Data representation - Text, sound, images and compression (paper 1) Flashcards
how and why does a computer represents text, using Unicode
- allows for a greater range of characters and symbols than ASCII, including different languages (Russian, Chinese, Arabic) and emojis
what is the disadvantage of Unicode
- Unicode requires more bits per character than
ASCII - requires 16 bits per character
how many bits does ASCII use to represent a character
7 - allows up to 128 characters
how many bits does Extended ASCII use to represent a character
8 - allows up to 256 characters
why was extended ASCII introduced
- additional characters in the set including symbols, common foreign languages + mathematical symbols introduced
what is character set
- each character of the keyboard has a binary code
- All of the characters, letters, numbers that is recognised by a computer system
Two standard character sets in common use are:
- American Standard Code for Information Interchange (ASCII)
- Unicode
does a ‘space’ count as a character
YES - it counts as one Byte
5 key stages
how are analogue sounds recorded
- analogue sound must be digitally recorded and converted into binary
- amplitude emitted is measures and recorded / sampled at regular intervals
- how often it is recorded is the sample rate
- accuracy to which the height is recorded = sample resolution
- duration of the recording will affect file size
what does the sample resolution have an affect on
the quality of the recorded sound when played back
- file size of the recording
what also increases when the sample rate and sample resolution increase
accuracy and file size increase
what does the sample resolution measure
number of bits per sample - accuracy to which the height is recorded
what does the sample rate measure
the number of samples taken
in a second
what is sample rate measured in
Hertz
Sound file size = ?
(Number of samples per second ) x (sample rate) x (Length of sample in seconds)
- always divide by the number of the bit sample
what is a image made up of
a series ofpixels that are converted to binary, which is processed by a computer
image resolution = ?
number of pixels (px) in the image
colour depth = ?
number of bits used to
represent each colour
if the file size and image quality increases what is the cause
resolution and colour depth increase
Image file size = ?
(width in pixels x height in pixels x colour depth) / 8 gives size in bytes
what is the purpose of data compression
- reduces file size by removing repeated / unnecessary data
what is the impact of having smaller data file size
- less bandwidth required
- less storage space required
- shorter transmission time
what is lossless compression and how does it compress data
reduces the file size
without permanent loss of data –> e.g. run length
encoding (RLE)
what is lossy compression and how does it compress data
reduces the file size by
permanently removing data –> reducing
resolution or colour depth, reducing sample rate
or resolution
3
what are the advantages of lossy compression
- smallest file size
- least transmission time
- reduces Internet traffic + collision
advantages of lossless compressions
- original quality preserved / no info or data is lost
disadvantages of lossy compression
- detail permanently lost by reducing colour depth, resolution or sample rate
disadvantages of lossless compression
less significant reduction in file size
examples of lossy compression
- music streaming
- online images / video
- image libraries on devices or in the Cloud
examples of lossless compression
- text documents
- electronic books
- hgh resolution print documents
what is the RLE algorithm
It groups repeating pieces of data and stores them using significantly less data
using the RLE algorithm rewrite: 00000111000001111100
50 31 30 51 20
