What is Computer Graphics

What is Computer Graphics?

Computer graphics is commonly understood to mean the creation, storage and manipulation of models and images.

Such models come from a diverse and expanding set of fields including physical, mathematical, artistic, biological, and even conceptual (abstract) structures. The term computer graphics was coined in 1960 by William Fetter to describe new design methods he was pursuing at Boeing.

He created a series of widely reproduced images on a pen plotter exploring cockpit design, using a 3D model of a human body.

What is Interactive Computer

User controls contents, structure, and appearance of objects and their displayed images via rapid visual feedback

Basic components of an interactive graphics system

input (e.g., mouse, tablet and stylus, force feedback device, scanner, live video streams)

processing (and storage)

display/output (e.g., screen, paper-based printer, video recorder, non-linear editor)

First truly interactive graphics system, Sketchpad, pioneered at MIT by Ivan Sutherland for his 1963 Ph.D. thesis

Environmental (R)evolution

Vector (Calligraphic, Line Drawing) Displays (1963 1980s)

Display: line drawings and stroke text; 2D and 3D transformation hardware

Object and command specification: command-line typing, function keys, menus

Control over appearance: pseudo-WYSIWYG

Application control: single or multitasked, mainframe host-minicomputer satellite distributed computing pioneered at Brown2D bitmap raster displays for PCs and workstations (1972 at Xerox PARC - now)

Display: windows, icons, legible text and flat earth graphics

Note: late 60s saw first use of raster graphics, especially for flight simulators

Object and command specification: minimal typing via WIMP (Windows, Icons, Menus, Pointer) GUI (Graphical User Interface): point-and-click selection of menu items and objects, widgets and direct manipulation (e.g., drag and drop), the messy desktop metaphor

Control over appearance: WYSIWYG (which is really WYSIAYG, What You See Is All You Get)

Application control: multi-tasking, networked client-server computation and window management (even X terminals)3D graphics workstations (1984 at SGI now)

Display: real-time, pseudo-realistic images of 3D scenes

Object and command specification: 2D, 3D and nD input devices (controlling 3+ degrees of freedom) and force feedback haptic devices for point-and-click, widgets, and direct manipulation

Control over appearance: WYSIWYG (still WYSIAYG)

Application control: multi-tasking, networked (client/server) computation and window management

High-end PCs with hot graphics cards (nVidia GeForce 3, 4, FX) are supplanting graphics workstations

Such PCs are clustered together over high speed buses or LANs to provide scalable graphics to drive tiled PowerWalls, Caves, etc.

New Forms of Computing: 1990-2003

Multimedia: text and graphics synchronized with sound and video

Hypermedia: multimedia with hypertextual links (also called Interactive Multimedia)

Discredited term: Digital Convergence, the merging of digital television and distributed computing, consumer electronics: set-top computers (e.g., for Interactive TV, Video-On-Demand)

The Internet and Internet appliances

Embedded computing (information appliances, Personal Digital Assistants)

Ubiquitous/pervasive/invisible/nomadic computing, active badges a la Xerox PARC, with hundreds of devices per person; seamless computing is the dream Virtual Reality:

Conceptual Framework for Interactive Graphics

Graphics library/package (e.g., OpenGL) is intermediary between application and the display hardware (Graphics System)

Application program maps application objects to views (images) of those objects by calling on graphics library

User interaction results in modification of model and/or image

Images are usually means to an end: synthesis, design, manufacturing, visualization,

This hardware and software framework is nearly 4 decades old but is still useful, indeed dominant

1-bit Bilevel Display Digital intensity value -> Digital to Analog Conversion (DAC) -> analog signal to drive electron beam

Black & White (or any 2 colors, depending on the monitor phosphor color)

Original Mac resolution was 512x384 pixels, now from 640x480 up to 1280x1024, even 3Kx3K in IBMs Roentgen display. Our PCs are 1280x1024

1280x1024 memory 15 nanosec/pixel => 32 pixel chunks stored in shift registers/buffers

n-Bit Display

2n intensities or colors: 1 (grayscale) or 3 (color) DACs & guns

1000 line color monitors cost < $250

Image Display System: Look-up Table

Any specific 2n colors may be inadequate (n typically 16-24 in low-end systems)

Look-up table allows 2n colors out of 224 colors to be used in one image, some other 2n in another image

224 = approx. 16.7 million, exceeds eyes ability to discriminate (somewhere between 7-10 million)

Color table is a resource managed (usually) by window manager

Color Look Up Table Operation

Pixel value is indexed to color look up table (CLUT) where color is stored. Here we use only 12 bits (4bits per color) for clarity typically, 24bits are used

CLUT look up done at video rates, overlapped with fetch and DAC!

In 24-bit true color systems, 3 x 8 bits for R, G, B; each color has its own 8-bit CLUT (0-255)

CLUT allows variety of effects

pseudo coloring (LandSat images, stress diagrams, thermograms)

fast image changes: change table rather than stored image

multiple images: select or composite/blend

animation hack

PAGE 5