Computer-generated imagery is the application of computer graphics to create or contribute
to images in art, printed media, video games, films, television programs, commercials, videos,
and simulators.
The visual scenes may be dynamic or static, and may be two-dimensional, though the term
"CGI" is most commonly used to refer to 3D computer graphics used for creating scenes
or special effects in films and television.
They can also be used by a home user and edited together on programs such as Windows Movie
Maker or iMovie.
The term computer animation refers to dynamic CGI rendered as a movie.
The term virtual world refers to agent-based, interactive environments.
Computer graphics software is used to make computer-generated imagery for films, etc.
Availability of CGI software and increased computer speeds have allowed individual artists
and small companies to produce professional-grade films, games, and fine art from their home
computers.
This has brought about an Internet subculture with its own set of global celebrities, clichés,
and technical vocabulary.
The evolution of CGI led to the emergence of virtual cinematography in the 1990s where
runs of the simulated camera are not constrained by the laws of physics.
Static images and landscapes
Not only do animated images form part of computer-generated imagery, natural looking landscapes, such
as fractal landscapes are also generated via computer algorithms.
A simple way to generate fractal surfaces is to use an extension of the triangular mesh
method, relying on the construction of some special case of a de Rham curve, e.g. midpoint
displacement.
For instance, the algorithm may start with a large triangle, then recursively zoom in
by dividing it into 4 smaller Sierpinski triangles, then interpolate the height of each point
from its nearest neighbors.
The creation of a Brownian surface may be achieved not only by adding noise as new nodes
are created, but by adding additional noise at multiple levels of the mesh.
Thus a topographical map with varying levels of height can be created using relatively
straightforward fractal algorithms.
Some typical, and easy to program fractals used in CGI are the plasma fractal and the
more dramatic fault fractal.
A large number of specific techniques have been researched and developed to produce highly
focused computer-generated effects, e.g. the use of specific models to represent the chemical
weathering of stones to model erosion and produce an "aged appearance" for a given stone-based
surface.
Architectural scenes
Modern architects use services from computer graphic firms to create 3-dimensional models
for both customers and builders.
These computer generated models can be more accurate than traditional drawings.
Architectural animation can also be used to see the possible relationship a building will
have in relation to the environment and its surrounding buildings.
The rendering of architectural spaces without the use of paper and pencil tools is now a
widely accepted practice with a number of computer-assisted architectural design systems.
Architectural modelling tools allow an architect to visualize a space and perform "walk-throughs"
in an interactive manner, thus providing "interactive environments" both at the urban and building
levels.
Specific applications in architecture not only include the specification of building
structures such as walls and windows, and walk-throughs, but the effects of light and
how sunlight will affect a specific design at different times of the day.
Architectural modelling tools have now become increasingly internet-based.
However, the quality of internet-based systems still lags behind those of sophisticated inhouse
modelling systems.
In some applications, computer-generated images are used to "reverse engineer" historical
buildings.
For instance, a computer-generated reconstruction of the monastery at Georgenthal in Germany
was derived from the ruins of the monastery, yet provides the viewer with a "look and feel"
of what the building would have looked like in its day.
Anatomical models
Computer generated models used in skeletal animation are not always anatomically correct.
However, organizations such as the Scientific Computing and Imaging Institute have developed
anatomically correct computer-based models.
Computer generated anatomical models can be used both for instructional and operational
purposes.
To date, a large body of artist produced medical images continue to be used by medical students,
such as images by Frank Netter, e.g. Cardiac images.
However, a number of online anatomical models are becoming available.
A single patient X-ray is not a computer generated image, even in the case of digitized x-rays.
However, in applications which involve CT scans a three dimensional model is automatically
produced from a large number of single slice x-rays, producing "computer generated image".
Applications involving magnetic resonance imaging also bring together a number of "snapshots"
to produce a composite, internal image.
In modern medical applications, patient specific models are constructed in "computer assisted
surgery".
For instance, in total knee replacement, the construction of a detailed patient specific
model can be used to carefully plan the surgery.
These three dimensional models are usually extracted from multiple CT scans of the appropriate
parts of the patient's own anatomy.
Such models can also be used for planning aortic valve implantations, one of the common
procedures for treating heart disease.
Given that the shape, diameter and position of the coronary openings can vary greatly
from patient to patient, the extraction of a model that closely resembles a patient's
valve anatomy can be highly beneficial in planning the procedure.
