10 - Interaction - display -.pdf

Chp 2-4: HCI Concepts: Human, Computer, Interaction SE234: Human Computer Interaction DISPLAY DEVICES  bitmap screens (CRT & LCD)  large & situated displays digital paper ©PRISCILLA OLAWALE (MSC) SPRING2024...

Chp 2-4: HCI Concepts: Human, Computer, Interaction SE234: Human Computer Interaction DISPLAY DEVICES  bitmap screens (CRT & LCD)  large & situated displays digital paper ©PRISCILLA OLAWALE (MSC) SPRING2024 2 bitmap displays screen is vast number of coloured dots ©PRISCILLA OLAWALE (MSC) SPRING2024 3 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 ©PRISCILLA OLAWALE (MSC) SPRING2024 4  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 ©PRISCILLA OLAWALE (MSC) SPRING2024 5 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 ©PRISCILLA OLAWALE (MSC) SPRING2024 6 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). ©PRISCILLA OLAWALE (MSC) SPRING2024 7 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 ©PRISCILLA OLAWALE (MSC) SPRING2024 8 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 ©PRISCILLA OLAWALE (MSC) SPRING2024 9 special displays Random 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 ©PRISCILLA OLAWALE (MSC) SPRING2024 10 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 ©PRISCILLA OLAWALE (MSC) SPRING2024 11 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 ©PRISCILLA OLAWALE (MSC) SPRING2024 12  Hermes a situated display small displays beside office doors handwritten notes left using stylus small displays office owner reads notes using web interface beside office doors handwritten office owner notes left reads notes using stylus using web interface ©PRISCILLA OLAWALE (MSC) SPRING2024 13 Digital paper appearance what? ◦ thin flexible sheets ◦ updated electronically cross ◦ but retain display section how? ◦ small spheres turned ◦ or channels with coloured liquid and contrasting spheres ◦ rapidly developing area ©PRISCILLA OLAWALE (MSC) SPRING2024 14 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 ©PRISCILLA OLAWALE (MSC) 15 SPRING2024 PAPER: PRINTING AND SCANNING  print technology  fonts, page description, WYSIWYG  scanning, OCR ©PRISCILLA OLAWALE (MSC) 16 SPRING2024 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!! ©PRISCILLA OLAWALE (MSC) 17 SPRING2024 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. ©PRISCILLA OLAWALE (MSC) 18 SPRING2024 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 ©PRISCILLA OLAWALE (MSC) 19 SPRING2024 Fonts Font – the particular style of text Courier font Helvetica font Palatino font Times Roman font §´  (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 ©PRISCILLA OLAWALE (MSC) 20 SPRING2024 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 ©PRISCILLA OLAWALE (MSC) 21 SPRING2024 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 ©PRISCILLA OLAWALE (MSC) 22 SPRING2024 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 ©PRISCILLA OLAWALE (MSC) 23 SPRING2024 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 similar but never quite the same so … need different designs, graphics etc, for screen and print ©PRISCILLA OLAWALE (MSC) 24 SPRING2024 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 ©PRISCILLA OLAWALE (MSC) 25 SPRING2024 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 ©PRISCILLA OLAWALE (MSC) 26 SPRING2024 Extra Topics Interaction Design, Design Paradigms in HCI User Modelling ©PRISCILLA OLAWALE (MSC) SPRING2024 27