1.2 - characters, images and compression Flashcards
What is a character set
All the characters a computer can use
Two standard character sets in common use
ASCII, Unicode
How many characters does ASCII have?
128, 7 bits
How many characters does extended ASCII have?
256, 8 bits
How many characters does Unicode have?
Over 65,000, 16 bits
What is a pixel
A tiny square with a binary value
Colour depth
Many images need colour, more bits are required for each pixel, more bits = more colours. The more colours, the more bits per pixel so the more the colour depth so the larger the image file
Image size
Number of pixels than an image contains, expressed as height and width
Resolution
How many pixels there are in a certain distance. Higher resolution looks better
Meta data
Data about the file itself e.g. file type, data created, author, height and width of image, resolution, colour depth
Two types of compression
Lossy and lossless
Lossy compression
Some data is removed thereby reducing the overall amount of data and file size
Image in lossy compression
Reduce colour depth, some shades will be discarded
Audio file in lossy compression
Reduce bit depth
Files compatible with lossy compression
JPEG, MPEG, MP3
Lossless compression
Files are reduced in size without removing data, can be done by looking for repeats in data and storing it as one item of data instead of many
Files compatible with lossless data
PDF, GIF
How is sound converted to binary
Capture a sound wave at regular intervals, using an analogue-to-digital converter, this is known as a sample. The sound recorded at each sample is converted to its nearest numeric equivalent
Sample rate
Number of samples recorded in a given time period, higher the sample rate = closer to original sound, measured in hertz
Bit depth
Number of bits used to record each sample
Bit rate
Measure of how much data is processed for each second of sound
