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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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