Alexander Reshetov

Morphological antialiasing

We present a new algorithm that creates plausibly antialiased images by looking for certain patterns in an original image and then blending colors in the neighborhood of these patterns according to a set of simple rules. We construct these rules to work as a post-processing step in ray tracing applications, allowing approximate, yet fast and robust antialiasing. The algorithm works for any rendering technique and scene complexity. It does not require casting any additional rays and handles all possible effects, including reflections and refractions.

Guided visibility sampling

This paper addresses the problem of computing the triangles visible from a region in space. The proposed aggressive visibility solution is based on stochastic ray shooting and can take any triangular model as input. We do not rely on connectivity information, volumetric occluders, or the availability of large occluders, and can therefore process any given input scene. The proposed algorithm is practically memoryless, thereby alleviating the large memory consumption problems prevalent in several previous algorithms. The strategy of our algorithm is to use ray mutations in ray space to cast rays that are likely to sample new triangles. Our algorithm improves the sampling efficiency of previous work by over two orders of magnitude.

Omnidirectional Ray Tracing Traversal Algorithm for kd-trees

We propose a new kd-tree traversal algorithm for incoherent groups of rays which reduces number of intersection tests by more than 1.5times compared with splitting the group into coherent subgroups

Faster ray packets - triangle intersection through vertex culling

Acceleration structures are used in ray tracing to sharply reduce number of ray-triangle intersection tests at the expense of traversing such structures. Bigger structures eliminate more tests, but their traversal becomes less efficient, especially for ray packets, for which number of inactive rays increases at the lower levels of the acceleration structures. For dynamic scenes, building or updating acceleration structures is one of the major performance impediments. We propose a new way to reduce the total number of tests by creating a special transient frustum every time a leaf is traversed by a packet of rays. This frustum contains intersections of active rays with a leaf node and eliminates over 90% of all potential tests. It allows a tenfold reduction in size of acceleration structure whilst still achieving a better performance.

Use of a single 13C NMR resonance of glutamate for measuring oxygen consumption in tissue

A kinetic model of the citric acid cycle for calculating oxygen consumption from13C nuclear magnetic resonance (NMR) multiplet data has been developed. Measured oxygen consumption (MV˙o 2) was compared with MV˙o 2 predicted by the model with 13C NMR data obtained from rat hearts perfused with glucose and either [2-13C]acetate or [3-13C]pyruvate. The accuracy of MV˙o 2 measured from three subsets of NMR data was compared: glutamate C-4 and C-3 resonance areas; the doublet C4D34 (expressed as a fraction of C-4 area); and C-4 and C-3 areas plus several multiplets of C-2, C-3, and C-4. MV˙o 2 determined by set 2(C4D34 only) gave the same degree of accuracy as set 3(complete data); both were superior to set 1(C-4 and C-3 areas). Analysis of the latter suffers from the correlation between citric acid cycle flux and exchange between α-ketoglutarate and glutamate, resulting in greater error in estimating MV˙o 2. Analysis of C4D34 is less influenced by correlation between parameters, and this single measurement provides the best opportunity for a noninvasive measurement of oxygen consumption.A kinetic model of the citric acid cycle for calculating oxygen consumption from (13)C nuclear magnetic resonance (NMR) multiplet data has been developed. Measured oxygen consumption (MVO(2)) was compared with MVO(2) predicted by the model with (13)C NMR data obtained from rat hearts perfused with glucose and either [2-(13)C]acetate or [3-(13)C]pyruvate. The accuracy of MVO(2) measured from three subsets of NMR data was compared: glutamate C-4 and C-3 resonance areas; the doublet C4D34 (expressed as a fraction of C-4 area); and C-4 and C-3 areas plus several multiplets of C-2, C-3, and C-4. MVO(2) determined by set 2 (C4D34 only) gave the same degree of accuracy as set 3 (complete data); both were superior to set 1 (C-4 and C-3 areas). Analysis of the latter suffers from the correlation between citric acid cycle flux and exchange between alpha-ketoglutarate and glutamate, resulting in greater error in estimating MVO(2). Analysis of C4D34 is less influenced by correlation between parameters, and this single measurement provides the best opportunity for a noninvasive measurement of oxygen consumption.

