Transcript Introduction and Display Technologies

Introduction and
Display Technologies
Chapter 1 and
Sections
2-1 to 2-4
(somewhat outdated)
Most of these slides have been prepared by Dr Ahmed Bashandy and some of the material have been adapted from
university of Virginia and MIT
We will Study:
● Graphics Fundamentals
● Graphics programming algorithms
● Graphics data structures
● Some of
■ Color and human vision
■ Applied geometry and modeling
■ Applied numerical computing
● DirectX in the sections
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We will NOT study
● Paint and Imaging packages (Adobe Photoshop)
● Art and Movies
● CAD packages (AutoCAD)
● Packages:
■ Rendering packages (Lightscape)
■ Modeling packages (3D Studio MAX)
■ Animation packages (Digimation)
■ Graphics Modeling and Languages (RenderMan)
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Why Computer Graphics
Why Computer Graphics
● What computers do....
■ process, transform, and communicate information
● Visual communication is very appealing to humans
● Computer graphics is a method of communication
● Computer Graphics is...
■ the technology for presenting information
■ Applied geometry and modeling
■ Applied numerical computing
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Many Application for Graphics
● Education
● CAD
● Entertainment
● Medicine
● Communication
● Games
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Medicine
● Precision and correctness
● Remote medicine
● Teaching and diagnosis (CAT, MRI)
● Modeling of medical data
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Computer Aided Design
● Wide range of processes from the design of tooling fixtures to
manufacturing.
● Architectural and product designs
● Verify tolerances and design from CAD tools directly
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Education and Scientific
Visualization
● Biology and Chemistry visualization
● Mathematicians use computer graphics to explore abstract and
high-dimensional functions and spaces.
● Physicists explore both microscopic and macroscopic worlds.
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Graphical User Interface
● Graphical elements such as windows, fonts, cursors, menus,
and icons
● Translation, scaling, rotation of graphical elements
● Humans prefer appealing interfaces
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Display Devices
Display Technologies
● Cathode Ray Tubes (CRTs): A CRT is an evacuated
glass tube, with a heating element on one end and a
phosphor coated screen on the other
■ Most common display device
(until recently)
■ Evacuated glass bottle (last
of the vacuum tubes)
■ Heating element (filament)
■ Electrons pulled towards
anode focusing cylinder
■ Vertical and horizontal deflection plates
■ Beam strikes phosphor coating on front of tube
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CRTs – Overview
■ CRT technology hasn’t changed much in 50 years
■ Early television technology
○ requires synchronization between video signal and electron beam
vertical sync pulse
■ Early computer displays
○ avoided synchronization using ‘vector’ algorithm
○ flicker and refresh were problematic
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CRTs – Vector Displays
● Vector displays
■ Early computer displays: basically an oscilloscope
■ Control X,Y with vertical/horizontal plate voltage
■ Often used intensity as Z
■ Show: http://graphics.lcs.mit.edu/classes/6.837/F98/Lecture1/Slide11.html
● Name two disadvantages
Just does wireframe
Complex scenes results in visible flicker
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CRTs – Raster Displays
■ Raster Displays (early 70s)
○ like television, scan all pixels in regular pattern
○ use frame buffer (video RAM) to eliminate sync problems
■ RAM
○ ¼ MB (256 KB) cost $2 million in 1971
○ Do some math…
-
1280 x 1024 screen resolution = 1,310,720 pixels
Monochrome color (8 bits per pixel) requires 160 KB
High resolution color (24 bits per pixel) requires 5.2 MB
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CRTs – Raster Displays
● Black and white television: an oscilloscope with a
fixed scan pattern: left to right, top to bottom
■ Paint entire screen 30 times/sec
○ Actually, TVs paint top-to-bottom 60 times/sec, alternating
between even and odd scanlines
○ This is called interlacing. It’s a hack. Why do it?
■ To paint the screen, computer needs to synchronize with
the scanning pattern of raster
○ Solution: special memory to buffer image with scan-out
synchronous to the raster. We call this the framebuffer.
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CRTs – Raster Displays
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CRTs – Raster Displays
● Raster Displays
■ Frame must be “refreshed” to draw new images
■ As new pixels are struck by electron beam, others are
decaying
■ Electron beam must hit all pixels frequently to eliminate
flicker
■ Critical fusion frequency
○ Typically 60 times/sec
○ Varies with intensity, individuals, phosphor persistence, lighting...
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Color CRTs
● Color CRTs are much more complicated
■ Requires manufacturing very precise geometry
■ Uses a pattern of color phosphors on the screen:
Delta electron gun arrangement
In-line electron gun arrangement
■ Why red, green, and blue phosphors?
