Horizon-Based Ambient Occlusion Plus (HBAO+)

What Is Ambient Occlusion?

To create realistic shadowing around objects, developers use an effect called ambient occlusion (AO). Unlike traditional shadowing, AO can account for the occlusion of light, creating non-uniform shadows that add depth to the scene. Most commonly, games use screen-space ambient occlusion (SSAO) for the rendering of AO effects. There are many variants of SSAO, but all are based on early AO tech; because of this, they suffer from a lack of shadow definition and quality and only show a minimal increase in image quality (IQ) compared to the same scene without AO.

How Is Horizon-Based Ambient Occlusion + Different?

Unlike previous SSAO variants, HBAO uses a physically based algorithm that approximates an integral with depth buffer sampling. This enables HBAO to generate higher-quality SSAO, increasing the number of samples per pixel and the definition, quality, and visibility of AO.

But for performance reasons, HBAO is typically rendered at half-resolution, reducing the number of AO pixels by three-quarters. Unfortunately, rendering HBAO at reduced resolutions causes flickering that’s challenging to hide in all situations.

To overcome these issues, NVIDIA has completely redeveloped and revamped SSAO to create HBAO+, a paradigm shift in the field of SSAO rendering. In comparison to HBAO, HBAO+ doubles the detail level of AO and runs three times faster.