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V-Ray comes equipped with a number of extremely powerful global illumination, or GI engines that can help us recreate pretty much any natural lighting scenario, and a good number of unnatural ones, should we have a mind to. If we just come up to our main toolbar, we can just click on our Render Settings window icon to pull that dialog up for ourselves, we'll just show you where V-Ray's indirect illumination tools are housed. If we come to the Indirect Illumination tab, you can see, with our systems enabled, with a check in the On box, all of the tools and controls that make up V-Ray's GI systems become available to us.
Now, the feature sets of these engines are robust; they are powerful. They give us the ability to easily switch between physically correct and artistically correct approaches to our lighting setups. They can be tuned to be fast enough for even the most demanding of production schedules, whilst still outputting high quality images for us. Ultimately, these systems can remove an awful lot of the guesswork that would otherwise be involved in manually recreating realistic lighting solutions. All we really need to do is evaluate the lighting needs of our current project, choose the tools we want or need to use, run through our usual lighting setup, of course, and then we can have V-Ray's GI engines assist us in achieving our artistic goals.
For the benefit of those somewhat newer to 3D rendering, we're just going to start this chapter, making the assumption that maybe we're somewhat unfamiliar with just what global illumination is, and so we would benefit from just a quick breakdown of its definition and workings. An understanding of just what global, or indirect illumination is can probably best be gained by contrasting it to its lighting opposite, which is local, or direct illumination, as we see in our slide here. By default, adding light into a scene, and rendering without any GI systems enabled will give us only this type of local illumination.
Of course, local illumination as we see it in computer graphics, is not how light behaves in the real world. This is why we need GI systems in our renderers. They allow us to simulate the physical reality of light, which of course, in the real world, spends a lot of time, and a lot of energy bouncing around our environments. The basic GI process goes a little like this: As direct light is emitted from a source, such as our light here, it will travel until it strikes the surface of an object in our scene.
At this point, a lighting phenomenon known as intersurface reflection occurs. All this phrase means is that a portion of that light's energy will reflect, or bounce, and create a global or indirect illumination effect in the scene. Dependent upon the amount of energy coming from our light source, we should actually see that our light is able to bounce from a number of surfaces. With each bounce, it will lose a little bit of energy, and with each bounce, it will pick up a bit of coloration inherited from the diffuse properties of surface it is interacted with so far.
The end result of all this bouncing is that, well, our surroundings become lit, and even the dark nooks and crannies of an environment will end up receiving at least some level of lighting, even though they may be far away from any direct light sources. This complex process is what gives us the ability to create lighting scenarios that have a very high degree of accuracy, and realism to them. We can even conduct lighting analysis tests that give architects and engineers the ability to measure just how much illumination a given environment, and the given set of light sources will produce.
And now, with that basic explanation of global illumination, we're ready to move on to examining a very specific aspect of V-Ray's GI implementation, and that is its use of primary and secondary bounce engines.
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