CHAPTER 2 Flashcards
a computer system is made up of various elements
The Computer
text entry and pointing
input devices
screen (small&large), digital paper
output devices
special interaction and display devices
virtual reality
e.g. sound, haptic, bio-sensing
physical interaction
as output (print) and input (scan)
paper
RAM & permanent media, capacity & access
memory
speed of processing, networks
processing
to understand human–computer interaction
… need to understand computers!
Interacting with computers
screen, or monitor, on which there are windows
keyboard
mouse/trackpad
typical
variations of typical computer system
– desktop
– laptop
– PDA
How many computers in your house?
PC
– TV, VCR, DVD, HiFi,
cable/satellite TV
– microwave, cooker,
washing machine
– central heating
How many computers in your pockets?
– PDA
– phone, camera
– smart card, card with
magnetic strip?
– electronic car key
– USB memory
try your pock
keyboards (QWERTY et al.)
chord keyboards, phone pads
handwriting, speech
text entry devices
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
Keyboards
Standardised layout
but …
– non-alphanumeric keys are placed differently
– accented symbols needed for different scripts
– minor differences between UK and USA keyboards
layout – QWERTY
alternative keyboard layouts
Alphabetic and Dvorak
keys arranged in alphabetic order
– not faster for trained typists
– not faster for beginners either!
Alphabetic
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
Dvorak
designs to reduce fatigue for RSI
• for one handed use
e.g. the Maltron left-handed keyboard
special 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
Chord keyboards
use numeric keys with
multiple presses
2 – a b c 6 - m n o
3 - d e f 7 - p q r s
4 - g h i 8 - t u v
5 - j k l 9 - w x y z
hello = 4433555[pause]
phone pad
type as if single key for each letter
– use dictionary to ‘guess’ the right word
– hello = 43556 …
– but 26 -> menu ‘am’ or ‘an
T9 entry
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!
Handwriting 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
Speech recognition
for entering numbers quickly:
– calculator, PC keyboard
• for telephones
Numeric keypads
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
Two methods for detecting motion
Mechanical
Optical
Ball on underside of mouse turns as mouse is moved
– Rotates orthogonal potentiometers
– Can be used on almost any flat surface
Mechanical
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
Optical
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
Touchpad
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.
Trackball
for accurate CAD – two dials for X-Y cursor position
– for fast scrolling – single dial on mouse
Thumbwheels
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
Joystick
for laptop computers
– miniature joystick in the middle of the keyboard
Keyboard nipple
works by interrupting matrix of light beams, capacitance changes
or ultrasonic reflections
– direct pointing device
Detect the presence of finger or stylus on the screen
fast, and requires no specialised pointer
– good for menu selection
– suitable for use in hostile environment: clean and safe from
damage.
Advantages
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
Disadvantages
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
Stylus
– now rarely used
– uses light from screen to detect location
Light Pen
very direct and obvious to use
– but can obscure screen
BOTH
Mouse like-device with cross hairs
• used on special surface
- rather like stylus
• very accurate
- used for digitizing maps
Digitizing tablet
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
Eyegaze
Four keys (up, down, left, right) on keyboard.
• Very, very cheap, but slow.
• Useful for not much more than basic motion for textediting tasks.
• No standardised layout, but inverted “T”, most common
Cursor keys
cursor pads or mini-joysticks
– discrete left-right, up-down
– mainly for menu selection
in phones, TV controls etc.
bitmap screens (CRT & LCD)
large & situated displays
digital paper
display devices
screen is vast number of coloured dots
bitmap displays
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
Resolution … used (inconsistently) for
ration between width and height
– 4:3 for most screens, 16:9 for wide-screen TV
Aspect ratio
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
Colour depth:
