Chapter 1 the human. Information i/o … – visual, auditory, haptic, movement Information stored in memory – sensory, short-term, long-term Information.

chapter 1

the human

the human

• Information i/o …– visual, auditory, haptic, movement

• Information stored in memory– sensory, short-term, long-term

• Information processed and applied– reasoning, problem solving, skill, error

• Emotion influences human capabilities• Each person is different

Vision

Two stages in vision

• physical reception of stimulus

• processing and interpretation of stimulus

The Eye - physical reception

• mechanism for receiving light and transforming it into electrical energy

• light reflects from objects• images are focused upside-down on retina• retina contains rods for low light vision and

cones for colour vision• ganglion cells (brain!) detect pattern and

movement

Interpreting the signal

• Size and depth– visual angle indicates how much of view object

occupies(relates to size and distance from eye)

– visual acuity is ability to perceive detail (limited)

– familiar objects perceived as constant size (in spite of changes in visual angle when far away)

– cues like overlapping help perception of size and depth

Interpreting the signal (cont)• Brightness

– subjective reaction to levels of light– affected by luminance of object– measured by just noticeable difference– visual acuity increases with luminance as does flicker

• Colour– made up of hue, intensity, saturation– cones sensitive to colour wavelengths– blue acuity is lowest– 8% males and 1% females colour blind

Interpreting the signal (cont)

• The visual system compensates for:– movement– changes in luminance

• Context is used to resolve ambiguity

• Optical illusions sometimes occur due to over compensation

Optical Illusions

the Ponzo illusion the Muller Lyer illusion

Reading• Several stages:

– visual pattern perceived– decoded using internal representation of language– interpreted using knowledge of syntax, semantics, pragmatics

• Reading involves saccades and fixations• Perception occurs during fixations• Word shape is important to recognition• Negative contrast improves reading from computer screen

Hearing• Provides information about environment:

distances, directions, objects etc.• Physical apparatus:

– outer ear – protects inner and amplifies sound– middle ear – transmits sound waves as

vibrations to inner ear– inner ear – chemical transmitters are released

and cause impulses in auditory nerve

• Sound– pitch – sound frequency– loudness – amplitude– timbre – type or quality

Hearing (cont)• Humans can hear frequencies from 20Hz to 15kHz

– less accurate distinguishing high frequencies than low.

• Auditory system filters sounds– can attend to sounds over background noise. – for example, the cocktail party phenomenon

Touch• Provides important feedback about environment.

• May be key sense for someone who is visually impaired.

• Stimulus received via receptors in the skin:– thermoreceptors – heat and cold– nociceptors – pain– mechanoreceptors – pressure

(some instant, some continuous)

• Some areas more sensitive than others e.g. fingers.

• Kinethesis - awareness of body position – affects comfort and performance

Movement• Time taken to respond to stimulus:

reaction time + movement time

• Movement time dependent on age, fitness etc.

• Reaction time - dependent on stimulus type:– visual ~ 200ms– auditory ~ 150 ms– pain ~ 700ms

• Increasing reaction time decreases accuracy in the unskilled operator but not in the skilled operator.

Movement (cont)• Fitts' Law describes the time taken to hit a screen target:

Mt = a + b log2(D/S + 1)

where: a and b are empirically determined constantsMt is movement timeD is Distance S is Size of target

Þ targets as large as possibledistances as small as possible

Memory

There are three types of memory function:

Sensory memories

Short-term memory or working memory

Long-term memory

Selection of stimuli governed by level of arousal.

sensory memory

• Buffers for stimuli received through senses– iconic memory: visual stimuli– echoic memory: aural stimuli– haptic memory: tactile stimuli

• Examples– “sparkler” trail– stereo sound

• Continuously overwritten

Short-term memory (STM)

