A data compression apparatus is disclosed for data compressing an information signal, which is in n-level form, n being larger than 2. The data compression apparatus comprises an input terminal (1) for receiving the n-level information signal, an entropy coder, such as an arithmetic coder (4) having an input (2) for receiving an input signal, which is adapted to carry out a lossless encoding step on the input signal, so as to obtain a data compressed output signal at an output (6). The apparatus further comprises a prediction filter (12) for carrying out a prediction step on the n-level information signal so as to obtain a prediction signal and a probability signal determining unit (18) for generating the probability signal in response to said prediction signal. An output terminal (8) is available for supplying said data compressed output signal. (FIG. 1) Further, a data expansion apparatus is disclosed. (FIG. 2)