2. Data Representation - Multimedia Flashcards
How do we perceive sound?
Series of air compression vibrates membrane in our ear –> sends signal to our brain
How does a stereo work?
Sends electrical signal to a speaker to produce sound
What is the signal in sound representations?
Analogous representation of sound wave
How do we digitize sound signal?
Sample sound periodically –> measure voltage –> record the numeric value
Sample rate of 40 000 times per second needed for reasonable sound
Audio Formats
WAV
MP3
Based on storage of voltage values sampled from analog signals
How do we perceive colour?
–> detect frequencies of light that reach the retinas of our eyes
–> retinas have 3 types of colour photoreceptors –> RGB
RGB
Values indicate the relative contribution of each of the primary colours
Colour depth
Amount of data used to represent per pixel
High colour –> 16 bit col depth:
-5 bits per RGB
-extra bit can represent transparency
True colour: 24 bit representation
- 8 bits per RGB
Representing graphics
Photo –> analogue rep of an image
Digitization: pixels used to rep an image
Raster Graphics
Stores data on pixel-by-pixel basis
BITMAP: contains pixel colour values of the image from left to right and top to bottom
GIF: limits number of colours per image to 256
JPEG: averages out colour hues over short distances
PNG: like GIF but achieves greater compression with wider range of colour depth values
Vector Graphics
Describes images in terms of lines and geometric shapes
Images created directly from geom. shapes that are defined on cartesian plane (points, lines, curve…)
Not every pixel is described –> smaller file size
Two formats:
1) Adobe & Flash
2) Scalable Vector Graphics (SVG)
Advantage: can be resized mathematically
NOT GOOD for representing real world images
Types of redundancy in digital image
1) Coding redundancy
2) Inter-pixel Spacial redundancy
3) Inter-pixel Temporal redundancy
4) Psychovisual Redundancy
Coding Redundancy
Grey levels of an image are coded using more code symbols than necessary
Inter-pixel Spacial Redundancy
Due to correlation between the neighboring pixels in an image
Inter-pixel Temporal Redundancy
Statistical correlation between pixels from successive frames in a video sequence