Data Compression Flashcards
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
