CS 450: COMPUTER GRAPHICS REVIEW: INTRODUCTION TO COMPUTER
GRAPHICS PART 1 SPRING 2015 DR. MICHAEL J. REALE
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WHAT IS COMPUTER GRAPHICS? Computer graphics generating and/or
displaying imagery using computers Example applications: Graphics,
Charts, and Data Visualization Challenges: large data sets, best
way to display data CAD/CADD/CAM Challenges: need pixel-perfect
rendering Computer Art / Movies Virtual-Reality Environments /
Training Simulations Games
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CHARACTERISTICS OF COMPUTER GRAPHICS Depending on your
application, your focus and goals will be different: Real-time vs.
Non-real-time Virtual Entities / Environments vs. Visualization /
Representation Developing Tools / Algorithms vs. Content
Creation
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CG DEFINITIONS Real-time 15 fps = BARE MINIMUM but still skips
24 fps = minimum without skips Computer-graphics application
programming interfaces (CG API) Interface between programming
language and hardware Common CG APIs: GL, OpenGL, DirectX, VRML,
Java 2D, Java 3D, etc.
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DISPLAY DEFINITIONS Refresh rate = frequency that picture is
redrawn Usually expressed in Hertz (e.g., 60 Hz) Persistence = how
long phosphors emit light after being hit by electrons in CRT Low
persistence need higher refresh rates LCD monitors have an
analogous concept response time
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MORE DISPLAY DEFINITIONS Pixels = picture element; single point
on screen Resolution = (number of pixels in width) x (number of
pixels in height) Aspect ratio = resolution width / height
(Although sometimes vice versa) Refresh buffer (or frame buffer) =
contains picture of screen you want to draw Each row = scan
line
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VIDEO DISPLAY DEVICES CRT Plasma LCD/LED 3D
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CRT Cathode-Ray Tube Primary video display mechanism for years
now replaced by LCD monitors/TVs Shoots electrons at phosphor
screen keeps redrawing (refreshing) Two types: Vector displays
Electron gun draws primitives directly Advantages: draws
non-aliased lines Disadvantages: not very flexible; cannot draw
shaded polygons Mostly abandoned in favor of raster-scan displays
Raster-scan displays Electron gun sweeps across screen, one row at
a time, from top to bottom, to draw refresh buffer Advantages:
flexible Disadvantages: lines, edge, etc. can look jagged (i.e.,
aliased)
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CRT Interlacing = first draw even-numbered scan lines, then do
odd- numbered lines Effectively doubles your refresh rate Also used
to save data in TV transmission Color CRTs Beam-penetration Have
red and green layer of phosphors speed of electrons determines
which turn on Inexpensive, but limited in number of colors
Shadow-mask Three electron guns and three phosphor dots (one for
red, one for green, and one for blue) Shadow mask makes sure 3 guns
hit the 3 dots
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PLASMA DISPLAYS Fire voltage through gas to make glowing plasma
For color use three subpixels (red, green, and blue) Advantages:
very thin display; pixels very bright good at any viewing angle
Disadvantages: expensive
http://electronics.howstuffworks.com/plasma-display2.htm
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LCD DISPLAYS LCD = Liquid Crystal Displays Liquid crystal =
maintain a certain structure, but can move around like liquid
Structure is twisted, but applying electrical current straightens
it out Basic idea: Two polarized light filters (one vertical, one
horizontal) Light passes through first filter polarized light in
vertical direction ON STATE no current crystal twisted causes light
to be reoriented so it passes through horizontal filter OFF STATE
current crystal straightens out light does NOT pass through
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LCD DISPLAYS Light Sources Mirror in back of display
Fluorescent light in center of display LED lights Two types:
Passive-matrix LCDs use grid that sends charge to pixels through
transparent conductive materials Simple Slow response time
Imprecise voltage control leakage to nearby pixels Active-matrix
LCDs use transistor at each pixel location using thin-film
transistor technology Transistors control voltage at each pixel
location prevent leakage to other pixels Control voltage get 256
shades of gray Color have 3 subpixels (one red, one green, and one
blue)
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3D DISPLAYS Humans see depth because of binocular vision each
eye sees different view Older approaches: Anaglyph 3D red/blue
glasses + showing red/blue images Poor color quality View Master
toys shows photograph from different angle in each eye
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3D DISPLAYS Newer approaches: Active 3D Special shutter glasses
that sync up with monitor TV Showing only one image at time (but
REALLY fast) glasses close opposite eye Advantages: can use
monitor/TV with high enough refresh rate; full screen resolution
Disadvantages: out of sync flickering; image looks darker; glasses
can be cumbersome Passive 3D Polarized light glasses + TV shows two
images at once on alternating lines of resolution Advantages:
lightweight (cheap) glasses; image brighter than active 3D
Disadvantages: need special TV; only seeing HALF the vertical
resolution Virtual reality displays (e.g., Oculus Rift) Separate
screens for each eye Advantages: no drop in resolution or
brightness Disadvantages: heavy headset
