TOPIC 2OVERVIEW OF GRAPHICS SYSTEM

CGMB214: Introduction to Computer Graphics

Objectives

To provide an understanding on the basic feature of graphic hardware components.

To provide an understanding on the operations of a video display device.

CATHODE RAY TUBE TECHNOLOGY

Video Display Devices

Video Display Devices

Video Display Devices

CRT Technology Flat Panel Displays

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e Ray Tubes

Raster Scan

Display

Random Scan Display

Colour CRT

MonitorNon Emissive

Display

Emissive Display

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Connector Pins

Base

Electron Gun

Focusing System

Magnetic Deflection

Coils

Phosphor-Coated Screen

Refresh Cathode Ray Tubes: Electron Gun

Heating Filament

Cathode

Control Grid

Focusing Anode

Accelerating Anode

Refresh Cathode Ray Tubes: Electron Gun

Refresh Cathode Ray Tubes: Electron Gun

Heating Filament

CathodeControl

GridFocusing Anode

Accelerating Anode

Current is directed through filament to supply heat

Electron is being emitted from the hot cathode surface

Control grid is a metal cylinder that is controlled by voltage.

A high negative voltage, will repel electron and stop them from

passing

A smaller negative decrease the number of electron passing

through

Refresh Cathode Ray Tubes: Electron Gun

Heating Filament

CathodeControl

GridFocusing Anode

Accelerating Anode

Once an electron is being released and the correct amount of voltage

is being supplied by the control grid, the electron will move in a straight line through the control

grid

The focusing anode which is charged with hundreds of positive volts, will force the

electron beam to converge to it. However, since there are two anode attracting the

electron, the electron will continue moving in a straight line

The accelerating anode which is charged with thousand of positive volts will have greater force on attracting the electron

beam to converge to it. As focusing anode, the built of the accelerating anode make

sure the electron will continue moving in a straight line

Refresh Cathode Ray Tubes

Connector Pins

BaseElectron

GunFocusing System

Magnetic Deflection

Coils

Phosphor-Coated Screen

Once the electron beam is emitted by the electron, it will pass through focusing and deflection system that direct the beam

toward a specific position on the phosphor-coated screen.

The phosphor emits a small spot of light at each position contacted by electron beam

The brightness of the of the display point is controlled by the voltage provided by the control grid in the electron gun

Refresh Cathode Ray Tubes

Resolution A max number of points that can be displayed without

overlap on CRT Typically 1028X1024 High resolution means high definition

Persistence How long the phosphors will emit light after beam

goes Phosphor with low persistence require higher refresh

rate to prevent flicker

Refresh Cathode Ray Tubes

Raster Scan Displays

The most common type of graphics monitor that employs CRT

The electron beam is swept across the screen one row at a time, from top to bottom

Each row is referred as a scan lineAs the electron beam moves across a scan

line, the beam intensity is turned on and off to create a pattern of illuminated spots

Screen is divided into smallest element of a rectangular array called pixel or pel (picture element)

Raster Scan Displays

Raster Scan Displays

Screen Display

Pixels/pels

Raster Scan Displays

Raster system commonly characterized by their resolution, which is the number of pixel positions that can be plotted

Another property of video monitors is aspect ratio: number of pixel columns divided by the number of

scan lines that can be displayed by the system number of horizontal points to vertical points (or vice

versa) necessary to produce equal-length lines in both directions on the screen

Raster Scan Displays

Picture definition is stored as set of color values for screen points in memory area called refresh buffer or color buffer or frame buffer (frame refers to total screen area).

Frame buffer with one bit per pixel is called bitmapFrame buffer with multiple bits per pixel is a

pixmap.Refresh rates are described in units of cycles per

second (Hertz) where a cycle corresponds to one frame. Raster scan displays normally perform refreshing at the rate of

60-80 Hz

Raster Scan Displays

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Random Scan Display

Electron beam is focussed only where lines need to be drawn

Random-scan also known as vector display or stroke-writing display or calligraphic displays

Scene definition stored in a display list as a set of line drawing instruction

Scene is drawn by cycling through the display list drawing one line at a time

Random Scan Display

Higher resolution than raster-scan and draw a smoother line because the path beam follows the line path

Designed for specialised line-drawing application e.g. CAD

Random Scan Displays

Random Scan Display

Zoom in

Colour CRT Monitor

Two ways of displaying colour: Beam penetration

2 layers of phosphors (red and green) Colour depends on the speed of the electron beams Non-expensive way to get colour

Shadow mask Used in raster scan Use 3 phosphor colour dots at each pixel (RGB) CRT needs to have 3 electron guns

Colour CRT Monitor: Beam Penetration

slow

Beam of SLOW electron excited only the outer layer producing red

moderatefast

Beam of FAST electron penetrates through the

red layer and excites the inner green layer

Moderate beam speeds will emits light

combination of red and green: orange and yellow

Red phosphor layer

Green phosphor layer

Colour CRT Monitor: Shadow Mask

Each pixel position has three phosphor colour dot: Red, Green and Blue (RGB). Each phosphor emits lights according to

their colour.

