MULTIMEDIA WHAT IS IT

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MULTIMEDIA - WHAT IS IT?

• DEFINITION 1 Uses a VARIETY of media ELEMENTS
  for instruction
• Media elements are text, sound, graphics, moving
  images (real or artificial)
• DEFINITION 2 Uses a VARIETY of media
  TECHNOLOGIES for instruction
• Technologies are correspondence study, satellite
  video, e-mail, etc.

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• A multimedia computer can run a slide show and/or
  display animated graphics with a full sound track
  of music, speech and sound effects.
• A multimedia presentation might contain
• Text
• Animation
• Digital Sound Effects
• Voices
• Video Clips
• Photographic Stills
• Music

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Overview of Graphics

• Properties of color
• Essentially, color is light.
• Colors has three fundamental characteristics
• hue, brightness, and saturation.
• Related to the three characteristics of light
  waveswavelength (hue), amplitude (brightness),
  and purity (saturation).

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Hue varies as you move around the cone in a
clockwise or counter-clockwise motion on a plane
perpendicular to the vector of the
cone. Brightness varies as you move up or down
the cone. The brightest color is at the top and
the least bright color is at the bottom.
Saturation changes as you move in toward the
center of the cone or outward toward the surface.
The least saturated colors are in the center
while the most saturated colors are at the
outside surface.
Color space model
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• Properties of Pixels
• A pixel is the smallest unit of programmable
  color on a computer display or in a computer
  image.
• Every computer graphic is made up of a grid of
  pixels. When these pixels are painted onto the
  screen, they form an image.

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Bitmap A bitmap is a collection of pixels that
describes an image.
enlarged


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Bit depth is the number of bits used to store
information about each pixel. The higher the
depth, the more colors are stored in an image.
1-bit image (21 2 colors, black or white)



