What is Computer Graphics?

Transcription

1 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 plotter exploring cockpit design using a 3D model of a human body. 31-May Computer Graphics : Chapter 1 Introduction I 1/31 What is Image Processing? Image processing is the analysis of scenes or reconstruction of model of 2D or 3D objects from their pictures. Simple image processing can be used in CG to help synthesize the image of a model. Also combining and transforming synthetic images depends largely on image processing operations. 31-May Computer Graphics : Chapter 1 Introduction I 2/31 1

2 What is Interactive Computer Graphics?(1/2) User controls contents, structure and appearance of objects and their displayed images via rapid visual feedback. Basic components of an interactive graphics system Input (mouse, tablet and stylus, joystick, scanner) Processing and storage Display/Output (screen, paper-based printer, video recorder) Batch mode has been used since 1950 s 31-May Computer Graphics : Chapter 1 Introduction I 3/31 What is Interactive Computer Graphics?(2/2) First truly interactive graphics system, Sketchpad, pioneered at MIT by Ivan Sutherland for his 1963 Ph.D. thesis. 31-May Computer Graphics : Chapter 1 Introduction I 4/31 2

3 Three Big Topics: Form, Behavior, Appearance Modeling: how to represent objects; how to build those representations Animation: representing/controlling the way things move Rendering: how to simulate the image forming process 31-May Computer Graphics : Chapter 1 Introduction I 5/31 Modeling How to represent real environment geometry: modeling surfaces, volumes photometry: light, color, reflactance How to build these representations declaratively: write it down interactively: sculpt it programmatically: let it grow via 3D sensing: scan it in 31-May Computer Graphics : Chapter 1 Introduction I 6/31 3

4 Animation Model how things move How to represent motion sequence of stills, parameter curves How to specify motion by hand: tweak it until it looks right rule-based behaviors: artificial life physics: simulate Newton s law motion capture: act it out yourself 31-May Computer Graphics : Chapter 1 Introduction I 7/31 Rendering What s an image? Distribution of light energy on 2D film : E(x, y, L, t) (L is wavelength) How do we represent and store images sampled array of pixels : I(x,y) How to generate images from scenes input: 3D description of scene, camera solve light transport through environment project to camera s viewpoint ray tracing 31-May Computer Graphics : Chapter 1 Introduction I 8/31 4

5 Hot Application Areas Special effects Feauture animation PC graphics boards Virtual environments/games Visualization (science, architecture, space, etc.) The web 31-May Computer Graphics : Chapter 1 Introduction I 9/31 Hot Research Topics Modeling getting models from the real world Animation physically based modeling motion capture Rendering more realistic: image-based modeling less realistic: impressionist, pen & ink 31-May Computer Graphics : Chapter 1 Introduction I 10/31 5

6 Evolution: Graphics in Context Graphics has been a key enabling technology in the evolution of computing environments: graphical user interfaces, visual computing, e.g., desktop publishing, scientific visualization, information visualization Hardware revolution drives everything: every months, computer power improves by factor of 2 in price/performance Moore s Law graphics memory and network speeds are on even faster exponentials Graphics chips have major improvements every six to nine months (e.g. Sony Playstation 2, nvidia GeForce 2, Nintendo) 31-May Computer Graphics : Chapter 1 Introduction I 11/31 Evolution: Character Display (1960s - now) Display: text plus alphamosaic pseudo-graphics Object and command specification: command-line typing Control over appearance: coding for text formatting Application control: single task 31-May Computer Graphics : Chapter 1 Introduction I 12/31 6

7 Evolution: Vector Displays ( s) 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, host-satellite distributed computing 31-May Computer Graphics : Chapter 1 Introduction I 13/31 Evolution: 2D bitmap raster displays for PCs and workstations (1972 at XEROX - now) Display: windows, icons, legible text and flat earth graphics Object and command specification: minimum typing via WIMP (Windows, Icons, Menus, Pointer) GUI (Graphical User Interface): point-and-click selection of menu items and objects, etc. Control over appearance: real WYSIWYG Application control: multi-tasking, networked client-server computation and window management 31-May Computer Graphics : Chapter 1 Introduction I 14/31 7

8 Evolution: 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 and force feedback haptic devices for point-and-click, etc. Control over appearance: WYSIWYG Application control: multi-tasking, networked client-server computation and window management 31-May Computer Graphics : Chapter 1 Introduction I 15/31 Evolution: Classic time-sharing is dead PCs and workstations merging in distributed heterogeneous computer networks (e.g. LANs, WANs, Internet) But file-, print- and compute-servers and network are shared Client/Server computing, component software technologies are dominant paradigms NC s (Network Computers), thin clients attached to powerful servers reprise dumb terminals and provide central control 31-May Computer Graphics : Chapter 1 Introduction I 16/31 8

9 New Forms of Computing: 1990s -(1/2) Multimedia: text and graphics synchronized with sound and video Hypermedia: multimedia with links (also called Interactive Multimedia) Digital Convergence : 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) Immersive Virtual Reality: desktop ( fishtank ) VR, immersive VR (via Head-mounted Displays, Cave (180 George St.), Responsive Workbench), augmented VR (via video see-through optics) 31-May Computer Graphics : Chapter 1 Introduction I 17/31 New Forms of Computing: 1990s -(2/2) New Interaction technology Inexpensive interaction devices from research lab into marketplace (makes 2D and 3D graphics no longer special ) 3D (even time-varying, 4D ) interactive illustrations as clip art/clip models coming soon Kids using computer graphics in gaming consoles; VR games and rides with HMD and force-feedback input devices New forms of user-interface 3D Widgets; gestures-based; VR demands new interaction technology Social interfaces (Microsoft s Bob bombed) Agents/knowbots for indirect control 31-May Computer Graphics : Chapter 1 Introduction I 18/31 9

