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Understanding primary and secondary bounces

From: V-Ray 2.0 for Maya Essential Training

Video: Understanding primary and secondary bounces

As we've already noted, in the real world, light doesn't just bounce once. After being emitted from a source, it will, for all intensive purposes, just keep on bouncing. Not that we are saying it stays infinitely bright, mind you. After an unspecified number of bounces, or after a certain distance traveled, the level of light energy will become so low, that is really is no longer contributing illumination to the environment that can be perceived by the human eye. The energy is still active, of course; the falloff or decay rate of light is such that, mathematically, it can be said to actually never reach absolute zero.

Understanding primary and secondary bounces

As we've already noted, in the real world, light doesn't just bounce once. After being emitted from a source, it will, for all intensive purposes, just keep on bouncing. Not that we are saying it stays infinitely bright, mind you. After an unspecified number of bounces, or after a certain distance traveled, the level of light energy will become so low, that is really is no longer contributing illumination to the environment that can be perceived by the human eye. The energy is still active, of course; the falloff or decay rate of light is such that, mathematically, it can be said to actually never reach absolute zero.

Now, I'm sure you can imagine that performing such an infinitely reducing calculation, in a manner completely true to the laws of physics, tracing every potential light path and bounce, well, that would be extremely expensive; extremely slow in terms of computation required. Thankfully, V-Ray has been designed in such a way so as to give us a very high level of flexibility and control regarding the way we calculate our global illumination solutions. In part, this is why we see V-Ray dividing its indirect illumination calculations into two parts; primary, and secondary bounces.

If we just come into our Render Settings window, we want to come across to our Indirect Illumination tab, and if we come down, with the GI Systems enabled, you can see we have Primary, and Secondary Bounce options, and we get to choose the type of GI engine that we use in that particular slot. Now, the Primary bounce engine controls only the first bounce of light. This initial bounce occurs only where surfaces are visible to the rendering camera. That can be either directly in its field of view, as we see inside our viewport here, or it can be through the material properties of reflections and/or refractions.

Using Primary bounce only, we can get some basic bounce light, or GI in the scene, instantly, of course, giving us a more realistic lighting solution. At this point, we are not really allowing the light to continue to bounce, nor are we calculating even an initial light bounce for areas of the scene not visible to the rendering camera. So for instance, in our scene here, you can see we have a back area, a backroom as it were, that travels behind this piece of geometry; behind the wall. Now, this area would not be included in this initial light bounce calculation.

Naturally, this would leave us quite a long way short of producing an accurate, or photo real lighting solution. For that, we would need to copy the real world behavior of light, as we've outlined it, and enable our Secondary bounce engine. This engine controls, naturally enough, every GI ray not counted as a primary bounce. Calculating the secondary bounces, of course, becomes more costly in terms of render time, as these are the ones that will be performing continuous intersurface reflections, or bounces.

Naturally, V-Ray allows us a measure of control over how much bouncing we allow. Just bear in mind that the more accurately we mimic real world light behavior by allowing more bounces, the more accurate, and probably believable, our lighting solutions will become. So we're armed, now, with an understanding of at least the basic workings of GI. We also understand that V-Ray splits its GI lighting calculations into two parts; primary, and secondary bounces. Time, then, to move on to looking at V-Ray's GI engines themselves.

Our first stop will be irradiance mapping.

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V-Ray 2.0 for Maya Essential Training

54 video lessons · 2210 viewers

Brian Bradley
Author

 
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  1. 4m 28s
    1. Welcome
      59s
    2. What you should know before watching this course
      51s
    3. Exercise files
      40s
    4. Workflow recommendation
      1m 58s
  2. 11m 32s
    1. Installing V-Ray
      4m 25s
    2. Setting up V-Ray
      3m 14s
    3. Locating V-Ray's tools and features
      3m 53s
  3. 24m 41s
    1. Image sampling explained
      3m 19s
    2. Understanding subdivs
      3m 49s
    3. Using the DMC Sampler
      6m 54s
    4. Overview of color mapping
      4m 45s
    5. Understanding the color-mapping modes
      5m 54s
  4. 27m 55s
    1. Dealing with lighting problems
      9m 26s
    2. Adding a spherical fill light
      8m 50s
    3. Creating a mesh light
      2m 43s
    4. Creating a skylight effect
      3m 18s
    5. Working with the dome light
      3m 38s
  5. 44m 25s
    1. Global illumination (GI) explained
      3m 55s
    2. Understanding primary and secondary bounces
      3m 34s
    3. How irradiance mapping works
      5m 30s
    4. Using irradiance mapping, part 1
      4m 35s
    5. Using irradiance mapping, part 2
      5m 44s
    6. How light cache works
      3m 48s
    7. Using light cache
      7m 58s
    8. Understanding brute force GI
      2m 18s
    9. Using brute force GI
      7m 3s
  6. 40m 3s
    1. Introduction to V-Ray-specific materials
      2m 22s
    2. Creating diffuse color
      8m 31s
    3. Making reflective materials
      5m 40s
    4. Blurring reflections
      8m 31s
    5. Making clear and colored glass
      8m 49s
    6. Creating a translucency effect
      6m 10s
  7. 24m 15s
    1. Introduction to image sampling
      2m 56s
    2. Using the Fixed-Rate sampler
      5m 57s
    3. How to use the Adaptive DMC sampler
      5m 21s
    4. Working with the Adaptive Subdivision sampler
      7m 7s
    5. Comparing image-sampling renders
      2m 54s
  8. 17m 23s
    1. The physical workflow explained
      2m 37s
    2. Working with VRaySun and VRaySky
      7m 39s
    3. Controlling the VRayPhysicalCamera
      7m 7s
  9. 45m 0s
    1. Depth of field: VRayPhysicalCamera
      5m 45s
    2. Depth of field: perspective viewport
      5m 49s
    3. Creating a motion blur effect
      9m 30s
    4. Generating caustic effects
      7m 51s
    5. Using VRayFur
      6m 2s
    6. Setting up render-time displacement effects
      10m 3s
  10. 34m 17s
    1. Render elements workflow
      6m 47s
    2. Preparing to composite
      2m 22s
    3. Compositing V-Ray elements
      7m 8s
    4. Putting extra elements to work
      6m 20s
    5. Post-lighting a scene
      11m 40s
  11. 11m 47s
    1. Overview of V-Ray RT
      5m 27s
    2. Demonstrating the RT workflow
      6m 20s
  12. 1m 8s
    1. What's next?
      1m 8s

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