Comparing lossy and lossless compression

Both lossy and lossless compression make a file smaller. The important difference is what happens to the original data and to the quality.

Lossy compression

Lossy compression makes a file smaller by discarding some of the data or detail. This can lose quality, especially if the file is compressed heavily, but it usually gives the largest reduction in file size: a 24 MB file might become 6 MB. Choose lossy compression when a much smaller file matters more than keeping every piece of original data or perfect quality. It does not delete whole files; it reduces the amount of detail stored inside the file.

Lossless compression

Lossless compression reduces file size without removing any data. Nothing is discarded, so the contents stay exactly the same and the original quality is kept. It usually gives a smaller reduction in file size: the same 24 MB file might become 18 MB. Choose lossless compression when the contents must stay exactly the same and any loss of data is unacceptable.

Comparing the two