Shadow mask CRT needs 3 electron guns, one for each colour dot.

Electron guns

Shadow mask

Screen

The three electron beams are deflect and focused as a group at a shadow mask. Here

it activated a dot triangle

The phosphor dots in the triangles are arranged so that each electron beam can only activate its corresponding colour dot

when it passes the shadow mask

Once all the electrons has been arranged in the shadow mask, it will be released on

the correct phosphor triangle on the screen

Colour variation is produced by varying the intensity level of the electron beams:Eg. To get yellow, blue gun need to be

switch off.

FLAT PANEL DISPLAYS

Video Display Devices

Flat Panel Displays

Flat Panel Displays

Refers to video devices that have reduced volume, weight and power requirement

Flat Panel Displays

Flat Panel

Display

Emissive display

Devices that converts electrical energy to

lights

Plasma Panels

Thin-film electroluminescent

displays

Light emitting diode (LED)

Non Emissive display

Uses optical effects to convert

sunlight/light into graphics

patterns

Liquid crystal device

Emissive Display:Plasma Panel

Constructed by filling a mixture of gases (usually includes neon), in the region between two glass plates.

Emissive Display:Plasma Panel

Glass Plate

Vertical Conductor/ Display Electrode

Horizontal Conductor/ Address Electrode

Gas (neon, xenon, helium)

Plasma Cell

Plasma Cell

RGB phosphor coated cells

Pixel

Emissive Display:Plasma Panel

Glass PlateVertical Conductor/ Display Electrode

Horizontal Conductor/ Address Electrode

Gas (neon, xenon, helium)Plasma

Cell

The electrodes are being charged

Voltage difference is created between front

and back

Gas in the middle is being ionized and creating plasma

Ionized gas rush to electrodes, collide and

emits photons

The photons excite the plasma cell to give off

coloured lights

Emissive Display:Thin-Film Electroluminescent

Similar in construction to plasma panels, except that the region between the glass plate is replaced with phosphor

Disadvantages: Requires more power than plasma Good colour displays are harder to achieve

Emissive Display:Light Emitting Diode (LED)

Matrix of diodes is arranged to form pixel positions in the display

Picture definition is stored in a refresh bufferInformation is read from buffer and

converted to voltage levels that are applied to the diode to produce light patterns in display

Emissive Display:Light Emitting Diode (LED)

Non Emissive Display:Liquid Crystal Display (LCD)

Produce pictures by passing polarised light from the surroundings OR from an internal light source through a liquid-crystal material that can be aligned to either BLOCK or TRANSMIT the light

Graphics Workstations and Viewing Systems

Graphics Workstations and Viewing Systems

Graphics workstations range from small general-purpose computer systems to multi-monitor facilities, often with ultra-large viewing screen Personal PC screen

resolution range from 640 x 480 to 1280 x 1024 diagonal screen lengths measure from 12 inches to over

21 inches High-definition graphics system

resolution up to 2560 x 2048 commonly used in medical imaging, air-traffic control, simulation and CAD

High-end graphics workstations also include large viewing screen often with specialized features such as stereoscopic viewing etc

Multi-panel display screens are used for applications that require “wall-size” viewing area

Graphics Workstations and Viewing Systems

Input Devices

Input Device

Keyboards   KeypadsTouch padsMice TrackballsData glovesScanner

Reflective (print) Transparency (film)

Game pads  JoysticksLight pens & sensorsTablets Force-feedback Audio/Voice

Microphone MIDI (Musical

Instrument Digital Interface)

Input Device

Barcode reader price scanner or point-of-sale (POS) scanner

Magnetic stripe reader Credit card reader , ATM – petrol station

MICR – magnetic ink character recognition Banking environment – check color copies of payroll checks or

hand-altered characters

Input Device

OCR – optical character recognition Read typewritten text - is used in high-volume

financial applications such as payment processing, check reconciliation, and billing. It is also commonly used for high-volume document management in the insurance and healthcare industries

Input Device

OMR – optical mark recognition Paper marking - used for time and attendance, labor

tracking, inventory management, voting applications, exit surveys, polling, and all manner of questionnaires and evaluation studies

Input Device

Image scanning devices / digital camera Ex. Educational environment , New car technology

Hard-Copy Devices

Hard-Copy Devices

PrinterPlotterQuestion : What is the difference?

PlotterTaken from : http://ppscad.co.uk/images/canon%20ipf650%20plotter.jpg

Graphics Software

Graphics Software

Two broad classification Special purpose packages

Design for non-programmers who want to generate pictures

They don’t have to worry about the graphics procedure E.g. CAD software, paintbrush

General programming packages Provides a library of graphics functions that can be used

in a programming language such as C/C++, Java or Fortran

E.g. OpenGL, VRML, Java2D, Java3D

References

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