Query: Real Time Ambient occlusion

title: Approximating Global Illumination with Real Time Ambient Occlusion
abstract: Approximating global illumination has long been a problem that real time applications, such as games, have been trying to solve efficiently. For years, the best and most efficient techniques have been ambient occlusion algorithms based in screen space, such as Horizon Based Ambient Occlusion. Although efficient, such algorithms can suffer from artifacts, and a lack of realism due to being screen space algorithms trying to approximate a world space effect. In 2018, Nvidia released the first ever hardware accelerated ray tracing graphical processing units. Proper ray traced ambient occlusion could now be a viable alternative to screen space algorithms. However, to be a viable alternative, the results need to be of a certain quality, and its performance must be in the order of a few milliseconds. This thesis will show that although real time ambient occlusion is possible, and its results are of reasonable quality, it is still not quite ready to be used in real time applications such as games. This is due to some visual patterns in the results that are caused by the low sample count when calculating ambient occlusion, its sceneand viewpoint dependent performance, and lastly the time required to rebuild acceleration structures.

title: Learning real time ambient occlusion from distance representations
abstract: The computation of partial occlusion, as required for ambient occlusion or soft shadows, provides visually important cues but is notoriously expensive. In this paper we propose a novel solution to the ambient occlusion problem, combining signed distance scene representations and machine learning. We demonstrate how to learn and apply mappings which approximate a ray traced ground truth occlusion using only a few nearby samples of a signed distance representation. As representation for our trained mappings we use small feed forward neural networks which are fast to evaluate, allowing for real time occlusion queries. Our ambient occlusion approximation outperforms state of the art methods in both quality and performance, yielding temporally stable and smooth results. Since our training data is different from typical machine learning approaches which mostly deal with 2D/3D image data and our techniques are also applicable to other occlusion problems (e.g. soft shadows) we give an in depth overview of our framework. Furthermore, we discuss arising artifacts and possible extensions of our approach.

title: Approximating Global Illumination with Real Time Ambient Occlusion

title: Multi scale Visualization of Molecular Architecture Using Real Time Ambient Occlusion in Sculptor
abstract: The modeling of large biomolecular assemblies relies on an efficient rendering of their hierarchical architecture across a wide range of spatial level of detail. We describe a paradigm shift currently under way in computer graphics towards the use of more realistic global illumination models, and we apply the so called ambient occlusion approach to our open source multi scale modeling program, Sculptor. While there are many other higher quality global illumination approaches going all the way up to full GPU accelerated ray tracing, they do not provide size specificity of the features they shade. Ambient occlusion is an aspect of global lighting that offers great visual benefits and powerful user customization. By estimating how other molecular shape features affect the reception of light at some surface point, it effectively simulates indirect shadowing. This effect occurs between molecular surfaces that are close to each other, or in pockets such as protein or ligand binding sites. By adding ambient occlusion, large macromolecular systems look much more natural, and the perception of characteristic surface features is strongly enhanced. In this work, we present a real time implementation of screen space ambient occlusion that delivers realistic cues about tunable spatial scale characteristics of macromolecular architecture. Heretofore, the visualization of large biomolecular systems, comprising e.g. hundreds of thousands of atoms or Mega Dalton size electron microscopy maps, did not take into account the length scales of interest or the spatial resolution of the data. Our approach has been uniquely customized with shading that is tuned for pockets and cavities of a user defined size, making it useful for visualizing molecular features at multiple scales of interest. This is a feature that none of the conventional ambient occlusion approaches provide. Actual Sculptor screen shots illustrate how our implementation supports the size dependent rendering of molecular surface features.

title: Real time ambient occlusion and halos with Summed Area Tables
abstract: Volume models often show high depth complexity. This poses difficulties to the observer in judging the spatial relationships accurately. Illustrators usually use certain techniques such as improving the shading through shadows, halos, or edge darkening in order to enhance depth perception of certain structures. Both effects are difficult to generate in real time for volumetric models. Either they may have an important impact in rendering time, or they require precomputation that prevents changing the transfer function interactively, as it determines the occlusions. In this paper we present two methods for the fast generation of ambient occlusion on volumetric models. The first is a screen space approach that does not require any precomputed data structure. The second is a view independent method that stores volumetric information in the form of a Summed Area Table of the density values, and thus, allows the interactive change of transfer functions on demand, although at the expense of memory space. Despite the fact that similar quality results are obtained with both approaches, the 3D version is more suitable for objects with discontinuous structures such as a vessels tree or the intestines, and it yields better framerates. The screen space version is more suitable in limited GPU memory environments because it does not need extra 3D texture storage. As an extra result, our screen space technique also allows for the computation of view dependent, interactively configurable halos using the same data structure. We have also implemented both methods using CUDA and have analyzed their efficiency.

title: Real time ambient occlusion by curvature dependent occlusion function
abstract: We present the novel technique to compute ambient occlusion [2008] on real time graphics hardware. Because current real time ambient occlusion techniques like SSAO need at least 16 rays sampling and too high computational cost to implement on computer games. Our method approximates occlusion as a local illumination model by introducing curvature dependent function.

title: Real time ambient occlusion for dynamic character skins
abstract: We present a single pass hardware accelerated method to reconstruct compressed ambient occlusion values in real time on dynamic character skins. This method is designed to work with meshes that are deforming based on a low dimensional set of parameters, as in character animation. The inputs to our method are rendered ambient occlusion values at the vertices of a mesh deformed into various poses, along with the corresponding degrees of freedom of those poses. The algorithm uses k means clustering to group the degrees of freedom into a small number of pose clusters. Because the pose variation in a cluster is small, our method can define a low dimensional pose representation using principal component analysis. Within each cluster, we approximate ambient occlusion as a linear function in the reduced dimensional representation. When drawing the character, our method uses moving least squares to blend the reconstructed ambient occlusion values from a small number of pose clusters. This technique offers significant memory savings over storing uncompressed values, and can generate plausible ambient occlusion values for poses not seen in training. Because we are using linear functions our output is smooth, fast to evaluate, and easy to implement in a vertex or fragment shader.

title: Real time Ambient Occlusion

title: Real time Raytracing and Screen space Ambient Occlusion
abstract: This paper investigates the advances in real time ambient occlusion (AO) Topics discussed are state of the art screen space techniques and raytraced ambient occlusion. Methods compared are our scr

title: Real Time Computed Tomography Volume Visualization with Ambient Occlusion of Hand Drawn Transfer Function Using Local Vicinity Statistic
abstract: In this paper, we present an efficient method to visualize computed tomography (CT) datasets using ambient occlusion, which is a global illumination technique that adds depth cues to the output image. We can change the transfer function (TF) for volume rendering and generate output images in real time.  In preprocessing, the mean and standard deviation of each local vicinity are calculated. During rendering, the ambient light intensity is calculated. The calculation is accelerated on the assumption that the CT value of the local vicinity of each point follows the normal distribution. We approximate complex TF forms with a smaller number of connected line segments to achieve additional acceleration. Ambient occlusion is combined with the existing local illumination technique to produce images with depth in real time.  We tested the proposed method on various CT datasets using hand drawn TFs. The proposed method enabled real time rendering that was approximately 40 times faster than the previous method. As a result of comparing the output image quality with that of the conventional method, the average signal to noise ratio was approximately 40 dB, and the image quality did not significantly deteriorate.  When rendering CT images with various TFs, the proposed method generated depth sensing images in real time.