Generating cloth and skin images
Models of cloth generally fall into three groups: the geometric-mechanical structure
at yarn crossings, secondly the mechanics of continuous elastic sheets and thirdly the
geometric macroscopic features of cloth.
To date, making the clothing of a digital character automatically fold in a natural
way remains a challenge for many animators.
In addition to their use in film, advertising and other modes of public display, computer
generated images of clothing are now routinely used by top fashion design firms.
The challenge in rendering human skin images involves three levels of realism: photo realism
in resembling real skin at the static level; physical realism in resembling its movements
and functional realism in resembling its response to actions.
The finest visible features such as fine wrinkles and skin pores are size of about 100 µm or
0.1 millimetres.
Skin can be modelled as a 7-dimensional bidirectional texture function or a collection of bidirectional
scattering distribution function over the target's surfaces.
Interactive simulation and visualization
Interactive visualization is a general term that applies to the rendering of data that
may vary dynamically and allowing a user to view the data from multiple perspectives.
The applications areas may vary significantly, ranging from the visualization of the flow
patterns in fluid dynamics to specific computer aided design applications.
The data rendered may correspond to specific visual scenes that change as the user interacts
with the system, e.g. simulators such as flight simulators make extensive use of CGI techniques
for representing the world.
At the abstract level an interactive visualization process involves a 'data pipeline in which
the raw data is managed and filtered to a form that makes it suitable for rendering.
This is often called the "visualization data".
The visualization data is then mapped to a "visualization representation" that can be
fed to a rendering system.
This is usually called a "renderable representation".
This representation is then rendered as a displayable image.
As the user interacts with the system, e.g. by using joystick controls to change their
position within the virtual world, the raw data is fed through the pipeline to create
a new rendered image, often making real-time computational efficiency a key consideration
in such applications.
Computer animation
While computer generated images of landscapes may be static, the term computer animation
only applies to dynamic images that resemble a movie.
However, in general the term computer animation refers to dynamic images that do not allow
user interaction, and the term virtual world is used for the interactive animated environments.
Computer animation is essentially a digital successor to the art of stop motion animation
of 3D models and frame-by-frame animation of 2D illustrations.
Computer generated animations are more controllable than other more physically based processes,
such as constructing miniatures for effects shots or hiring extras for crowd scenes, and
because it allows the creation of images that would not be feasible using any other technology.
It can also allow a single graphic artist to produce such content without the use of
actors, expensive set pieces, or props.
To create the illusion of movement, an image is displayed on the computer screen and repeatedly
replaced by a new image that is similar to the previous image, but advanced slightly
in the time domain.
This technique is identical to how the illusion of movement is achieved with television and
motion pictures.
Virtual worlds
A virtual world is a simulated environment, which allows user to interact with animated
characters, or interact with other users through the use of animated characters known as avatars.
Virtual worlds are intended for its users to inhabit and interact, and the term today
has become largely synonymous with interactive 3D virtual environments, where the users take
the form of avatars visible to others graphically.
These avatars are usually depicted as textual, two-dimensional, or three-dimensional graphical
representations, although other forms are possible.
Some, but not all, virtual worlds allow for multiple users.
In courtrooms In recent years, the use of computer-generated
imagery has been made in courtrooms.
They are used to help judges or the jury to better visualize the sequence of events, evidence
or hypothesis.
But a 1997 study showed that people are poor intuitive physicists and easily influenced
by computer generated images.
Thus it is important that jurors and other legal decision-makers be made aware that such
exhibits are merely a representation of one potential sequence of events.
See also 3D modeling
Anime Studio Animation database
Blender - DIY CGI Digital image
Parallel rendering Photoshop is the industry standard commercial
digital photo editing tool.
Its FLOSS counterpart is GIMP.
Poser DIY CGI optimized for soft models Ray tracing
Shader Virtual human
Virtual Physiological Human Maya, 3ds Max, Cinema4D, E-on Vue, Poser,
and Blender are popular software packages that allow 3D modeling and CGI creation - see
also the list of 3D computer graphics software.
References
External links A Critical History of Computer Graphics and
Animation – a course page at Ohio State University that includes all the course materials
and extensive supplementary materials.
CG101: A Computer Graphics Industry Reference ISBN# 073570046X Unique and personal histories
of early computer graphics production, plus a comprehensive foundation of the industry
for all reading levels.
F/X Gods, by Anne Thompson, Wired, February 2005.
“History Gets A Computer Graphics Make-Over” Tayfun King, Click, BBC World News
NIH Visible Human Gallery