Post on 19-Jan-2016
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
single sample
two samples
two samples
three samples
three samples
four samples
four samples
five 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
• http://en.wikipedia.org/wiki/Defragmentation
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
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
LGVX3400
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
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
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
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
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 1.544 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 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
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
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
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
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
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
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
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
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
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
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?