The other day my dad — who speaks English okay — thought “lossless” meant “loose less”. That’s what prompted me to write this entry. There are two different ways of compressing video (and this holds for audio too). Lossless and lossy.

When compressing a video sequence with a lossy method, then decompressing it again, the decompressed images will be close to the original, but not quite the same. Even when using a low compression factor, where the decompressed images can’t be distinguished from the original simply by looking at them, there is a difference, which can be computed. Almost all of the video compression methods we use today use such a lossy method, where the least important image data is thrown away.

In the lossless case there’s no data lost. The compressed/decompressed images are exactly the same as the original. There’s a big penalty though: lossless compression methods don’t compress very well. The resulting files take up much more space or bandwidth. Lossless image or video compression methods are still used though, for instance in the medical field, and when storing fingerprint information.