Join Eric Keller for an in-depth discussion in this video Combining final gathering with global illumination, part of Lighting and Rendering with mental ray in Maya.
To improve the quality of your indirect lighting, you can actually use both global illumination and final gathering techniques at the same time within a single scene. This can help deal with some of the quality issues of both types of indirect lighting. So to just show you quickly how you can set this up, I'm in my simple room scene. I'm going to press 5 to switch to Shaded mode. You can see I have my lamp here and my three simple shapes. So, I'll do a quick render here to see what this looks like. The lamp is using an area light. The shape of the area light is set to sphere, so that the area light is casting nice, soft shadows.
You can see this right here. So, the softness of the shadows is created by the area light, and it's also coming through the lampshade just a little bit. So now I want to add some indirect lighting into the room, so that the light coming out of the lamp is bouncing around, and we can start to see the other objects in the room. So, I'll store this really quickly, and I'll start by creating a point light that will emit photons, essentially global illumination. So, I'll switch to the Wireframe view by pressing 4 and pull this over so that it's basically inside my lamp.
I'm going to switch to the Top view and position this right here so it's in the center of the lamp, and I'll go back to the camera1 and tuck it in the lampshade. That's pretty good! So, now that I have my point light, I'll just call this photonCaster, so we know what it's doing, I'll go to the photonCasterShape node in the Attribute editor by clicking on this tab. I'm going to turn on Emit Photons. This is the default setting, so I have my Photon Color, the Intensity, and the Exponent are all default settings.
Notice that I can't get to the number of photons. In order to make this active, for some reason, you have to turn on Global Illumination first. So, I'll go to the Render Settings window, click on the Indirect Lighting tab, and turn on Global Illumination. So, now I have these settings and these settings, and once again, sometimes, if you turn this off and turn it on again, now I have my Global Illumination Photons available. I'm going to boost this up to about 100,000 and create another render. A couple of things that you want to make sure that you don't forget.
I need to set the Intensity to 0, because I don't want this shedding any direct lighting. So that should be 0. So all this light is doing is emitting photons into the scene, no direct lighting. So, let's create another test render. I'm going to store that. It's a little bit blotchy, as you could see, and some of this is somewhat blown out. So, couple things I can do to fix that problem. I'm going to reduce this scale a little bit, bring this down, so it's not making so much brightness in the room. I'm going to improve the Accuracy of the Global Illumination.
I'll set this up to 1500 and do another test render. So, this is what we get. It looks better in terms of its less blotchy, but you could see on the sphere here, we still have some blotchiness in the green color. The quality of the shadow, of course, this can be improved by adjusting the Sampling setting on the area light. I'm going to leave that alone for right now. Just so you know, this doesn't have anything to do with the Indirect Lighting settings; that's all based on the area light sampling. So, I'll save that image, and now what I'm going to do is I'm going to turn on Final Gathering.
So, I'll scroll in the Render Settings window, under the Indirect Lighting tab, down to Final Gathering. I'll turn this on, and I like to increase my Secondary Diffuse Bounces, so that we get more bounces out of our indirect lighting. So, I'm going to set this up to 1, and store this image, and create another render. Now this one will take longer, but we'll see if it actually helps deal with some of the blotchiness on this green sphere. So, now we have our renders complete, and you can see that some of the problems on the sphere have been alleviated just by turning on Final Gathering.
If I store this and compare it with the previous render, you can see, this is what I get. So, there we have fairly blotchy coloring on the sphere, and now some of those problems have gone away. We've improved the image quality. This is with using fairly low Final Gathering settings. So, if I store this image, and just as an experiment, turn off Global Illumination, let's see how it looks with just Final Gathering and no Global Illumination. So, this is the rendering with just Final Gathering settings put on.
You can see I'm getting some strange green glowing down here. So you can see how using them both together at the same time in the scene can help create much more realistic lighting than using just one or the other. They really work well together if you start to combine the strengths of both. So, there's just Global Illumination, here's just Final Gathering, and here is Global Illumination and Final Gathering together.
- 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