Filtering approaches for real-time anti-aliasing

For more than a decade, supersample anti-aliasing (SSAA) and multisample anti-aliasing (MSAA) have been the gold-standard anti-aliasing solutions in games. However, these techniques are not well suited for deferred shading or fixed environments like the current generation of consoles. In recent years, industry and academia have been exploring alternative approaches, where anti-aliasing is performed as a post-processing step. The original, CPU-based morphological anti-aliasing (MLAA) method gave birth to an explosion of real-time anti-aliasing techniques that rival MSAA. Most of these techniques share concepts and ideas, so the main goal of this course is to establish a conceptual link between them, identifying novelties and differences. The presenters explain how sub-pixel data can be used to improve quality and performance tradeoffs at post-processing steps, which is a cutting-edge research area today. The course includes an overview of both research and industry filter-based anti-aliasing techniques in games for all modern platforms (AMD and NVIDIA GPUs, PlayStation 3, and Xbox 360), low-level insight to ease adoption of these techniques and give attendees a complete concept-to-implementation roadmap, and deep quality, performance, and ease-of-integration comparisons of each technique.

Faster Ray Packets - Triangle Intersection through Vertex Culling

Acceleration structures are used in ray tracing to sharply reduce number of ray-triangle intersection tests at the expense of traversing such structures. Bigger structures eliminate more tests, but their traversal becomes less efficient, especially for ray packets, for which number of inactive rays increases at the lower levels of the acceleration structures. For dynamic scenes, building or updating acceleration structures is one of the major performance impediments. We propose a new way to reduce the total number of tests by creating a special transient frustum every time a leaf is traversed by a packet of rays. This frustum contains intersections of active rays with a leaf node and eliminates over 90% of all potential tests. It allows a tenfold reduction in size of acceleration structure whilst still achieving a better performance.

Reducing aliasing artifacts through resampling

Post-processing antialiasing methods are well suited for deferred shading because they decouple antialiasing from the rest of graphics pipeline. In morphological methods, the final image is filtered with a data-dependent filter. The filter coefficients are computed by analyzing the non-local neighborhood of each pixel. Though very simple and efficient, such methods have intrinsic quality limitations due to spatial undersampling and temporal aliasing. We explore an alternative formulation in which filter coefficients are computed locally for each pixel by supersampling geometry, while shading is still done only once per pixel. During pre-processing, each geometric subsample is converted to a single bit indicating whether the subsample is different from the central one. The ensuing binary mask is then used in the post-processing step to retrieve filter coefficients, which were precomputed for all possible masks. For a typical 8 subsamples, it results in a sub-millisecond performance, while improving the image quality by about 10 dB. To compare subsamples, we use a novel symmetric angular measure, which has a simple geometric interpretation. We propose to use this measure in a variety of applications that assess the difference between geometric samples (rendering, mesh simplification, geometry encoding, adaptive tessellation).

Consistent normal interpolation

Rendering a polygonal surface with Phong normal interpolation allows shading to appear as it would for a true curved surface while maintaining the efficiency and simplicity of coarse polygonal geometry. However, this approximation fails in certain situations, especially for grazing viewing directions. Well-known problems include physically impossible reflections and implausible illumination. Some of these artifacts can be mitigated through special-case processing, although no universal or generally accepted approaches are available. In particular, all known solutions that guarantee that reflected rays will always point outward from the surface also create discontinuities in the reflection ray direction. We present a simple modification of Phong normal interpolation that allows physically plausible reflections and creates an appearance of a smooth surface. We introduce an additional scalar parameter that characterizes the deviation between per-vertex normals and per face normals and use it to adjust linearly interpolated normals. The proposed technique eliminates perceptually objectionable artifacts caused by inconsistencies between the shading and geometric normals while retaining most of the practical advantages and simplicity of the original Phong formulation.

Efficient post-processing antialiasing on integrated GPUs

Most modern games use deferred shading, in which shading is performed only for visible pixels, allowing greater artistic freedom in scene composing and lighting. However, traditional antialiasing techniques, such as super-sampling and multi-sampling, are not well-suited for deferred shading pipeline, since all subsamples have to be explicitly written to output buffer.