Chapter-3-The-Computer.pdf

chapter 3 the computer The Computer a computer system is made up of various elements each of these elements affects the interaction – input devices – text entry and pointing – output devices – screen (small&large), digital paper – virtual reality – special interaction and display devices...

chapter 3 the computer The Computer a computer system is made up of various elements each of these elements affects the interaction – input devices – text entry and pointing – output devices – screen (small&large), digital paper – virtual reality – special interaction and display devices – physical interaction – e.g. sound, haptic, bio-sensing – paper – as output (print) and input (scan) – memory – RAM & permanent media, capacity & access – processing – speed of processing, networks Interacting with computers to understand human–computer interaction … need to understand computers! what goes in and out devices, paper, sensors, etc. what can it do? memory, processing, networks  A ‘typical’ computer system ? screen, or monitor, on which there are windows keyboard window 1 mouse/trackpad window 2 variations – desktop – laptop – PDA 12-37pm the devices dictate the styles of interaction that the system supports If we use different devices, then the interface will support a different style of interaction How many … computers in your house? – hands up, … … none, 1, 2 , 3, more!! computers in your pockets? are you thinking … … PC, laptop, PDA ?? How many computers … in your house? in your pockets? – PC – PDA – TV, VCR, DVD, HiFi, – phone, camera cable/satellite TV – smart card, card with – microwave, cooker, magnetic strip? washing machine – electronic car key – central heating – USB memory – security system try your pockets and can you think of more? bags Interactivity? Long ago in a galaxy far away … batch processing – punched card stacks or large data files prepared – long wait …. – line printer output … and if it is not right … Now most computing is interactive – rapid feedback – the user in control (most of the time) – doing rather than thinking … Is faster always better? Richer interaction sensors and devices everywhere text entry devices keyboards (QWERTY et al.) chord keyboards, phone pads handwriting, speech Keyboards Most common text input device Allows rapid entry of text by experienced users Keypress closes connection, causing a character code to be sent Usually connected by cable, but can be wireless  The keyboard is still one of the most common input devices in use today. It is used for entering textual data and commands. The vast majority of keyboards have a standardized layout, and are known by the first six letters of the top row of alphabetical keys, QWERTY QWERTY KEYBOARD alphanumeric chord/chorded keyboard Keypad/T9 Handwriting recognition Speech recognition Figure 3.2 TOP: QWERTY and Alphabetic Keyboard. Bottom: DVORAK and Chord/Chorded Keyboard Figure 3.3 Keypad and T9, Handwriting recognition and voice recognition layout – QWERTY Standardised layout but … – non-alphanumeric keys are placed differently – accented symbols needed for different scripts – minor differences between UK and USA keyboards QWERTY arrangement not optimal for typing – layout to prevent typewriters jamming! Alternative designs allow faster typing but large social base of QWERTY typists produces reluctance to change. QWERTY (ctd) 1 2 3 4 5 6 7 8 9 0 Q W E R T Y U I O P A S D F G H J K L Z X C V B N M ,. SPACE alternative keyboard layouts Alphabetic – keys arranged in alphabetic order – not faster for trained typists – not faster for beginners either! Dvorak – common letters under dominant fingers – biased towards right hand – common combinations of letters alternate between hands – 10-15% improvement in speed and reduction in fatigue – But - large social base of QWERTY typists produce market pressures not to change special keyboards designs to reduce fatigue for RSI for one handed use e.g. the Maltron left-handed keyboard Chord keyboards only a few keys - four or 5 letters typed as combination of keypresses compact size – ideal for portable applications short learning time – keypresses reflect letter shape fast – once you have trained BUT - social resistance, plus fatigue after extended use NEW – niche market for some wearables phone pad and T9 entry use numeric keys with multiple presses 2 –abc 6 - mno 3 -def 7 - pqrs 4 -ghi 8 - tuv 5 -jkl 9 - wxyz hello = 