerably faster than the original one, thanks to the Irradiance Mapping and the small tweaks you did to the scene.