Week 5

LBSC 690

Information Technology

Multimedia

Agenda

• Questions

• Images

• Video

• Audio

• Streaming

• SMILe

• XML?

• (HCI)

Georges Seurat, A Sunday Afternoon on the Island of La Grande Jatte

Nothing new…

Visual Perception

• Closely spaced dots appear solid– But irregularities in diagonal lines can stand out

• Any color can be produced from just three– Red, Blue and Green: “additive” primary colors

• High frame rates produce apparent motion– Smooth motion requires about 24 frames/sec

• Visual acuity varies markedly across features– Discontinuities easily seen, absolutes less crucial

Basic Image Coding

• Raster of picture elements (pixels)– Each pixel has a “color”

• Binary - black/white (1 bit)• Grayscale (8 bits)• Color (3 colors, 8 bits each)

– Red, green, blue

• Screen– A 1024x768 image requires 2.4 MB

• So a picture is worth 400,000 words!

Monitor Characteristics

• Technology (CRT, Flat panel)• Size (15, 17, 19, 21 inch)

– Measured diagonally– For CRT, key figure is “viewable area”

• Resolution– 640x480, 800x600, 1024x768, 1280x1024, …

• Layout (three dot, lines)• Dot pitch (0.26, 0.28)• Refresh rate (60, 72, 80 Hz)

Some Questions

• How many images can a 1 GB flash card store?– But mine holds about 500. How?

• How long will it take to send an image at 64kb/s?– But my Web page loads faster than that. How?

Compression

• Goal: reduce redundancy– Send the same information using fewer bits

• Originally developed for fax transmission– Send high quality documents in short calls

• Two basic strategies:– Lossless: can reconstruct exactly– Lossy: can’t reconstruct, but looks the same

Palette Selection• Opportunity:

– No picture uses all 16 million colors– Human eye does not see small differences

• Approach: – Select a palette of 256 colors– Indicate which palette entry to use for each pixel– Look up each color in the palette

……

“The rain in Spain falls mainly in the plain”

→ [*=ain,^=in] “The r* ^ Sp* falls m*ly ^ the pl*”

Run-Length Encoding

• Opportunity:– Large regions of a single color are common

• Approach:– Record # of consecutive pixels for each color

• An example of lossless encoding

Sheep go baaaaaaaaaa and cows go moooooooooo→ Sheep go ba<10> and cows go mo<10>

GIF

• Palette selection, then lossless compression• Opportunity:

– Common colors are sent more often

• Approach:– Use fewer bits to represent common colors

• 1 Blue 75% 75x1= 75 75x2=150• 01 White 20% 20x2= 40 20x2= 40• 001 Red 5% 5x3= 15 5x2= 10

130 200

JPEG

• Opportunity:– Eye sees sharp lines better than subtle shading

• Approach:– Retain detail only for the most important parts– Accomplished with Discrete Cosine Transform

• Allows user-selectable fidelity

• Results:– Typical compression 20:1

Variable Compression in JPEG

37 kB (20%) 4 kB (95%)

Vector Graphics

Vector Graphics

• Raster images (“bitmap graphics”)– Actually describe the contents of the image– Good for natural scenes

• Vector images– Mathematically describe how to draw the image– Rescalable without loss of resolution

Discussion Point:Selecting an Image Format

• Should I use GIF, JPEG, or vector graphics for …• Color photos?• Scanned black & white text?• Line drawings?

Hands-On Exercise: Convert Between Formats

• Download and save two images– http://www.umiacs.umd.edu/~daqingd/image1.jpg

– http://www.umiacs.umd.edu/~daqingd/image2.gif

• Use Microsoft Paint to convert each to the other format, and compare quality and the file size

• Why the difference?

