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Lighting and Rendering with mental ray in Maya
Illustration by John Hersey

Tuning global illumination


From:

Lighting and Rendering with mental ray in Maya

with Eric Keller

Video: Tuning global illumination

So I've added global illumination to this scene. You can see from the initial rendering that the default settings don't look very good. So there are a few things I need to do in order to improve the quality of this render. So I want to store this image and minimize it. And I'm going to take a look at my lights in the scene. So here is the point light, which is the photon-casting light. The way in which Global Illumination works is virtual photons are shot out from the point light, and when they contact the surface, a round area of lightness is created. So each photon has a round area of light.
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  1. 3m 46s
    1. Welcome
      1m 32s
    2. Using the exercise files
      2m 14s
  2. 19m 8s
    1. What is a CG light?
      1m 22s
    2. Types of CG lights
      10m 55s
    3. Direct lighting
      4m 48s
    4. Indirect lighting
      2m 3s
  3. 53m 20s
    1. Decay rate
      6m 30s
    2. Previewing lighting and shadows
      2m 37s
    3. Creating depth map shadows
      1m 57s
    4. Troubleshooting depth map shadows
      2m 38s
    5. Shadow map overrides
      5m 30s
    6. Using the shadow map camera
      5m 31s
    7. Saving and reusing shadow maps
      2m 48s
    8. Creating raytraced shadows
      1m 56s
    9. Adding softness to raytraced shadows
      3m 42s
    10. Creating area light shadows
      5m 11s
    11. Sample: mental ray area light
      4m 23s
    12. Setting area light visibility
      8m 7s
    13. Creating soft shadows with spot lights
      2m 30s
  4. 43m 35s
    1. Setting global illumination for interiors
      2m 33s
    2. Tuning global illumination
      5m 56s
    3. Global illumination photons
      1m 12s
    4. Activating caustic light effects
      3m 28s
    5. Tuning caustic settings
      3m 35s
    6. Setting caustic light effects on metal
      2m 35s
    7. Using final gathering for indirect lighting
      2m 9s
    8. Tuning final gathering
      4m 2s
    9. Reusing final gathering maps
      3m 21s
    10. Adding light with shaders
      5m 27s
    11. Creating final gathering maps for animation
      4m 26s
    12. Combining final gathering with global illumination
      4m 51s
  5. 1h 2m
    1. Activating the Physical Sun and Sky network
      2m 33s
    2. Tuning the Physical Sun and Sky settings
      7m 18s
    3. Applying physical light shaders
      8m 54s
    4. Applying image-based lighting
      8m 57s
    5. Tone mapping
      6m 23s
    6. Applying portal light shaders
      7m 45s
    7. Creating light beams with participating media
      10m 9s
    8. Adding depth of field with the Bokeh lens shader
      10m 39s
  6. 48m 21s
    1. Introducing render layers
      6m 13s
    2. Creating render layers
      4m 28s
    3. Splitting a scene into render layers
      15m 36s
    4. Applying render layer presets
      7m 47s
    5. Setting render layer overrides
      7m 7s
    6. Creating render layer composites
      3m 52s
    7. Organizing renders with tokens
      3m 18s
  7. 42m 24s
    1. Introducing render passes
      2m 56s
    2. Comparing render passes and render layers
      6m 44s
    3. Editing render passes
      10m 41s
    4. Using appropriate materials
      5m 51s
    5. Batch-rendering passes
      5m 56s
    6. Compositing in After Effects
      6m 41s
    7. Rendering the EXR image format
      3m 35s
  8. 23m 3s
    1. Anti-Aliasing Quality
      6m 44s
    2. Setting color profiles
      2m 53s
    3. Diagnosing raytracing
      5m 7s
    4. Adjusting motion blur
      6m 57s
    5. Finding mental ray help
      1m 22s
  9. 21s
    1. Goodbye
      21s

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Lighting and Rendering with mental ray in Maya
4h 56m Intermediate Jul 22, 2010

Viewers: in countries Watching now:

Lighting and Rendering with mental ray in Maya with Eric Keller shows how to master practical mental ray techniques for rendering models created in Maya. This course walks through the most efficient and innovative mental ray techniques, including direct versus indirect lighting methods, creating different types of shadows, using the new ShadowMap camera, and reusing shadow and final gathering maps. A chapter on optimizing render times and enhancing render quality is also included. Exercise files are included with the course.