4433555[pause]555666 surprisingly fast! T9 predictive entry – type as if single key for each letter – use dictionary to ‘guess’ the right word – hello = 43556 … – but 26 -> menu ‘am’ or ‘an’ Handwriting recognition Text can be input into the computer, using a pen and a digesting tablet – natural interaction Technical problems: – capturing all useful information - stroke path, pressure, etc. in a natural manner – segmenting joined up writing into individual letters – interpreting individual letters – coping with different styles of handwriting Used in PDAs, and tablet computers … … leave the keyboard on the desk! Speech recognition Improving rapidly Most successful when: – single user – initial training and learns peculiarities – limited vocabulary systems Problems with – external noise interfering – imprecision of pronunciation – large vocabularies – different speakers Numeric keypads for entering numbers quickly: – calculator, PC keyboard for telephones 1 2 3 7 8 9 not the same!! 4 5 6 4 5 6 7 8 9 1 2 3 ATM like phone 0 # 0. = * telephone calculator positioning, pointing and drawing mouse, touchpad trackballs, joysticks etc. touch screens, tablets eyegaze, cursors the Mouse Handheld pointing device – very common – easy to use Two characteristics – planar movement – buttons (usually from 1 to 3 buttons on top, used for making a selection, indicating an option, or to initiate drawing etc.) the mouse (ctd) Mouse located on desktop – requires physical space – no arm fatigue Relative movement only is detectable. Movement of mouse moves screen cursor Screen cursor oriented in (x, y) plane, mouse movement in (x, z) plane … … an indirect manipulation device. – device itself doesn’t obscure screen, is accurate and fast. – hand-eye coordination problems for novice users How does it work? Two methods for detecting motion Mechanical – Ball on underside of mouse turns as mouse is moved – Rotates orthogonal potentiometers – Can be used on almost any flat surface Optical – light emitting diode on underside of mouse – may use special grid-like pad or just on desk – less susceptible to dust and dirt – detects fluctuating alterations in reflected light intensity to calculate relative motion in (x, z) plane Even by foot … some experiments with the footmouse – controlling mouse movement with feet … – not very common :-) but foot controls are common elsewhere: – car pedals – sewing machine speed control – organ and piano pedals Touchpad small touch sensitive tablets ‘stroke’ to move mouse pointer used mainly in laptop computers good ‘acceleration’ settings important – fast stroke lots of pixels per inch moved initial movement to the target – slow stroke less pixels per inch for accurate positioning Figure 3.4. Top, Touch pad. Below, Nipple. Right, Thumbwheel/Trackball Figure 3.5 From left to right: digitizing tablet, eye gaze, touchscreen and joy stick Trackball and thumbwheels Trackball – ball is rotated inside static housing like an upsdie down mouse! – relative motion moves cursor – indirect device, fairly accurate – separate buttons for picking – very fast for gaming – used in some portable and notebook computers. Thumbwheels … – for accurate CAD – two dials for X-Y cursor position – for fast scrolling – single dial on mouse Joystick and keyboard nipple Joystick – indirect pressure of stick = velocity of movement – buttons for selection on top or on front like a trigger – often used for computer games aircraft controls and 3D navigation Keyboard nipple – for laptop computers – miniature joystick in the middle of the keyboard Touch-sensitive screen Detect the presence of finger or stylus on the screen. – works by interrupting matrix of light beams, capacitance changes or ultrasonic reflections – direct pointing device Advantages: – fast, and requires no specialised pointer – good for menu selection – suitable for use in hostile environment: clean and safe from damage. Disadvantages: – finger can mark screen – imprecise (finger is a fairly blunt instrument!) difficult to select small regions or perform accurate drawing – lifting arm can be tiring Stylus and light pen Stylus – small pen-like pointer to draw directly on screen – may use touch sensitive surface or magnetic detection – used in PDA, tablets PCs and drawing tables Light Pen – now rarely used – uses light from screen to detect location BOTH … – very direct and obvious to use – but can obscure screen  Eyegaze control