10 Powerful, Inexpensive Processing Chips are Key in graphics subsystems CPU Advances driven by Moore s Law Price/performance improves 2x every 18 months due to doubling of number of transistors (Only exponential in technology except growth of WWW) Intel Pentium III, AMD Athlon, IBM/Motorola PowerPC, Sun UltraSPARC, MIPS Technologies MIPS, Compaq Alpha, Hewlett Packard HPPA, IBM POWER, SGI/Cray vector processors Graphics subsystems Chip vendors for games and set-top boxes, and for PC boards Sun s VIS, Intel s MMX/KNI, PowerPC s Altivec, and AMD s 3Dnow! Instructions add multimedia support to main processor; in the future, 3D graphics in every chip 31-May Computer Graphics : Chapter 1 Introduction I 19/31 Chip Technology Advances in games & Graphics Cards New Game platforms and set-top boxes use high-end processors (128-bit architectures, great graphics capabilities) Nintendo N-Cube Sega Dreamcast Sony Playstation 2 3Dfx Voodoo5 nvidia GeForce 2 Significant advances in commodity graphics chips every 6 months, outrunning CPU chip advances Intel s Pentium 4 chip due out this fall has 42 million transistors, compared with only 26 million in the Pentium III Seriously threatening high-end workstations 31-May Computer Graphics : Chapter 1 Introduction I 20/31 10

11 Application Distinctions: two basic paradigms(1/2) Sampled-based graphics: discrete samples are used to describe visual information Pixels can be created by digitizing images, using a samples-based painting program, etc. Often some aspect of the physical world is sampled for visualization, e.g. temperature across Thailand Example programs: Adobe Photoshop, The GIMP (on UNIX) 31-May Computer Graphics : Chapter 1 Introduction I 21/31 Application Distinctions: two basic paradigms(2/2) Geometry-based graphics: a geometrical model is created, along with various attributes, and is then sampled for visualization (this process is called rendering ) Often some aspect of the physical world is visually simulated or synthesized Example 2D programs: Adobe Illustrator, Macromedia Freehand, Corel CorelDraw, Microsoft PhotoDraw Example 3D programs: Alias/Wavefront Studio and Maya, Avid s SoftImage 3D, Autodesk s AutoCAD and 3D StudioMax 31-May Computer Graphics : Chapter 1 Introduction I 22/31 1

12 Sampled-based Graphics(1/2) Images are made up of a grid of discrete pixels for 2D picture elements Pixels are point locations with associated sample values usually of light intensity/colors, transparency, and other control information 31-May Computer Graphics : Chapter 1 Introduction I 23/31 Sampled-based Graphics(2/2) Samples can be created directly in a paint-type program or as a result of sampling continuous (analog) visual materials, e.g. a photograph can be sampled using many devices including: flatbed and drum scanners, digital still camera, frame grabbers Sample values can be input numerically (e.g. from database) Once an image is defined as a pixel-array, it can be manipulated Image editing (cut & paste, using brush tools, etc.) Image processing (blurring, sharpening, rotating, etc.) 31-May Computer Graphics : Chapter 1 Introduction I 24/31 12

13 Sampling an Image Lets do some sampling of an image of a building A color value is measured at every grid point Note: this poor sampling creates blocky image when reconstructed 31-May Computer Graphics : Chapter 1 Introduction I 25/31 What s the Advantage? Once image is defined in terms of colors at (x,y) locations on grid, we can change the image easily by altering location or color values Two or more images can be combined 31-May Computer Graphics : Chapter 1 Introduction I 26/31 13

14 What s the Disadvantage? WYSIWYG (What You See Is What You Get): There is no additional information No depth information can t examine scene from a different point of view at most can play with the individual pixels or groups of pixels to change colors, enhance contrast, find edges, etc. 31-May Computer Graphics : Chapter 1 Introduction I 27/31 Examples of 2D Image Manipulation(1/2) There are Many things one can do with sampled images (military, entertainment, art, design, medicine) Digitally enhanced images are more and more common (magazines cover, etc.) Movies: A Bug s Life, Babe, Titanic, Jurassic Park Photorealistic images no way to tell if news photos are real photographs photographic evidence no longer considered proof 31-May Computer Graphics : Chapter 1 Introduction I 28/31 14

15 Examples of 2D Image Manipulation(2/2) Photography and painting are merging in the art of digital imaging Father, mother and son, all at 3 years of age This course emphasizes geometry-based graphics 31-May Computer Graphics : Chapter 1 Introduction I 29/31 Geometry-Based Graphics Geometry-based graphics applications store mathematical descriptions or models of geometric elements (lines, polygons, polyhedrons ) and their associated attributes (color, material properties). These elements are primitive geometric shapes (primitive for short). Images are created as pixels arrays (via sampling of the geometry) for viewing, but are not store as part of the model. Image of many different views can be generated from the same model. Can t work directly with the individual pixels The geometric elements are manipulated and redisplayed 31-May Computer Graphics : Chapter 1 Introduction I 30/31 15

16 Composition of a Geometric Model Primitives are assembled to create the final object 31-May Computer Graphics : Chapter 1 Introduction I 31/31 16