survey in computer graphics - department of computing science

Survey in Computer GraphicsComputer Graphics and Visualization

Fall 2010

Pedher JohanssonDepartment of Computer Science

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Example of a Marble Ball

I Where did this image come from?

I What hardware/software/algorithms did we need toproduce it?

Survey in Computer Graphics Pedher JohanssonComputer Graphics and Visualization Department of Computer Science

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A Basic Graphics System

I Input devicesI Image formed in FBI Output device


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History of Computer Graphics1200-2008


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HISTORY

Before 1960

1200 Chinese Abacus1450 Gutenberg1826 Photography (Niepce)1842 FAX (Alexander Bain)1885 CRT1888 Record Motion pic. on vax cylinder (Edison,

Dickson)1926 First television (J.L. Baird)1946 ENIAC Computer1954 Fortran1958 Integrated circuit (IC, or Chip)


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HISTORY

Alexander Bain’s Fax Machine

Bain’s fax machine used a detector toscan an image. As the detector passedover the page it emitted an electricalsignal which registered at one strengthas it passed through the image’s blackpoints and at a different strength as itpassed over white points. The twodistinct signals were transmitted overtelegraph wires to a receiver whichapplied them to chemically treated paperto reproduce the image.


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HISTORY

CRT

Can be used asI line-drawing device (calligraphic) or toI display contents of frame buffer (raster mode).


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HISTORY

1960-1969

1961 Spacewars, 1st Videogame1963 DEC-1 First comersial CAD system1963-1969 Hidden line, Warnock, Watkins alg.,

lineclippng1969 UNIX developed1969 GUI developed by Xerox (Alan Kay)


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HISTORY

Spacewars


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HISTORY

1960-1969

I Wireframe graphicsI Draw only linesI Display ProcessorsI Storage tube


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HISTORY

Display Processor

I Rather than have the host computer try to refreshdisplay use a special purpose computer called adisplay processor (DPU)

I Graphics stored in display list (display file) on displayprocessor


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HISTORY

1970-1979

1972 Atari founded1973,1975 z-buffer, phong

shading1975 Microsoft founded1976 Apple founded1977 Death Star simula-

tion for Star Wars


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HISTORY

1970-1979

I Raster GraphicsI Beginning of graphics standardsI Workstations and PCs


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HISTORY

Raster Graphics

I Image produced as an array(the raster) of pictureelements (pixels) in the framebuffer

I Allows us to go from linesand wire frame images tofilled polygons


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HISTORY

1980-1989

1980 Donkey Kong introduced by Nintendo1980 Hanna-Barbera, comp. automation of

anim. process1982 Silicon Graphics Inc, Sun microsystems,

Adobe1984 Macintosh1985 Pixar Image Computer goes to market1986-1987 TIFF, GIF1987 VGA1988 Willow (Lucasfilm) morphing,

Who Framed Roger Rabbit1989 Photoshop


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HISTORY

1980-1989

I Realism comes to computer graphics

Smooth Shading EnvironmentMapping

Bump Mapping


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HISTORY

1991-1999

1991 World Wide Web(CERN)

1991 Terminator 21991 JPEG/MPEG1992 OpenGL1993 Doom, Myst1994 Linux 1.01995 Toy Story1995 Java1996 Quake1998 MPEG-4

1991: February (premiere)issue of DV magazine advises

"[to be able to do digital video,get] the most souped upsystem you can get your handson. A fast processor (68040 onAmiga or Mac, 80486 on PC)and lots of RAM (8-64 MB) arein order. So is a large harddrive (200 MB - 1 GB) if youwant to take on seriousproduction."