interface by eye gaze direction – e.g. look at a menu item to select it uses laser beam reflected off retina – … a very low power laser! mainly used for evaluation (ch x) potential for hands-free control high accuracy requires headset cheaper and lower accuracy devices available sit under the screen like a small webcam Cursor keys Four keys (up, down, left, right) on keyboard. Very, very cheap, but slow. Useful for not much more than basic motion for text- editing tasks. No standardised layout, but inverted “T”, most common Discrete positioning controls in phones, TV controls etc. – cursor pads or mini-joysticks – discrete left-right, up-down – mainly for menu selection  display devices bitmap screens (CRT & LCD) large & situated displays digital paper Figure 3.6, left, top, clockwise: punched card, paper tape, folded and banks of lights bitmap displays screen is vast number of coloured dots resolution and colour depth Resolution … used (inconsistently) for – number of pixels on screen (width x height) e.g. SVGA 1024 x 768, PDA perhaps 240x400 – density of pixels (in pixels or dots per inch - dpi) typically between 72 and 96 dpi Aspect ratio – ration between width and height – 4:3 for most screens, 16:9 for wide-screen TV Colour depth: – how many different colours for each pixel? – black/white or greys only – 256 from a pallete – 8 bits each for red/green/blue = millions of colours anti-aliasing Jaggies – diagonal lines that have discontinuities in due to horizontal raster scan process. Anti-aliasing – softens edges by using shades of line colour – also used for text Cathode ray tube Stream of electrons emitted from electron gun, focused and directed by magnetic fields, hit phosphor-coated screen which glows used in TVs and computer monitors electron beam electron gun focussing and deflection phosphor- coated screen Figure 3.7. From left to right: Cathode ray tube, LCD, LED and Plasma Figure 3.8 Digital Paper Health hazards of CRT ! X-rays: largely absorbed by screen (but not at rear!) UV- and IR-radiation from phosphors: insignificant levels Radio frequency emissions, plus ultrasound (~16kHz) Electrostatic field - leaks out through tube to user. Intensity dependant on distance and humidity. Can cause rashes. Electromagnetic fields (50Hz-0.5MHz). Create induction currents in conductive materials, including the human body. Two types of effects attributed to this: visual system - high incidence of cataracts in VDU operators, and concern over reproductive disorders (miscarriages and birth defects). Health hints … do not sit too close to the screen do not use very small fonts do not look at the screen for long periods without a break do not place the screen directly in front of a bright window work in well-lit surroundings « Take extra care if pregnant. but also posture, ergonomics, stress Liquid crystal displays Smaller, lighter, and … no radiation problems. Found on PDAs, portables and notebooks, … and increasingly on desktop and even for home TV also used in dedicted displays: digital watches, mobile phones, HiFi controls How it works … – Top plate transparent and polarised, bottom plate reflecting. – Light passes through top plate and crystal, and reflects back to eye. – Voltage applied to crystal changes polarisation and hence colour – N.B. light reflected not emitted => less eye strain large displays used for meetings, lectures, etc. technology plasma – usually wide screen video walls – lots of small screens together projected – RGB lights or LCD projector – hand/body obscures screen – may be solved by 2 projectors + clever software back-projected – frosted glass + projector behind situated displays displays in ‘public’ places – large or small – very public or for small group display only – for information relevant to location or interactive – use stylus, touch sensitive screen in all cases … the location matters – meaning of information or interaction is related to the location  Hermes a situated display small displays beside office doors handwritten notes left using stylus small displays beside office owner reads notes using web interface office doors handwritten office owner notes left reads notes using stylus using web interface Digital paper appearance what? – thin flexible sheets – updated electronically cross section – but retain display how? – small spheres turned – or channels with coloured liquid and contrasting spheres – rapidly developing area