A) Coding schemes incorporated into the information before it is transmitted (or stored) in such a way that errors which may arise in transmission can be detected and corrected before restoration or retrieval. In PCM systems, error correction effectively improves the SNR of the system. b) Ingenious software programmes make it possible to cheque that the digital stream of image information has not been corrupted by the loss of a few bits here and there. Additional information introduced as “overhead” to the image bit stream (thereby increasing the bit rate, recording) is chosen to conform to specific rules of construction.

Departures from this construction can be detected readily, so that many potential errors can not only be identified, but corrected so that the information can be restored with high probability. Error correction contributes to the reliability of recording/reproducing and is a normal part of all data recording.