A software process that reduces the storage space taken up by photo or video image files. It comes in two type: ‘lossless’ and ‘lossy’ compression. Lossless compression is used by TIFF files, for example and retains all the image data but does not produce the biggest savings. Lossy compression is used for the JPEG format and produces much smaller files, but some data is lost in the process – though this may not be visible in real-world viewing conditions.