Datenbank Glossar – CGI

Mentalray

The mental ray® for Maya® renderer can render using a feature called Global Illumination. Global Illumination simulates the effect of all lighting and inter-reflection in the scene, whether the items are lit directly by a light source or indirectly illuminated by other objects (and diffuse sources of illumination in the scene).

For example, when a photographer lights an object in a studio, some of the lighting for the object in the final image comes directly from the lights that are used, while additional illumination comes from objects that are placed near the subject to act as light reflectors. These are referred to as fill cards. Light bounces off the fill cards, indirectly lighting nearby objects with a secondary source of diffuse light. The color of the fill card colors the light that gets reflected onto the object. The final illumination of the object comes from this combination of multiple sources (direct light, specular reflections, and diffuse light).

The Global Illumination feature in the mental ray® for Maya® renderer simulates this effect and provides for a realistic illumination simulation in your Maya scenes.

About mental ray

mental ray® generates images of outstanding quality and unsurpassed realism and achieves scalable performance through the exploitation of parallelism on both multiprocessor machines and across networks of machines. The software uses advanced and proprietary acceleration and recursive sampling techniques for faster rendering on even the smallest, single processor machines.

mental ray accepts scene data using its .mi scene description language in either ASCII or mixed ASCII/binary form, whose specification is precisely defined in the documentation. Supported geometric primitives include polygons, trimmed free-form surfaces, hair, and subdivision surfaces (in conjunction with the mental matter® product). Run-time linking of user-supplied C and C++ code allows the creation of procedural textures, materials, new lighting models, volume and lens effects, control of global illumination simulation through photon shaders and the Photon Map™ as well as displacement maps. The free-form surface processing and approximation capabilities, and the mathematical accuracy of the software are superior to those of competing rendering software products.

mental ray is also available as a library for direct integration. It incorporates significant developments of the European Union’s DESIRE project such as a novel proprietary parallel rendering algorithm and a distributed database. The message passing based software is capable of running on single processor workstations and on shared memory parallel platforms as well as on distributed memory architectures such as heterogeneous networks of workstations and scalable parallel supercomputers.

mental ray is the first rendering software which combines the physically correct simulation of the behavior of light with full programmability for the creation of any imaginable visual phenomena.

A fully interactive integration of mental ray with a graphical user interface for creation and editing of visual phenomena by means of mental ray Phenomena™ in the Phenomenon Creator™ and Phenomenon Editor™, creation and editing of the lighting, full control of all rendering related options and parameters, and management of the rendering process has been developed in cooperation with Softimage Co. (a division of Avid Technology, Inc.), and is available in the Softimage|XSI product.

A fully interactive integration of mental ray with a graphical user interface for the creation and editing of visual phenomena by means of mental ray Phenomena in Maya’s Hypershade work space, creation and editing of the lighting, full control of all rendering related options and parameters, and management of the rendering process has been developed in cooperation with Alias Systems, Inc. and Autodesk, and is integrated into all Maya products by Autodesk.

mental ray has been integrated into Softimage|3D and Softimage|XSI, Autodesk 3ds max and VIZ, Autodesk Maya, Side Effects Software’s Houdini 5, SolidWorks PhotoWorks 2, and Dassault Système’s CATIA V4 and V5 products. A number of translators and translator plug-ins allow for using mental ray in conjuction with various 3D modeling and animation front-end systems.

Global illumination

Global illumination is a general name for a group of algorithms used in 3D computer graphics that are meant to add more realistic lighting to 3D scenes. Such algorithms take into account not only the light which comes directly from a light source (direct illumination), but also subsequent cases in which light rays from the same source are reflected by other surfaces in the scene (indirect illumination).

Theoretically reflections, refractions, and shadows are all examples of global illumination, because when simulating them, one object affects the rendering of another object (as opposed to an object being affected only by a direct light). In practice, however, only the simulation of diffuse inter-reflection or caustics is called global illumination.

Images rendered using global illumination algorithms often appear more photorealistic than images rendered using only direct illumination algorithms. However, such images are computationally more expensive and consequently much slower to generate. One common approach is to compute the global illumination of a scene and store that information with the geometry, i.e., radiosity. That stored data can then be used to generate images from different viewpoints for generating walkthroughs of a scene without having to go through expensive lighting calculations repeatedly.

Radiosity, ray tracing, beam tracing, cone tracing, path tracing, metropolis light transport, ambient occlusion, photon mapping, and image based lighting are examples of algorithms used in global illumination, some of which may be used together to yield results that are fast, but accurate.

Dynamics

Dynamics is a branch of physics that describes how objects move using physical rules to simulate the natural forces that act upon them. Dynamic simulations are difficult to achieve with traditional keyframe animation techniques.

With Particle Effects, you can create the illusions of smoke, fireworks, rain, fire, and explosions.

With Rigid Body Dynamics, you can simulate real-world physical interactions between objects, such as collisions between surfaces. For example, you can simulate a bowling ball crashing through pins or simulate the effects of gravity when a ball falls to the ground. You can also simulate natural forces, such as wind.