Image and graphic representation
Image and graphic representation
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Image storage:
The way to store images in consecutive pixels is called raster-graphics format.
Common methods of storing scanned images: BMP, JPEG, GIF
BMP (bitmap): the simplest way to store, each pixel is represented by a color value (according to a set of 3 RGB values)
GIF: uses a color palette to represent colors (up to 256 colors)
JPEG: stores images based on the color perception characteristics of the human eye
Image and graphic representation
Image storage:
Vector graphic: instead of storing each pixel, we represent images through lines and geometric shapes.
A vector graphic is a sequence of instructions that describes
line, thickness, color and direction
Small storage size but not suitable for storage
real world photos!
Used to store line drawings and animations
The most popular vector image today is Flash
1.4.8 Video presentation
•Video performance
•Encoding standards
Video performance
Video is one of the most complex data to represent.
and compression
A video clip is equivalent to many continuous still images
Many video compression techniques (CODECs) have been developed in recent years.
CODEC: COmpressor/DECompressor (compression and decompression)
Video codec is a method of reducing the size of a video so that it can be viewed and transmitted over the network.
Most video compression methods are lossy.
Video performance
Most use block coding (dividing a frame into
multiple rectangular blocks)
Different encryption methods differ in the way they encrypt blocks.
Video codecs apply two types of encoding:
Temporal (time-based) considers the difference between two consecutive frames, encoding only the different parts
Spatial reduces information redundancy in a frame. Groups blocks of pixels of the same color together and stores information about the color and position of the block.
Popular Video codecs: Sorenson, Cinepak, MPEG, and Real Video
1.5 Gates and circuits
•Basic concepts
•6 common types of gates
•Circuit
Gate and circuit
Signals in computers are represented by voltage.
Voltage 0-2V: low level, represents binary value 0
Voltage 2-5V: high level, represents binary value 1
A gate is a device that performs basic operations on electrical signals.
A gate can have 1 or more inputs but only 1 output
Gates are combined together to form circuits,
perform complex operations. Eg. Add two binary values