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?