Digital Media Dr. Jim Rowan ITEC 2110 Wednesday, August 30.
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Transcript of Digital Media Dr. Jim Rowan ITEC 2110 Wednesday, August 30.
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Digital Media
Dr. Jim Rowan
ITEC 2110
Wednesday, August 30
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Roll call
Barton, Paul H.Bois, Lauren C.Bonds, Allison E.Duncan, Jarred T.Lawson, Joseph I.Mulongo, Julio B.Pennison, Heather L.Reilly, Daniel J.
Sanchez-Casas, Jon F.Simson, DavisSinnock, Grant A.Swaim, Mark S.Tran, Dung Q.Vyas, Anand A.Woldeyohannes,
Tesfamichael
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Class capture access
http://seacubed.ggc.usg.edu/
password same as login
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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
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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
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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
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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”
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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
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Hardware requirements
• Video capture requires large areas of contiguous disk space
• Frequent disk defragmentation is required
• http://en.wikipedia.org/wiki/Defragmentation
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defragmentation black is occupied spacewhite is available space
memory before
memory after
largest contiguousspace is 5
largest contiguousspace is 11 and thereare 6 of these
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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
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Hardware requirements Form factor...
Displayed unmodified
laptop display of my GGCwiki site
Treo
LGVX3400
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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)
• http://en.wikipedia.org/wiki/RAID
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RAIDredundant
94731990
94731990
94731990
94731990
94731990
94731990
94731990
94731990
94731990
disk #1
disk #2
disk #3
disk #4
disk #5
disk #6
disk #7
disk #8
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RAIDoverlapped(fast)
7
3
1
9
9
4
0
9
94731990
disk #1
disk #2
disk #3
disk #4
disk #5
disk #6
disk #7
disk #8
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Networks
• Local Area Network (LAN)– local routers, bridges, switches...
• Internet– Uses TCP/IP protocol (the rules your
communication must follow)– http://en.wikipedia.org/wiki/TCP/IP– you get access through an ISP
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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
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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
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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
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Commercial internet users
• Provide web servers for others to put websites on
• Large commercial enterprises will have their own web server
• T1 connection 1.544 mbps
• T3 connection 44.7 mbps
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Servers & Clients...
• Clients consume internet content• Your browser is a client• Clients request content from servers
– by sending a server an HTTP://URL 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
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Servers & Clients...
• URL is a human-readable name• uniform resource locator• takes the form
www.amazon.com/newStuff/index.html • The domain name: www.amazon.com• The file you want to see is: newStuff.index.html• the name maps to a number called an IP
address• http://en.wikipedia.org/wiki/IP_address
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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: 10.0.106.91
• my IPv6 address (new addressing scheme) is fe80:0000:0000:0000:0211:24ff:fe8f:abb6
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yahoo.com(server)
235.01.30.564
The Internet
you at home running a browser
(client)DHCP:
walmart.com(server)
100.43.153.07
ggc.usg.edu(server)
145.67.33.73
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yahoo.com(server)
235.01.30.564
The Internet
you at homerunning a browser
(client)DHCP: 10.0.91.35
walmart.com(server)
100.43.153.07
ggc.usg.edu(server)
145.67.33.73
ISP
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yahoo.com(server)
235.01.30.564
The Internet
www.yahoo.com=
235.01.30.564
you at homerunning a browser
(client)http://www.yahoo.com
walmart.com(server)
100.43.153.07
ggc.usg.edu(server)
145.67.33.73
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yahoo.com(server)
235.01.30.564
The Internet
you at GGCrunning a browser
(client)DHCP:
walmart.com(server)
100.43.153.07
ggc.usg.edu(server)
145.67.33.73
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yahoo.com(server)
235.01.30.564
The Internet
you at GGCrunning a browser
(client)DHCP: 322.21.5.36
walmart.com(server)
100.43.153.07
ggc.usg.edu(server)
145.67.33.73
ISP
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yahoo.com(server)
235.01.30.564
The Internet
www.walmart.com=
100.43.153.07
you at starbucksrunning a browser
(client)HTTP://www.walmart.com
walmart.com(server)
100.43.153.07
ggc.usg.edu(server)
145.67.33.73
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MIME types
• Multipurpose Internet Mail Extension• Allows the transmission of more than
just ASCII text (like you’d expect in an email)
• MIME types are specified in the header• Huge variety of MIME types are allowed
– audio, images, video– compressed files
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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
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Questions?