• Scratch-pad for temporary recall

– rapid access ~ 70ms

– rapid decay ~ 200ms

– limited capacity - 7± 2 chunks

Examples

212348278493202

0121 414 2626

HEC ATR ANU PTH ETR EET

Long-term memory (LTM)• Repository for all our knowledge

– slow access ~ 1/10 second– slow decay, if any– huge or unlimited capacity

• Two types– episodic – serial memory of events– semantic – structured memory of facts,concepts, skills

semantic LTM derived from episodic LTM

Long-term memory (cont.)• Semantic memory structure

– provides access to information– represents relationships between bits of information– supports inference

• Model: semantic network– inheritance – child nodes inherit properties of parent nodes– relationships between bits of information explicit– supports inference through inheritance

LTM - semantic network

Models of LTM - Frames

• Information organized in data structures• Slots in structure instantiated with values for instance of data• Type–subtype relationships

DOG

Fixed legs: 4

Default diet: carniverous sound: bark

Variable size: colour

COLLIE

Fixed breed of: DOG type: sheepdog

Default size: 65 cm

Variable colour

Models of LTM - Scripts

Model of stereotypical information required to interpret situation

Script has elements that can be instantiated with values for context

Script for a visit to the vet

Entry conditions: dog illvet openowner has money

Result: dog betterowner poorervet richer

Props: examination tablemedicineinstruments

Roles: vet examines diagnoses treatsowner brings dog in pays takes dog out

Scenes: arriving at receptionwaiting in roomexaminationpaying

Tracks: dog needs medicinedog needs operation

Models of LTM - Production rules

Representation of procedural knowledge.

Condition/action rules if condition is matchedthen use rule to determine action.

IF dog is wagging tailTHEN pat dog

IF dog is growlingTHEN run away

LTM - Storage of information• rehearsal

– information moves from STM to LTM

• total time hypothesis– amount retained proportional to rehearsal time

• distribution of practice effect– optimized by spreading learning over time

• structure, meaning and familiarity– information easier to remember

LTM - Forgettingdecay

– information is lost gradually but very slowly

interference– new information replaces old: retroactive interference– old may interfere with new: proactive inhibition

so may not forget at all memory is selective …

… affected by emotion – can subconsciously `choose' to forget

LTM - retrieval

recall – information reproduced from memory can be assisted by cues, e.g.

categories, imagery

recognition– information gives knowledge that it has been seen before– less complex than recall - information is cue

Thinking

Reasoningdeduction, induction, abduction

Problem solving

Deductive Reasoning• Deduction:

– derive logically necessary conclusion from given premises.e.g. If it is Friday then she will go to work

It is FridayTherefore she will go to work.

• Logical conclusion not necessarily true:e.g. If it is raining then the ground is dry

It is rainingTherefore the ground is dry

Deduction (cont.)

• When truth and logical validity clash …e.g. Some people are babies

Some babies cryInference - Some people cry

Correct?

• People bring world knowledge to bear

Inductive Reasoning• Induction:

– generalize from cases seen to cases unseen e.g. all elephants we have seen have trunks

therefore all elephants have trunks.

• Unreliable:– can only prove false not true

… but useful!

• Humans not good at using negative evidence e.g. Wason's cards.

Wason's cards

Is this true?

How many cards do you need to turn over to find out?

…. and which cards?

If a card has a vowel on one side it has an even number on the other

7 E 4 K

Abductive reasoning

• reasoning from event to cause e.g. Sam drives fast when drunk. If I see Sam driving fast, assume drunk.

• Unreliable:– can lead to false explanations

Problem solving• Process of finding solution to unfamiliar task using knowledge.

• Several theories.

