[TopAce]

I was taught that archiving may bring about a certain degree of loss of data, so I've mostly used Low or Medium compression in WinZip/WinRAR, out of fear of losing data. However, the Jeff Vader in the Campaign pre-release checklist recommended that 7z Ultra compression must be used.

My question: Was my teacher incorrect about lossy compressions? What are people's experience with compressing files?

[The E]

Oh god. The wrongness can not be put into words.

The entire point of compression schemes like zip, 7z and rar is that they are lossless, and guaranteed so. If they weren't, they couldn't be used for data compression at all.

Now, lossy compression schemes (like mp3, jpg and basically every movie codec ever) always introduce a compromise between quality and size. With media like those, compromises can be accepted, but try using a lossy compression on a text file (for example) would guarantee a loss of meaning.

[Iss Mneur]

I was taught that archiving may bring about a certain degree of loss of data, so I've mostly used Low or Medium compression in WinZip/WinRAR, out of fear of losing data. However, the Jeff Vader in the Campaign pre-release checklist recommended that 7z Ultra compression must be used.

My question: Was my teacher incorrect about lossy compressions? What are people's experience with compressing files?

No, you teacher was 100% correct about lossy compression, the higher the compression the more loss (in general).

The problem is Zip/RAR/7z/etc are lossless compression systems. So the only thing that you lose by cranking them up to max is the increased time to compress/decompress and the increased memory usage during the compression/decompression operation.  Obviously by using maximum compression you actually get a smaller file size which is why Jeff Vader (and actually anyone else that is wanting to offer data on the internet) will use the maximum compression practical.

For the record, lossy compression is normally used to compress media (pictures (dds, jpeg), music (mp3, ogg vorbis), movies (mpeg, mp4, ogg theora)) and not data (text documents, web pages, .tbls, and .tbms, etc.).  That being said, there are lossless compression availability for media as well (pictures[tiff, png, gif (as long as you don't mind only 256 colours), jpeg], music [FLAC], and movies [dv (very basic)]).

EDIT: so someone did post while I was writing, the forum told me that someone did but would not show the post

[headdie]

i believe the different compression within winzip, winrar, 7z are so the person compressing the files can make a decision on the compromise between the desired end file size, compression time and decompression time especially with larger amounts of data where these can be notable

[TopAce]

Okay. Thanks for the replies.