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Western University
Computer Science
Computer Science 1033A/B

Computer Science Final Exam Notes • Lecture 2 History of Multimedia • 1928 - debut of Steamboat Willie: first cartoon to use synchronized sound • 1930s – technicolour introduced • 1969 – Network technology introduced  Arpanet (Advanced Research Projects Agency NETwork) is created  First packet switching network and predecessor to Internet  Began talking about it in 1962  Objective: build a network to share information • 1977: Apple dominated PC market • 1991: Tim Berners-Lee debuts World Wide Web • 1992: HTML debuts • 1993: first graphical browser: Mosaic • 1994: Rolling Stones’ first live performance on Internet • 1995: Toy Story: first feature length computer generated movie • 1998: Google: Larry Page & Sergey Brins • 1991: Napster: download and share mp3s Top 3 Applications: 1. Entertainment 2. Publishing 3. Education/training • Education - E-learning became “real” not just substitute for lack of teachers - Learning facilitated on-line - All learning technology mediated in some way • Shopping & Retail - Traditional shopping replaced by on-line shopping - Shopping experience changes • Entertainment - Electronic games- more virtual reality and on-line - Media on demand • Communications - Internet telephone and video phone systems Multimedia Features 1. Interactivity - User control over the application - Experience active rather than passive 2. Hyperactivity - Index/table of contents allows for “jumping” - Sequential: you start at the beginning and move to the end - Hyperlinking: an index allows for “jumping around” to different sections • Computer based multimedia applications integrate the various components of media and allow interactivity and hyperlinking • CD/DVD - Access time: view in an instant by inserting into drive - Cannot change content • World Wide Web - Access time: may encounter slow connection speeds - Content can be changed • Development Systems: systems used by multimedia developers to create applications • User Systems: systems used to play back multimedia applications Text • Use of text in multimedia applications varies on the type of application and audience • Change the look of your webpage by changing text attributes & design/layout/placement Text Attributes • Font type - Serif: tails, script, body paragraphs - Sans-Serif: no tails, block oriented, headings/titles • Style - Regular, bold, italics • Kerning - Spaces between characters • Leading - Vertical space between lines of text • Special Effects - Underline, shadow, super script, subscript • Size - Points vs. Pixels PIXEL (px) POINT (pt) • Smallest discrete component of an • A linear unit measuring the size of text image or picture on a monitor • Points are a print unit of measure • Pixels are a measurement for text and images on the web • 72 pt = 1 inch, 36 pt = 0.5 inch • If webpage expresses font sizes in • If webpage expresses font sizes in pixels text will display more precisely points text can be displayed much the size you want on the screen larger or smaller than you expect Colour • Hexadecimal code • Represented as a number of 6 digits • Made up of decimals (0-9) and letters (A-F) - #RRGGBB - 0-9 = darker colours, A-F = lighter colours (black = #000000, white = #FFFFFF) Text Design Considerations • Readability • Visual appeal: position, layout, coordinate with graphics • Mood creation: appropriate font attributes & layout, headings C ontrast - avoid making 2 elements just similar R epetition - repeat some aspect of design throughout entire design A lignment - items are aligned; creates stronger cohesive unit P roximity - group related items together • Lecture 3 What is digitization? • Refers to the process of translating a piece of information into bits • Bits = binary digits - Fundamental units of information in a computer system (“0” and “1”) - Electric signals translate into “bits” (“0” and “1”) • 1 Byte = 8 bits - x bits = # of digits, y values = # of combinations ex: 2 (4 bit) = 16 values,  x=4, y=16 Pixels • an image is represented by a grid (array, matrix) of squares called pixels (Picture Elements) • pixel = the smallest image component   shows smallest detail • arranged in columns and rows • each pixel is given a numerical value that represents the corresponding colour Colour Coding • range of colours  associated with number of bits • if a pixel colour is represented by 1 bit only (0=black, 1=white)   1 bit allows for 2 colours • Rule: more bits=more shades (colours) • In true colour each pixel represents same colour shade Colour Models • Used for Web: o Additive model (RGB) - Primary colours = red, green, blue - Adding light to black background (monitor) in order to obtain colour shades • Used for Printing: o Subtractive model (CYMK) - Cyan, magenta, yellow - Ink when applied removes (“subtracts”) from a white background RGB Code • Each pixel is represented by three values (R, G, B) • Syntax - Each value ranges from 0-255 - 0 = no colour, 255 = max amount - 256 colour shades = 1 bits - Need 3 bytes for true colour (8 bits = 1 byte) - RGB Code: <0-255,0-255,0-255> (black = <0,0,0>, white = <255,255,255>) • The human eye can detect about 10 million colours Types of Graphics • Affects how the graphics are displayed on a computer screen: 1. Quality 2. File Size 3. Time to display graphics Bitmap Graphics • Also known as RASTER graphics • Made up of pixels • Editing pixels = changing colour, shade and brightness • If you start with a small image & make it larger by resizing… - squares