Decompression

Decompression is the process of restoring a compressed file so it can be opened, read, played or used. When you download a compressed file, the software you use usually decompresses it first, because most apps can only work with a file once its data is back in its usual format. The decompressed file also takes up more storage space again.

The result depends on how the file was compressed. With lossless decompression, the decompression algorithm rebuilds every piece of the original data, so the decompressed file is exactly the same as the file before compression. For example, a scanned copy of a signed trip consent form might be compressed losslessly to save space when emailed; when the school office decompresses it, every letter and signature is identical to the original scan.

With lossy decompression, the file is rebuilt so it can be used, but the data removed during compression cannot be put back. The decompressed file is not exactly the original. A recording of a school choir rehearsal compressed lossily for a highlights video will still play after decompression, but the quietest details that were discarded are gone for good.

Compression and decompression are different

Compression reduces file size. Decompression restores a compressed file for use. They are opposite processes, not the same one.