1.2.4 & 1.2.5 - Data Storage and Compression Flashcards
A character set is…
All the characters a computer can represent with a unique binary code representing each character
The size of an ASCII character is…
8 bits
The size of a Unicode character is…
2-4 bytes
Unicode character sets represent…
All the different characters/languages of the world
ASCII character sets represent…
A few European languages’ characters
An image is made up of…
Pixels
Image metadata includes…
- Image height
- Image width
- Geoloaction of the image’
- Date that the image was taken
An image colour depth is…
The number of bits needed to store the colour of each pixel
An image resolution is..
The number of pixels per inch. controls the fineness of detail of the image
The file size of an image is reliant on…
Colour depth and resolution
A computer sound file is created by measuring…
The height of a sound wave
The sample rate is…
Taking measurements of the amplitude of the sound wave at regular intervals. The higher the sample rate, the higher the quality and file size
measured in Hz
A computer sound file bit depth is…
The number of bits used to store each sample (each wave). The higher the bit depth, the closer the playback sound will be in quality to the original sound
Compression is when…
A file reduces its size
Lossy compression is when…
Data is removed from a file which reduces the file size more than lossless by removing less important data
This reduces the image quality but ofen it is unnoticeable
Lossless compression is when…
Data is more efficiently stored
Used in text files as lossy can’t be used as none of the data can be removed otherwise it would mkae the file unreadable
Name an image sound and movie example for lossy
JPEG mp3 and MPEG
Name a text image sound and movie example for lossless
PDF gif flac and mp4
How to calculate image file size
file size = bit depth x number of pixels
To find number of pixels, you do height x width
How to calculate the size of a sound file
file size = bit depth x sample rate x duration of sound
BEnefits of compression
- Takes up less space on servers
- Faster upload time to server
- FAster download for users
What is an overflow error
- When a computer attempts to store something larger than 8 bits in a single byte
- This is often done when two 8 bit numbers are added together
Differences between lossy and lossless compression
- The quality often decreases when using lossy compression but the quality is the sames as the original in lossless
- Lossless files can be decompressed to get the original but lossy files can’t be used to retrive the original
- Lossy compression greately reduces the file size more than lossless compression
What happens to an image when you increase the resolution
- Image quality will improve as the image has more pixles so can show finer detail images
- Image file size will increase because there are more pixels to store
Different ways of storing images and their properties
- Bitmap - image made up of different coloured squares with each square having a binary value
- Vector - the mathematics to draw the image is stored eg. the width and colour
How is a sound recording taken
- Analogue sound recieved by a microphone
- This is converted into a digital form using an ADC
- Sound is sampled at regular time intervals (sample rate)
- The amplitude of the wave is stored as binary
