Shadow (computer graphics)

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Computer graphics with objects casting shadows

Shadows in computer graphics are used to anchor objects in a scene. In this way you can make statements about the position of the objects in the scene (depth, distance to the surface). Furthermore, the direction of the lighting is emphasized by a shadow.

It divides the shadows in umbra (Umbra) and penumbra (penumbra). The umbra is the central, clearly defined dark part in the center, the penumbra is the lighter area surrounding the umbra. The latter is very complex to calculate, which is why one almost exclusively uses point light sources in real-time rendering, which only generate the umbra.

Another possibility is to calculate the projection of a shadow-casting object from the light source onto a plane. To render soft shadows, a flat light source can be replaced by several point light sources; the resulting shadow is the sum of the shadows of these light sources. It is also possible to blur a hard shadow or to draw color gradients. So-called shadow volumes can also be used to render hard shadows . Another possibility are shadow maps . The scene is drawn in a Z-buffer from the point of view of the light source (shadow buffer) so that it contains the distance to the next illuminated objects. By comparing the depth information in the normal Z-Buffer with the depth information in the Shadow Buffer, it can be determined whether a point is in the shadow.

A lot of time is required to calculate the shadows realistically, i.e. according to physical models. Examples of algorithms for creating photorealistic shadows are diffuse ray tracing or radiosity .

literature

  • David Rogers: Procedural Elements for Computer Graphics, pp. 502-517. WCB / McGraw-Hill, Boston 1998, ISBN 0-07-053548-5
  • Tomas Akenine-Möller, Eric Haines: Real-Time Rendering, pp. 248-276. AK Peters, Natick, Mass. 2002, ISBN 1-56881-182-9

Individual evidence

  1. ↑ Thant Tessman: Casting Shadows on Flat Surfaces. IRIS Universe 16 (Winter 1989): 16-19, ISSN  1061-6608
  2. ↑ Paul Bert Stern, Michael Herf: Simulating Soft Shadows with graphics hardware. Technical Report CMU-CS-97-104, Carnegie Mellon University, Jan. 1997 ( Online )
  3. ↑ Cyril Soler, François Sillion: Fast Calculation of Soft Shadow Textures Using Convolution. In SIGGRAPH '98 Proceedings, pp. 219-230. ACM, New York 1998, ISBN 0-89791-999-8 ( online )
  4. ↑ Eric Haines: Soft Planar Shadows Using Plateaus. Journal of Graphics Tools 6, 1 (Sep. 2001): 19–27, ISSN  1086-7651 ( PDF, 330 kB  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. )@1@ 2Template: Dead Link / tog.acm.org  
  5. ^ Franklin Crow: Shadow Algorithms for Computer Graphics. ACM SIGGRAPH Computer Graphics 11, 2 (Summer 1977): 242-248, ISSN  0097-8930
  6. ^ Lance Williams: Casting Curved Shadows on Curved Surfaces. ACM SIGGRAPH Computer Graphics 12, 3 (Aug 1978): 270-274