Join Brian Bradley for an in-depth discussion in this video How irradiance mapping works, part of V-Ray 3.0 for 3ds Max Essential Training.
- 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 basic level, pretty easy to use. In this particular video, given that understanding the basic principles behind how a technology works can often times go a long way toward helping us make good production choices, we want to quickly run through the basics of how irradiance mapping as a technology works. A couple of things that we need to know right from the start are that, firstly, irradiance mapping is a view-dependent global illumination technique.
This means that the GI solution is calculated only from the rendering camera's point of view. If we move that camera once the irradiance map has been computed, the GI solution will most probably need to be recalculated. This is why by default, V-Ray's irradiance mapping system is set to completely recalculate each and every time we take a new render. We do, of course, have options available for working with moving objects and moving cameras in a scene. If I jump inside the GI tab of the Render Setup dialogue, we can see with irradiance mapping set as our primary bounce engine and using just the basic UI configuration, we gain access to an opperating mode for the irradiance mapping system.
By default, this is set to single frame, which basically means that each and every time we take a new render, we get, as the tool hint says here, a brand new irradiance map being created, replacing the one that sits in memory from any previous renders. If we want to work with animated objects, or even animated cameras in the scene, however, this operating mode simply won't work for us as it will produce lots of flickering artifacts. What we need to do then, is choose a different operating mode, and we do have a number of options available.
All of which can help us out when working in a variety of moving camera and moving object scenarios. In fact, if I just select one of them, we get a helpful tool tip that outlines a possible best use scenario for this mode. A second fact we need to be aware of in connection with irradiance mapping is that it only traces a single bounce of light, which means it can only be used as a primary bounce engine. In fact, if we come to our secondary engine options, you see in the drop-down that irradiance mapping is not even available.
Let's use our example scene here, then, to walk us through the basics of how irradiance mapping actually works. As irradiance mapping is a view-dependent technique, the initial set of rays used in the calculation are traced from the rendering camera out into the scene. This allows the engine to make an evaluation, looking for areas of contrast in the scene, that can help it decide where on the geometric surfaces it needs to place the initial set of irradiant samples or points.
Areas with bigger changes in contrast tend to get more of the initial sample count allotted to them. Remember, these samples can only be placed in areas of the scene that are directly visible to the rendering camera, or that can be seen through material reflections and/or refractions. Once the irradiant samples have been placed, and here we will focus in on just a single sample, a hemispherical dome of rays will then be traced from each and every irradiant sample in the scene. These rays are sent out to help calculate illumination levels throughout the entirety of the 3D environment.
This primary bounce is the only bounce of light that the irradiance map system will trace. Any additional light calculations needed will have to be supplied by a secondary bounce engine. The number of rays used for this part of the process will be controlled by the Hemispherical Subdiv's parameter. One of the great things about the irradiance mapping solution is that it can, if needed, be created over the course of several adaptive passes. Each pass can and will add more samples to the solution, should they be needed, with the first pass adding samples based on the minimum rate setting.
The number of passes taken will be determined by the difference in value between the minimum and maximum rate control. These, in fact are the quality control options for our irradiance mapping solution, with more samples being progressively added, until either the color or noise threshold requirements are met, or the max number of samples allowed is reached. Once this phase is done, V-Ray will take a number of neighboring samples from the now completed irradiance map, and then interpolate or blend them together in order to create a smoother GI solution.
The number of samples used for this interpolation, or blending, will be controlled by the Interp. samples parameter. At this point, V-Ray is ready to begin the rendering process, and produce a final image for us. One word of warning well worth taking note of here, is the fact that when using the "Custom" option from the presets dropdown, we do have the ability to set the minimum and maximum rate values to the same number, so 0 and 0, for instance. This, typically speaking, is a very bad idea as it effectively kills adaptivity in the irradiance mapping system.
In this scenario, one pass using a fixed number of samples is all we would get. Samples that would be calculated whether the scene actually needed them or not. Well, let's move on, and, using a scene that presents a GI lighting challenge, see what kind of lighting solution we can produce whilst using the irradiance mapping controls.
- Using the new UI elements, Quick Settings, and revamped Frame Buffer
- Understanding color mapping modes
- Adding V-Ray light types
- Working with the V-Ray Sun and Sky systems and dome light
- Using irradiance mapping and light cache
- Working with diffuse color maps
- Making reflective materials
- Creating a translucency effect
- Using the new SSS and skin shaders
- Ensuring quality with image sampling
- Working with the adaptive subdivision engine
- Controlling the physical camera
- Working with FX tools such as VRayFur and VRayMetaball
- Stereoscopic 3D rendering
- Using Render Mask
Skill Level Intermediate
Q: This course was updated on 02/02/2016. What changed?
A: We added tutorials on the new 3ds Max camera tool, which replaces the defunct V-Ray Physical Camera. The author also includes a method for creating a V-Ray camera via scripting.
Q: This course was updated on 04/19/2018. What changed?
A: New videos were added that cover V-Ray 3.1 to 3.3 updates.