What Is Ambient Occlusion? (SSAO, HBAO, HDAO And VXAO)

The gaming industry is thriving thanks to technological advancements in hardware, processing power, and graphics. With new generation graphics cards, many gaming companies strive to deliver increasingly realistic ambient lighting. Gamers know that there are a lot of graphics settings they can play with to make the game visually appealing and more dynamic, such as ambient occlusion.

So, what is ambient occlusion?

This guide provides an overview of this setting and details different types of it.

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What Is Ambient Occlusion?

What Is Ambient Occlusion
Ambient occlusion is enabled on the left side and disabled on the right side. Can you tell the difference?

Ambient occlusion is a rendering method that provides an approximation of how bright the light should be at different parts of the visible surface. It considers different factors such as the environment of the game and the position of the light source. It provides a realistic simulation of the shadowing objects that block the ambient light from different sources, adding realism to 3D video games by mimicking light distribution in reality.

Ambient occlusion first surfaced in 2001. The movie Pearl Harbor introduced it for the very first time. Although it wasn’t a masterpiece, it helped pave the way for gaming graphics to rise.

Ambient occlusion in the gaming industry was first introduced in 2007. The game development company Crytek introduced it in their game Crysis, which earned a lot of accolades and sold over 3 million copies.

However, given that the shadowing was too graphically demanding for many gaming machines in the 2000s, a lot of gamers couldn’t benefit from this feature until much later. Nevertheless, many still enjoyed the realistic pinch that the game had to offer.

Much like any other technology, ambient occlusion has improved over time. Below are some different types of it.

Types Of Ambient Occlusion

The Witcher 3 Ambient Occlusion None
The Witcher 3 without ambient occlusion enabled

Different graphics cards and their architectures and rendering technologies contributed to various ambient occlusion enhancements, so there are different types prominent in today’s titles.

Some of the most commonly found settings include SSAO, HBAO, HDAO and VXAO.

SSAO

The Witcher 3 Ambient Occlusion SSAO
The Witcher 3 with SSAO enabled

SSAO or Screen-Space Ambient Occlusion was the type of occlusion introduced by Crytek in their debut of Crysis. However, to save the processing power, SSAO doesn’t consider the space and elements that produce shadows.

Instead, SSAO looks at the pixels around the element and their depth, which makes CPU usage more efficient, while introducing a dynamic rendering to make the ambient more realistic.

That said, instead of focusing on the entire screen, SSAO measures ambient occlusion in pixel depth at a part of the screen. Still, that brings some drawbacks, such as noise and potential inaccurate shadow distribution if the pixels aren’t properly measured.

SSAO didn’t have loading times, which made games run smoother. However, graphics card performance and video game demands have increased over time, which brought in new techniques.

HBAO

The Witcher 3 Ambient Occlusion HBAO+
The Witcher 3 with HBAO+ enabled

HBAO, also known as Horizon Based Ambient Occlusion, was the next enhancement in graphic rendering techniques. Nvidia introduced this approach to address the grain and noise that came with pixel depth measurements of SSAO. It does so by considering the ambient and the environment instead of just the pixels.

With the help of geometry, it’s much more effective at rendering shadows and lighting. The major disadvantage of HBAO is that, unlike SSAO, it requires more processing power in both the CPU and GPU. Later on, HBAO+ was featured to provide a less performance-tasking algorithm of light and shadow sampling.

HDAO

What Is HDAO Ambient Occlusion

HDAO or High Definition Ambient Occlusion is a similar technique, although it’s meant for AMD graphics cards to compete with Nvidia’s HBAO. There’s no difference between HBAO and HDAO, except that they’re native to their respective distributer’s GPU.

VXAO

What Is VXAO Ambient Occlusion

VXAO, or Voxel Ambient Occlusion, is the closest video games can get to reality in terms of lighting and shadow rendering. However, not many games boast this setting, mainly because it’s too tasking and will push the limits of your processor and graphics card. It also has a different approach than SSAO and other techniques.

In short, VXAO will render geometrical objects and approximate the shadowing outside the scene you’re experiencing. This approach gives scenes an even more realistic touch, providing a great comparison between modern-day games and what video games used to look like in the past.

More technically put, VXAO converts pixelated objects on the screens into voxels, which are 3D, cube-shaped pixels, hence the voxel ambient occlusion. As a result of their 3D structure, voxels can estimate the dimensions of certain geometrical objects inside games, which results in precise and sleek light and shadow rendering.

Ambient Occlusion vs. Ray Tracing

Ambient Occlusion vs Ray Tracing

SSAO focuses on pixel-depth and doesn’t take shapes and objects into account, leading to darkened corners, grain, and inaccurate shadows. On the other hand, Ray Tracing, being a more recent technology, focuses on more factors like the geometry of different shapes and objects, surfaces, and light to render accurate and realistic shadows.

It’s also a step forward from HBAO and HDAO, which focus purely on geometry. Additionally, Ray Tracing processes and renders only what’s visible to the player. In other words, the approximation of lighting and shadows is only performed on the camera view field.

Currently, not too many gamers use Ray Tracing, mostly because the feature is native to RTX 2000, 3000 and RX 6000 cards, and only a handful of games support this next-generation feature. However, as the gaming industry is progressing more games will support this technology.

Conclusion

Ambient occlusion is a method that calculates and approximates the right brightness in the in-game ambient, bringing players closer to the digital world. Different types of ambient occlusion have been developed throughout the years together with new graphics.

While more occlusion methods such as Ray Tracing will inevitably emerge, it’s important to note that ambient occlusion isn’t the only way to make your game look closer to reality. Still, it’s a complex yet fascinating technique which undoubtedly enhances both games and movies.

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Branko Gapo
Branko Gapo

Keeping up with the incredibly fast evolution of computer technology is impossible. That is why Branko will be using his knowledge on this matter to share news and information on all the latest essential technological innovations and advancements.