Basic Video Coding

• Display a sequence of images– Fast enough for smooth motion and no flicker

• NTSC Video– 60 “interlaced” half-frames/sec, 512x486

• HDTV– 30 “progressive” full-frames/sec, 1280x720

Video Data Rates

• “NTSC” Quality Computer Display– 640 X 480 pixel image– 3 bytes per pixel (red, green, blue)– 30 Frames per Second

• Bandwidth– 26.4 MB/second– Exceeds bandwidth of most disk drives

• Storage– CD-ROM would hold 25 seconds worth– 30 minutes would require 46.3 GB

Video Compression• Opportunity:

– One frame looks very much like the next

• Approach: – Record only the pixels that change

• Standards:– MPEG-1: Web video (file download)– MPEG-2: HDTV and DVD– MPEG-4: Web video (streaming)

MPEG Encoding

Frame Types

• • • • • •

I1 B1 B2 B3 P1 B4 B5 B6 P2 B7 B8 B9 I2

I Intra Encode complete image, similar to JPEGP Forward Predicted Motion relative to previous I and P’sB Backward Predicted Motion relative to previous & future I’s & P’s

Frame Reconstruction

• • •• • •

I1

P1 P2

I2

updates

I1+P1 I1+P1+P2

I frames provide complete image

P frames provide series of updates to most recent I frame

Frame Reconstruction

• • •• • •

I1 I2I1+P1 I1+P1+P2

B1 B2 B3 B4 B5 B6 B7 B8 B9

Interpolations

B frames interpolate between frames represented by I’s & P’s

Basic Audio Coding

• Sample at twice the highest frequency– 8 bits or 16 bits per sample

• Speech (0-4 kHz) requires 8 kB/s– Standard telephone channel (1-byte samples)

• Music (0-22 kHz) requires 172 kB/s– Standard for CD-quality audio (2-byte samples)

Sampler

Music Compression• Opportunity:

– The human ear cannot hear all frequencies at once

• Approach:– Don’t represent “masked” frequencies

• Standard: MPEG-1 Layer 3 (.mp3)

Temporal MaskingIf we hear a loud sound, then it stops, it takes a while until we can hear a soft tone at about the same frequency.

“Psychoacoustic compression”– Eliminate sounds below threshold of hearing – Eliminate sounds that are frequency masked – Eliminate sounds that are temporally masked – Eliminate stereo information for low frequencies

Speech Compression

• Opportunity:– Human voices vary in predictable ways

• Approach:– Predict what’s next, then send only any corrections

• Standards:– Real audio can code speech in 6.5 kb/sec

• Demo at http://www.data-compression.com/speech.html

– Scroll down to near the bottom

Narrated PowerPoint

• Create your slides

• Slide Show -> Record Narration– Set microphone level

• Record the narration– Slide transitions are automatically captured

• Narration plays automatically when displayed

Adding Video to PowerPoint

• Insert->Movies and Sounds– Movies from file (a .mpg file)

• Decide whether you want autostart– If not, it starts when you click on it

The “Last Mile”

• Traditional modems– “56” kb/sec modems really move ~3 kB/sec

• Digital Subscriber Lines– 384 kb/sec downloads (~38 kB/sec)– 128 kb/sec uploads (~12 kB/sec)

• Cable modems– 10 Mb/sec downloads (~1 MB/sec)– 256 kb/sec uploads (~25kB/sec)

Multimedia on a Web Server

• Object stored in a file

• File transferred as an HTTP object:– Received entirely at the client– Passed to media player

WebBrowser

MediaPlayer

WebServer

Streaming

• Browser gets metafile over HTTP– Launches media player to interpret the metafile

• Media player contacts streaming server

WebBrowser

MediaPlayer

WebServer

StreamingServer

Streaming Audio and Video

• Begin replay after only a portion received

• Buffer provides time to recover lost packets

• Interrupts replay when “rebuffering”

Media Sever

Internet

Buffer

constant bit rate video playout at client

bu

ffere

dvid

eo

constant bit rate videotransmission

Cum

ula

tive

data

time

variablenetworkdelay

client videoreception

client playoutdelay

Client Buffering

• Client-side buffering: – Playout delay compensates for network delay

Playout Delay

• Receiver attempts to playout each chunk exactly q ms after chunk was generated– Chunk has time stamp t: play out chunk at t+q– Arrives after t+q: too late for playout, data “lost”

• Tradeoff for q:– Large q: less packet loss– Small q: better interactive experience

• Easy to increase q by inserting a pause– Decreasing q requires skipping or accelerating

Lost Packets

• Network loss – Packets completely lost (e.g., due to collisions)

• Delay loss– Packets arrives too late for playout

• Queueing; sender and receiver processing delays

• Loss tolerance– 1% to 10% packet loss may be tolerable

• Some encoding schemes are more tolerant than others

Hands On: RealPlayer

• View streaming real video– http://www.c-span.org

• Select “Tools/Playback statistics”

• Pay attention to bandwidth and lost packets

Multiple Client Rates

Q: how to handle different client receive rate capabilities?

