Ambient Occlusion: Everything You Need to Know

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ambient occlusion
The first time we saw what ambient occlusion could really achieve was in 2007 when the game Crysis used it to produce surprisingly crisp graphics. Everything in Crysis looked hyper-realistic, like being teleported to a different world, and it was all thanks to ambient occlusion. Crysis ultimately sold over 3 million copies.

Ambient occlusion is also used in movies now. The first time this was done was in 2001’s Pearl Harbor – the movie was mediocre but helped the precedent for the use of ambient occlusion in entertainment media. Read on to learn more about how it works!

What is Ambient Occlusion?

So what exactly is ambient occlusion? Simply put, it a method of lighting used for the scenery in games or films. Occlusion means to block or obstruct, so ambient occlusion in graphics means the point at which an object stops light from a source and thus throws a shadow in its created world. This then adds depth to scenes in video games or films. Ambient occlusion can be done in various forms with slightly different results.

Types of Ambient Occlusion

Techniques like ambient occlusion take a heavy toll on graphics cards, and since graphic cards haven’t always been as powerful as they are now, ambient occlusion techniques have evolved over time. The most common ones are discussed below.

Screen space ambient occlusion (SSAO)

SSAO was created by Crytek, the company that released Crysis, and was the first form of ambient occlusion used in video games. And yes, it was revolutionary at the time, but SSAO is not complete ambient occlusion because it doesn’t take into account every element of the game-world, it just a certain pixel and those around it.

This means several things: approximated semi-realistic shadow effects, no loading time, a shifting off the load from the CPU to the GPU which is better suited to handle it. This is why SSAO was a great starting point; even if it did result in jagged edges and less accurate lighting it was perfect for GPU performance at the time and made you feel like you were part of the game you were playing.

Screen space directional occlusion (SSDO)

Naturally, when technology advanced and GPU power increased, there came a much better ambient lighting technique. SSDO does what SSAO couldn’t – it takes into account the light coming directly at an object and the light being reflected off it, instead of focusing on mere pixels. This gives an extra layer of depth to games.

SSDO is used by companies like Unity and Unreal because it is able to produce spectacular worlds with very realistic lighting and accurate shading, although it is still prone to some of the potential issues that SSAO has. What makes SSDO stand out most is that it allows the player to better differentiate between objects to achieve a noticeably better sense of depth than SSAO ever could. This is the best option we have currently given the limitations of today’s GPUs.

Global illumination (GI)

Global illumination (GI) is also called indirect illumination, and it is the most elite form of ambient occlusion – it is the closest thing we have to photorealism within digital images. GI can account for light from every source in a world in how they relate to each other. If a tree in a game using GI was a few hundred yards away from you, its shadow would reach you even without being in the current frame.

However, true and real-time GI hasn’t been used in a game yet. It was used by Pixar in the movie Monsters University though, where they used cutting-edge technology to create even more realistic images.

Overall, ambient occlusion is a pretty neat trick and does a lot for the overall beauty of a game. Why then, isn’t it used in most games? Well, firstly it’s very demanding in terms of GPU use (if extreme settings are used). Since companies want to reach as wide an audience as possible, and not everyone in that audience will be able to afford expensive GPUs that can handle ambient occlusion, companies often end up omitting this feature. Even if they include it, most people simply stick to the basic AO setting as it has a minimal effect on performance.

Secondly, competing graphics effects have arisen with time – ones that may not deliver the exact same effect as ambient occlusion, but are close enough and less taxing on one’s GPU. Distortion and bloom lighting are two such effects that can make a player feel like a part of the game’s world. Skyrim is a good example of a game that utilizes these effects and is also accessible to a large demographic as it can be played on almost every platform.

Conclusion: Does Ambient Occlusion Even Make That Big a Difference?

So again, most companies refrain from using ambient occlusion. This leads to the question; does it even make that noticeable of a difference? No, not really. Some might even call ambient occlusion a straight-up gimmick! While there are plenty of substitutes, like we’ve already talked about, the simple truth is that a lot more goes into making games and movies look good than just lighting techniques. Things like story, content, timing, etc. also contribute to the overall experience.

A good example of why things other than looks are important is EA. A lot of their games have missed their initial sales targets, like Star Wars Battlefront II (and of course the absolute mess that was the Battlefield 5 launch) because of the number of microtransactions in the game ruined the experience for some players and gave an unfair advantage to others.

While graphics are important, they are often not what makes or breaks a game. The fact that most people do not use Ambient Occlusion means that no matter how it changes the look of a game, it does not contribute to the experience in a significant way. While AO may be a huge part of games in the future, it is little more than a nice additional feature to have right now.

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