Ambient Occlusion part 2

Ambient Occlusion pt 2

Ambient Occlusion (AO): Why it’s needed.

Last time we talked about Ambient Occlusion in Game Art (Part 1), let’s delve a little deeper.

When we first look at objects, for a fraction of a second, we evaluate shapes and contours, and determine the silhouette of things around us. That allows us to mentally compartmentalize things into, say, “That area is a car” and “that bunch of stuff is a tree” and so on.

Once we identify individual objects’ boundaries, we then see the inner details within the boundaries, like “That’s a car mirror” or “That’s a hubcap” and so on.

In both cases contrast is what we are seeing. Or “where one thing ends, and another begins.” Contrast defines boundaries. That’s why the pictures in this very blogpost have a black stroke, or boundary, around the text; to aid in readability. Strokes work very well for 2D elements, which is why virtually all game interface elements have them, game company logos have them, and important text like game titles have them.

In 3D games, the silhouette of an object is determined mostly by the actual polygon modeling itself. But all the details within that silhouette are determined by the textures, or images, applied to the polygon surface.

Imagine for a moment, that we have a 3D model of a giant mech robot, with one generic color applied to the whole thing.

Contours only

Virtually everything that has been modeled isn’t visible or noticeable, besides the outer contour.

That’s where lighting comes in. To actually see the surfaces and details clearly, we need value changes, or contrast.

Lit robot

Light hits things, making objects a bit brighter on one side, and darker on the other.

Let’s add Ambient Occlusion into the mix.

Lit, with Ambient Occlusion

Now we can see finer details more easily.

Lastly, here’s our robot with proper color texture maps applied (that include AO in them).

Diffuse Color robot

There you have it. AO is important because it lets us see what is there. Without AO, or advanced lighting techniques, we might not notice the majority of small surface details a game artist put there. AO accentuates the details, making them easier for a human eye to discern them by providing contrast.

But then it gets strange… You can also accentuate details that are not there.

But that’s a topic for another article, which may include some killer game art tips!


Rupert Morris is a Game Art instructor at VFS