Digital Media Dr. Jim Rowan ITEC 2110 Wednesday, August 29

Roll call Jones, Crystal L. Marsh, Kerreen A. Thompson, Daniel G. Tran, Christopher V.

single sample

two samples

three samples

four samples

five samples

How frequently should I sample? too few –small file size (good) –not a faithful representation when replayed too many –large file size (bad) –excellent representation when replayed The Nyquist rate –twice as many samples as the frequency –ok file size –faithful representation when replayed

Sampling Artifacts Under-sampling (too few samples) of continuous data can produce undesired artifacts –audio distortion –jagged edges on images –Moire’ patterns on images –retrograde motion on video

Sampling Artifacts (cont.) Not enough quantization levels when sampling continuous data can produce undesired artifacts Images –too few color: colors look artificial –loss of fine distinction –too few grey levels: gradients become steps –too few brightness levels: posterization

Sampling Artifacts (cont.) Not enough quantization levels when sampling continuous data can produce undesired artifacts Audio –too few amplitude levels, quantization noise - hiss 8 bits (256 amplitude levels) produces discernable noise 16 bits (65536 amplitude levels) CD quality, no discernable hiss –general sound “fuzziness”

Multimedia Hardware Requirements Multimedia consumption? –requires only a lower powered machine Multimedia production? –requires a more powerful computer –consider “fields of gold.mp3” 26+megabytes of data uncompressed 1.2 megabytes of data compressed –images are produced in layers then flattened for consumption

Hardware requirements Video capture requires large areas of contiguous disk space Frequent disk defragmentation is required n

defragmentation black is occupied space white is available space memory before memory after largest contiguous space is 5 largest contiguous space is 11 and there are 6 of these

Hardware requirements: Form factor... screen real estate makes a difference –size is smaller? –can/should affect the format of the display cannot simply display the same page on –a desktop computer –a cell phone –a pda

Hardware requirements Form factor... Displayed unmodified laptop display of my GGCwiki site Treo LG VX3400

Hardware... RAID Redundant Array of Inexpensive Disks Designed as a hardware failsafe –multiple copies of the same data Can be used to speed data transfer –(you may need this in multimedia production)

RAID redundant disk #1 disk #2 disk #3 disk #4 disk #5 disk #6 disk #7 disk #8

RAID overlapped (fast) disk #1 disk #2 disk #3 disk #4 disk #5 disk #6 disk #7 disk #8

Networks Local Area Network (LAN) –local routers, bridges, switches... Internet –Uses TCP/IP protocol (the rules your communication must follow) – –you get access through an ISP

Network access... dial up connection –phone modem –limited to 56,000 bps (bits, not bytes) max downstream (internet to modem) –33.6 kbps upstream (modem to internet) –rarely get these speeds

Network access... ADSL –asymmetric digital subscriber line –over copper phone wires –limited to short distance from phone switch –6.1 mbps (million bps) downstream –640 kbps upstream

Network access... Other options –Cable modem (also asynchronous) –satellite with phone (also asynchronous) –satellite alone (expensive but available in the boonies) –local wireless networks –high altitude tethered balloons –transmission over power lines

Commercial internet users Provide web servers for others to put websites on Large commercial enterprises will have their own web server T1 connection mbps T3 connection 44.7 mbps

Servers & Clients... Clients consume internet content Your browser is a client Clients request content from servers –by sending a server an message which is a request for a web page Servers respond to requests for internet content –send requested web pages to Clients The content is sent in HTML code –HTML is interpreted by the client (browser) and displayed on your machine

Servers & Clients... URL is a human-readable name uniform resource locator takes the form The domain name: The file you want to see is: newStuff.index.html the name maps to a number called an IP address

Servers & Clients... servers have fixed IPs so they are easy to find your computer probably uses DHCP which is a dynamic (changing) IP An example: my IP right now (assigned through dhcp) is: my IPv6 address (new addressing scheme) is fe80:0000:0000:0000:0211:24ff:fe8f:abb6

yahoo.com (server) The Internet you at home running a browser (client) DHCP: walmart.com (server) ggc.usg.edu (server)

yahoo.com (server) The Internet you at home running a browser (client) DHCP: walmart.com (server) ggc.usg.edu (server) ISP

yahoo.com (server) The Internet = you at home running a browser (client) walmart.com (server) ggc.usg.edu (server)

yahoo.com (server) The Internet you at GGC running a browser (client) DHCP: walmart.com (server) ggc.usg.edu (server)

yahoo.com (server) The Internet you at GGC running a browser (client) DHCP: walmart.com (server) ggc.usg.edu (server) ISP

yahoo.com (server) The Internet = you at starbucks running a browser (client) walmart.com (server) ggc.usg.edu (server)

MIME types Multipurpose Internet Mail Extension Allows the transmission of more than just ASCII text (like you’d expect in an ) MIME types are specified in the header Huge variety of MIME types are allowed –audio, images, video –compressed files

A word about standards Standards allow cooperation But standards require agreement Works well during slow growth But in a rapidly changing environment... –frequently obsolete before adopted One company may dominate the market becoming the de-facto standard

Questions?