Computer-generated imagery - AbsoluteAstronomy.com

Computer-generated imagery (CGI) is the application of the field of computer graphics

Computer graphics

Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....

or, more specifically, 3D computer graphics

3D computer graphics

3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...

to special effects in art

Art

Art is the product or process of deliberately arranging items in a way that influences and affects one or more of the senses, emotions, and intellect....

, video games, film

Film

A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...

s, television program

Television program

A television program , also called television show, is a segment of content which is intended to be broadcast on television. It may be a one-time production or part of a periodically recurring series...

s, commercials, simulators and simulation generally, and printed media. The visual scenes may be either dynamic or static.

The term computer animation

Computer animation

Computer animation is the process used for generating animated images by using computer graphics. The more general term computer generated imagery encompasses both static scenes and dynamic images, while computer animation only refers to moving images....

refers to dynamic CGI rendered as a movie. The term virtual world

Virtual world

A virtual world is an online community that takes the form of a computer-based simulated environment through which users can interact with one another and use and create objects. The term has become largely synonymous with interactive 3D virtual environments, where the users take the form of...

refers to agent-based, interactive environments.

3D computer graphics software

3D computer graphics software

3D computer graphics software refers to programs used to create 3D computer-generated imagery. This article covers only some of the software used.-Uses:...

is used to make computer-generated imagery for movies, etc. Recent 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.

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

Polygon mesh

A polygon mesh or unstructured grid is a collection of vertices, edges and faces that defines the shape of a polyhedral object in 3D computer graphics and solid modeling...

method, relying on the construction of some special case of a de Rham curve

De Rham curve

In mathematics, a de Rham curve is a certain type of fractal curve named in honor of Georges de Rham.The Cantor function, Césaro curve, Minkowski's question mark function, the Lévy C curve, the blancmange curve and the Koch curve are all special cases of the general de Rham...

, 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 triangle

Sierpinski triangle

The Sierpinski triangle , also called the Sierpinski gasket or the Sierpinski Sieve, is a fractal and attractive fixed set named after the Polish mathematician Wacław Sierpiński who described it in 1915. However, similar patterns appear already in the 13th-century Cosmati mosaics in the cathedral...

s, then interpolate the height of each point from its nearest neighbors. The creation of a Brownian surface

Brownian surface

A Brownian surface is a fractal surface generated via a fractal elevation function.For instance, in the three-dimensional case, where two variables X and Y are given as coordinates, the elevation function between any two points and can be set to have a mean or expected value that increases as the...

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

Architectural animation

Architectural Animation is a short architectural movie created on a computer. A computer-generated building is created along with landscaping and sometimes moving people and vehicles. Unlike an architectural rendering, which is a single image from a single point of view, an architectural animation...

(which provides animated movies of buildings, rather than interactive images) 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 modeling 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 modeling tools have now become increasingly internet-based. However, the quality of internet-based systems still lags those of sophisticated inhouse modeling 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

Georgenthal

Georgenthal is a municipality in the district of Gotha, in Thuringia, Germany....

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

Skeletal animation

Skeletal animation is a technique in computer animation in which a character is represented in two parts: a surface representation used to draw the character and a hierarchical set of interconnected bones used to animate the mesh...

are not always anatomically correct, however, organizations such as the Scientific Computing and Imaging Institute

Scientific Computing and Imaging Institute

The Scientific Computing and Imaging Institute is a permanent research institute at the University of Utah. It is a leader in engineering and research in the areas of scientific computing, visualization, and imaging...

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 image

Medical imaging

Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...

s 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

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

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

Magnetic resonance imaging

Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

also bring together a number of "snapshots" (in this case via magnetic pulses) 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

Knee replacement

Knee replacement, or knee arthroplasty, is a surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve the pain and disability of osteoarthritis. It may be performed for other knee diseases such as rheumatoid arthritis and psoriatic arthritis...

, 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

Aortic valve

The aortic valve is one of the valves of the heart. It is normally tricuspid , although in 1% of the population it is found to be congenitally bicuspid . It lies between the left ventricle and the aorta....

implantations, one of the common procedures for treating heart disease

Heart disease

Heart disease, cardiac disease or cardiopathy is an umbrella term for a variety of diseases affecting the heart. , it is the leading cause of death in the United States, England, Canada and Wales, accounting for 25.4% of the total deaths in the United States.-Types:-Coronary heart disease:Coronary...

. Given that the shape, diameter and position of the coronary openings can vary greatly from patient to patient, the extraction (from CT scans) 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

Yarn

Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting, knitting, weaving, embroidery and ropemaking. Thread is a type of yarn intended for sewing by hand or machine. Modern manufactured sewing threads may be finished with wax or...

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

Human skin

The human skin is the outer covering of the body. In humans, it is the largest organ of the integumentary system. The skin has multiple layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs. Human skin is similar to that of most other mammals,...

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.

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

Fluid dynamics

In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...

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 simulator

Flight simulator

A flight simulator is a device that artificially re-creates aircraft flight and various aspects of the flight environment. This includes the equations that govern how aircraft fly, how they react to applications of their controls and other aircraft systems, and how they react to the external...

s 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

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

Virtual world

is used for the interactive animated environments.

Computer animation is essentially a digital successor to the art of stop motion

Stop motion

Stop motion is an animation technique to make a physically manipulated object appear to move on its own. The object is moved in small increments between individually photographed frames, creating the illusion of movement when the series of frames is played as a continuous sequence...

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

Miniature effect

A miniature effect is a special effect created for motion pictures and television programs using scale models. Scale models are often combined with high speed photography or matte shots to make gravitational and other effects appear convicing to the viewer...

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

Computer display

A monitor or display is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure...

and repeatedly replaced by a new image that is similar to the previous image, but advanced slightly in the time domain (usually at a rate of 24 or 30 frames/second). This technique is identical to how the illusion of movement is achieved with television

Television

Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

and motion pictures

Film

Virtual worlds

A virtual world

Virtual world

is a simulated environment

Computer simulation

A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...

, which allows user to interact with animated characters, or interact with other users through the use of animated characters known as avatars

Avatar (computing)

In computing, an avatar is the graphical representation of the user or the user's alter ego or character. It may take either a three-dimensional form, as in games or virtual worlds, or a two-dimensional form as an icon in Internet forums and other online communities. It can also refer to a text...

. Virtual worlds are intended for its users

User (computing)

A user is an agent, either a human agent or software agent, who uses a computer or network service. A user often has a user account and is identified by a username , screen name , nickname , or handle, which is derived from the identical Citizen's Band radio term.Users are...

to inhabit and interact, and the term today has become largely synonymous with interactive 3D virtual environments, where the users take the form of avatar

Avatar (computing)

s visible to others graphically. These avatars are usually depicted as textual, two-dimensional, or three-dimensional graphical

3D computer graphics

3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...

representations, although other forms are possible (auditory and touch sensations for example). Some, but not all, virtual worlds allow for multiple users.

External links

A Critical History of Computer Graphics and Animation – a course page at Ohio State University
Ohio State University
The Ohio State University, commonly referred to as Ohio State, is a public research university located in Columbus, Ohio. It was originally founded in 1870 as a land-grant university and is currently the third largest university campus in the United States...

that includes all the course materials and extensive supplementary materials (videos, articles, links).
Pixar and Disney's Toy Story
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 (2004-11-19)
NIH Visible Human Gallery
CGI Studio

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Static images and landscapes

Architectural scenes

Anatomical models

Generating cloth and skin images

Interactive simulation and visualization

Computer animation

Virtual worlds

See also

External links