IMAGE SIGNAL ENCODING METHOD AND DECODING METHOD, INFORMATION SOURCE ENCODING METHOD AND DECODING METHOD, APPARATUSES THEREFOR, PROGRAMS THEREFOR, AND STORAGE MEDIA WHICH STORE THE PROGRAMS TO PROCESS GAUSSIAN INTEGER SIGNAL

An information source encoding method for encoding a Gaussian integer signal includes the steps of: inputting a signal value sequence of a Gaussian integer signal as an encoding target; transforming signal values included in the input signal value sequence into integer pairs, each having two integers, arranged in the input order; regarding each of the integer pairs as a lattice point on two-dimensional coordinates, and obtaining integer values greater than or equal to zero by performing a two-dimensional-to-one-dimensional mapping in which the shorter the distance from each lattice point to the origin, the smaller the value assigned to the lattice point by the mapping; and encoding the integer values using codes which are used for encoding an information source that follows an exponential distribution.