Multimedia image formats, manipulating images, Audio

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Multimedia image formats, manipulating images,
Audio

• Norman White

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Features of image formatsBitmapped

• Compression
• Lossless GIF, PNG
• Bit for bit representation
• Lossy JPEG, PNG
• User controls amount of compression
• Higher compression, fuzzier image
• Colors
• GIF 256 (8bit)
• JPEG 24 million (24 bit)
• PNG 48 million (25 bit)
• Transparency
• GIF yes, JPEG no, PNG no
• Animation
• GIF yes, JPEG no , PNG no
• Progessive Download
• Gif - yes, JPEG yes, PNG - no

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Image formats

• Gif, Gif89a (Graphics Interchange Format)
• Lossless format developed by compuserve
• Proprietary ? licenses
• Gif89a includes animation, transparency,
  progressive download
• Only 256 different colors, not great for photos
• Since it is lossless, best for images that have
  text in them or line art.
• JPEG doesnt support transparency

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JPEG

• Joint Photographic Experts Group
• Lossy compression (controllable by user)
• No animation
• No transparency
• Millions of colors
• Progressive download support

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PNGPhotographic Experts Group

• Developed in response to licensing issues with
  GIF
• Supports lossless or lossy compression
• Not supported by all browsers
• No animation

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Animated GIFS

• Animated GIFs are just multiple images
  sandwiched together into 1 file so that each
  image plays for a fixed amount of time.
• Process
• Create the image sequence
• Use a program like Gif Constructor to merge
  images and specify timing.

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Animating other images

• We can use Javascript programming to animate
  other kinds of images like JPEGs.

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Vector Graphics

• Another way to store images is a sequence of
  commands that are used to recreate (draw) the
  image on the users computer.
• The commands that it takes to describe the image
  are almost always much smaller than representing
  the image as a bitmap (even compressed)

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Example of Vector Graphics

• Draw a red circle
• Circle (100, 100,30)
• Move (100,100)
• Fill (RED)
• This method only takes about 50 characters (i.e
  downloads in a fraction of a second)
• Note, we can also animate by sending commands to
  move objects around the screen
• Fireworks, Flash etc. all use vector graphics
• Downside is that you need more processing power
  and software on client computer, not a problem in
  todays environment

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3D Images

• We can use vector graphics to draw 3D images (see
  text)
• 3D images include external light sources
• Need to compute (render) the final image by using
  ray tracing techniques to determine final
  representation.

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Color Maps

• Depending on the graphics card, monitor, graphics
  etc. you can only display a finite number of
  colors at one time
• How do you choose the color palette?

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Audio and Video Formats

• Wave file s(.WAV) Windows internal sound format
• MIDI Not digitized sound, but a computerized
  score. Played back by different devices
  (synthesizers)
• Other formats au, AIF

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Digitized vs Synthesized Sound

• Digitized sound
• Sample original sound
• Higher quality ? larger files
• Larger files than MIDI
• Only choice for voice
• MIDI
• Stored as an actual score
• Can choose instruments, tempo
• Plays differently on different computers
• Smaller files than WAV
• Can be manipulated, edited etc.
• Can use midi generators to generate the score

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Digital Sampling Rates for WAVE files

• Low quality Mono
• 11kHZ, 8bit mono sound (Lousy voice)
• Files size 11000 8 no. of secs /8 bytes
• 8 seconds 88,000 bytes
• 22khZ, 8 bit stereo sound (Hi FI)
• 22000 8 no. of secs/ 8 2
• 8 seconds 352,000 bytes
• 44khz 16 bit stereo (CD Quality)
• 8 secs 44000168/82 bytes 1,408,000 bytes

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Recording a Wave file

• Run Windows sound recorder
• Adjust recording levels
• Too high, wave gets clipped
• Too low, sound is muffled, scratchy

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Editing Audio

• Trimming Cut out dead space
• Splicing put together multiple sound files
• Volume adjustments Adjust volume of different
  clips to be comparable
• Format Conversion
• Resampling or downsizing create lower quality
  version
• Fade-ins Fade-outs
• Equalization Adjust tone, brightness
• Time stretching
• Digital Signal Processing Add Reverb etc.
• Reversing Play it backwards

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Summary

• Many choices in developing multimedia
• Need to know the technologies and be able to
  choose the correct approach for your project
• Tradeoff of quality, bandwidth, development time,
  cost, user capabilities
• Todays choices may not be the correct ones for
  tomorrow, need to keep looking ahead