Lossless compression reduces file size without losing data, making it useful for transferring and archiving files. Zip software and GIF images use lossless compression. Lossy compression removes redundant data to achieve higher compression ratios, but at the cost of some quality. JPEG and MP3 use lossy compression. Balancing lossless and lossy compression is important for achieving high quality results.
Lossless compression “compresses the data” into a smaller file size using some sort of internal shorthand for redundant data. If an original file is 1.5 MB (megabytes), lossless compression can reduce it to about half that size, depending on the type of file being compressed. This makes it convenient for transferring files over the Internet, as smaller files are transferred faster. This process is also useful for archiving files as they take up less space.
The zip convention, used in programs such as WinZip, uses lossless compression. This is why zip software is popular for compressing programs and data files. This is because when these files are decompressed, all bytes must be present to ensure their integrity. If a program is missing bytes, it won’t run. If bytes are missing from a data file, it will be incomplete and garbled. GIF image files also use lossless compression.
Lossless compression has advantages and disadvantages. The benefit is that the compressed file will decompress into an exact duplicate of the original file, mirroring its quality. The downside is that the compression ratio isn’t that high, precisely because no data is lost.
To achieve a higher compression ratio, to significantly reduce a file beyond 50%, lossy compression must be used. Lossy compression will remove some of its redundant data from a file. Because of this data loss, only a few applications are suitable for lossy compression, such as graphics, audio, and video. Lossy compression necessarily reduces the quality of the file to arrive at the resulting highly compressed size, but depending on the need, the loss can be acceptable and even imperceptible in some cases.
JPEG uses lossy compression, which is why converting a GIF file to JPEG will reduce its size. It will also reduce the quality to some extent.
Lossless and lossy compression has become part of our everyday vocabulary largely due to the popularity of MP3 music files. A standard WAV format audio file converted to an MP3 file will lose a lot of data because MP3 uses a high compression lossy algorithm that discards much of the data. This makes the resulting file much smaller so that several dozen MP3 files could fit on, say, a single compact disc, versus a handful of WAV files. However, the sound quality of the MP3 file will be slightly lower than that of the original WAV, noticeably for some.
As always, whether you’re compressing video, graphics, or audio, the ideal is to balance the high quality of lossless compression with the convenience of lossy compression. Choosing the right lossy convention is a matter of personal choice and good results are highly dependent on the quality of the original file.
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