■ We will see later that the human eye contains cells that
sense these 3 colors
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Color CRTs
● Color CRTs have
■ Three electron guns
■ A metal shadow mask to differentiate the beams
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Raster CRTs Pros and Cons
● Raster CRT pros:
■ Allows solids, not just wireframes
■ Leverages low-cost CRT technology (i.e., TVs)
■ Bright! Display emits light
● Cons:
■ Requires screen-size memory array
■ Discreet sampling (pixels)
■ Practical limit on size (call it 40 inches)
■ Bulky
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Display Technology: LCDs
● Liquid Crystal Displays (LCDs)
■ LCDs: organic molecules, naturally in crystalline state, that liquefy
when excited by heat or E field
■ When LCDs are used as optical (light) modulators they are actually
changing polarization. In their unexcited or crystalline state the LCDs
rotate the polarization of light by 90 degrees. In the presence of an
electric field, LCDs behave like a liquid and align the small
electrostatic charges of the molecules with the impinging E field.
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Display Technology: LCDs
● Liquid Crystal Displays (LCDs)
■ LCDs, like phosphors, remain "on" for some time after the
E field is applied. Thus the image is persistent like a CRT's,
but this lasts just until the crystals can realign themselves,
thus they must be constantly refreshed, again, like a CRT.
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Display Technology: LCDs
● Transmissive & reflective LCDs:
■ LCDs act as light valves, not light emitters, and thus rely
on an external light source.
■ Laptop screen: backlit, transmissive display
■ Palm Pilot/Game Boy: reflective display
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Display Technology: Plasma
● Plasma display panels
■ Similar in principle to
fluorescent light tubes
■ Small gas-filled capsules
are excited by electric field,
emits UV light
■ UV excites phosphor
■ Phosphor relaxes, emits
some other color
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Display Technology: Plasma
● Plasma Display Panel Pros
■ Large viewing angle
■ Good for large-format displays
■ Fairly bright
● Cons
■ Expensive
■ Large pixels (~1 mm versus ~0.2 mm)
■ Phosphors gradually deplete
■ Less bright than CRTs, using more power
■
For more details visit http://www.howstuffworks.com/lcd4.htm
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Display Technology: DMD
● Digital Micromirror Devices (projectors)
● A DMD chip has on its surface several hundred thousand
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microscopic mirrors
Arranged in a rectangular array correspond to the pixels in the
image to be displayed.
Individually rotated ±10-12°, to an on or off state.
Fast on-off to produce grey scale
Mirrors made out of aluminium16 mm across.
Mirrors mounted on hinge, the axle is fixed and literally twists
in the middle
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Display Technology: DMDs
■ Microelectromechanical (MEM) devices, fabricated with
VLSI techniques
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Display Technology: DMDs
● DMDs are truly digital pixels
● Vary grey levels by modulating pulse length
● Color: multiple chips, or color-wheel
● Great resolution
● Very bright
● Flicker problems
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Display Technologies:
Organic LED Arrays
● Organic Light-Emitting Diode (OLED) Arrays
■ The display of the future? Many think so.
■ OLEDs function like regular semiconductor LEDs
■ But with thin-film polymer construction:
○ Thin-film deposition of organic, light-emitting molecules through
vapor sublimation in a vacuum.
○ Dope emissive layers with fluorescent molecules to create color.
○ Not grown like a crystal, no high-temperature doping
○ Thus, easier to create large-area OLEDs
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Display Technologies:
Organic LED Arrays
● OLED pros:
■ Transparent
■ Flexible
■ Light-emitting, and quite bright (daylight visible)
■ Large viewing angle
■ Fast (< 1 microsecond off-on-off)
■ Can be made large or small
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Display Technologies:
Organic LED Arrays
● OLED cons:
■ Not quite there yet (96x64 displays)
○ Cell phones (especially back display)
■ Not very robust, display lifetime a key issue
■ Currently only passive matrix displays
○ Passive matrix: Pixels are illuminated in scanline order (like a raster
display), but the lack of phosphorescence causes flicker
○ Active matrix: A polysilicate layer provides thin film transistors at each
pixel, allowing direct pixel access and constant illumination
■ Hard to compete with LCDs, a moving target
■ See http://www.youtube.com/watch?v=mGVbEBOzACs for more info
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Framebuffers
● So far we’ve talked about the physical display device
● How does the interface between the device and the
computer’s notion of an image look?
● Framebuffer: A memory array in which the computer
stores an image
■ On most computers, separate memory bank from main
memory (why?)
■ Many different variations, motivated by cost of memory
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Display Technologies: CRTs
● Raster Displays
■ Raster: A rectangular array of points or dots
■ Pixel: One dot or picture element of the raster
■ Scanline: A row of pixels
■ Rasterize: find the set of pixels corresponding to a 2D
shape (line, circle, polygon)
■ Scan Conversion: Rasterize
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