Methods for Alias-Free Shadows Rendering

Tato práce se zabývá metodami pro odstranění aliasingu při zobrazení stínů. Je zde popsána metoda stínových map, její principy, postup a hlavně nedostatky v podobě vzniku aliasu. Pro odstranění tohoto nechtěného jevu je popsáno několik metod, které aliasing potlačují, Percentage closer filter, Variance shadow map, Convulotion shadow map, Exponential shadow map, Bilaterální filtr.  Závěrem práce je návrh a realizace demonstrační aplikace, která vhodně ukazuje implementované výsledky. Nechybí ani srovnání jednotlivých metod na základě kvality a výpočetní náročnosti.This paper concerns aliasing removal methods during the shadow displaying. Method of shadow mapping, its principles, procedure and mainly its drawbacks in the form of aliasing development are described. For the removal of this undesirable phenomenon, several aliasing suppressing methods are described - Percentage Closer Filter, Variance Shadow Map, Convulotion Shadow Map, Exponential Shadow Map a Bilateral Filter. I conclude my work with a proposal and implementation of a demonstrative application, which demonstrates the implemented results adequately. Also, the comparison of individual methods on the basis of their quality and computational demands is included.

Master of Science in Computing

thesisThis document introduces the Soft Shadow Mip-Maps technique, which consists of three methods for overcoming the fundamental limitations of filtering-oriented soft shadows. Filtering-oriented soft shadowing techniques filter shadow maps with varying filter sizes determined by desired penumbra widths. Different varieties of this approach have been commonly applied in interactive and real-time applications. Nonetheless, they share some fundamental limitations. First, soft shadow filter size is not always guaranteed to be the correct size for producing the right penumbra width based on the light source size. Second, filtering with large kernels for soft shadows requires a large number of samples, thereby increasing the cost of filtering. Stochastic approximations for filtering introduce noise and prefiltering leads to inaccuracies. Finally, calculating shadows based on a single blocker estimation can produce significantly inaccurate penumbra widths when the shadow penumbras of different blockers overlap. We discuss three methods to overcome these limitations. First, we introduce a method for computing the soft shadow filter size for a receiver with a blocker distance. Then, we present a filtering scheme based on shadow mip-maps. Mipmap-based filtering uses shadow mip-maps to efficiently generate soft shadows using a constant size filter kernel for each layer, and linear interpolation between layers. Finally, we introduce an improved blocker estimation approach. With the improved blocker estimaiton, we explore the shadow contribution of every blocker by calculating the light occluded by potential blockers. Hence, the calculated penumbra areas correspond to the blockers correctly. Finally, we discuss how to select filter kernels for filtering. These approaches successively solve issues regarding shadow penumbra width calculation apparent in prior techniques. Our result shows that we can produce correct penumbra widths, as evident in our comparisons to ray-traced soft shadows. Nonetheless, the Soft Shadow Mip-Maps technique suffers from light bleeding issues. This is because our method only calculates shadows using the geometry that is available in the shadow depth map. Therefore, the occluded geometry is not taken into consideration, which leads to light bleeding. Another limitation of our method is that using lower resolution shadow mip-map layers limits the resolution of the shadow placement. As a result, when a blocker moves slowly, its shadow follows it with discrete steps, the size of which is determined by the corresponding mip-map layer resolution

Shadow Mapping: Shadow Filtering in OpenGL

Obsah této bakalářské práce pojednává o generování a způsobech filtrování stínů v 3D aplikacích. Popisuje možnosti potlačení jevu diskretizace některými technikami a dokumentuje artefakty pro ně typické. Čtenář se v něm zároveň dozví o jejich výkonnostích a kvalitativních rozdílech, čímž bude schopen zhodnotit nabízené implementace.The content of this bachelor thesis discusses generation, and filtration ways of shadows in 3D applications. It describes possibilities to surpress the discretization phenomenon using certain techniques, and documents the artifacts typical for them. The reader will also learn about their performance, and quality differences, thereby being able to judge offered implementations.

Analytical motion blurred shadows

A rendering framework supporting analytical visibility is extended with shadow mapping. Shadow maps containing analytical visibility data are used, leading to cases where both the projections to the shadow map and the depth tests can be time-dependent. For receivers that are static with respect to the camera, the depth tests are solved analytically over time. For dynamic receivers, point sampling is used. Problems arising from time-dependence, limited precision and necessary simplifications are investigated, and potential solutions are discussed.En rastrerare med stöd för analytisk rörelseoskärpa integreras med shadow mapping. Shadow maps med analytisk synlighetsinformation används för detta, vilket leder till situationer där både projiceringarna till shadow map:en och djupjämförelserna kan vara tidsberoende. Djupjämförelserna utförs analytiskt över tiden för mottagare som är statiska i förhållande till kameran. För dynamiska mottagare används point sampling istället. Problem som uppstår på grund av tidsberoende, begränsad precision och nödvändiga förenklingar undersöks, och potentiella lösningar diskuteras

