Hardware concept for graphics

Computer Graphics
Hardware Concepts
[Note: This presentation is a reference. For detailed
study, students must read the text book]

Video Display Devices
 Cathode Ray Tube (CRT)
 Components:
 Electron Gun  composed of heated metal
cathode and control grid
 Accelerating Anode
 Focusing System
 Deflection system
 Phosphor Screen

CRT Operation
 Heat generated in cathode boils off the electrons
 Electrons are accelerated towards phosphor screen with high
positive voltage applied at accelerating anode
 The negative voltage applied at cylindrical control grid controls the
intensity of electron beam by repealing electrons
 High negative voltage stops electron passing from the hole of control
grid while small negative voltage decreases electron passage
 Focusing system concentrates electron beam to a small spot
 In electrostatic focusing, electrons pass through positively charged
metal cylinder
 In magnetic focusing, coils are mounted outside of CRT Envelope which
produces smallest spot
 Deflection System deflects electron beam horizontally and
vertically
 Magnetic two pairs of coils
 Electrostatic  two pairs of deflection plates
 Refresh rate depends on persistence of phosphor

Raster Scan Displays
 The electron beam is swept across the screen, one row at a time
from top to bottom
 The illuminated spot pattern is created by turning on or off when
electron beam moves along each scan line
 Picture definition is stored in a memory area called Refresh
Buffer (Frame Buffer)
 Refresh Buffer holds the set of intensity values for all the screen points
 Each screen points is known as pixel (short form of picture element)
 Example: Home television sets and printers
 For bilevel system (black and white ) only 1 bit memory per pixel
is sufficient
 For color system more bits per pixel are needed
 For screen with resolution 1024 by 1024, and 24 bits per pixel (8 bits
each for RGB) requires 3 MB of storage is needed
 Refreshing rate for raster scan display is usually 60 to 80 frames
per second (i.e 1/80 or 1/60 seconds is taken for electron beam to
scan from top left corner to bottom right corner)

Random Scan Display
 Electron beam is directed to the part
of screen where picture is to be
drawn
 Picture definition is stored as set of
line-drawing commands in memory
are known as refresh display file or
simply refresh buffer
 Also known as Vector display

Color CRT Monitors
 Uses combination of phosphors that emit different colored
light (usually Red, Green and Blue)
 Two basic methods for color picture display
 Beam penetration method
 Two layers of phosphor outer red layer and inner green layer
 slow electron strikes outer to produce red and faster strikes
inner layer to produce green color while intermediate produces
orange and yellow
 Only four colors are possible
 Shadow mask method
 Has three phosphor color dots (RGB) for each pixel position
 Three electron guns one for each color dot
 A shadow mask grid with holes aligned with the phosphor dot
patterns
 Electron beams passed from a hole of shadow mask activate
the phosphor dot pattern to display color picture

Flat Panel Displays
 Emissive  converts electrical energy
to light
 Eg: plasma panels, thin-film
electroluminescent display, LEDs
 Non Emissive uses optical effects
to convert sunlight or light from other
source into graphics pattern
 Eg: Liquid Crystal Display (LCD)

EMISSIVE
 Plasma Panel (gas discharge display)
 The region between two glass plates are filled with a mixture of gases (usually
includes neon)
 Series of vertical conducting ribbon is placed on one plate and horizontal on the
other
 When firing voltage is applied between one horizontal and vertical conductor, the
gas at intersection breaks up into glowing plasma ion and electrons
 Refresh is needed
 Monochromatic device; but now are capable of displaying color and grayscale
 Thin Film electroluminescent Display
 Similar to plasma panel, but the space between glass plates is filled with
phosphor, such as zinc sulfide doped with manganese
 When electricity is passed through two electrodes, the phosphor become the
conductor in that area and the electrical energy is absorbed by manganese atom
to release the energy as a spot of light
 Good color and grayscale are hard to achieve
 Light Emitting Diode (LED)
 Diode matrix is arranged to form pixel position
 Various voltage level produces various color lights

NON Emissive
 Liquid Crystal Display (LCD)
 Uses liquid having crystalline arrangement of molecules
 The liquid crystal compounds keep the long axes of the rod shaped
molecules aligned
 Two glass plates each containing light polarizer at right angles to other
plate are placed to sandwich the liquid crystal
 Horizontal conductors in one and vertical in other plate are placed thus
intersection forms a pixel
 When no voltage is applied between conductors, the molecules are in
on state so the polarized light is twisted by the molecule thus passes
through the two plates and seen by the viewer
 When voltage is applied, the molecules are in off state, and light
passing through one plate is stopped at other thus no light is seen by
viewer
 passive matrix: voltage is applied to intersecting conductor to turn off
the pixel
 Active matrix: uses transistor to control voltage at pixel locations
 Color display is possible by using different materials or dyes and by
placing a triad of color pixels at each screen location

 3D viewing Devices
 Displays 3-D scene
 Displayed by reflects CRT image from a vibrating mirror
 As mirror vibrates it changes focal length
 The vibration is synchronized with the display of an object on CRT
so that each point in object is reflected from the mirror into a
spatial position corresponding to distance of that point from a
specified viewing position
 Stereoscopic and Virtual Reality Systems
 READ YOURSELF

Input Devices
 Keyboards
 ASCII keys are used to input text string
 Provides with features to facilitate entry of screen coordinates, menu selections or
graphics functions
 Function keys allow user to enter frequently used operations in a single stroke and
cursor cont keys are used for cursor position or picture selection
 Some keyboards consist of trackball or joystick
 Mouse
 Pointing device to position cursor
 Wheel or rollers are used to record the amount and direction of movement
 Optical mouse uses optical sensors to detect mouse motion
 One two or three buttons are included
 [Note: For operation detail, please refer to internet sites such as wikipedia]
 Trackball and Spaceball
 Joysticks
 Data Globe
 Digitizers
 Image Scanners
 Touch Panels
 Light Pens

Hard Copy Devices
 Printers
 Character Impact (Dot matrix) printers
 Similar to raster scan system
 Prints one character at a time and scans one line at a time
while for next line paper is scrolled
 Non impact
 Laser printers, ink jet, bubble jet
 In laser printers, laser beam creates a charge distribution on a
rotating drum coated with a photoelectric materials such as
selenium an tonner is applied to the drum and then transferred
to paper
 In ink jet printer, the ink is squirted in horizontal rows across a
roll of paper. The electrically charged ink stream is deflected
by an electric field to produce ot matrix patterns
 In bubble jet printers, ink is heated in a heating chamber to
produce ink bubble. The heating chamber consists of heating
filament

Hardware concept for graphics

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Hardware concept for graphics