• Gestalt– problem solving both productive and reproductive– productive draws on insight and restructuring of problem– attractive but not enough evidence to explain `insight' etc.– move away from behaviourism and led towards information processing

theories

Problem solving (cont.)Problem space theory

– problem space comprises problem states– problem solving involves generating states using legal operators– heuristics may be employed to select operators

e.g. means-ends analysis– operates within human information processing system

e.g. STM limits etc.– largely applied to problem solving in well-defined areas

e.g. puzzles rather than knowledge intensive areas

Problem solving (cont.)• Analogy

– analogical mapping:• novel problems in new domain?• use knowledge of similar problem from similar domain

– analogical mapping difficult if domains are semantically different

• Skill acquisition– skilled activity characterized by chunking

• lot of information is chunked to optimize STM– conceptual rather than superficial grouping of problems– information is structured more effectively

Errors and mental modelsTypes of error

• slips – right intention, but failed to do it right– causes: poor physical skill,inattention etc.– change to aspect of skilled behaviour can cause slip

• mistakes– wrong intention– cause: incorrect understanding

humans create mental models to explain behaviour.if wrong (different from actual system) errors can occur

Emotion

• Various theories of how emotion works– James-Lange: emotion is our interpretation of a physiological

response to a stimuli– Cannon: emotion is a psychological response to a stimuli– Schacter-Singer: emotion is the result of our evaluation of our

physiological responses, in the light of the whole situation we are in

• Emotion clearly involves both cognitive and physical responses to stimuli

Emotion (cont.)

The biological response to physical stimuli is called affect Affect influences how we respond to situations positive creative problem solving negative narrow thinking

“Negative affect can make it harder to do even easy tasks; positive affect can make it easier to do difficult tasks”

(Donald Norman)

Emotion (cont.)

• Implications for interface design– stress will increase the difficulty of problem

solving– relaxed users will be more forgiving of

shortcomings in design– aesthetically pleasing and rewarding interfaces

will increase positive affect

Individual differences• long term

– sex, physical and intellectual abilities• short term

– effect of stress or fatigue• changing

– age

Ask yourself:will design decision exclude section of user population?

Psychology and the Design of Interactive System

• Some direct applications– e.g. blue acuity is poor

blue should not be used for important detail

• However, correct application generally requires understanding of context in psychology, and an understanding of particular experimental conditions

• A lot of knowledge has been distilled in– guidelines (chap 7)– cognitive models (chap 12)– experimental and analytic evaluation techniques (chap 9)

chapter 2

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 outdevices, paper,sensors, etc.

what can it do?memory, processing,

networks

A ‘typical’ computer system• screen, or monitor, on which there are windows• keyboard• mouse/trackpad

• variations– desktop– laptop– PDA

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

window 1

window 2

12-37pm

?

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?

– PC– TV, VCR, DVD, HiFi,

cable/satellite TV– microwave, cooker,

washing machine– central heating– security system

can you think of more?

in your pockets?

– PDA– phone, camera– smart card, card with

magnetic strip?– electronic car key– USB memory

try your pockets and 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

sensorsand deviceseverywhere

text entry deviceskeyboards (QWERTY et al.)

chord keyboards, phone padshandwriting, 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

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)

2 3 4 5 6 7 8 9 0

Q W E R T Y U I

1

O P

S D F H J LA G K

Z X C V B N M , .

SPACE

alternative keyboard layoutsAlphabetic

– 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 keyboardsonly a few keys - four or 5letters typed as combination of keypressescompact size

– ideal for portable applicationsshort learning time

– keypresses reflect letter shapefast

– once you have trained

BUT - social resistance, plus fatigue after extended useNEW – niche market for some wearables

phone pad and T9 entry• use numeric keys with

multiple presses2 – a b c 6 - m n o3 - d e f 7 - p q r s4 - g h i 8 - t u v5 - j k l 9 - w x y z

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

not the same!!

ATM like phone

4 5 6

7 8 9

*0 #

1 2 3

4 5 6

1 2 3

0 . =

7 8 9

telephone calculator

positioning, pointing and drawingmouse, 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 cursorScreen 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

Trackball and thumbwheels Trackball

– ball is rotated inside static housing• like an upside 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

– indirectpressure of stick = velocity of movement

– buttons for selection on top or on front like a trigger

– often used for computer gamesaircraft 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

Digitizing tablet• Mouse like-device with cross hairs

• used on special surface - rather like stylus

• very accurate- used for digitizing maps

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 displaysdigital paper

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 gun

focussing and deflection

electron beam

phosphor- coated screen

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

special displaysRandom Scan (Directed-beam refresh, vector display)