Efficient shadow map filtering

Schatten liefern dem menschlichen Auge wichtige Informationen, um die räumlichen Beziehungen in der Umgebung in der wir leben wahrzunehmen. Sie sind somit ein unverzichtbarer Bestandteil der realistischen Bildsynthese. Leider ist die Sichtbarkeitsberechnung ein rechenintensiver Prozess. Bildbasierte Methoden, wie zum Beispiel Shadow Maps, verhalten sich positiv gegenüber einer wachsenden Szenenkomplexität, produzieren aber Artefakte sowohl in der räumlichen, als auch in der temporalen Domäne, da sie nicht wie herkömmliche Bilder gefiltert werden können. Diese Dissertation präsentiert neue Echtzeit-Schattenverfahren die das effiziente Filtern von Shadow Maps ermöglichen, um die Bildqualität und das Kohärenzverhalten zu verbessern. Hierzu formulieren wir den Schattentest als eine Summe von Produkten, bei der die beiden Parameter der Schattenfunktion separiert werden. Shadow Maps werden dann in sogenannte Basis-Bilder transformiert, die im Gegensatz zu Shadow Maps linear gefiltert werden können. Die gefilterten Basis-Bilder sind äquivalent zu einem vorgefilterten Schattentest und werden verwendet, um geglättete Schattenkanten und realistische weiche Schatten zu berechnen.Shadows provide the human visual system with important cues to sense spatial relationships in the environment we live in. As such they are an indispensable part of realistic computerenerated imagery. Unfortunately, visibility determination is computationally expensive. Image-based simplifications to the problem such as Shadow Maps perform well with increased scene complexity but produce artifacts both in the spatial and temporal domain because they lack efficient filtering support. This dissertation presents novel real-time shadow algorithms to enable efficient filtering of Shadow Maps in order to increase the image quality and overall coherence characteristics. This is achieved by expressing the shadow test as a sum of products where the parameters of the shadow test are separated from each other. Ordinary Shadow Maps are then subject to a transformation into new so called basis-images which can, as opposed to Shadow Maps, be linearly filtered. The convolved basis images are equivalent to a pre-filtered shadow test and used to reconstruct anti-aliased as well as physically plausible all-frequency shadows

Large-Scale Rendering Using Shadowmaps

Shadow mapovanie je najpoužívanejšia metóda ktorá sa využíva v real-time 3D grafike na tvorbu tieňov v lokálnych osvetlovacích modeloch. Táto práca krok-za-krokom vysvetľuje proces vytvárania shadow máp. Porovnané su metódy výpočtu hĺbkovej odchylky ako aj filtrovacie metódy, a zároveň je odvodený výpočet normálovej odchýlky pre filtrovacie kernely s premennou veľkosťou. Taktiež popíšeme proces ako efektívne obaliť frustum kamery kaskádovým frustumom. Popri tom vysvetlíme ako využiť moderné OpenGL API na zníženie výkonnostných nedostatkov.Shadow mapping is the most widely used method in real-time 3D graphics for producing shadows in local light models. This thesis step-by-step explains the process of creating shadow maps. Depth biasing as well as filtering methods are analysed, then the calculation of normal offset bias for variable sized kernels is derived. We describe the process of efficiently fitting stable cascade frustums to view frustum. Also shown is how to use modern OpenGL to reduce performance overhead.

Differentiable Shadow Mapping for Efficient Inverse Graphics

We show how shadows can be efficiently generated in differentiable rendering of triangle meshes. Our central observation is that pre-filtered shadow mapping, a technique for approximating shadows based on rendering from the perspective of a light, can be combined with existing differentiable rasterizers to yield differentiable visibility information. We demonstrate at several inverse graphics problems that differentiable shadow maps are orders of magnitude faster than differentiable light transport simulation with similar accuracy -- while differentiable rasterization without shadows often fails to converge.Comment: CVPR 2023, project page: https://mworchel.github.io/differentiable-shadow-mappin

Rendering Antialiased Shadows using Warped Variance Shadow Maps

Shadows contribute significantly to the perceived realism of an image, and provide an important depth cue. Rendering high quality, antialiased shadows efficiently is a difficult problem. To antialias shadows, it is necessary to compute partial visibilities, but computing these visibilities using existing approaches is often too slow for interactive applications. Shadow maps are a widely used technique for real-time shadow rendering. One major drawback of shadow maps is aliasing, because the shadow map data cannot be filtered in the same way as colour textures. In this thesis, I present variance shadow maps (VSMs). Variance shadow maps use a linear representation of the depth distributions in the shadow map, which enables the use of standard linear texture filtering algorithms. Thus VSMs can address the problem of shadow aliasing using the same highly-tuned mechanisms that are available for colour images. Given the mean and variance of the depth distribution, Chebyshev's inequality provides an upper bound on the fraction of a shaded fragment that is occluded, and I show that this bound often provides a good approximation to the true partial occlusion. For more difficult cases, I show that warping the depth distribution can produce multiple bounds, some tighter than others. Based on this insight, I present layered variance shadow maps, a scalable generalization of variance shadow maps that partitions the depth distribution into multiple segments. This reduces or eliminates an artifact - "light bleeding" - that can appear when using the simpler version of variance shadow maps. Additionally, I demonstrate exponential variance shadow maps, which combine moments computed from two exponentially-warped depth distributions. Using this approach, high quality results are produced at a fraction of the storage cost of layered variance shadow maps. These algorithms are easy to implement on current graphics hardware and provide efficient, scalable solutions to the problem of shadow map aliasing

LEO object’s light-curve acquisition system and their inversion for attitude reconstruction

In recent years, the increase in space activities has brought the space debris issue to the top of the list of all space agencies. The fact of there being uncontrolled objects is a problem both for the operational satellites in orbit (avoiding collisions) and for the safety of people on the ground (re-entry objects). Optical systems provide valuable assistance in identifying and monitoring such objects. The Sapienza Space System and Space Surveillance (S5Lab) has been working in this field for years, being able to take advantage of a network of telescopes spread over different continents. This article is focused on the re-entry phase of the object; indeed, the knowledge of the state of the object, in terms of position, velocity, and attitude during the descent, is crucial in order to predict as accurately as possible the impact point on the ground. A procedure to retrieve the light curves of orbiting objects by means of optical data will be shown and a method to obtain the attitude determination from their inversion based on a stochastic optimization (genetic algorithm) will be proposed