– 28.8 Kbps dialup

– 100Mbps Ethernet

A: server stores, transmits multiple copies of video, encoded at different rates

1.5 Mbps encoding

28.8 Kbps encoding

Internet Telephony

• Characteristics:

– “Live” (<400 ms delay)

– Alternating talk spurts

Illustrating RealAudio

• Create a .ram file– URL for the RealAudio– Dimensions of the picture– URL for the picture

http://www.umiacs.umd.edu/~oard/teaching/690/fall05/notes/4/media.html

Synchronizing Multiple Media

• Scripting Languages– Synchronized Multimedia Integration Language (SMIL)

• Custom applications– Macromedia Flash

• Content representation standards– MPEG 4

SMILe

• W3C standard– Player-specific extensions are common

• XML, with a structure similar to HTML<smil>

<head> … </head>

<body> … </body>

</smil>

Elements in SMIL

• Window controls (in <head>)– Controlling layout: <region>, <root-layout>

• Timeline controls (in <body>)– Sequence control: <seq>, <excl>, <par>

– Timing control: <begin>, <end>, <dur>

• Content types (in <body>)– <audio>, <video>, <img>, <ref>

SMIL Examples

• Implemented in RealOne Player

• Example:http://www.umiacs.umd.edu/~oard/teaching/690/fall05/notes/4/media.html

– First, run the executable– Then, view .smil file

What’s Wrong with the Web?

• HTML– Confounds structure and appearance (XML)

• HTTP– Can’t recognize related transactions (Cookies)

• URL– Links breaks when you move a file (PURL)

What’s a Document?

• Content

• Structure

• Appearance

• Behavior

History of Structured Documents

• Early standards were “typesetting languages”– NROFF, TeX, LaTeX, SGML

• HTML was developed for the Web– Too specialized for other uses

• Specialized standards met other needs– Change tracking in Word, annotating manuscripts, …

• XML seeks to unify these threads– One standard format for printing, viewing, processing

eXtensible Markup Language (XML)

• SGML was too complex• HTML was too simple• Goals for XML

– Easily adapted to specific tasks• Rendering Web pages• Encoding metadata• “Semantic Web”

– Easily created– Easily processed– Easily read– Concise

Some XML Applications

• Text Encoding Initiative– For adding annotation to historical manuscripts– http://www.tei-c.org/

• Encoded Archival Description– To enhance automated processing of finding aids– http://www.loc.gov/ead/

• Metadata Encoding and Transmission Standard– Bundles descriptive and administrative metadata– http://www.loc.gov/standards/mets/

Really Simple Syndication (RSS)

See example at http://www.nytimes.com/services/xml/rss/

<?xml version="1.0"?> <rss version="2.0"> <channel> <title>Lift Off News</title> <link>http://liftoff.msfc.nasa.gov/</link> <description>Liftoff to Space Exploration.</description> <language>en-us</language> <pubDate>Tue, 10 Jun 2003 04:00:00 GMT</pubDate> <lastBuildDate>Tue, 10 Jun 2003 09:41:01 GMT</lastBuildDate> <docs>http://blogs.law.harvard.edu/tech/rss</docs> <generator>Weblog Editor 2.0</generator> <managingEditor>editor@example.com</managingEditor> <webMaster>webmaster@example.com</webMaster> <ttl>5</ttl> <item> <title>Star City</title> <link>http://liftoff.msfc.nasa.gov/news/2003/news-starcity.asp</link> <description>How do Americans get ready to work with Russians aboard the International Space Station? They take a crash course in culture, language and protocol at Russia's Star City.</description> <pubDate>Tue, 03 Jun 2003 09:39:21 GMT</pubDate> <guid>http://liftoff.msfc.nasa.gov/2003/06/03.html#item573</guid> </item> </channel> </rss>

