CGMB214: Introduction to Computer Graphics Topic 2 Overview of Graphics System

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 Cathode Ray Tube Technology

Refresh Cathode Ray Tubes Video Display Devices Video Display Devices CRT Technology Flat Panel Displays Refresh Cathode Ray Tubes Raster Scan Display Random Scan Display Colour CRT Monitor Non Emissive Display Emissive Display

Refresh Cathode Ray Tubes Focusing System Electron Gun Magnetic Deflection Coils Phosphor-Coated Screen Base Connector Pins

Refresh Cathode Ray Tubes: Electron Gun Heating Filament Control Grid Accelerating Anode Focusing Anode Cathode

Refresh Cathode Ray Tubes: Electron Gun

Refresh Cathode Ray Tubes: Electron Gun 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 Control Grid Focusing Anode Heating Filament Accelerating Anode Cathode

Refresh Cathode Ray Tubes: Electron Gun 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 Control Grid Focusing Anode Heating Filament Accelerating Anode Cathode

Refresh Cathode Ray Tubes Magnetic Deflection Coils Phosphor-Coated Screen Connector Pins Base Electron Gun Focusing System The brightness of the of the display point is controlled by the voltage provided by the control grid in the electron gun The phosphor emits a small spot of light at each position contacted by electron beam 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.

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 line As 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 bitmap Frame 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 Zoom in

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 fast moderate slow Moderate beam speeds will emits light combination of red and green: orange and yellow Beam of FAST electron penetrates through the red layer and excites the inner green layer Beam of SLOW electron excited only the outer layer producing red Red phosphor layer Green phosphor layer

Colour CRT Monitor: Shadow Mask Colour variation is produced by varying the intensity level of the electron beams: Eg. To get yellow, blue gun need to be switch off. The three electron beams are deflect and focused as a group at a shadow mask. Here it activated a dot triangle Once all the electrons has been arranged in the shadow mask, it will be released on the correct phosphor triangle on the screen 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. 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 Electron guns Shadow mask Screen

Video Display Devices Flat Panel Displays

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 Horizontal Conductor/ Address Electrode Gas (neon, xenon, helium) Plasma Cell Vertical Conductor/ Display Electrode Plasma Cell RGB phosphor coated cells Pixel

Emissive Display:Plasma Panel Horizontal Conductor/ Address Electrode Gas (neon, xenon, helium) Vertical Conductor/ Display Electrode Plasma Cell Glass Plate The photons excite the plasma cell to give off coloured lights Ionized gas rush to electrodes, collide and emits photons Voltage difference is created between front and back The electrodes are being charged Gas in the middle is being ionized and creating plasma

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 buffer Information 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

Non Emissive Display:Liquid Crystal Display (LCD)

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 Keypads Touch pads Mice Trackballs Data gloves Scanner Reflective (print) Transparency (film) Game pads  Joysticks Light pens & sensors Tablets Force-feedback Audio/Voice Microphone MIDI (Musical Instrument Digital Interface)

Input Device Barcode reader Magnetic stripe 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 Printer Plotter Question : What is the difference? Taken 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 http://ppscad.co.uk http://www.ellenfinkelstein.com http://www.pangolin.com/ http://creativecurio.com http://www.powayusd.com http://www.cartoonstock.com http://www.diytrade.com http://www.machine-information-systems.com http://ppscad.co.uk