– draw the lines to be displayed directly– no jaggies– lines need to be constantly redrawn– rarely used except in special instruments

Direct view storage tube (DVST)

– Similar to random scan but persistent => no flicker– Can be incrementally updated but not selectively erased– Used in analogue storage oscilloscopes

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 screem

• in all cases … the location matters– meaning of information or interaction is related to the location

• small displays beside office doors• handwritten notes left using stylus• office owner reads notes using web interface

Hermes a situated display

small displaysbeside

office doors

handwrittennotes left

using stylus

office ownerreads notes

using web interface

Digital paper• what?

– thin flexible sheets– updated electronically– but retain display

• how?– small spheres turned– or channels with coloured liquid

and contrasting spheres– rapidly developing area

appearance

crosssection

virtual reality and 3D interactionpositioning in 3D space

moving and graspingseeing 3D (helmets and caves)

positioning in 3D space• cockpit and virtual controls

– steering wheels, knobs and dials … just like real!• the 3D mouse

– six-degrees of movement: x, y, z + roll, pitch, yaw • data glove

– fibre optics used to detect finger position• VR helmets

– detect head motion and possibly eye gaze• whole body tracking

– accelerometers strapped to limbs or reflective dots and video processing

pitch, yaw and roll

pitch

yaw

roll

3D displays

• desktop VR– ordinary screen, mouse or keyboard control– perspective and motion give 3D effect

• seeing in 3D– use stereoscopic vision– VR helmets– screen plus shuttered specs, etc.

VR headsets

• small TV screen for each eye• slightly different angles• 3D effect

VR motion sickness

• time delay– move head … lag … display moves– conflict: head movement vs. eyes

• depth perception– headset gives different stereo distance– but all focused in same plane– conflict: eye angle vs. focus

• conflicting cues => sickness– helps motivate improvements in technology

simulators and VR caves

• scenes projected on walls• realistic environment• hydraulic rams!• real controls• other people

physical controls, sensors etc.special displays and gauges

sound, touch, feel, smellphysical controls

environmental and bio-sensing

dedicated displays

• analogue representations:– dials, gauges, lights, etc.

• digital displays:– small LCD screens, LED lights, etc.

• head-up displays – found in aircraft cockpits– show most important controls

… depending on context

Sounds

• beeps, bongs, clonks, whistles and whirrs

• used for error indications

• confirmation of actions e.g. keyclick

Touch, feel, smell

• touch and feeling important– in games … vibration, force feedback– in simulation … feel of surgical instruments– called haptic devices

• texture, smell, taste– current technology very limited

BMW iDrive• for controlling menus• feel small ‘bumps’ for each item• makes it easier to select options by feel • uses haptic technology from Immersion Corp.

physical controls

• specialist controls needed …– industrial controls, consumer products, etc.

large buttonsclear dials

tiny buttons

multi-functioncontrol

easy-cleansmooth buttons

Environment and bio-sensing

• sensors all around us– car courtesy light – small switch on door– ultrasound detectors – security, washbasins– RFID security tags in shops– temperature, weight, location

• … and even our own bodies …– iris scanners, body temperature, heart rate,

galvanic skin response, blink rate

paper: printing and scanningprint technology

fonts, page description, WYSIWYGscanning, OCR

Printing

• image made from small dots– allows any character set or graphic to be printed,

• critical features:– resolution

• size and spacing of the dots• measured in dots per inch (dpi)

– speed• usually measured in pages per minute

– cost!!

Types of dot-based printers• dot-matrix printers

– use inked ribbon (like a typewriter– line of pins that can strike the ribbon, dotting the paper.– typical resolution 80-120 dpi

• ink-jet and bubble-jet printers– tiny blobs of ink sent from print head to paper– typically 300 dpi or better .

• laser printer– like photocopier: dots of electrostatic charge deposited on drum, which picks

up toner (black powder form of ink) rolled onto paper which is then fixed with heat

– typically 600 dpi or better.