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HISTORY

1991-1999

I OpenGL APII Completely computer-generated feature-length

movies (Toy Story) are successfulI New hardware capabilities


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HISTORY

2000-

I PhotorealismI Graphics cards for PCs dominate market Nvidia, ATII Game boxes and game players determine direction

of marketI Computer graphics routine in movie industry: Maya,

LightwaveI Programmable pipelinesI 3-D reenters animations


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Image Formation


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IMAGE FORMATION

Image Formation

I In computer graphics, we form images which aregenerally two dimensional using a processanalogous to how images are formed by physicalimaging systems

– Cameras– Microscopes– Telescopes– Human visual system


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IMAGE FORMATION

Elements of Image Formation

I ObjectsI ViewerI Light source(s)

I Attributes that govern how light interacts with thematerials in the scene

I Note the independence of the objects, the viewer,and the light source(s)


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IMAGE FORMATION

Light

I Light is the part of the electromagnetic spectrum thatcauses a reaction in our visual systems

I Generally these are wavelengths in the range ofabout 350-750 nm (nanometers)

I Long wavelengths appear as reds and shortwavelengths as blues


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IMAGE FORMATION

Luminance and Color Images

I Luminance Image– Monochromatic– Values are gray levels– Analogous to working with black and white film or

television

I Color Image– Has perceptional attributes of hue, saturation, and

lightness– Do we have to match every frequency in visible

spectrum? No!


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IMAGE FORMATION

Three-Color Theory

I Human visual system has two types of sensorsRods: Monochromatic, night vision

Cones: Color sensitiveI Three types of conesI Only three values (the tristimulus values) are sent to

the brainI Need only three primary colors


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IMAGE FORMATION

Additive and Subtractive Color

Additive color Form a color by adding amounts ofthree primaries

I LCDs, projection systems, positivefilm

I Primaries are Red (R), Green (G),Blue (B)

Subtractive color Form a color by filtering white light withcCyan (C), Magenta (M), and Yellow(Y) filters

I Light-material interactionsI PrintingI Negative film


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IMAGE FORMATION

Synthetic Camera Model


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IMAGE FORMATION

Pinhole Camera

I Use trigonometry to find projection of point at(x ,y ,z)

xp =− xy/d yp =− y

x/d z = d


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IMAGE FORMATION

Advantages

I Separation of objects, viewer, light sourcesI Two-dimensional graphics is a special case of

three-dimensional graphicsI Leads to simple software API

– Specify objects, lights, camera, attributes– Let implementation determine image

I Leads to fast hardware implementation


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IMAGE FORMATION

Global vs Local Lighting

I In Local Lighting we compute color or shade of eachobject independently

I But!– Some objects are blocked from light.– Light can reflect from object to object.– Some objects might be translucent.


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IMAGE FORMATION

Pipeline Architecture

I Process objects one at a time in the order they aregenerated by the application

I All steps can be implemented in hardware on thegraphics card

Vertices Vertex Processor

Rasterizer Fragment Processor

PixelsClipper andPrimitive Assambler


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IMAGE FORMATION

Vertex Processing

I Much of the work in the pipeline is in convertingobject representations from one coordinate systemto another

– Object coordinates– Camera (eye) coordinates– Screen coordinates

I Every change of coordinates is equivalent to amatrix transformation

I Vertex processor also computes vertex colors





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IMAGE FORMATION

Clipping and Primitive Assembly

I Vertices must becollected into geometricobjects before clippingand rasterization cantake place

I Objects that are notwithin this volume areclipped out of the scene





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IMAGE FORMATION

Rasterization

I If an object is not clipped out, the appropriate pixelsin the frame buffer must be assigned colors

I Rasterizer produces a set of fragments for eachobject

I Fragments are ”potential pixel”– Have a location in frame buffer– Color and depth attributes

I Vertex attributes are interpolated over objects by therasterizer





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IMAGE FORMATION

Fragment Processing

I Fragments are processed to determine the color ofthe corresponding pixel in the frame buffer

I Colors can be determined by texture mapping orinterpolation of vertex colors

I Fragments may be blocked by other fragmentscloser to the camera (Hidden-surface removal)





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IMAGE FORMATION

The Programmer’s Interface

I Objects– Points (0D)– Line segments (1D)– Polygons (2D)– Some curves and

surfaces– All are defined

through locations inspace or vertices

I Viewer (Camera)

I Light Source(s)– Point sources vs

distributed sources– Spot lights– Near and far

sources– Color properties

I Materials– Color properties– Diffuse or specular


survey in computer graphics - department of computing science

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