Compression of video signals is used in order either to reduce the bandwidth of the transmission channel (e.g. satellite TV or network) or to reduce the amount of data to be saved (e.g. DVD or Blu-ray). There are two different kinds of compression – lossless and lossy. Lossless compression allows the encoded data to be decoded without any differences to the original. Lossy compression implies that not all the data from the original has to be present in the decoded video in order to achieve good perceptual quality.