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Computer rendering(Redirected from Rendering system)
Rendering is the process of generating an image from a description of three dimensional objects, by means of a software program. The description is in a strictly defined language or data structure, and would contain geometry, viewpoint, texture and lighting information. The image is a digital image / raster graphics image. It is one of the major sub-topics of 3D computer graphics, and in practice always connected to the others. In the 'graphics pipeline' its the last major step, giving the final appearance to the models and animation. With the increasing sophistication of computer graphics since the 1970s onward, it has become a more distinct subject. It has uses in: computer games, simulators, movies/tv special effects, and design visualisation. Each employing a different balance of features and techniques. As a product, a wide variety of renderers are available. some are integrated into larger modelling and animation packages, some are stand-alone, some are free open-source projects. On the inside, a renderer is a carefully engineered program, based on a selective mixture of disciplines related to: light physics, visual perception, mathematics, and software development. In the case of 3D graphics, rendering is a slow, computationally intensive process (typically for movie creation), or supported by realtime 3D hardware accelerators in graphics cards (typically for 3D computer games). The term is by analogy with an "artist's rendering" of a scene.
UsageWhen the pre-image (a wireframe sketch usually) is complete, rendering is used, which adds in Bitmap textures or Procedural textures, lights, bump mapping, and relative position to other objects. The result is a completed image the consumer or intended viewer sees. For movie animations, several images (frames) must be rendered, and stitched together in a program capable of making an animation of this sort. Most 3-D image editing programs can do this.
FeaturesA rendered image can be understood in terms of a number of visible features. Rendering research and development has been largely motivated by finding ways to simulate these efficiently. Some relate directly to particular algorithms and techniques, while others are produced together.
TechniquesTwo families of overall, light transport, techniques have emerged: radiosity — related to finite element mathematics, and ray tracing — related to monte carlo mathematics. Both can provide a framework for a fairly complete solution to the rendering equation. Such approaches can be very slow and computationally-intensive. For real-time, a complete calculation is not currently possible. Much faster is to simplify with one or both of these common approximations: No illumination, just texture mapping — since the intrinsic colors of an object has the greatest influence on its appearance. Or direct illumination — light from light-source to surface, then reflected from surface to camera/eye, since this light path is usually dominant in a scene. These would often be augmented with other special-case effects, or precalculations.
Rendering for movies often takes place on a network of tightly connected computers known as a render farm. The current state of the art in 3-D image description for movie creation is the RenderMan scene description language designed at Pixar. (compare with simpler 3D fileformats such as VRML or APIs such as OpenGL and DirectX tailored for 3D hardware accelerators). Movie type rendering software includes:
Academic CoreMost rendering development and use aims at photorealism — to produce images indistinguishable from photographs. The implementation of a realistic renderer always has some basic element of physical simulation or emulation — some computation which resembles or abstracts a real physical process. The term 'physically-based' indicates the use of physical models and approximations that are more general and widely accepted outside rendering. A particular set of related techniques have gradually become established in the rendering community. The basic concepts are moderately straightforward, but intractable to calculate; and a single elegant algorithm or approach has been elusive for more general purpose renderers. In order to meet demands of robustness, accuracy, and practicality, an implementation will be a complex combination of different techniques. Rendering research is concerned with both the adaptation of scientific models and their efficient application. the rendering equationThis is the key academic/theoretical concept in rendering. It serves as the most abstract formal expression of the non-perceptual aspect of rendering. All more complete algorithms can be seen as solutions to particular formulations of this equation. Meaning: at a particular position and direction, the outgoing light (Lo) is the sum of the emitted light (Le) and the reflected light. The reflected light being the sum of the incoming light (Li) from all directions, multiplied by the surface reflection and incoming angle. By connecting outward light to inward light, via an interaction point, this equation stands for the whole 'light transport' in a scene. the BRDFThis expresses a simple model of light interaction with a surface. Light interaction is often approximated by the even simpler models: diffuse reflection and specular reflection, although both can be BRDFs. geometric opticsRendering is practically exclusively concerned with the particle aspect of light physics — known as geometric optics. Treating light, at its basic level, as particles bouncing around is a simplification, but appropriate: the wave aspects of light are negligable in most scenes, and are significantly more difficult to simulate. Notable wave aspect phenomena include diffraction — as seen in the colours of CDs and DVDs — and polarisation — as seen in LCDs. Both types of effect, if needed, are made by appearance-oriented adjustment of the reflection model. visual perceptionThough it receives less attention, an understanding of human visual perception is valuable to rendering. This has two causes: image displays have restricted ranges, and human perception has restricted ranges. A renderer can simulate an almost infinite range of light brightness and color, but current displays — movie screen, computer monitor, etc. — cannot handle so much, and something must be discarded or 'compressed'. Human perception also has limits, and so doesn't need to be given large-range images to create realism. This can help solve the problem of fitting images into displays, and, furthermore, suggest what short-cuts could be used in the rendering simulation, since certain subtleties won't be noticeable. Mathematics used in rendering includes: linear algebra, calculus, numerical mathematics, signal processing, monte carlo.
Chronology of published ideas
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