For each pel signal capable of taking each of a plurality of levels with a first probability dependent on a reference signal, binary prediction error codes are produced to represent one of serial numbers assigned to the first probabilties arranged in a monotonously decreasing order that is coincident with the actually taken level. Mode codes are allotted to the respective prediction error codes with each mode cods made to represent a second probability that the prediction error code allotted therewith is binary zero. The prediction error codes for a sequence of pel signals are grouped according to the mode codes allotted thereto and then compression encoded. Preferably, the code codes are produced in consideration of the prediction error code or codes of more significant binary bit. A compassion encoded signal is expansion decoded by alternatingly reproducing the mode codes and the prediction error codes. Reproductions of the prediction error codes provide reproduced pel signals. When the pel signal is variable among a great number of levels, the pel signal is preferably represented by a combinattion of one each of a plurality of partial pel signals, each representative of a smaller number of levels.
ENCODER-DECODER SYSTEM FOR MULTILEVEL PICTURE ELEMENTS TO PREDICTION ERROR CODES FOR EACH PEL SIGNAL AND A DECODER THEREFOR