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2.6 Data representation


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Character set
A defined list of characters recognised by the computer hardware and software. Each character is represented by a number.
Lossless compression
When a file that has been compressed can be decoded back into its original form with no loss of information.
How Lossless works
Looks for redundancy � looking for areas with the same information
Lossy compression
Original file cannot be brought back to its original form
Metadata
descriptive information embedded inside an image or other type of file
Sample rate
The number of times per second that the sound is sampled. Mesaured in kHz or kilohertz.
Bit depth
The number of bits used to store the information of each sample of the sound being recorded.
CD sample rate
44.1 kHz
Number of characters represented in 1 byte
256
ASCII
Each character is given a numeric code, This code is then stored in binary. Each character takes 1 byte.
UNICODE
Much larger character set and can represent many more characters/ characters from all alphabets. Uses 16 bits instead of 8 bits
Pixels hold information on which three colours?
Red green blue
Pixel
the smallest individual element in an image. Picture and element.
Dimensions
Refers to the total number of pixels along an image�s width and height e.g.�640 x 480
Resolution
refers to the density of pixels in an image � the greater the density, the greater the image sharpness and clarity. Measured in pixels per inch (ppi) or dots per inch (dpi).
suitable resolution for viewing an image on screen
72ppi
suitable resolution for printing an image
300ppi
Lossless image formats
RAW, TIFF, BMP, PNG
Lossy image format
JPEG, GIF
Information stored in metadata
Date, geographical coordinates, camera name and model, camera speed, aperture setting, file size
Digital recording advantage
Can be edited and manipulated easily. More portable. It has allowed people to produce their own commercial music at home.
Machine code
A system of instructions and data executed directly by the central processing unit of a computer
Instruction set
The range of instructions that can be executed. The instructions are unique for each processor type
Opcode
The portion of a�machine language instruction that specifies the operation to be performed by a microprocessor.
Operand
Contains either the data that has to used in an operation or a memory address where data can be found or stored.
Mnemonic
A word that is used to represent an opcode, as it is difficult for programmers to remember all of the opcodes in binary format and use them accurately when coding algorithms
Digital recording advantage
It can be played over and over again without deterioration.
Why compress files?
Reduces the size of the file which needs to be transmitted so less storage needed = saves money.
Digital recording advantage
It can be easily copied on a computer
Digital recording advantage
Equipment to record and process digital sound is relatively cheap
Why compress files?
It shortens download time.
Why compress files?
It reduces Internet traffic (and hence probability of lost packets).
Why use Hex?
Much easier to express binary numbers.
Why use Hex?
Easier for humans to remember and express binary numbers in hex