Chapter 1 Information representation and multimedia

1.1 Data Representation

Denary

• base-10 number system

Binary

• base-2 number system based on values 0 and 1 only

• bit: binary digit

• 128	64	32	16	8	4	2	1
  0	0	0	0	0	0	0	0

BCD (binary coded decimal)

• 4 bits represent 1 digit
• e.g. 36 -> 00110110
• addition in BCD -> if a digit is greater than 9, we add 6 to it
• usage: displaying alpha-numeric

Haxadecimal numbers

• base-16 number system

• A(10)	B(11)	C(12)	D(13)	E(14)	F(15)
  1010	1011	1100	1101	1110	1111

• quick way of translating hexadecimal to binary is by converting to BCD

• e.g. A5 in binary -> 1010 0101

• usage: color code, addresses

Two's complement

• making the MSB (most significant bit) a sign bit

• -128	64	32	16	8	4	2	1
  0	0	0	0	0	0	0	0

• conversion between negative denary and binary two's complement

  1. flip all the bits: 0 to 1, 1 to 0
  2. add 1

Ascii Code

• 32	48	65	97
  Space	0	A	a

• 8 bits per letter

Unicode (UTF-8)

1.2 Multimedia

Image

Bit-map image

• system that uses pixels to make up an image
• pixel: smallest picture element that makes up an image, color of which is stored in bits
• file header: contained in a bit-map image, represents basic information of the image, such as image resolution, size, and number of colors
• image resolution: amount of pixels an image contains per inch
• screen resolution: the number of pixels per row by the number of pixels per column (total number of pixels = width * height)
• color depth: number of bits used to represent color of a pixel
• file size = number of pixels * color depth
• pros: not big in file size and can be easily manipulated by general users

Vector Graphics

• image defined using mathematics and geometry
• i.e. points, lines, curves etc.
• vector graphics are scalable, they can be resized without losing quality
• usage: logos

Sound

Analogue to digital converter (ADC)

• microphone pick up analogue sound wave -> ADC convert to digital signal -> then the sound wave can be stored and manipulated

Digital to analogue converter (DAC)

Sampling

• the height of analogue sound waves can be sampled regularly with the height being represented by a bit-code

• sampling Rate: number of samples taken per second

• sampling Resolution(Bit depth): no. of bits assigned to each sample

• bit rate: number of bits required to store 1s of sound

  bit rate = sampling rate * sampling resolution

• file size = bit rate * length of sound

Video

• frame rate (fps): number of video frames per second

1.3 File Compression

Lossy Compression

• original version can't be retrieved
• reduces file size more than lossless
• perceptual music shaping: reducing certain parts of a sound which are less audible to human hearing

Lossless Compression

• original version can be retrieved

• Run-lenth encoding: consecutive values are stored as a single data value and count

  e.g. 00002111 can be written as (0-4)2(1-3)