Printing in the workplace• shop tills

– dot matrix– same print head used for several paper rolls– may also print cheques

• thermal printers– special heat-sensitive paper– paper heated by pins makes a dot– poor quality, but simple & low maintenance– used in some fax machines

Fonts• Font – the particular style of text

Courier font Helvetica font Palatino font

Times Roman font• §´ ¿ ¿~ µº Â Ä (special symbol)

• Size of a font measured in points (1 pt about 1/72”)(vaguely) related to its height

This is ten point Helvetica This is twelve point

This is fourteen point This is eighteen point

and this is twenty-four point

Fonts (ctd)Pitch

– fixed-pitch – every character has the same width e.g. Courier

– variable-pitched – some characters wider e.g. Times Roman – compare the ‘i’ and the “m”

Serif or Sans-serif– sans-serif – square-ended strokes

e.g. Helvetica

– serif – with splayed ends (such as) e.g. Times Roman or Palatino

Readability of text

• lowercase– easy to read shape of words

• UPPERCASE– better for individual letters and non-words

e.g. flight numbers: BA793 vs. ba793

• serif fonts– helps your eye on long lines of printed text– but sans serif often better on screen

Page Description Languages• Pages very complex

– different fonts, bitmaps, lines, digitised photos, etc.

• Can convert it all into a bitmap and send to the printer… but often huge !

• Alternatively Use a page description language– sends a description of the page can be sent,– instructions for curves, lines, text in different styles, etc.– like a programming language for printing!

• PostScript is the most common

Screen and page• WYSIWYG

– what you see is what you get– aim of word processing, etc.

• but …– screen: 72 dpi, landscape image– print: 600+ dpi, portrait

• can try to make them similarbut never quite the same

• so … need different designs, graphics etc, for screen and print

Scanners• Take paper and convert it into a bitmap

• Two sorts of scanner– flat-bed: paper placed on a glass plate, whole page converted into bitmap– hand-held: scanner passed over paper, digitising strip typically 3-4” wide

• Shines light at paper and note intensity of reflection– colour or greyscale

• Typical resolutions from 600–2400 dpi

Scanners (ctd)

Used in

– desktop publishing for incorporating photographs and other images

– document storage and retrieval systems, doing away with paper storage

+ special scanners for slides and photographic negatives

Optical character recognition

• OCR converts bitmap back into text• different fonts

– create problems for simple “template matching” algorithms

– more complex systems segment text, decompose it into lines and arcs, and decipher characters that way

• page format– columns, pictures, headers and footers

Paper-based interaction• paper usually regarded as output only

• can be input too – OCR, scanning, etc.

• Xerox PaperWorks– glyphs – small patterns of /\\//\\\

• used to identify forms etc.• used with scanner and fax to control applications

• more recently– papers micro printed - like wattermarks

• identify which sheet and where you are– special ‘pen’ can read locations

• know where they are writing

memoryshort term and long term

speed, capacity, compressionformats, access

Short-term Memory - RAM• Random access memory (RAM)

– on silicon chips– 100 nano-second access time– usually volatile (lose information if power turned off)– data transferred at around 100 Mbytes/sec

• Some non-volatile RAM used to store basic set-up information

• Typical desktop computers:64 to 256 Mbytes RAM

Long-term Memory - disks• magnetic disks

– floppy disks store around 1.4 Mbytes– hard disks typically 40 Gbytes to 100s of Gbytes

access time ~10ms, transfer rate 100kbytes/s

• optical disks– use lasers to read and sometimes write– more robust that magnetic media– CD-ROM

- same technology as home audio, ~ 600 Gbytes– DVD - for AV applications, or very large files

Blurring boundaries

• PDAs– often use RAM for their main memory

• Flash-Memory– used in PDAs, cameras etc.– silicon based but persistent– plug-in USB devices for data transfer

speed and capacity• what do the numbers mean?