8-bit image (28 256 colors)
24-bit image (224 16777216 colors)
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Resolution Refers to the number of pixels per
unit length on a monitor. It is usually measured
in pixels per inch or dots per inch (dpi).
Monitors come in a variety of resolutions. They
can get as small as 320 ? 200 pixels or as large
as 1280 ? 1024 pixels.
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Vector graphics Vector graphics is defined by a
sequence of commands or mathematical statements
that place lines and shapes in a given
two-dimensional or three-dimensional space. For
example, instead of containing each bit of a line
drawing, a vector graphic file describes a series
of points to be connected.
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A straight line may be defined as In bitmap
graphics 000000000000000000 000111111111111000 000
000000000000000 In vector graphics line
(4,2,15,2), where 4,2 and 15,2 are
coordinates of two points, and line() is a
command drawing a line between two points
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Different features between bitmap and vector
graphics File size vector graphics smaller bitmap
graphics larger Change of an image size
(rescale) vector graphics without loss of
resolution bitmap graphics with loss of
resolution
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Vector graphics
File size 12 Kbytes
Bitmap graphics
File size 228 Kbytes
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Some common file formats of bitmap graphics GIF
commonly used for Web graphics. It only supports
256 colors. With compression. JPEG commonly used
for Web graphics. It supports millions colors.
With compression. BMP Microsoft's native graphic
file format. PICT Apple Macintosh's native
graphic file format. TIFF primarily used for
scanned images (mostly scanned photographs) and
is suitable for desktop publishing applications.
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Some common file formats of vector graphics EPS
(Encapsulated PostScript) for the PostScript
language. It uses a combination of PostScript
commands and TIFF or PICT formats. DXF (Data
Exchange File) created by AutoDesk. Almost all
PC-based Computer-Aided Design (CAD) systems
support DXF.   WMF (Windows Metafile Format)
for exchanging graphics between Microsoft Windows
applications.
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Digital Audio Capture Analog (continuous)
signal digital (discrete) signal
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When the amplitude of the analog signal is
sampled at the instant, it is converted into a
digital signal consisting of a number of digits.
It is an approximation.
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Factors affecting the conversion process 1)
Number of bits used to represent different
amplitudes of a sound signal The greater the
number of bits, the better the approximation. 4
bits ? 24 16 levels 8 bits ? 28 256 levels 16
bits ? 216 65536 levels (for CD player)
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Factors affecting the conversion process 2) The
sampling frequency (number of samples taken in
one second) The higher the sampling frequency,
the better the approximation. Nyquist's sampling
theorem If sampling frequency gt 2 ? highest
frequency, the signal can be reconstructed with
no distortion.
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Telephone quality speech Range 300 to 3400
Hz sampling frequency 8000 Hz gt 2 ? 3400 Hz CD
quality sound Up to 20 kHz sampling frequency
44.1 kHz gt 2 ? 20 kHz
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Factors affecting the conversion process 3)
Number of channels One channel mono Two
channels stereo file size of stereo sound file
2 ? file size of the mono sound file.
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Bit rate (number of bits / second) at the
output number of bits used in sampling ?
sampling frequency ? number of channel
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Example of bit rate calculation For CD, number of
bits 16 channel 2 (stereo) sampling frequency
44.1 kHz Bit rate 16 ? 2 ? 44.1k 1411 Kbits /
second 176 Kbytes / second A song of 4 minutes
long 176 Kbytes ? 4 ? 60 41 Mbytes
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Example of bit rate calculation For telephone
quality speech, number of bits 8 channel 1
(mono) sampling frequency 8 kHz Bit rate 8 ?
1 ? 8k 64 Kbits / second 8 Kbytes / second
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Some common audio file formats 1) MIDI (Musical
Instrument Digital Interface) It is designed for
recording and playing back music on digital
synthesizers. It records information about how
music is produced note-ons, note-offs, key
velocity, pitch bend and other methods of
controlling a synthesizer. Advantage very small
file size. Disadvantage lack of specific sound
control.
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Some common audio file formats 2) MP3 (MPEG-1
Audio Layer-3) It is a standard technology and
format for compressing a sound sequence into a
very small file (about 112) while preserving the
original level of sound quality. A compression
algorithm reduces data about sound that most
listeners cannot perceive.
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Some common audio file formats 3) Wave file It is
an audio file format created by Microsoft. It
has become a standard PC audio file format for
everything from system and game sounds to
CD-quality audio. 4) RealAudio and
Shockwave They are designed to allow real-time
playback of audio directly from a Web site.
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Digital Video Capture What is digital
video? Essentially, it is a sequence of images
output at a certain rate (e.g. 30 images/second)
to make the eye believe that the objects in the
images are in continuous motion. What is Video
Capture? Using computer hardware, we are able to
capture images from a video source (usually a
video tape). Once captured, the video (or images)
can be edited and manipulated.
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Storage consideration Consider a single frame
(image) being displayed on a TV monitor. Assume
the frame size is 640 ? 480 pixels and one pixel
requires 2 bytes (216 65536 colors). Storage
space 640 ? 480 ? 2 600 KB The frame rate of
a regular TV is 30 fps (i.e. frames per
second). The total amount of required space for
one second 600 KB ? 30 17.6 MB
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• Storage size of a CD-ROM is about 650 Mbytes.
• It can store video of 650/17.6 37 seconds long
  !!
• Thus it is necessary to decrease
• frame rate (i.e. number of images per second)
• frame size (i.e. size of an image)
• image quality (i.e. number of colors used)
• Usually captured video clips are smaller, play at
  a slower rate, or have colours less rich than the
  original.

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Another approach to reducing storage requirement
is compression. Lossless compression retain
original data, with low compression rate
(13) Lossy compresssion remove data that is
unlikely to be noticed by the viewer, with high
compression rate (130).
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Some common video file formats 1) MPEG It is the
most popular standard. MPEG stands for Moving
Picture Experts Group. It develops data model
for compression of moving pictures and audio
signals. Compression ratio 2001 Different
MPEG standards MPEG-1 released in 1993 MPEG-2
released in 1995 MPEG-3 most popular version now
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Different MPEG standards MPEG-4 latest format,
for video transmission over the Internet and
mobile phones MPEG-7 latest development project,
an international standard by 2001 Note that .mp3
file suffixes indicate MP3 (MPEG-1 audio layer-3)
files, not MPEG-3 standard files.
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Some common video file formats 2) RealVideo It is
a kind of streaming video. When the user
accesses a web site, the video clip continuously
downloads while being viewed. RealPlayer (a free
plug-in program for the web browser) is required
to play the RealVideo file. 3) Quicktime It is
the proprietary standard of Apple Macintosh.
The latest version includes the streaming feature
(like RealVideo). Quicktime file can be run on
both Macintosh and x86 computers.
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Some common video file formats 4) AVI It stands
for Audio Video Interlaced, developed by
Microsoft. It was the first video editing
system. But it now has some problems (e.g. file
size restriction and lack of driver support in
interface cards).