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So now that we've covered the basic kinds of lamps that add light to a scene, I would like to cover what's called ambient occlusion or ambient lighting and radiosity or other people call that global illumination. There's lots of different terms that are thrown about, and I can just present you the way Blender approaches the problem of lighting. So in this first scene, which is called 0 point, when you press F12 you get a very quick render of a sphere sitting on a little pedestal.
However, you'll notice there are no lights in the scene at all. So where is this light coming from and why is it so flat? That's called ambient light. Ambient light is set up in your Shading World, World panel down here under ambient light, and here's where you set the color and the brightness of the ambient light. Ambient light is light that is in a room. Imagine if you are in a room and the sun is shining outside and there aren't any lights on inside the house.
Inside the room there's still lights that is coming through the windows and it's filtered in and it's bouncing all around and that's called ambient light. We can simulate the different colors and intensities of ambient light by setting these values in these red, green and blue sliders here. Each material in Blender then is affected by that ambient light to the degree, which is specified here in the Shading Material Shaders panel down here under this Ambient Light slider, and this surface is affected by combining the base material plus all the other lights that are shining on it and half of the ambient light which as you saw was white, so half of white is gray.
So that's why this is a gray color. Now if we were filming let's say our CG scene in a volcano or underground and we use more of a red color then you can see that this globe in addition to the lighting that's in the scene, this globe would be affected and be colored red because there's a red color that's in that scene. Now I'm using the Render window here, because the Render window is kind of neat in that if you press J, you go back to the previous render.
So you can jump back and forth between renders just by pressing J in this key. So as you work through this exercise with me, go ahead and be pressing this J back and forth and you can be comparing the different kinds of renders you can get. The next topic is called Ambient Occlusion. Ambient Occlusion happens when you have creases and corners in a room and the light cannot scatter and be reflected as much into a corner as much it is on the flat wall.
So you get this darkening kind of effect as you go into corners. Here we have a sphere that's in a little box, I just made a cute little set here, that is being lit only by ambient light or ambient occlusion. Other people call this a dirt shader because this sort of simulates the dirt that might accumulate in an old house. And here is a little set and this is a standard kind of lighting test set that we'll be using throughout this video and then in subsequent videos where we talk about lighting because it provides a very nice controlled lighting situation.
In this render, we have the different shades of gray computed based on the ambient light color, the degree to which each material is affected by the ambient light, and then what we have done is as we have added in the Ambient Occlusion, which is shown here on this Ambient Occlusion tab. Ambient Occlusion then takes all of that ambient flat lighting and subtracts or adds or both, as you can see here, the plain color of the ambient light based on the geometry and the creases of where the geometries intersect and either adds to lightens or darkens the area in order to compute the overall image.
So this is exactly what a severe setting on a pedestal in a very indirect lit room like in an art gallery or something like that where they don't have direct lighting. They use a lot of ambient light color. So Ambient Occlusion has a couple of settings I would like to go over. The first is the number of Samples. You can see a little bit of graininess as you zoom in here. You can see this grainy. This graininess gets better with the more Samples that you use. 32 Samples is the most and the degree to which the ambient lights falls off is computed here.
The most intensive way of computing ambient light is to use the Raytrace method. But Blender also has an Approximate Ambient Occlusion, which is much, much faster to use, especially on the lower powered computers. So you can use a higher number of passes and have a better correction with lower error if you use Approximate Ambient Occlusion. Normally, you use the ambient light color set here, but you can also use the SkyColor, which is this horizon light green with up to a darker blue, to be used so that it would almost look like this globe is sitting outside under a tree, let's say, under some very diffused lighting.
And you don't want to use Ambient Occlusion as the only lighting, but combined with all of the other lighting rigs and the other kinds of lights, it can provide very photorealistic lighting. The next kind of lighting is called Radiosity. Radiosity happens when light hits something like say a red chair or in this case, the pink base of the sphere. Some of the light that hits that sphere is radiated back out into the environment and then that light hits the object next to it and colors it next.
So if you take a bright red ball and you roll it up against a white wall, you will see that the wall turns a little red and that's called Radiosity. Radiosity is set here in this little Radiosity buttons and basically you select the meshes in the scene, collect them and then go. And what happens is Blender will go through and based on the patch size, compute how much each little section of the scene is affected by the color that would be radiated out from all the other mesh sections in the whole scene.
So it takes a long time to compute, but it gives a very accurate representation of not just the light hitting something, but the light then bouncing off and reflecting and coloring everything else in the scene. So I have already recollected the meshes and then this is the effect that would be added. Now again this is a very dramatic effect. I really cranked it up so you can visually see it. Usually you crank it way down and make it a very subtle addition to the light to give the realism.
When you combine these two for example, we have a combination of both Ambient Occlusion and Radiosity, and you can see how they kind of work together to provide a very realistic even amount of lighting even without any lights in the scene. This is actually with no actual light being shown on the objects, and again, the Radiosity is little strong than what I would recommend. But it gives you an idea of the kind of effect you can get using Ambient Occlusion and Radiosity.
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