Lossy compression

Lossy compression is a type of compression where the original file can’t be perfectly reconstructed from the compressed version - some data is lost when we compress it. This can lead to a loss in quality, and if we compress it too much, it can look really bad.

In lossy compression, we cannot perfectly reconstruct the original file from the compressed version, as some data was lost during compression.

Examples of lossy compression

• JPEG images
• MP3 audio files
• MP4 video files, encoded with lossy codecs like H.264 or H.265

Benefits of lossy compression

• It can massively reduce the file size, which can save a lot of storage space and make it much faster to transfer over the internet.
• We usually don’t need 100% of the original data to get a good quality image, video or audio file - for example, if we have a photo of a cat, we don’t need to keep every single pixel to have a good quality image of the cat - we can lose some of the data without worrying.

Drawbacks of lossy compression

• The original file can’t be perfectly reconstructed, so if we compress it too much, it can look really bad.
• 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.
  • This is called generational loss
• If all we have is a lossy compressed version, the original is lost forever.
  • This is especially important in archive projects.