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					Digital Media

 Dr. Jim Rowan

   Chapter 2
        Today’s Question!
• Who suggested that in order to best
  predict the future one should invent it?
         First, some
mac software you will be using
         (found in the application folder)
• Grab - used to do a screen capture
• TextEdit - used as a simple word
  processor
• PhotoBooth - used to take your picture
  with the built in camera and take video
  with the built in camera
• Quicktime Pro - to convert videos to a
  number of different formats and check
  the sample rate and sample size
About file formats and extensions
          (like .au, .doc, .ppt, .mov)
 • Indication to us (the humans) what kind
   of file this is
 • Some software looks at the extension
   – so... some software will try to open files
     with improper extensions
   – results in “file corrupted” error message
   – try it... change the extension from .doc to
     .jpg
  File formats and extensions
• Some software looks at the data in the file for
  more definitive answer (the header)
      • important file-related information is encoded in the data
        of the file
      • for example: some image formats have color tables to
        reduce the size of the file
      • some video just saves the changes from one frame to the
        next
      • we’ve seen the header before when we used hexFiend
        to look at images… image size is stored in the header
           The Question:
• How do you put stuff in a computer
  – so that you can manipulate it
  – so that you can send it
  – so that someone else can see and use it?


• How do you represent the real world in
  a digital world?
              The answer:
•   Represent the real world as numbers
•   Store the numbers
•   Transmit the numbers
•   Retrieve the numbers
•   Display them in a form humans
    understand
                  Today:
• Chapter 2 is a “first cut” of nearly all the
  material that will be covered in greater
  detail this semester

• About the real world
• About digital representation
• From the first day’s lecture we saw
  different types of real world stuff as a
  bunch of numbers
Note on paper
Picture
Song: fieldsOfGold.mp3
Video
So it’s all just numbers, and
  binary numbers at that!

 First we must talk about
   numbering systems!
Numbering systems:

     Decimal
      Binary
   Hexadecimal
Which statement is True?

        5 + 5 = 10

        1 + 1 = 10

        7 + 1 = 10
      well… it depends…
        5 + 5 = 10 (in decimal)

        1 + 1 = 10 (in binary)

        7 + 1 = 10 (in octal)


welcome to numbering systems!
       Numbering systems
• Humans: decimal
  – Humans: 10 fingers, 10 digits
  – 0, 1, 2, 3, 4, 5, 6, 7, 8 & 9


• Computers: binary
  – Computers: 1 finger, 2 digits
  –0&1
               Hexadecimal
• Humans and Computers: hexadecimal
  – Hexadecimal: 16 fingers, 16 digits
  – 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
       Why Hexadecimal?
• You can use one hexadecimal instead of 4 binary
  digits
• While this seems complicated.. it is actually easier
  (after some practice!) for humans to deal with 16
  different digits than 4 0s and 1s
• In Hex: 0123456789ABCDEF
• In binary: 0000 0001 0010 0011 0100 0101 0110
  0111 1000 1001 1010 1011 1100 1101 1110 1111
      How many different things?
• In Decimal 1 digit can represent 10 different things:
   – 0123456789
• In Decimal 2 digits can represent 100 different things:
   – 00 01 02 03 04 05 06 07 08 09 10 11 12… 97 98 99


• In Binary 1 digit can represent 2 different things:
   – 0 and 1
• In Binary 2 digits can represent 4 different things:
   – 00 01 10 11

• In Hexadecimal 1 digit can represent 16 different things:
   – 0123456789ABCDEF
• In Hexadecimal 2 digits can represent 256 different things:
   – 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15
     16 17 18 19 1A 1B 1C 1D 1E 1F 20 21… F9 FA FB FC FD FE FF
       How many different things?
• So… how many things can you count with 4 hex digits?
   – USE THE FORMULA!
   – [number of digits in the numbering system]**[number of
     digits used]…
   – [16]**[4] = 65,536
• How many things can you count with 4 decimal digits?
   – [number of digits in the numbering system]**[number of
     digits used]…
   – [10]**[4] = 10,000
• How many things can you count with 4 binary digits?
   – [number of digits in the numbering system]**[number of
     digits used]…
   – [2]**[4] = 16
            Counting…
with a different number of fingers
(it’s the same process but different number sets)

 • 10 fingers: Counting in decimal
   – 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 then… start over with 0
     and increment the digit to the left ==> 10
 • 1 finger: Counting in binary
   – 0, 1 then… start over with 0 and increment the
     digit to the left ==> 10
 • 16 fingers: Counting in hexadecimal
   – 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F then…
     start over with 0 and increment the digit to the left
     ==> 10
             Binary Coding
• Data for a computer... Binary
  – zeros and ones
• Data for humans... Hex
  – 1 Hexadecimal represents 4 binary digits
• Data for humans… ASCII (the alphabet)
  – 2 hex codes ==> 1 ASCII code


  For example ==>
        Example: ASCII Code
• Humans and Computers: ASCII
  – The ASCII code for C is
    • in hexadecimal: 43 (In decimal: 67)
    • which is binary: 0100 0011
   Stuff in the Real World
               to
Stuff on a computer… HOW?
• A note…
  – Letters of the alphabet-> bits (0s and 1s)
• A picture…
  – Reflected light -> bits (0s and 1s)
• A song…
  – Pressure waves in air -> bits (0s and 1s)
• A video…
  – Pressure waves in air and Reflected light ->
  bits (0s and 1s)
        HOW?

