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The ambient occlusion map for this scene darkens only the innermost angles of corners.

In computer graphics, ambient occlusion is used to represent how exposed each point in a scene is to ambient lighting. So the enclosed inside of a tube is typically more occluded (and hence darker) than the exposed outer surfaces; and deeper inside the tube, the more occluded (and darker) it becomes. The result is diffuse, non-directional lighting throughout the scene, casting no clear shadows, but with enclosed and sheltered areas darkened. In this way, it attempts to approximate the way light radiates in real life, especially off what are normally considered non-reflective surfaces.

Unlike local methods like Phong shading, ambient occlusion is a global method, meaning the illumination at each point is a function of other geometry in the scene. However, it is a very crude approximation to full global illumination. The soft appearance achieved by ambient occlusion alone is similar to the way an object appears on an overcast day.

Implementation

In real-time games, Screen space ambient occlusion can be used as a faster approximation of true ambient occlusion, using pixel depth rather than scene geometry to form an ambient occlusion map. However, newer technologies are making true ambient occlusion feasible even in real-time.

Ambient occlusion is related to accessibility shading, which determines appearance based on how easy it is for a surface to be touched by various elements (e.g., dirt, light, etc.). It has been popularized in production animation due to its relative simplicity and efficiency. In the industry, ambient occlusion is often referred to as "sky light".Potter or Ceramic Artist Truman Bedell from Rexton, has interests which include ceramics, best property developers in singapore developers in singapore and scrabble. Was especially enthused after visiting Alejandro de Humboldt National Park.

The ambient occlusion shading model has the nice property of offering a better perception of the 3d shape of the displayed objects. This was shown in a paper where the authors report the results of perceptual experiments showing that depth discrimination under diffuse uniform sky lighting is superior to that predicted by a direct lighting model.

The occlusion $A_{\bar {p}}$ at a point ${\bar {p}}$ on a surface with normal ${\hat {n}}$ can be computed by integrating the visibility function over the hemisphere $\Omega$ with respect to projected solid angle:

$A_{\bar {p}}={\frac {1}{\pi }}\int _{\Omega }V_{{\bar {p}},{\hat {\omega }}}({\hat {n}}\cdot {\hat {\omega }})\,\operatorname {d} \omega$

where $V_{{\bar {p}},{\hat {\omega }}}$ is the visibility function at ${\bar {p}}$, defined to be zero if ${\bar {p}}$ is occluded in the direction ${\hat {\omega }}$ and one otherwise, and $\operatorname {d} \omega$ is the infinitesimal solid angle step of the integration variable ${\hat {\omega }}$. A variety of techniques are used to approximate this integral in practice: perhaps the most straightforward way is to use the Monte Carlo method by casting rays from the point ${\bar {p}}$ and testing for intersection with other scene geometry (i.e., ray casting). Another approach (more suited to hardware acceleration) is to render the view from ${\bar {p}}$ by rasterizing black geometry against a white background and taking the (cosine-weighted) average of rasterized fragments. This approach is an example of a "gathering" or "inside-out" approach, whereas other algorithms (such as depth-map ambient occlusion) employ "scattering" or "outside-in" techniques.

In addition to the ambient occlusion value, a "bent normal" vector ${\hat {n}}_{b}$ is often generated, which points in the average direction of unoccluded samples. The bent normal can be used to look up incident radiance from an environment map to approximate image-based lighting. However, there are some situations in which the direction of the bent normal is a misrepresentation of the dominant direction of illumination, e.g.,

In this example the bent normal N_b has an unfortunate direction, since it is pointing at an occluded surface.

In this example, light may reach the point p only from the left or right sides, but the bent normal points to the average of those two sources, which is, unfortunately, directly toward the obstruction.

Recognition

In 2010, Hayden Landis, Ken McGaugh and Hilmar Koch were awarded a Scientific and Technical Academy Award for their work on ambient occlusion rendering.

See also

• Global illumination
• Photon mapping
• Radiosity
• Ray tracing
• Reflection occlusion
• Screen space ambient occlusion

External links

• Depth Map based Ambient Occlusion
• NVIDIA's accurate, real-time Ambient Occlusion Volumes
• Assorted notes about ambient occlusion
• Ambient Occlusion Fields — real-time ambient occlusion using cube maps
• PantaRay ambient occlusion used in the movie Avatar
• Fast Precomputed Ambient Occlusion for Proximity Shadows real-time ambient occlusion using volume textures
• Dynamic Ambient Occlusion and Indirect Lighting a real time self ambient occlusion method from Nvidia's GPU Gems 2 book
• GPU Gems 3 : Chapter 12. High-Quality Ambient Occlusion
• ShadeVis an open source tool for computing ambient occlusion
• xNormal A free normal mapper/ambient occlusion baking application
• 3dsMax Ambient Occlusion Map Baking Demo video about preparing ambient occlusion in 3dsMax