I'm confused about file compression?

Question

Basically I need to know that when you compress a file on a Mac by right clicking and pressing 'Compress', is it lossy or lossless? Same with Windows

Answer 1

Generic file compression is always lossless. Of course.

Answer 2

Despite what you may hear, it is lossless... It has to be otherwise the file you compress would degrade and be worthless! Compression works by looking for repeat patterns or frags within a file and storing them in a sort of pattern map. Unfortunately things like videos or images generally speaking do not have many repeating patterns/frags which is why when you compress them they turn out only slightly smaller than the original. Hope this help!

Answer 3

'Lossy compression' is a term used in audio/video/image data ENCODING, e.g. in audio/video editing or image editing like in Photoshop, etc. The term is not used in in the field of general file compression/archiving, which is what you are asking about (ZIP, RAR, 7ZIP, etc.)



Why is that? Because video and audio data can take loss of some parts of the video or audio information without it being too visible/audible in the end product.



In video/audio/image encoding, the data compression is applied during the creation of a file, e.g. when an .mp3 file is generated in an audio editing program, an .mp4 video file is rendered from an iMovie project, a photo or graphic is saved as JPG file... In the field of audio and video compression, the software parts that define the various compression methods/algorithms are called 'codec' (coder/decoder). There are lossless codecs for media encoding, too.



This is different from the application of file archiving/compression programs on already existing files of any kind where data loss would simply render the archived/compressed file(s) corrupt, meaning unusable. So, file archiving/compression is always lossless.



Of course you can still use archiving programs (in OS X: right-click>Compress) to compress existing mp3 or other media files into one archive file (ZIP), which is often done when multiple files in a folder need to be sent over the Internet.

Answer 4

Depends on what you are compressing. Regular files are typically lossless, since they recreate the exact file as it was when you extract it.



However when you're talking specifically about media compression (like audio/image/video compression), then typically it depends on the codec/format you're using).



MPEG/JPEG formats are typically lossy formats, while AVI/BMP/PNG are typically uncompressed, or compressed to a minimum, which could *possibly* be defined as "lossless", but not so much.

Answer 5

can't answer for macs.

but for windows it is "generally" lossless.

in so far as that term applies.

it really depends on what you are using to compress the file.

Answer 6

Hello,

WinRar is the software you need to decompress all kind of compressed files, documents or folders.

Here I got Winrar for free http://bit.ly/1p3P1iw

Cheers.