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Digital Media & Data Representation. Why Digital Media Requirements Matter. Storage Management and Planning How much must be stored? How to store it efficiently? Compression Approaches Lossy vs. Lossless Formats Transmission Management and Planning

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Digital media data representation l.jpg

Digital Media &Data Representation


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Why Digital Media Requirements Matter

  • Storage Management and Planning

    • How much must be stored?

    • How to store it efficiently?

    • Compression Approaches

      • Lossy vs. Lossless Formats

  • Transmission Management and Planning

    • Sound & Music (Phone, Radio, CD vs. MP3 quality)

    • Graphics (BMP, JPEG, GIF, etc).

      • Note: Size matters especially for web transmission

    • Quality versus Size Tradeoffs



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Information Theory

  • Permutations (Unique Combinations) translate to how many different states can be stored and transmitted

  • Series of bits represents permutations through unique sequences of “on” “off”

  • Powers of 2 (2n)


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Understanding Binary

  • Most modern media, data representations, transmissions and computer based addressing schemes use binary, Eg.:

    • Images including pictures & video (jpg, mpeg)

    • Sound and Music (CDs, MP3)

    • Digital Photography (RAW, jpg, tiff)

    • Color schemes on Web Pages (RGB=005533)

    • Internet Protocol (IP) addresses (192.23.55.231)


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Powers of 2: Binary Numbers

23 * 23 = 26

23 * 23 = 26

23 = 8 ; 26 = 64

Same as

8 * 8 = 64


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Media File Compression

Definition:

“Image and sound files can be quite large, and larger files mean more storage space and slower downloads. Compression means “file size reduction.” Compression schemes can be lossy or lossless.”


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Lossy vs. Lossless Compression

  • Lossy:

    “Lossy algorithms accept some degradation in the image or sound in order to achieve smaller file size.”

  • Lossless:

    “A lossless compression algorithm discards no information. It looks for more efficient ways to represent an image or sound, while making no compromises in accuracy.”


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Number of Color Options

  • # of color options in a pixel is given by the following formula:

    color options = 2# of bits of image

  • Example: if a file format is said to have 8 bits (or one Byte), it supports 28 = 256 colors



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Quality Comparison

JPG, High quality (319 K)

JPG, absurdly high compression (18 K)


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Representing Graphics and Video

  • Storage per representation scheme

    • Resolution: Number of pixels per image

    • Color Quality: Number of bits/pixel

    • Motion Quality: Number of frames/second

    • Duration: Number of seconds

    • Codec: Compression ratio

  • Image File sizes and quality:

    • Bitmap (original) vs. JPEG (lossy compressed)

      See next slide


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.BMP (442 KB) vs. .JPG (21KB)


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Vector Graphics: GIF example

  • Combines geometrical shapes to create artificial images.

  • Generally uses much less storage space than real images.

  • Adobe Illustrator Software


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Digital Media Applications

  • Desktop Publishing

  • CAD (Computer Assisted Design)

  • Computer Animation (Toy Story)

  • Photo Editing (Photoshop/Elements)

  • Digital Video (Movies, editing, Forensic Graphics, etc.)

  • Education and Training. (e.g. Virtual Chemistry Lab – developed at BYU)

  • Video Games (Halo, Madden NFL Football)

  • Advertising Promotion (Prius)

  • Interactive TV (Video on Demand, tCommerce, PVR)


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Digital Photo Editing

  • Another advantage of digitizing images and sound is that computers and software may be used to enhance or modify the original artifact. This is much easier and less expensive than using analog methods.

  • The following modification was a simple edit using Photoshop elements.



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High Definition TV

  • HD “Lines per screen” – horizontal scan

    • 480

    • 720

    • 1080 – highest resolution

  • Scanning Formats

    • i = Interlaced: 2 half-frames (every other line) make a complete picture

    • p = Progressive: full frame displayed – generally best

  • Capability Terminology

    • HD Ready = Display only – requires HD source (e.g. HD tuner)

    • Integrated HDTV = Has HD TV tuner built-in; only needs antenna

      • (this is also called “HD Built-in”)

    • HD Built-in DCR = “digital cable ready” requires a cable card to receive digital cable, or antenna to receive over-the-air broadcasts.


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Representing Sound

  • Sampling rates (frequency) (Hertz)

  • Sampling resolution (bits per sample)

  • Number of channels (mono vs. stereo)

  • Duration of sound (Time)


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HDTV - Two Important Dates:

  • March 1, 2007 – After this date all new TV and video products imported to the US or shipped to retailers that include an analog (NTSC) tuner must also include a digital (ATSC) tuner. (Note: existing old stock may still be sold – be CAREFUL!!)

  • February 17, 2009 – US cutoff date for “over the air” broadcast of analog TV signals. Afterwards all “over the air” broadcasts will be digital.

  • (NOTE: this does not apply to cable TV or monitors which do not include any “over the air” tuner.)


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Common Sound File Formats

  • .aac – Advanced Audio Coding (Apple)

  • .au – Audio – used with Apple & Linux OS

  • .cda - Compact Disc Audio – traditional CD

  • .mid – MIDI commands

  • .mp3 – common music compression format

  • .ra – Real Audio (company)

  • .wav – Waveform Audio (Windows raw audio)

  • .wma – Windows Media Audio - compressed


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MP3 vs. CD: Can You Hear the Difference?

Source: http://www.pcmag.com/print_article/0,3048,a=35271,00.asp



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