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SLR3: Data Representation - Coggle Diagram
SLR3: Data Representation
ASCII
Stands for: "American Standard Code for Information Interchange"
Normal: 7 bits, 128 possible combination
Extended ASCII: 8 bits, 256 possible combinations
Allows computers to understand characters
Includes alphanumerics and some special characters (like new line)
Character set: defined list of characters recognised by the computer hardware and software
Unicode
Provides a unique code for each symbol or character that is not covered by ASCII or extended ASCII
Allows other languages and symbols such as emojis to be represented digitally
16- bit or more
Images
Bitmap: A map showing the location and arrangement of pixels on a digital image
Resolution: the amount of pixels in a digital image
Pixel: short for picture element, it is a single dot of colour in a digital bitmap image or on a computer screen. Also known as the smallest addressable unit on a digital image.
Colour depth: the number of bits that make up a single pixel, which determines the range of colours an image can display
Calculations and Expressions
Image size = width (in pixels) x height (in pixels)
Image file size = width (in pixels) x height (in pixels) x colour depth
After completing an equation, divide by 8 and then by 1024 as many times as needed to get the right measurement of data
file size = sample rate (Hz) x bit depth x duration (s)
Side note: when a question includes 'CD quality' , that refers to 44.1 kHz (44100 Hz) and a bit depth of 16.
'Stereo quality' refers to the audio coming out of two speakers. To show this in the expression, just x2.
Sound
Analogue sound = natural sound (vibration of particles in the air) Digital sound = when analogue sound is converted into a digital form
Sample rate / sample frequency: how many samples of data are taken per second. Measured in hertz, eg an audio file usually uses samples of 44.1 kHz (44,100 audio samples per second).
Bit depth / sample resolution: the number of bits used to store an audio sample
Bit rate: number of bits processed per second
Sample interval: the time or distance between samples that are taken
Compression
Lossy
Reduces file size by a very significant amount
Cannot be used on files where no data is allowed to be lost
Images, videos, audio files are commonly compressed using lossy
Data that the computer deems unnecessary is removed
Non reversible: data is removed, the file cannot be restored to its original form
Common file formats that use lossy compression include JPEG for images, MP3 for audio, and MPEG for video
Lossless
Reduces file size by a moderate amount
Doesn't remove any data, only compacts it
Used for files and data that cannot afford to lose any data, including word documents and text files
Reversible: file can be restored to its original form
Common file formats that use lossless compression for images include PNG, BMP, RAW, and GIF, while for audio, WAV, FLAC, and AIFF/AIFC are commonly used
Definition
A method of reducing file sizes, particularly in digital media such as photos, audio and video.