• some sizes (all uncompressed) …– this book, text only ~ 320,000 words, 2Mb– the Bible ~ 4.5 Mbytes– scanned page ~ 128 Mbytes

• (11x8 inches, 1200 dpi, 8bit greyscale)– digital photo ~ 10 Mbytes

• (2–4 mega pixels, 24 bit colour) – video ~ 10 Mbytes per second

• (512x512, 12 bit colour, 25 frames per sec)

virtual memory• Problem:

– running lots of programs + each program large– not enough RAM

• Solution - Virtual memory :– store some programs temporarily on disk– makes RAM appear bigger

• But … swopping– program on disk needs to run again– copied from disk to RAM– s l o w s t h i n g s d o w n

Compression• reduce amount of storage required• lossless

– recover exact text or image – e.g. GIF, ZIP– look for commonalities:

• text: AAAAAAAAAABBBBBCCCCCCCC 10A5B8C• video: compare successive frames and store change

• lossy– recover something like original – e.g. JPEG, MP3– exploit perception

• JPEG: lose rapid changes and some colour• MP3: reduce accuracy of drowned out notes

Storage formats - text• ASCII - 7-bit binary code for to each letter and character• UTF-8 - 8-bit encoding of 16 bit character set• RTF (rich text format)

- text plus formatting and layout information• SGML (standardized generalised markup language)

- documents regarded as structured objects • XML (extended markup language)

- simpler version of SGML for web applications

Storage formats - media• Images:

– many storage formats :(PostScript, GIFF, JPEG, TIFF, PICT, etc.)

– plus different compression techniques(to reduce their storage requirements)

• Audio/Video– again lots of formats :

(QuickTime, MPEG, WAV, etc.)– compression even more important– also ‘streaming’ formats for network delivery

methods of access• large information store

– long time to search => use index– what you index -> what you can access

• simple index needs exact match• forgiving systems:

– Xerox “do what I mean” (DWIM)– SOUNDEX – McCloud ~ MacCleod

• access without structure …– free text indexing (all the words in a document)– needs lots of space!!

processing and networksfinite speed (but also Moore’s law)

limits of interactionnetworked computing

Finite processing speed• Designers tend to assume fast processors, and make interfaces more and

more complicated

• But problems occur, because processing cannot keep up with all the tasks it needs to do– cursor overshooting because system has buffered keypresses– icon wars - user clicks on icon, nothing happens, clicks on another, then system

responds and windows fly everywhere

• Also problems if system is too fast - e.g. help screens may scroll through text much too rapidly to be read

Moore’s law

• computers get faster and faster!• 1965 …

– Gordon Moore, co-founder of Intel, noticed a pattern– processor speed doubles every 18 months– PC … 1987: 1.5 Mhz, 2002: 1.5 GHz

• similar pattern for memory– but doubles every 12 months!!– hard disk … 1991: 20Mbyte : 2002: 30 Gbyte

• baby born today– record all sound and vision– by 70 all life’s memories stored in a grain of dust!

the myth of the infinitely fast machine

• implicit assumption … no delaysan infinitely fast machine

• what is good design for real machines?• good example … the telephone :

– type keys too fast– hear tones as numbers sent down the line– actually an accident of implementation– emulate in deisgn

Limitations on interactive performance

Computation bound– Computation takes ages, causing frustration for the user

Storage channel bound– Bottleneck in transference of data from disk to memory

Graphics bound– Common bottleneck: updating displays requires a lot of effort - sometimes

helped by adding a graphics co-processor optimised to take on the burden

Network capacity– Many computers networked - shared resources and files, access to printers

etc. - but interactive performance can be reduced by slow network speed

Networked computing Networks allow access to …

– large memory and processing– other people (groupware, email)– shared resources – esp. the web

Issues– network delays – slow feedback– conflicts - many people update data– unpredictability

The internet• history …

– 1969: DARPANET US DoD, 4 sites– 1971: 23; 1984: 1000; 1989: 10000

• common language (protocols):– TCP – Transmission Control protocol

• lower level, packets (like letters) between machines– IP – Internet Protocol

• reliable channel (like phone call) between programs on machines– email, HTTP, all build on top of these