become larger, edges more jagged - quality decreases pixelation - file size increases Vector Graphics • Image represented with lines and arcs that have a mathematical relationship which describes the drawing of the shape • It doesn’t matter what size the image is • As the image is resized larger/smaller... - Edges still clean, crisp - No distortion going up/down in size - Quality is maintained - File size increases (if resized larger) Graphic Software 1. Vector Based - Geared towards drawings - Greater control and precision - Display more accurately - Download faster - More details - Need a draw program (ex: Adobe Illustrator, Paint, etc.) 2. Bitmapped Based - Editing an image’s pixels - Images from scanners, cameras, etc. - Need a paint program (ex: Photoshop) What affects Image Quality? • Resolution o Digital Camera - Describes the size of an image (width x height) - Higher resolution = larger image, better quality, bigger prints - Megapixel = how many millions of pixels you can capture in a photo with your digital camera o Monitor/Screen - Describes the dimensions of the pixels displayed on a screen - A resolution of 800 x 600 = 800 pixels wide x 600 pixels high - Monitor size does not matter - The higher the resolution, the smaller it appears Image Resolution • Controlled through graphics package • Number of pixels per square inch • Higher resolution = larger size • dpi = ppi • Web  set resolution to 72 ppi • Laser printer  set resolution to 300-600 ppi • High end image setters  1200-2400 ppi or higher Image Bit-Depth • Refers to the total number of colours in an image • Amount of digital space used to record information about the colour of a pixel • More bits you use = more info stored to describe the colour of a pixel,  quality improves & larger file size File Formats • Universally supported files - universally supported by graphics industry (.jpg, .gif) • Proprietary (aka: Native files) - bitmap or vector images used by specific graphic programs (original default formats, ex: .psd, .fla) - can save in both native and universal formats o Native  preserves layering o Universal  ability to save files in .jpg , .gif, etc. • .GIF - Graphics Interchange Format - Bitmapped • .JPG/.JPEG - Joint Photographic Experts Group - Bitmapped - Compact file Graphics Software • Illustration - Drawing program - Work with vector images - More flexibility with artwork that has to be resized (ex: create logos) • Photo Image Editors - Paint programs - Work with bitmap images - Needed for working with photos, scans, or other “realistic” images - For the web or adding special effects to photos Servers • Advantages of a server: 1. Connect: computer is on all the time and connected to the Internet 2. Always Available: since it never gets turned off, your website will always be available 3. Taken Care of: the people running the severs will take care of security and computer maintenance issues • Lecture 4 Image Optimization • Optimization Techniques 1. File Formats: choose .jpg or .gif 2. Compression: compress the image data 3. Colour resolution: number of colours used File Format • GIF Properties - Supports max of 8 bit colour scheme (good for clip art, not photos) - Best for large areas of solid, flat colour - Tiny file sizes in comparison with .jpg - Summary: smaller file sizes but only 8 bit colour • JPG Properties - Stores full colour information - Supports max of 24 bits per pixel (1 million colours) - Best for blends of colour, softer shadow effects, subtle changes in colour - Not for well defined lines or sharp contrast between colours  distorts them - Summary: full colour scheme but larger file size Compression • To reduce file size  choose a compression technique appropriate for the web • Role of compression is to: - Reduce the redundancy of image data  gives ability to store or transmit data in an efficient form - Compress as much as you can without compromising quality Compression Techniques • Lossless - Compress the original bits and bytes into less bits and bytes without losing any of the image’s original information - When we reopen the file, all original info is still there - No information is lost - Gifs  lossless compression o Does not get blurry or messy o Uses technique called “L2W” compression  reduces file sizes of images by finding repeated patterns of pixels (ex: 12341234 turns into 11) o This compression maintains the image quality • Lossy - When compression occurs, some of the original information is lost - Discards selected portions of image that are least missed or noticed - Cannot get information back once it is discarded - Quality degrades - JPGs  lossy compression o Not all information from the original image is preserved  not the same as the original; discards data o Degrades image quality each time you save o Compression is achieved by “forgetting” certain details about the image, which the JPG will try to fill in later when being displayed o Human eye more sensitive to brightness details than to colour details 1. The quality of a JPG file is proportional to the file size 2. A higher image quality setting has lower compression value,  results in less data being distorted Colour Resolution • Colour resolution = bit depth Dithering • Definition: juxtaposing (placing side by side) pixels of two colours to create the illusion that a third colour is present (grainy look) • Can lower download time • Most common method of reducing colour range of images down to 256 (or fewer) colours seen in 8 bit .gif images • If an image uses colour hues outside of browser-safe palette  