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Computing 6 - Networks > Data Compression > Flashcards

Flashcards in Data Compression Deck (22):

what do the terms lossy and lossless describe

whether compressed data is fully recovered when uncompressed


what is lossless compression

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


what is lossy compression

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


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


what technique can be used to shrink files

compression techniques


what is the aim of file compression

making the file smaller than its uncompressed version


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


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


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


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

run-length encoding


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


what file is a common expression of a lossless compression technique

PNG files


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


what is zipping

zipping is packing multiple files into a single file


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


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


what happens after several files are zipped

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


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


what are the pros of lossy compression

- greatly reduced file size meaning more files can be stored
- takes up less bandwidth so files can be downloaded quicker
- lots of software can already read lossy files so its commonly used


what are the cons of lossy compression

- loses data so the file cant be turned back to the original
- cant be used on text or software files as they need to retain all information
- worse quality than the original file but it is unnoticable usually


what are the pros of lossless compression

- data is only removed temporarily so there is no loss of data or reduction if file quality
- lossless files can be decompressed or tuned back to the original
- can be used on text and software files


what are the cons of lossless compression

- only a slight reduction in file size so the file still takes up a lot of space on the device