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Data (Image Representation (Bitmap Image Grid of dots (pixels), Each dot…
Data
Image
Representation
Bitmap Image
Grid of dots (pixels), Each dot a binary no.
Colour Depth
Code to represent pixel colour
No. of bits for each pixel's colour
Number of colours = 2^depth
2 bits = 4; 5 bits = 32
Resolution
aka Pixel density
pixels per inch (PPI)
Resolution is prop. to quality
File Size Formula
Height * Width * Res^2
For Bytes - /8
Sound
Representation
Analogue vs Digital
Digital (discrete):
ltd set of values
Analogue (continuous):
Infinite possible values
Sampling
Samples taken at regular intervals/fractions of a second
Sampling rate measured in Hz (samples per second)
Bit depth - no. of bits for each sample
CD = 16 bits, DVD = 24bits
Nyquist Rate
Sample rate should be double
highest frequency in signal
(Human range = 40Hz - 40kHz)
File Size Formula
Sampling * Rate * Depth * Channels * Time
Binary Style
Sign and Magnitude
1100 1010 = 202 (normal) 128+64+8+2
1 100 1010 = -74 (S&M) -(64+8+2)
Doesn't work with Addition
Normal Byte Size = 0 to 255 (256)
S&M Byte Size = -127 to 127 (255)
Two's compliment
1000 1100 = 140 (normal) 128+8+4
1 000 1100 = -116 (2's) -128+8+4
Does work with Addition
Normal Byte Size = 0 to 255 (256)
2's Byte Size = -128 to 127 (256)
Fixed Point
Follows 8,4,2,1;½,¼,⅛...
6.75 = 0110.0110
Move to first '01' combo (0.1100110)
Note down no. of movements (0011)
0011 01100110
Mantisah, Exponent
File
Compression
Lossless
Reduce size w/ original data
No data loss; Smaller Compress Ratio
(.zip .rar)
Lossy
Reduce size w/ lost data
Larger Compress Ratio; Data loss
(.mp4 .jpg .wav)
Superchannel
Reduce size w/ kept special data
Needed data is kept
Binary
Arithmetic
Addition
1 + 0 = 1
1 + 1 = 10 (0 carry 1)
1 + 0 carry 1 = 10 (0 carry 1)
1 + 1 carry 1 = 11 (1 carry 1)
Subtraction
1 - 0 = 1
0 - 1 = 1 (take 10)
1 - 0 take 10 = 0
1 - 1 take 10 = 1 (take 10)
0 - 0 take 10 = 1 (take 10)
0 - 1 take 10 = 0 (take 10)
Hexadecimal
Reason
Shorthand Binary:
1x Hex no. = 4x Binary no.
4A = 0100 1010 = 74
Work
0 - 16 = 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
Instead of 8,4,2,1; Use 4096,256,16,1
2^4, 2^3, 2^2, 2; 16^4, 16^3, 16^2, 16,
Character
Encoding
ASCII
American Standard Code
for Information Interchange
Was 7-bits (not enough) now 8-bit
7 = 128; 8 = 256
Unicode
Alternative Coding System, extends ASCII
8-bit (256), 16-bit (65,536),
32-bit (16,777,216), 64-bit (4,294,967,296)
Fore other languages and characters, emojis