First, the real world of:

       Discrete
          &
      Continuous
Phenomena in the Real world:
   discrete vs continuous
•   Things in the real world can be discrete
•   They either ARE or they ARE NOT
•   These things can be counted
•   Examples:
    – The number of cars in the parking lot
    – The number of beans in a jar
Phenomena in the Real world:
   discrete vs continuous
• Things in the real world can be continuous
• Continuous can’t be counted, it must be
  measured
• Examples:
  – Atmospheric pressure
  – Height of an ocean wave
  – Frequency of a sound wave
      The problem is...
   computers can only count
• Discrete data is easy for a computer
  – count it and store it as a number

• Continuous data... easy? not so much
  – music:
     • measure the frequency & amplitude
     • encode as a collection of numbers
  – pictures:
     • measure the amount (intensity) and frequency of light
       (color) in a number of spots of light (pixels)
     • encode the frequency and the intensity as a collection of
       numbers
             Question...
• If computers only store 0s and 1s...
• How does all this continuous stuff end
  up in a computer so that we can save it
  and play it back?
• Answer
  – Continuous data must be converted to
    discrete data
        From the Real World
           …and Back!
Converting continuous phenomenon to digital data:
 -You must SAMPLE to convert it to discrete
  Sampling consists of two processes
             1) stop to take a measurement
                     the number per time period is called the sample rate
             2) take the measurement
                     the number of different values each sample can take
                        on is called the quantization level
Digital data back to continuous phenomenon:
  – Display samples using “sample and hold”
     • Play the sample for the duration of the sample time
        But...
How many samples do you
        need?

      It depends…
single sample
single sample
  single sample
(sample and hold)
two samples
two samples
  two samples
(sample and hold)
three samples
three samples
  three samples
(sample and hold)
four samples
four samples
  four samples
(sample and hold)
five samples
five samples
   five samples
(sample and hold)
Taking it a lot farther…
Taking it a lot farther…
     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 being
    captured
  – Results in an ok file size
  – Results in faithful representation when replayed
        CD quality is
 44,100 samples per second
• Why?
  – Human hearing response is in the range of 20
    to 22,000 cycles per second


• Nyquist sample rate =
  highest frequency to be captured = 22,050 CPS
  2 x 22,050 = 44,100 samples per second
Looking at FieldsOfGold.mp3…
• 4 minutes and 59 seconds long
• 1,201,173 bytes in length
Can this be right?
• CD quality
  – 44,100 samples per second (sample rate)
  – 16 bit samples (quantization level is 16 bit)
  – 16 bits can store 65,536 different levels
     • (2**16 = 65,536 individual levels)
           FieldsOfGold.mp3
• 4’59 = 299 seconds long
• 299 x 44,100 samples per second
    = 13,156,000 samples
• 13,185,900 x 2 bytes/sample (2 bytes = 16 bits)
    – 26,371,800 bytes
•   Stereo: 2 channels => 52,743,600 bytes
•   Should be 52+ megabytes!
•   Why does it show only 1.2 megabytes?
•   HMMMmmm...
             FieldsOfGold.mp3

• Why 52+ megabytes not 1.2 megabytes?
  – wait for it…
            FieldsOfGold.mp3

• Why 52+ megabytes not 1.2 megabytes?

• This is an MP3!
• The data is COMPRESSED!
• If you had the song on a CD it would be 52+
  megabytes long and in .aiff format
  Two types of compression
• Lossy
• Lossless




         run length encoding   .mp3 audio
         table compression     .jpeg images
          Further reading
• http://en.wikipedia.org/wiki/Nyquist_rate
• http://en.wikipedia.org/wiki/Sampling_%
  28signal_processing%29
• http://en.wikipedia.org/wiki/Mp3
The side effects of sampling:
     sampling artifacts

    Sampling Artifacts
are the negative side effects
caused by having to sample
      continuous data
        Sampling Artifacts
• Under-sampling: not enough samples
  being taken of continuous data can
  produce undesired artifacts
• Examples might be:
  – Moire’ patterns on images
  – retrograde motion on video
   Sampling Artifacts (cont.)
• Not enough quantization levels when
  sampling continuous data can produce
  undesired artifacts
• Examples might be:
  – too few grey levels: gradients become steps
  – too few brightness levels: posterization
       Sampling Artifacts
       Retrograde Motion