Topics include:
  • Understanding computer-generated lighting
  • Creating depth map and ray traced shadows
  • Softening and shaping shadows
  • Working with global illumination
  • Lighting with the caustic settings
  • Applying physical and portal shaders
  • Adding depth of field with the Bokeh shader
  • Splitting a scene into render layers
  • Comparing render passes and render layers
Subjects:
3D + Animation Rendering Photography Lighting
Software:
Maya
Author:
Eric Keller

Tuning global illumination

So I've added global illumination to this scene. You can see from the initial rendering that the default settings don't look very good. So there are a few things I need to do in order to improve the quality of this render. So I want to store this image and minimize it. And I'm going to take a look at my lights in the scene. So here is the point light, which is the photon-casting light. The way in which Global Illumination works is virtual photons are shot out from the point light, and when they contact the surface, a round area of lightness is created. So each photon has a round area of light.

These are blended together by mental ray to sort of create that indirect lighting effect. So the first thing I can do in order to improve the effect is increase the number of photons that are being shot out of this light. So the default setting is 10,000. I want to set this up to 100,000, and create another test render, and see if that's improved. It looks a little bit better. We're getting some place, and compare this to what we had before. And you can see in this case that render time is increased by a second. That's not too bad.

So the other thing I can do is increase the accuracy of the Global Illumination effects. So I'm just going to go into the Render Settings, and under the Indirect Lighting tab, I'm going to switch to the Global Illumination settings, which are found right here. And I'm going to increase the Accuracy to about 2400 and see how that looks. Now, we're getting something a lot more pleasing. For the most part it's fairly smooth on the walls, but it does look a little bit bright. So in order to decrease the brightness, I'm going to decrease the Scale, bring this down to about this level right here.

And now when I render, I am going to get something a little bit more realistic. So all this lighting on the wall is just created by the direct light coming in here, and we're simulating the effect of it bouncing around. And as we'll see some of the nicer effects of Global Illumination, we're getting color bleeding; the green color of the sphere is on the wall. The red color of this cube is being picked up right here. We're also seeing ambient occlusion shadowing. This darkness right here behind this cube, as well as down here - these are shadows that are not created by the direct light.

The direct light is only casting this shadow right here and on the floor. These are essentially indirect shadows, or ambient occlusion created by Global Illumination. And you'll notice that what I did is created a point light from my Global Illumination photons, rather than using the direct light to cast the photons, and there is a good reason for doing this. I'll demonstrate this because I'll delete this light, and so now I just have the direct light in the scene. And I am going to turn on Emit Photons, and I'll even set this up to 100,000, just like I had for the point light, and take a look at the Render Settings.

So my Accuracy is at 2400, and my Scale is sort of a dark gray. If I do a render here, for one thing, directional lights don't work very nicely with global illumination. Direct lights tend to get extremely bright and overblown. I already have the Scale down here at a dark gray; if I bring this Photon Intensity even down to like 10 and create a test render, it's going to be very difficult to get something nice out of this light.

And I think it's going to almost impossible to get something that works. So as a general rule: Direct lights do not work well as photon casting lights, so avoid turning on Emit Photons for directional lights. Likewise, for instance if I create a point light here and put it up towards the roof here, and I'll get rid of my directional light. And I'm going to use this light to cast both direct light and global illumination photons. So I have this light on.

I'm going to turn on Ray Trace Shadows. I want to set the Decay Rate to Linear, and even put this up to 10. And finally, I'm going to turn on use photons. And if I use a similar setting to what I have before of 100,000, and turn on the brightness, you can see there is some bleeding right here. There is also some other effects, but overall it's not looking great.

Another thing that you may encounter is a very blown out area near the light itself. If I move it close to the wall here, yeah, you can see this is extremely hot right here. So I'm having trouble resolving that issue. So as a general rule: To get the best out of global illumination, try and keep your photon-casting lights and your direct lights separate; don't use the same light to do both. So I have one light cast global illumination photons and set the Intensity of that light to zero, and have your second light cast your shadows and your direct lights.

So for instance, like I had before, this directional light is casting using raytrace shadows, casts a direct light and the direct shadows. And then you can, for your photon-casting lights in the Caustics and Global Illumination section, that's where you'll adjust the specific light settings for the number of photons and the photon intensity, and so on. And then to further refine the look of the global illumination, go to the Indirect Lighting tab at the Render Settings window. And under Global Illumination, you can tune the Accuracy which improves the quality of the render, the Scale which will adjust the overall scale of all the global illumination in the scene.

So you could just bring this down to a great color to darken it. And that's basically how you go about starting to adjust your global illumination settings.

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