Atom Feeds<?xml version="1.0" encoding="utf-8"?> <feed xmlns="http://www.w3.org/2005/Atom"> <title>Example Feed</title> <subtitle>A subtitle.</subtitle> <link href="http://example.org/feed/" rel="self"/> <link href="http://example.org/"/> <updated>2003-12-13T18:30:02Z</updated> <author> <name>John Doe</name> <email>johndoe@example.com</email> </author> <id>urn:uuid:60a76c80-d399-11d9-b91C-0003939e0af6</id> <entry> <title>Atom-Powered Robots Run Amok</title> <link href="http://example.org/2003/12/13/atom03"/> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2003-12-13T18:30:02Z</updated> <summary>Some text.</summary> </entry> </feed>

XML: A Family of Standards

• Definition: DTD– Known types of entities with “labels”– Defines part-whole and is-a relationships

• Markup: XML– “Tags” regions of text with labels

• Markup: XLink– Defines “hypertext” (and other) link relationships

• Presentation: XSL– Specifies how each type of entity should be “rendered”

XHTML Example

• View “The Song of the Wandering Aengus” – http://www.umiacs.umd.edu/~oard/teaching/690/spring08/notes/3/xml.htm

• Built from three files– yeats01.xml – poem01.dtd – poem01.xsl

XML Example<?xml version="1.0"?>

<!DOCTYPE POEM SYSTEM "poem01.dtd">

<?xml-stylesheet type="text/xsl" href="poem01.xsl"?>

<POEM>

<TITLE>The Song of Wandering Aengus</TITLE>

<AUTHOR> <FIRSTNAME>W.B.</FIRSTNAME>

<LASTNAME>Yeats</LASTNAME>

</AUTHOR>

<STANZA>

<LINE>I went on to the hazel wood,</LINE>

<LINEIN>Because a fire was in my head,</LINEIN>

<LINE>And cut and peeled a hazel wand,</LINE>

</STANZA>

</POEM>

Document Type Definition (DTD)

<!ELEMENT poem ( (title, author, stanza)* )>

<!ELEMENT title (#PCDATA) >

<!ELEMENT author (firstname, lastname) >

<!ELEMENT firstname (#PCDATA) >

<!ELEMENT lastname (#PCDATA) >

<!ELEMENT stanza (line+ | linein+) >

<!ELEMENT line (#PCDATA) >

<!ELEMENT linein (#PCDATA) >#PCDATA span of text a,b a followed by ba|b either a or ba* 0 or more a’sa+ 1 or more a’s

Specifying Appearance: XSL

<xsl:template match="POEM">

<HTML>

<BODY BGCOLOR="#FFFFCC">

<xsl:apply-templates/>

</BODY>

</HTML>

</xsl:template>

<xsl:template match="TITLE">

<H1>

<FONT COLOR="Green">

<xsl:value-of/>

</FONT>

</H1>

</xsl:template>

XLink Example……<poem xmlns:xlink="http://www.w3.org/1999/xlink"> <author xlink:href="yeatsRDFS3.xml“ xlink:type="simple">W. B. Yeats</author> <poems> <poem1 xlink:href="http://www.kirjasto.sci.fi/wbyeats.htm" xlink:type="simple">The Rose</poem1> <poem2 xlink:href="http://www.kirjasto.sci.fi/wbyeats.htm" xlink:type="simple">The Tower</poem2> </poems> </poem> ……….

XHTML: Writing HTML as XML

<?xml version="1.0" encoding="iso-8859-1"?><html xmlns="http://www.w3.org/TR/xhtml1" ><head> <title> Title of text XHTML Document </title></head><body><div class="myDiv"> <h1> Heading of Page </h1> <p> here is a paragraph of text. I will include inside this paragraph a bunch of wonky text so that it looks fancy. </p> <p>Here is another paragraph with <em>inline emphasized</em> text, and <b> absolutely no</b> sense of humor. </p> <p>And another paragraph, this one with an <img src="image.gif" alt="waste of time" /> image, and a <br /> line break. </p></div> </body></html>

Some Basic Rules for XML• XML is case sensitive• XML declaration is the first statement

– <?xml version="1.0"?>

• An XML document is a “tree”– Must contain one root element

– Other elements must be properly nested

• All start tags must have end tags• Attribute values must have quotation marks

– <item id=“33905”>

• Certain characters are “reserved”– For example: &lt; is used to represent <

Multiple XML Namespaces<?xml version="1.0"?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rss="http://purl.org/rss/1.0/" xmlns:dc="http://purl.org/dc/elements/1.1/"> <rss:channel rdf:about="http://www.xml.com/xml/news.rss"> <rss:title>XML.com</rss:title> <rss:link>http://xml.com/pub</rss:link> <dc:description> XML.com features a rich mix of information and services for the XML community. </dc:description> <dc:subject>XML, RDF, metadata, information syndication services</dc:subject> <dc:identifier>http://www.xml.com</dc:identifier> <dc:publisher>O'Reilly & Associates, Inc.</dc:publisher> <dc:rights>Copyright 2000, O'Reilly & Associates, Inc.</dc:rights> </rss:channel></rdf:RDF>

