Lossless compression

Lossless compression is a type of compression where the original file can be perfectly reconstructed from the compressed version - no data is lost when we compress it.

That means that we don’t lose any quality / details when we compress a file with lossless compression.

In lossless compression, we can perfectly reconstruct the original file from the compressed version, as no data was lost during compression.

How does lossless compression work?

The main two ways that we can losslessly compress a file are:

• Run-length encoding
• Dictionary encoding

Examples of lossless compression

• PNG images
• GIF images
• ZIP files (and things like gzip)
• FLAC audio files
• Lossless x264 video files

Benefits of lossless compression

• The original file can be perfectly reconstructed, so we don’t lose any quality or details when we compress it.
• If we need to edit the file later, it’s better to have a lossless version of it, as we can make edits without losing quality. If we edit a lossy compressed file, we will lose more quality each time we save it, as more data is lost each time we save it.
  • We don’t experience generational loss
• If we have a lossless compressed version, we can always get the original back if we need it.
• Archive projects can store the original file with no lost detail.

Drawbacks of lossless compression

• It often uses a lot of CPU power to compress and decompress the file, which can make it slow to work with (think if you’ve ever tried to extract a large zip / gzipped-tarball file - it can take a long time).
• It doesn’t reduce the file size as much as lossy compression, so it may not save as much storage space or make it as fast to transfer over the internet.
  • If we don’t need the original file, and we just want a smaller file to save space or transfer over the internet, lossy compression may be a better choice, as it can reduce the file size much more than lossless compression.