Data Compression Flashcards Preview

Computing 6 - Networks > Data Compression > Flashcards

Flashcards in Data Compression Deck (18):
1

what do the terms lossy and lossless describe

whether compressed data is fully recovered when uncompressed

2

what is lossless compression

- when all data that was initially in the file remains when it is uncompressed
- shrinks data and keeps quality

3

what is lossy compression

- when some data is permanently removed
- reduces quality of the file

4

why would you want to compress a file

- makes it easier to store digital files as less space is taken when downloading
- the file can be transmitted quickly

5

what technique can be used to shrink files

compression techniques

6

what is the aim of file compression

making the file smaller than its uncompressed version

7

what does the term 'smaller' mean in terms of data compression

less bits (actual bits like 0 and 1) are used to store the file

8

why is the sending of compressed files quicker than an uncompressed files in terms of rate

- transmission time is measured in bits per second
- fewer bits results in fewer seconds for a given rate of transmission

9

how do compression techniques even compress files or what do they look for

- they work by identifying patterns in the binary digits that make up a file
- for example, a number stored 100 times could be stored once with the reference to how many numbers (100)
are being stored

10

what compression technique stores several bits of data into one file with the reference of how many bits there are

run-length encoding

11

how does huffman coding compress files

- it identifies commonly used sequences of bits
- converts them to shorter bit patterns
- so that they take up less space
- example is like simplifying x x x x x into 5x

12

what file is a common expression of a lossless compression technique

PNG files

13

what file is a common expression of a lossy compression technique and what is specifically compressed

- JPG files
- colour of every pixel isnt stored precisely
- but enough colour data is stored

14

what is zipping

zipping is packing multiple files into a single file

15

what can zipping do

it can take any number of files and folders with any number of levels of sub folder, and convert everything into a single file

16

when is zipping useful and why

- when it comes to emailing files
- because when you send an email, you can attach a file but not a folder
- to email a complex folder structure, you would need to attach files individually

17

what happens after several files are zipped

the new file created from zipping is often compressed and organised into a complete single file

18

what type of compression does a zipped file go through and why

- a lossless compression technique is used
- because you might have saved spreadsheets or a database that you might want to preserve perfectly