Example from http://www.xml.com/pub/a/2000/10/25/dublincore/

Some Ajax Applications

• Google Maps– http://maps.google.com

• Google Suggest– http://www.google.com/webhp?complete=1&hl=en

• Sajax Tables– http://labs.revision10.com/?p=5

• Sajax– http://www.modernmethod.com/sajax/

Database

Server-side Programming

Interchange Language

Client-side Programming

Web Browser

Client Hardware

Server Hardware (PC, Unix)

(MySQL)

(PHP)

(HTML, XML)

(JavaScript)

(IE, Firefox)

(PC)

Bus

ines

sru

les

Inte

ract

ion

Des

ign

Inte

rfac

eD

esig

n

• Relational normalization• Structured programming• Software patterns• Object-oriented design• Functional decomposition

Even More Uses of XML …

• CML – Chemical Markup Language

• CellML – biological models

• BSML – bioinformatic sequences

• MAGE-ML – MicroArray Gene Expression

• XSTAR – for archaeological research

• MARCXML – MARC in XML

• AML – astronomy markup language

• SportsML – for sharing sports data

Interaction

• Forming an intention– Internal mental characterization of a goal

• Selection of an action– Review possible actions, select most appropriate

• Execution of the action– Carry out appropriate actions with the system

• Evaluation of the outcome– Compare results with expectations

Where the Mental Model FitsGoals

Intention

Selection

Execution System Perception

Interpretation

EvaluationExpectation

Mental Activity

Physical Activity

MentalModel

Mental Models

• How the user thinks the machine works– What actions can be taken?– What results are expected from an action?– How should system output be interpreted?

• Mental models exist at many levels– Hardware, operating system, and network– Application programs– Information resources

Input Devices

• Text– Keyboard, optical character recognition– Speech recognition, handwriting recognition

• Direct manipulation– 2-D: mouse, trackball, touch pad, touch panel– 3-D: wand, data glove

• Remote sensing– Camera, speaker ID, head tracker, eye tracker

Keyboard

• Produces character codes– ASCII: American English

– Latin-1: European languages

– UNICODE: (nearly) Any language• Pictographic languages need “entry methods”

• Keyboard shortcuts help with data entry– Different conventions for standard tasks abound

• VT-100 standard” functions are common– Differing layouts can inhibit usability

Design Example: QWERTY Keyboard

From http://home.earthlink.net/~dcrehr/whyqwert.html

Dvorak Keyboard

From http://www.mwbrooks.com/dvorak/

Direct Manipulation

• Match control actions with on-screen behavior– Use a cursor for visual feedback if needed

• Rotary devices– Mouse, trackball

• Linear devices– Touch pad, touch screen, iPod shuttle, joystick

• Rate devices – Laptop eraserhead

Modeling Interaction

Task System

Mental Models SightSound

HandsVoice

Task User

Software Models KeyboardMouse

DisplaySpeaker

Human

Computer

Human Senses

• Visual– Position/motion, color/contrast, symbols

• Auditory– Position/motion, tones/volume, speech

• Haptic– Mechanical, thermal, electrical, kinesthethic

• Olfactory– Smell, taste

• Vestibular

Commodity Output

• Image display– Fixed view, projection

• Acoustic display– Speakers, headphones

“Virtual Reality” Output• Immersive visual

– Surround projection, Movable view

• Force feedback– Pen, joystick, exoskeleton

• Tactile– Vibrotactile, pneumatic, piezoelectric

• Vestibular– Motion-based simulators

• Locomotive– Stationary bicycle, treadmill

• Thermal, Olfactory

What makes a Wii fun?