4 samples/cycle, 2 cycles



2 samples/cycle, 2 cycles
   Sampling Artifacts (cont.)
• Audio
  – too few amplitude levels, quantization
    noise
     • 8 bits (256 amplitude levels) produces
       discernable noise
     • 16 bits (65,536 amplitude levels) CD
       quality, no discernable hiss
  – general sound “fuzziness” or a “flat”
    sound
    Data Representations
How stuff is stored in a computer
 • Images
    • Bitmapped
    • Vector
 • Audio
 • Animation
 • Video
 • Text
        Images, bitmapped
• Are stored as arrays of pixels
• Can be stored directly
  – TIFF for example
• Can have an associated color map
  – JPEG for example
• Generating these pixels from the stored
  model is called rendering
     Images, vector graphic
• Are stored as mathematical descriptions
• Often smaller than bitmapped
• Size of the file is independent of
  resolution or image size
• Not suitable for some type of images
      Example & Comparison
• Bitmapped graphics
   – Defined as spots (pixels) of color
   – Problems scaling
   – File size unaffected by image complexity
   – File size affected by the image size
• Vector graphics
   – Defined by their parts
   – File size affected by image complexity
   – File size unaffected by the image size
      (scaling is easy)
           Moving images
• Captured live with camera
  – iMovie
  – Stored as video
• Generated from animation
  – Blender
  – Similar to 2D vector graphics… but in 3D and
    with a means of creating motion
Network communication
         But first…
   what this stuff means:
Bit: binary digit
Byte: 8 Bits
KB: kilo byte (1000 bytes)
MB: mega byte (1,000,000 bytes)
GB: giga byte (1,000,000,000 bytes)
TB: tera byte (1,000,000,000,000 bytes)
KBPS: kilo (1,000) bits per second
MBPS: mega (1,000,000) bits per second
               Note this!
• Communications are usually stated in
  bps (bits per second)
• Filesize is usually stated in bytes

• AND: 8 bits per byte
  – you will have to convert from one to the
    other when you do download/upload
    calculations
         Network access...
• dial up connection
  – phone modem
  – asymmetric
     • 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
 – asymmetric
   • 6.1 mbps 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
     Network access...
  Commercial internet users
• T1 connection 1.544 mbps
• T3 connection 44.7 mbps
• Provide web servers for others to put
  websites on
• Large commercial enterprises will have
  their own web server
   Time-to-download/upload
         calculations
• The Speeds:
  – Dial-Up
     • 56,000 bps internet to modem (downstream)
     • 33,600 bps modem to internet (upstream)
  – ADSL
     • 6.1 mbps (million bps) downstream
     • 640 kbps (thousand bps) upstream
  – T1                                     NOTE!
     • 1.544 mbps                          bps is bits per
  – T3                                     second while filesize
     • 44.7 mbps                           is stated in   bytes
    Time-To-Load calculations

For a 1.2 megabyte video:

How long would it take to load it to youTube over
  -fastest dialup
  -adsl
  -T1
  -T3
How long would it take to download it from youTube over
  -fastest dialup
  -adsl
  -T1
  -T3
Servers and Clients
              Servers & Clients...
• Clients consume and display 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 sent by the server is interpreted by the client (browser) and
     displayed on your display
• Look at http://www.pondliner.com/ and view source
       URL (uniform resource locator)…
          a human-readable name

• URL takes the form:

 http://www.amazon.com/newStuff/index.html
• URL has 3 parts
  – the protocol that you are using (http://)
  – The domain name: (www.amazon.com)
  – The directory and file you want to see:
    (newStuff.index.html)
  – the URL 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 from connection to connection) IP

• An example: my IP right now (assigned through
  dhcp) is: (look it up in system preferences)
• IPv4 vs IPv6
                                         requested
      your browser                       webpages
      (Safari)(client)
                         DHCP:
your computer                          yahoo.com
                                         (server)
                                      235.01.30.164

                                       walmart.com
                                         (server)
                    The Internet      100.43.153.07

           Domain Name System (DNS)
                                        requested
     your browser                       webpages
     (Safari)(client)
        DHCP: 135.10.34.143
your computer                         yahoo.com
             ISP                        (server)
                                     235.01.30.164

                                      walmart.com
                                        (server)
                   The Internet      100.43.153.07

          Domain Name System (DNS)
                                                 requested
      your browser                               webpages
      (Safari)(client) http://www.yahoo.com
         DHCP: 135.10.34.143
your computer                                  yahoo.com
                                                 (server)
                                              235.01.30.164

                                               walmart.com
                                                 (server)
                  The Internet                100.43.153.07

          Domain Name System (DNS)
          http://www.yahoo.com =
          235.01.30.164
                                                 requested
      your browser /index.html                   webpages
      (Safari)(client) http://www.yahoo.com
         DHCP: 135.10.34.143
your computer                                  yahoo.com
                                                 (server)
                                              235.01.30.164

                                               walmart.com
                                                 (server)
                  The Internet                100.43.153.07

          Domain Name System (DNS)
          http://www.yahoo.com =
          235.01.30.164
Questions?

				
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posted:1/21/2013
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