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One of the big advantages of mental ray is that it allows you to create what's called indirect lighting. Now in the most basic form, indirect lighting is bounce lighting. So if you shine a light at a wall, the wall will bounce some light back into the room. Now typically, we can't simulate this unless we have something like mental ray which has options that allow us to do this sort of lighting. So let's take a look at how this works. I've got a basic scene here and I want to make sure that I'm lighting using mental ray.
And under Indirect Lighting, we have an option here called Final Gathering and this is the first step in creating bounce lighting. Now I'm going to keep this off for just a second and let's just do a render of the scene. Now this scene has two lights; it has one light shining through the window, it's a spotlight, and then we have a point light up here just illuminating the scene in a general way. So I'm going to make sure I'm in my Camera 1 Viewport and let's go ahead and render this.
Now it took a little while to render this on my machine. But as you can see, we've got the basic lighting from these two lights. Now one of the things I'm noticing here is we get a lot of darkness right here on the back of the chairs, and the shadows under the table are pretty dark. This is because we're not getting much bounce lighting, we have this really white floor and these yellow walls and they are not contributing any light to the room. So let's go ahead and add in some bounce lighting using Final Gather. Now before I do that, I'm going to hit this button here which keeps this image, and that way, we can compare image to image as we go through the rendering process.
So I'm going to make sure I keep my image, and then let's go into Render Settings. I'm going to go down to Indirect Lighting > Final Gathering and turn on Final Gather. Now we have a number of different options here for Final Gather; one is Accuracy, Point Density, and a bunch of other ones. We're not going to get too into these, the defaults work pretty well. We also have another one for Quality, for a Final Gather Map which allows you to make it more efficient and Final Gather Tracing.
Do we want to actually gather reflections and refractions? We're not going to do any of this, we're just going to leave this at the default. I want you to understand the basics of Final Gather. So once we turn this on, let's go ahead and render. Now this may take a little bit longer. Okay, now we've got our image, and you can see how the backs of the chairs aren't as dark. In fact, if we scroll through these here, you can see this is the previous image. And Final Gather added in a lot of bounce lighting, and you can see this particularly on the legs of the chairs and under the table.
Now one of the things the scene doesn't have is a back wall. I'm going to go ahead and minimize this. I want to keep this window open, but just minimized, and I'm going to hop out into my three views here, and let's go into this top view here. In fact, let's change this into a Perspective view, so that way, I can see what's in the scene. And as you see there's no back wall to this scene, but conveniently, I've actually created one here and we can slide that into place.
Now the reason I'm doing this is because this will bounce additional lighting into the scene. So when you start working with things like Final Gather, you want to make sure that your scene is reasonably realistic. That way, you get the most realistic lighting. So now that I have that slid into place, I'm going to go ahead and bring up my Render View window here one more time, and I'm going to save out this image. I'm going to make sure I do a Keep Image here, so I've got my dark image, and my light image, and we're going to do one more here.
I'm just going to render this one more time, and again, this may take a little bit of time. Okay, so now we've got our final image here, and we've got now three separate ones. So I've got my initial image which is no Final Gather, this one which has Final Gather but no back wall and this one which has a back wall. Now notice how all I had to do was turn on Final Gather, and make the room complete, and now I have much more realistic lighting.
And so this is a great way to get realistic lighting without too much additional effort, but perhaps a little more render time.
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