Irradiance mapping is probably the most widely used of V-Ray's primary bounce GI engines, simply because it is effective, flexible, and at the base level, pretty easy to use. In this video, we just want to run over for you the basics of how a irradiance mapping works, because, well, understanding the basic principles of the technology can go a long way towards helping us make good production choices when it comes to our irradiance mapping parameters. Now, if we just pull up our Render Settings window, go to the main toolbar, use the icon to pull out for ourselves, inside of the Indirect Illumination tab, you can see we have Irradiance map set as the Primary bounce engine.
So let's just come and look at some of its controls. A couple of things we need to note right from the start are, firstly that irradiance mapping is a view-dependent GI technique. This means that the global illumination solution is calculated only from the rendering camera's point of view. If we move the camera, then the GI solution will need to be recalculated, because, well, our lighting solution would have holes left in it that would become very obvious in our final render. This is why, if we just come down our Irradiance mapping controls, inside of its Mode option -- this is why the Single frame option, which really recalculates the irradiance mapping solution each time we start our render, that is why this is set as the default.
Now, there are methods for calculating irradiance maps that do allow for animation of cameras, and objects in the scene. If we just come up a little bit inside of the control sheet, in the Options section, we have this Use camera path option for moving cameras; we would want to be using that. We also, in our dropdown options in the Mode options, have Multiframe incremental, Incremental add to current map, Animation (pre-pass), and Animation (rendering). These are all options that can be used if we have animated cameras and/or objects in the scene.
The second thing we need to note is that irradiance mapping only traces a single bounce of light; this means it can only be used as the primary bounce engine. In fact, if we come up to our Primary and Secondary bounce options, you'll see that in the Secondary bounce slot, Irradiance mapping does not even appear. Let's use our example scene, then, to just walk through the basics of how irradiance mapping works. As irradiance mapping is view-dependent, the initial set of rays used for the calculation are traced out from the camera and into the scene.
This is done so that V-Ray can make an evaluation of the scene; it is looking for areas of contrast, deciding where on our geometric surfaces it wants to place the required irradiance samples. Remember, these can only be placed in areas of the scene directly visible to the rendering camera, or seen through reflections and/or refractions. Once the irradiance samples have been placed -- and we woll focus, here, just on a single sample -- a hemispherical dome of rays will be traced from every sample in the scene.
These go out to calculate the level of illumination found in the environment. The number of traced rays will be determined by the hemispherical subdivision's parameter, which is found in our Irradiance mapping controls. This primary bounce is the only bounce of light that irradiance mapping will trace. Everything else would need to be taken up by our secondary bounce engine. Now, one of the great things about irradiance mapping is that it can, if needed, be created on several passes. It can be adaptive; each pass adding more samples to the solution if they are needed.
The first pass will add samples to the scene, according to the minimum rate setting, and if we just look in our Irradiance mapping controls here, you can see, we have this Min and Max rate setting. In fact, if we just flick through these presets, you'll see that these, along with our color threshold values, change according to the resolution we set for our irradiance map. Once that initial pass is taken care of, if extra samples are required, then they will be added to the scene, up to the value set in, of course, our Max rate setting.
As you can probably guess, these are the controls that will determine the quality of our finished irradiance mapping solution. They determine the resolution at which the map is calculated. Just as a word of warning, one of the options we have in our presets is to just come into the Custom options, and you can see we can now set Min and Max rate values manually. One of the things we would really want to avoid is setting the same values. So I've just set 1 and 1 here; we would want to avoid setting the same value in each of these fields.
Essentially, now we have killed V-Ray's ability to be adaptive in its irradiance mapping calculations. Now, one pass is all we will get, and this fixed number of samples will be used, whether the scene requires them or not. To complete the GI calculation, V-Ray will take a number of samples from the already completed irradiance map, and interpolate our blend between them in order to create a smooth GI solution. This value here, the interpolation samples setting, is the one that will determine how much blending, or averaging between samples takes place.
Now V-Ray can begin the rendering process, and produce a final image for us. Well, let's move now to actually using irradiance mapping in a test scene for ourselves, and see how we can create a GI solution using this particular engine.
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