Interaction Styles

• Language-based interfaces– Command line interfaces– Interactive voice response systems

• Graphical User Interfaces (GUI)– Direct manipulation– Menus

• Virtual Reality (VR)– Direct manipulation

• Ubiquitous computing

Direct Manipulation

• Select a metaphor– Desktop, CD player, map, …

• Use icons to represent conceptual objects– Watch out for cultural differences

• Manipulate those objects with feedback– Select (left/right/double click), move (drag/drop)

GUI Components

• Windows (and panels)– Resize, drag, iconify, scroll, destroy

• Selectors – Menu bars, pulldown lists

• Buttons– Labeled buttons, radio buttons, checkboxes

• Icons (images)– Select, open, drag, group

Metaphor: Fundamental for Thought• Theories as buildings:

– The foundation of the theory is shaky

– Theory was toppled

– Buttress your claims

• Mind as a container– Suddenly came into my head

– Back of my mind

• Time as space: – The end of the semester is getting closer

– The best part of the show is coming up

– The week just whizzed by

Transfer Effects

• People transfer expectations from similar objects– Positive: prior learning applies to new situation– Negative: prior learning conflicts with new situation

Caller: Hello, is this Tech Support?"Tech: Yes, it is. How may I help you? Caller: The cup holder on my PC is broken and I am within my warranty

period. How do I go about getting that fixed?Tech: I'm sorry, but did you say a cup holder?Caller: Yes, it's attached to the front of my computer. Tech: Please excuse me if I seem a bit stumped, it’s because I am. Did

you receive this as part of a promotional, at a trade show? How did you get this cup holder? Does it have any trademark on it?

Caller: It came with my computer, I don't know anything about a promotional. It just has '4X' on it.

At this point the Tech Rep had to mute the call, because he couldn't stand it. The caller had been using the load drawer of the CD-ROM drive as a cup holder, and snapped it off the drive.

Positive and Negative Transfer

“First we thought the PC was a calculator. Then we found out how to turn numbers into letters with ASCII — and we thought it was a typewriter. Then we discovered graphics, and we thought it was a television. With the World Wide Web, we've realized it's a brochure.” ― Douglas Adams

Visual Affordance• The perceived and actual fundamental properties

of the object that determine how it could be used– Appearance indicates how the object should be used

• Chair for sitting• Table for placing things on• Knobs for turning• Slots for inserting things into• Buttons for pushing

• Complex things may need explaining but simple things should not– When simple things need instructions, design has failed

Visual Affordance ProblemsSliders for sliding?

Are these buttons? What does this button do?

Dials for turning?

Mapping

backright

frontleft

backleft

frontright

24 possibilities, requires: -visible labels + memory

arbitrary

full mapping

back front front back

2 possibilities per side = 4 total possibilities

paired

Visible Constraints

• Limitations of the actions possible perceived from object’s appearance– provides people with a range of usage possibilities

Push or pull? Which side? Can only push,side to push clearly visible

Visible Constraints: Date Entry

Causality

• The thing that happens right after an action is assumed by people to be caused by that action

• Incorrect effect– Invoking unfamiliar function just as computer hangs– Causes “superstitious” behaviors

• Invisible effect– Command with no apparent result often repeated

• e.g., mouse click to raise menu on unresponsive system

Effects visible only after Exec button is pressed• Ok does nothing!• Awkward to find appropriate color level

LViewPro

Causality: An Example

Cultural Associations• Because a trashcan in Thailand may look like

this:

• A Thai user is likely to be confused by this image popular in Apple interfaces:

• Sun found their email icon problematic for some American urban dwellers who are unfamiliar with rural mail boxes.

• People learn “idioms” that work in a certain way– Red means danger– Green means safe

• Idioms vary in different cultures– Light switches

• America: down is off• Britain: down is on

– Faucets• America: counter-clockwise on• Britain: counter-clockwise off

Stereotypes

WIMP Interfaces

• Windows– Spatial context

• Icons– Direct manipulation

• Menus– Hierarchy

• Pointing devices– Spatial interaction

Menus

• Conserve screen space by hiding functions– Menu bar, pop-up

• Hierarchically structured– Logical grouping– Conventional positioning

• Tradeoff between breadth and depth– Too deep can become hard to find things– Too broad becomes direct manipulation

Dynamic Queries

• Keyboard-initiated direct manipulation

• Select menu items by typing part of a word– After each letter, update the menu– Once the word is displayed, user can click on it

