Introduction to Multimedia

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Introduction to Multimedia
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Multimedia

• Its not new
• It encompasses
• Pictures
• Sounds
• Text
• Just about anything to communicate
• Well focus how it applies to computing/PC
• PC is the only media that can use all forms

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Whats on the Web?

• Play voice recordings
• Display images
• Display text
• Play video
• Play music
• Virtual Reality

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Digitization

• The act of converting multimedia to numbers
• Before digitization, each form of technology had
  its own technology
• Text book
• Images photographs (later magazines)
• Moving Images theater or TV
• Sound the wax cylinder
• Storytelling humans
• All of these are independent
• All of these are non-interactive

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Digitization

• Didnt really occur until the 1980s
• Web explosion in the 1990s
• Analog
• Exact copy (continuous information)
• Infinite resolution
• Digitization
• Approximation
• Break signal into tiny pieces and assign a number
  to it

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What is this?
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What about this?
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Now?
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Guess who
Original
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How it works

• The computer views the pre-digitized image from
  left to right
• Looks at the average color of that area and
  assigns a number (1 pixel)
• A pixel is the smallest light-emitting speck on
  your screen
• Lets see an example

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Original Image
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Computers View(72 x 47)
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Make Approximations(Obvious Color Choices)
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Make Approximations(Not-so-obvious)
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Before
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After!
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Assign Numbers(white0, off-white2, black255,
red128, green28)
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Our Final Teletubbies Pic

• Just numbers in a file
• To display picture
• read from file
• Use those numbers as color values

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 204, 206, 198, 67,
42, 0, 0, 0, 0, 0,
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Same is True for Sound

• Computer samples or listens to the sound wave
• Sample rate
• Number of bits/sample
• Later on in course
• Convert continuous wave into discreet numbers

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File Formats

• All files are just a series of numbers
• Extension tells you what kind of file it is
• .wav
• .wmf
• .mov
• Its up to the application to interpret the data
• /dev/sound

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Bandwidth

• How much data can pass through a connection
• If a picture is 320 pixels by 240 pixels
• 76,800 pixels
• If theres 16 bits per pixel 76,800x16
• 1.22M bits
• Modem is 56Kbps
• DSL and Cable are 512Kbps
• Ethernet 10/100Mbps

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Math

• 1,228,800 bits / 56,000 bps 21.94 seconds
• This sucks
• 1,228,800 bits / 512,000 bps 2.4 seconds
• Better
• 1,228,800 bits / 100,000,000 bps 0.012 sec
• Not bad
• Do you wait 21.94 seconds at home?
• How do they speed it up?

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Compression

• Reduces the size of the file to be sent over the
  connection
• Compression is a must (bandwidth)
• Compression
• Done by the author of the media
• User gets the compressed version
• User decompresses to see/hear media
• The more a file is compressed
• The faster it travels over the connection
• The lower its quality (usually)

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CodecsCompressor/Decompressor

• Different kinds of codecs (example .jpg)
• Lossy vs lossless
• Work by
• Removing repetition (images - lossless)
• Averaging (images - lossy)
• Range reduction (sound/images - lossy)
• Selectivity (sound - lossy)
• Frame-Difference (video lossless)
• http//www.howstuffworks.com/file-compression.htm

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Picture of Jim Graham (Java Guru)
JPG 28K
Gif 133K
JPG 12K
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File Formats(Well study these in detail later)

• Usually contain a header
• Identifies the type of file (image? Size? Codec?)
• Common audio
• .wav, .aiff, .mp3, .au, .ra, .mid
• Common image
• .bmp, .jpg, .gif, .png, .tga
• Common video
• .wmf, .mov, .avi, .mpg, .ram
• Plugins helper programs

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Screen Resolution

• Determined by of pixels across by of pixels
  down
• Common Resolutions
• 320x240 (old games)
• 640x480 (VGA)
• 800x600 (A lot of laptops)
• 1024x768 (SVGA)
• 1600x1200 (sweet)

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Why Resolution Matters
On a 1600x1200 screen
On a 640x480 screen
Conclusion lower resolution less space
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