Real-Time Shadows ppt

[...]... lights 1.2 Importance of Shadows Why should we care about shadows? One obvious reason is that for photorealistic rendering, one tries to produce images that are indistinguishable from real photographs This necessarily includes computing shadows and, in particular, accurate and physically based shadows But even when dropping the hard constraint of photorealism, computing reasonable shadows is important... [Kersten96] found that more natural shadows with a soft boundary can lead to even stronger cues than shadows with a crisp border Figure 1.6 Shadows have an important influence on the interpretation of spatial relationships in a scene (left) Nevertheless, even coarse approximations can achieve the same effect (right) 1.2 Importance of Shadows Figure 1.7 Superpositions of shadows can look much less appealing... also cast shadows On the one hand, shadows are important for the understanding of scenes We better comprehend spatial relationships between objects and better succeed in localizing them in space Further, we can deduce shape information, not only of the shadow-casting elements but also of the receiver, by interpreting shadow deformations Shadows are also an artistic means Many movies exploit shadows to... think of the hundreds of Dracula movies out there) Figure 1.1 shows an example where shadows are used in this manner While we cannot directly see the camels, their shadows complete our understanding of the scene Consequently, shadows are naturally a crucial element of image synthesis—and remain a particular challenge for real-time graphics: while conceptually relatively simple to compute, naive methods... particular, the illusion often breaks when shadows start to overlap or move in proximity to each other As a direction for future research, however, this is a promising field This also concerns the degree to which approximations can be applied to shadows It is actually hard to fake shadows, especially if lights and objects are dynamic One should be careful because incorrect shadows decrease the realism of an... can compute shadows by approximating the light source with many point lights Adopting such a sampling scheme, even the more general Equation (1.4) can be well approximated We will discuss this approach in more detail in Section 6.2.4 Note that this also offers a direct link between hard shadows produced by point light sources and soft shadows: shrinking an area light to a point leads to hard shadows, ... even novices to better understand design choices 1.3 Difficulty of Computing Shadows For a faithful rendition of light interaction, also indirect, meaning bounced, light that is reflected from the surrounding usually needs to be taken into account Shadows play an important role in this simulation and are often the first step of a real-time global illumination algorithm Recent work on global (including... physically based shadows seem to be convincing in all situations Fortunately, it is not always necessary to have a solution that works for all cases This book will help you decide when to apply which technique in order to achieve the best effect But before coming to solutions, we will first illustrate some of the main failure cases that make shadows such a challenging topic 1.3 Difficulty of Computing Shadows. .. main failure cases that make shadows such a challenging topic 1.3 Difficulty of Computing Shadows It is difficult to compute shadows This fact can be particularly well illustrated when looking at soft shadows, so let’s go back to Equation (1.6) One major challenge of computing soft shadows according to this formula is that occluders can usually not be considered independently Even if an accurate blocking... shows an extreme case for a very simple scene where shadows can become very unrealistic if blocking contributions are not combined properly Figure 1.10 Even for simple scenes (left), classical approximations can cause noticeable artifacts (right) As can be seen, the umbra is overestimated 1.3 Difficulty of Computing Shadows 17 entire scene casts shadows one layer (first visible surfaces) Figure 1.11 .