• Examples: Google queries, Windows help

Design Concept Summary• Visual affordance• Visible constraints• Mapping• Causality• Transfer effects• Idioms• Metaphors• Cultural associations• Individual differences

“Seamless Interfaces”• Informative feedback• Easy reversal• User in control

– Anticipatable outcomes– Explainable results– Browsable content

• Limited working memory load– Query context– Path suspension

• Alternatives for novices and experts– Scaffolding

The Discipline of HCI

From ACM SIGCHI Curricula for Human-Computer Interaction

Human-Computer Interaction

Design Implementation

Evaluation

A discipline concerned with the

of interactive computing systems for human use

Evaluation Approaches

• Formative vs. summative

• Extrinsic vs. intrinsic

• Quantitative vs. qualitative– Deductive vs. inductive

• User study vs. simulation

Evaluation Examples• Direct observation

– Evaluator observes users interacting with system• in lab: user asked to complete pre-determined tasks• in field: user goes through normal duties

– Validity depends on how contrived the situation is

• Think-aloud– Users speak their thoughts while doing the task– May alter the way users do the task

• Controlled user studies– Users interact with system variants– Correlate performance with system characteristics– Control for confounding variables

Evaluation Measures

• Time to learn

• Speed of performance

• Error rate

• Retention over time

• Subjective satisfaction

Learning More

• LBSC 733: Networks

• LBSC 795: HCI Design and Evaluation

• INFM 700: Information Architecture

• LBSC 790: HCI Implementation

Some Style Guidelines

• Design for generic browsers– And test on every version you wish to support

• Provide appropriate “access points”– User needs and navigation strategies differ

• Design useful navigational aids– A Web search may lead to the middle of a site

• Include some indication of currency– Date of last update, “new” icons, etc.

• Indicate who is responsible for the content– Helps readers assess authority

Some Accessibility Guidelines

• Design for device independence• Maintain compatibility with earlier browsers

– Provide alternative pages if necessary

• Provide alternatives to aural and visual content– Alt tags for images, transcripts for audio

• Make is easy for assistive devices to work– Use structural (rather than layout-oriented) markup– Give a title to each frame– Only use HTML tables for table data (not content layout)– Use markup to indicate language switching

Section 508 (Federal Web pages)• A text equivalent for every non-text element shall be provided. • Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation. • Web pages shall be designed so that all information conveyed with color is also available without color. • Documents shall be organized so they are readable without requiring an associated style sheet. • Redundant text links shall be provided for each active region of a server-side image map. • Client-side image maps shall be provided instead of server-side image maps except where the regions cannot be defined with an available geometric

shape. • Row and column headers shall be identified for data tables. • Markup shall be used to associate data cells and header cells for data tables that have two or more logical levels of row or column headers. • Frames shall be titled with text that facilitates frame identification and navigation. • Pages shall be designed to avoid causing the screen to flicker with a frequency >2 Hz and <55 Hz. • A text-only page, with equivalent information or functionality, shall be provided when compliance cannot be accomplished in any other way. The

content shall be updated when the primary page changes • When pages use scripting languages to display content or to create interface elements, the information provided by the script shall be identified with

functional text that can be read by assistive technology. • When a web page requires that an applet, plug-in or other application be present on the client system to interpret page content, the page must provide a

link to a plug-in or applet that complies with the above. • When electronic forms are designed to be completed on-line, the form shall allow people using assistive technology to access the information, field

elements, and functionality required. • A method shall be provided that permits users to skip repetitive navigation links. • When a timed response is required, the user shall be alerted and given sufficient time to indicate more time is required.

HTML Editors

• Goal is to create Web pages, not learn HTML!• Several are available

– Macromedia Dreamweaver available commercially– Microsoft Word (Page->Edit with Word in IE 7– Many more options available on www.tucows.com

• Tend to use physical layout tags extensively– Detailed control can make hand-editing difficult

• You may still need to edit the HTML file– Some editors use browser-specific features– Some HTML features may be unavailable– File names may be butchered when you upload

HTML Validators

• Syntax checking: cross-browser compatibility– http://validator.w3.org– Try it on http://www.umd.edu

• Style checking: Section 508 compliance– http://www.cynthiasays.com/– Try it on http://www.umd.edu

Before You Go!

• On a sheet of paper (no names), answer the following question:

What was the muddiest point in today’s class?