browser automatically dithers image into browser safe colours Animation • .gif allows for animation • Don’t need plug in for .gif animation (universal format) Interlacing • When the image is drawn in a series of passes rather than all at the same time (file size bigger) • How images are downloaded to your screen Transparency • Allows the page background to display through the image • Only formats that support transparency = GIF and PNG • Transparent: every pixel in the image is either completely visible or completely see-through so that what’s underneath the image shows through PNG (Portable Network Graphics) • Developed as a replacement for GIF due to legal issues resulting from GIF’s use of the L2W compression scheme • Lossless compression  no discard • Allows for image to have up to 48 bit colour • Supports opacity and translucency PNG-8 • Similar to GIF • Only allows 8 bit colour • One transparent colour • Smaller than GIF counter parts PNG-24 • Allows 24 bit colour • Lossless   JPG will be smaller • Allows for transparency on each pixel Advantages for PNG • Lossless compression • Smaller or same size as GIF • Supports opacity and translucency Disadvantages for PNG • Older browsers may not support format • No animation • File size for 24 bit is bigger than JPG GIF or JPG??? GIF JPG • Line art, logos, illustrations • photos, computer game screenshots, movie stills • 8 bit colour resolution max (256 • 24 bit colour resolution colours) • Lossless compression • Lossy compression • Supports dithering • Does not support dithering • Allows for transparency • Does not support transparency • Interlace process • Progressive JPG • animation • Not for animation GIF JPG PNG-8 PNG-24 Best For Logos, cartoons, photographs Logos, cartoons, Photographs that drawings drawings need transparency Compression Lossless Lossy Lossless Lossless Browsers All All All Not on IE Transparency One colour only No One colour only Translucency Animation Yes No No No Dithering Yes No Yes No Interlacing Yes No (progressive) Yes Yes Shape of IMG Rectangular • Lecture 5 Computer Network • Network: a group of interconnected computers (connected by wires, wirelessly, or satellites) • Network configurations: group of millions of computers around the world that are all connected to one another The Internet • Internet: a global system of interconnected networks that use the Standardized Internet Protocol Suite (TCP/IP) to serve billions of users worldwide • A network of networks • The Internet is hardware, not software • The World Wide Web: software that runs on the Internet • Uses TCP/IP - A standard protocol - Rules for the format and transmission of data TCP • At the sending end - Takes large chunk of data and breaks into small packets • At the receiving end - Detects lost packets - Rearranges and reassembles the packets • Packet: a small group of bytes consisting of… - Header (usually 64 bytes) o Destination, source - Body (512 bytes) o Actual message IP • IP = Internet Protocol • Picks a route for a packet, stopping at routers which pick the next best machine/network to send the packet to • If communication line is down/broken  sends the message back to TCP and tries a different route • All computers on the Internet need to be identifiable IPAddress • Identifies each computer or device connected to the internet • Consists of 4 numbers with dots between them • Each number ranges from 1-255 (ex: • IP addresses are not geographical Summary • TCP breaks webpage into packets of bytes • TCP figures out IP address of where it wants to send the packets (destination) • TCP figures out IP address of where the packet is coming from (source) • Sends off each packet to first machine (IP address) on the route – does not re-plan route • Packet stops at first machine, likely a router, then the router sends it to the next machine on the journey (IP address) and so on until it reaches the final IP address (destination) Domain Name • The text name corresponding to the numeric IP address of a computer on the Internet • A DNS (Domain Name System) maps the domain name to the correct IP address so data can route to the correct computer URL • Uniform Resource Locator • A web document address on a computer • Established by Tim Berners-Lee Second level domain Top level domain (TLD) World Wide Web Third level domain (sub domain) (Not part of domain) Sub Domains • Used to organize your web server (just like folders and directories organize your computer) Starting a Website 1. Choose a domain name - TLD identifies type of organization associated with the domain - Cost: you pay for securing the domain name on a per year basis Suggestions: - Keywords: pick a domain name with keywords in it - Be memorable: descriptive, memorable, and easy to spell - Avoid hyphens: use only if you don’t have a choice - Buy “.com” first: default extension in most people’s mind - Keep it short: people remember short names - Kill procrastination: register ASAP - Get creative: if first name is taken, add “e” or “i” or # in front of name - Know the rules of domain name - Test it out before buying - Buy up misspelled domains 2. Order Web Hosting - Web Hosting: the source that provides Internet users with online systems for storing information, images, video, or any content accessible via web - Web Hosts: (Internet Service Provider- ISP) Companies that provide space on a server they own for use by their clients as well as providing Internet connectivity - ISP provides user accounts for accessing Internet, email access,
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