Page 62 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes A 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.
• shading—how the colour and brightness of a surface varies with lighting
• texture-mapping—a method of applying detail to surfaces

• bump-mapping—a method of simulating small-scale bumpiness on surfaces
• fogging/participating medium—how light dims when passing through non-clear
atmosphere or air
• shadows—the effect of obstructing light
• soft shadows—varying darkness caused by partially obscured light sources
• reflection—mirror-like or highly glossy reflection
• transparency (optics), transparency (graphic) or opacity—sharp transmission of light through
solid objects
• translucency—highly scattered transmission of light through solid objects

• refraction—bending of light associated with transparency
• diffraction—bending, spreading and interference of light passing by an object or aperture
that disrupts the ray
• indirect illumination—surfaces illuminated by light reflected off other surfaces, rather than
directly from a light source (also known as global illumination)

• caustics (a form of indirect illumination)—reflection of light off a shiny object, or focusing
of light through a transparent object, to produce bright highlights on another object

• depth of field—objects appear blurry or out of focus when too far in front of or behind the
object in focus
• motion blur—objects appear blurry due to high-speed motion, or the motion of the
camera
• non-photorealistic rendering—rendering of scenes in an artistic style, intended to look like
a painting or drawing
Many rendering algorithms have been researched, and software used for rendering may employ
a number of different techniques to obtain a final image.
Tracing every particle of light in a scene is about completely impractical and would take a
stupendous amount of time. Even tracing a portion large enough to produce an image takes an
inordinate amount of time if the sampling is not intelligently restricted.
Therefore, four loose families of more-efficient light transport modelling techniques have
emerged: rasterization, including scanline rendering, geometrically projects objects in the scene
to an image plane, without advanced optical effects; ray casting considers the scene as observed
from a specific point-of-view, calculating the observed image based only on geometry and very
basic optical laws of reflection intensity, and perhaps using Monte Carlo techniques to reduce
artifacts; and ray tracing is similar to ray casting, but employs more advanced optical simulation,
and usually uses Monte Carlo techniques to obtain more realistic results at a speed that is often
orders of magnitude slower. The fourth type of light transport techique, radiosity is not usually
implemented as a rendering technique, but instead calculates the passage of light as it leaves the
light source and illuminates surfaces. These surfaces are usually rendered to the display using
one of the other three techniques.

56 LoveLy professionaL University