Transcript Document 43316

Object Orientated
Data
Topic 5: Multimedia Technology
Object Orientated Data Types
• Created on a computer not by sampling
real world information
• Details are stored on the attributes
(properties) of each object that is stored in
the file.
• Each object can be altered by changing its
attributes…
Examples
• Text
– A character in a text file can be given a different size,
colour or font
• MIDI music
– A note in a MIDI sound can be given a different
volume, length or pitch
• Drawing
– A shape in a drawing can be given a different size or
fill colour
• 3D image
– An object in a 3D image can be given a different
location, rotation or texture
Object Orientated Data Files
• All data is stored as a group of objects
within a file
• Each object can be edited individually
without affecting any others
• All aspects of each object are decided by
its properties (attributes)
• These files are basically a collection of
objects with details about them. This
means they can be stored as plain text
files.
Input of Object Orientated
Data
Although OOD can be created using nothing
but a simple text editor there are specialised
input devices to help users create and edit
them
• You are already familiar with a keyboard
for entering text
Specialised Input Devices
• To create drawings or 3D
images a graphics tablet
– More accurate than using a
mouse
• To enter musical notes a MIDI
keyboard
– Easier than using a computer
keyboard
• 3D digitisers can measure
points on an object and
generate a 3D object from data
Output / Display of OOD
• The quality of object orientated data is
very dependant on the hardware &
software used to output it.
• For example:
– Web browser setting can cause the same text
to be displayed in different ways on different
computers
– Different graphics cards for rendering 3D
images on screen may produce different
quality and support different features
Rasterisation
• Converting an object orientated file to a
discrete (bitmap) file type
• The equivalent of capturing data (as with
digitised sound or bitmap image)
• Difference is no input hardware is required
• All the information about each object is
lost.
• Attributes can no longer be altered
Converting from OOD
OOD
How it can be converted
Discrete data
2D
drawing
Often in ‘Save As’ or ‘Export’ menu of
drawing program
3D Image
Called ‘rendering’. Generates a flat (2D)
Bitmap Image
image from a given point of view.
Text
Scanning printed text or doing a
‘screen shot’ and pasting it into bitmap Bitmap Image
image software
Midi
music
Often using ‘Save As’ or ‘Export’
function but can also be recorded
internally
Bitmap Image
Digitised
Sound file
Object Orientated
Data
Topic 5: Multimedia Technology
Recap
• Object Orientated Data
– All data is stored as a group of objects within
a file
– Details are stored on the attributes
(properties) of each object that is stored in the
file.
– Each object can be edited individually without
affecting any others
– These files are basically a collection of
objects with details about them. This means
they can be stored as plain text files.
Vector Vs
Bitmap
Can be scaled to large sizes,
keeping original quality.
Scaling causes pixellation.
Individual objects can be
edited.
Only the image as a whole can
be edited.
Are easily converted to bitmap
formats.
Are very difficult to convert to
vector formats
File sizes are relatively small.
File sizes can be large.
Difficult to create realistic
images
Images can be very realistic
(e.g. digital photograph).
Vector Vs Bitmap
Size of image can be increased
keeping quality and file size the
same.
Increasing the image size needs resampling and increases the file size.
Only individual objects can be edited
Pixel level editing is allowed - allowing
(it is sometimes impossible to edit only effects such as spray paint, blur,
part of the object).
effects and so on.
Dependent on output hardware or
software for appearance & quality.
Same appearance in all systems,
regardless of hardware or software.
Suitable for graphic, unrealistic
images and designs.
Suitable for natural, hand-drawn
looking, realistic images.
Attributes
• Attributes are the properties that
determine what and how objects will
appear
• These files can include a bitmap as a
separate object…
Objects & Attributes
Object 2
Object 5
Object 3
Object 4
Object 1
Object 6
Object 7
Object Orientated File
Formats
Drawing : SVG
3D : VRML/WML
Synthesised sound : MIDI
Drawing File Formats
Scalable Vector Graphics (SVG)
• A format for encoding vector graphics in
XML (eXtensible Markup Language)
• Designed to provide vector graphic
content in Web pages.
• Viewing:
– You must have an SVG capable Browser, a
plug-in for your browser or a stand-alone SVG
viewer.
Additional Attributes for
3D images
• Surface texture – give surface definition
• Shadow – simulates direction of light
• Angle of rotation (to view from different
angles)
• Z coordinate
File format for 3D vector imag:VRML/WML
3D Image File Formats
Virtual Reality Modelling Language/ World
Representation Language (VRML/WRL)
• Standard for describing interactive 3D
objects and worlds
• Capable of representing static and
animated 3D & multimedia objects with
hyperlinks to other media such as text,
sounds, movies and images
VRML/WRL
• Creating/authoring VRML
– Authoring tools vary from expensive 3D
modellers to freeware utilities
– WRL are text based so any text editor can be
used. The suffix ‘.wrl’ is used to save
• Viewing VRML
– A VRML plug-in is needed
VRML/WRL
• Navigating in VRML
– Each player has slightly different features
– Most have at least three navigation
modes:
• Walk – Allows you to move around
• Fly – move around, up and down
• Examine – rotate whole VRML world
viewing from different angles
Synthesised Sound Data
(MIDI)
• MIDI is a standard that was created to allow
musical instruments to be able to communicate
with each other
• A MIDI file consists of Channels (up to 16)
• Each channel consists of a sequence of
messages including:
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Start of a note
Channel to use
Pitch of the note
Volume to play it at
End of note
Synthesised Sound Data
(MIDI)
Attribute
Meaning
Instrument
Defines instrument being played
Pitch
Sets musical tone of note which is
determined by the frequency
Volume
Controls loudness/amplitude of note
Duration
Determines length of note (number of
beats)
Tempo Rate
Speed at which the piece of music is
set
Synthesised Sound Data
(MIDI)
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Advantages
Smaller file size
All aspects of music
can be edited
Effects can be applied
to individual
instruments
There is no
interference from the
recording
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Disadvantages
Never sounds as
realistic as digitised
sound
Dependent on
soundcard for quality
Does not contain
vocals
Fewer effects can be
applied to sound