Multimedia Lecture

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Multimedia Lecture

• Multimedia Lecture
• Mr Glyn Hughes / Mr Henry Forsyth

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Some Definitions

• Multimedia is the seamless integration of text,
  sound, image and controlling software within a
  single digital environment
• Multimedia Systems encompass the computer and
  software systems that are used in multimedia
  environments
• Distributed Multimedia Systems operate over some
  form of network infrastructure

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Classify Media Types
Static Media
Dynamic Media
Created electronically
Text
Synthesised Audio
Computer Graphics
Computer Animation
Captured from the real world
Video
Images
Natural Audio
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Relative Media Sizes
smaller
larger
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The Big Picture
Multimedia Systems
Distributed MultimediaSystems
Multimedia
Image
Video
Media Asset Management
Network
Text
Authoring
Frameworks
Speech
Audio
Tools
Streaming Video
Web Pages
Virtual Worlds
Streaming Audio
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Brief Multimedia History

• Early IBM PCs had no sound other than the beep
• Apple Mac, Amiga, Atari ST had better sound
• Video or graphics capabilities were also limited
• Generally text based or small, few colour
  graphics
• CD-ROM (Compact Disk-Read Only Memory)
• 72 minutes of audio or 650 MB of data
  (approximately)
• DVD (Digital Versatile Disk . . . not Video)

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Modern Multimedia PC

• 3D graphics cards with 128 or 256 MB of memory
• 64 note sound cards with wavetable synthesis
• 1GB or 2GB of system memory (DDR, DDR2)
• 100s of GBs of hard disk space
• 52 speed CD-R CD-RW
• 512kbps, 1mbps or even 10 mbps broadband internet

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Multimedia Applications

• Multimedia applications can be linear or
  interactive
• Linear multimedia plays from some start position
  to some end position with little or no
  intervention
• Just like this lecture
• Interactive multimedia allows the user to jump
  around the material by interacting with it
• It has no enforced hierarchy

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Barriers To Multimedia

• What works on Microsoft Windows operating systems
  does not necessarily work on Apple Mac or Linux
• Different hardware on each type of machine
• e.g. two different graphics cards may not
  be able to display
  fog effects as intended
• Do you produce multimedia applications for the
  best specification or the lowest common
  denominator?
• PC Games vs. Console Games

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Multimedia Development
Input
Output
Process
Capture from device Read from a
file Receive over a network
Apply effect filters and transforms Compress or
decompress Convert between formats
Present Save to a file Send across a network
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What is an Image?

• An image is the graphical and visual
  representation of some information that can be
  displayed on a computer screen or printed out
• Images play an important part in multimedia
• Navigation
• User Interface Components
• Help Systems
• Clip Art

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Image Types

• Images can be generally divided into two formats
• Bitmapped or Raster Images
• Vector Graphics
• Bitmapped images are stored as an array of pixels
• Vector graphics are stored as the set of graphic
  primitives required to represent the image

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Bitmaps

• A pixel is the smallest element of
  resolution on a computer screen
• A bitmap is an array of pixels
• Each pixel can be in a specific colour
• The range of these colours is known as the colour
  depth
• The more colours that are allowed per
  pixel, the greater the size of the
  image

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Colour Depth

• Colour depth is measured in bits per pixel
• 1 bit per pixel 2 colours (monochrome)
• 4 bits per pixel 16 colours
• 8 bits per pixel 256 colours
• Generally good enough for colour images
• 16 bits per pixel 65536 colours
• Better quality for photographs, also known as
  high colour
• 24 bits per pixel gt16 million possible colours
• Used to recreate photo realistic images, also
  known as true colour

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Colour Depth Example
24 bit colour (16 million colours)
4 bit colour (16 colours)
1 bit colour (2 colours)
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Scaling Bitmapped Images
Original Image
Shown Magnified
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Anti Aliasing

• This is a technique used to avoid the jagged
  edges found in bitmapped graphics
• It fools the eye into thinking that edges are
  smooth by colouring neighbouring pixels in
  similar colours
• Most modern bitmap graphics editing
  software can perform anti aliasing
• Usually only on 24 bit colour images
• We can see this in action in the lab exercise

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Anti Aliasing Example
Anti Aliased Line
Jagged Line
Try squinting at the anti aliased line from a
distance, do the same for the jagged line. Which
line looks best?
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Popular Bitmap Formats

• Microsoft Bitmap (.bmp)
• Used in Microsoft Windows
• JPEG - Joint Photographic Expert Group (.jpg)
• Useful for storing photographic images
• GIF - Graphics Interchange Format (.gif)
• Used a lot on web sites
• PNG - Portable Network Graphics (.png)
• A new format for web graphics

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Calculating Raster Images Sizes

• Where
• Width is measured in pixels
• Height is measured in pixels
• Colour depth is measured in bits per pixel
• Remember
• 1024 bytes 1 kilobyte (KB)
• 1024 kilobytes 1 megabyte (MB)

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An Example

• A 640 x 480 pixel image in 24 bit colour
  would require how much disk space?

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Vector Images

• Vector images are stored as the set of graphic
  primitives required to represent the image
• A graphic primitive is a simple graphic shape
• e.g. square, line, ellipse, arc, etc
• Each primitive has various attributes
  that go to make up the entire
  image
• e.g. x/y location, fill colour, line colour, line
  style, etc
• Example
• RECTANGLE (0, 0, 200, 200, red)

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Graphic Primitives

• Basic
• Line
• Polyline
• Arc
• Bezier Curve

• Shapes
• Circle
• Ellipse
• Rectangle
• Square
• Pie Segment
• Triangle
• Pentagon, hexagon, etc

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Vector Images

• Resizing a vector does not introduce
  jagged edges like resizing a bitmap
• Scaling a vector is a mathematical operation,
  only the attributes
  change, the image is unaffected
• e.g. to double the size of a square whose sides
  are 4 units long we multiply the
  side length by 2
• The file size of a vector image is proportional
  to the number of graphic primitives it contains
  (and the number of attributes for each primitive)

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Scaling Vector Images
Original Image
Shown Magnified
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3D Models

• A 3D Model is a variation on the vector format
• The location is specified using x, y and z
  co-ordinates
• Further primitives can be found in 3D Models
• Cube, sphere, pyramid, etc

X
Y
Z
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Summary

• Today we have met the various types of image that
  are useful when creating multimedia
  applications
• Any Questions?