Recursively splitting the low-frequency band with successively fewer

Abstract

A sub-band encoding method for splitting the frequency spectrum of an input signal into plural bands, encoding the signals of the respective bands and transmitting the encoded signal, is disclosed. The encoding method includes a first step of splitting the input signal into a signal of a high frequency band and a signal of a low frequency band using a first-stage low-pass filter and a first-stage high-pass filter, a second step of downsampling signals of respective frequency bands obtained by the first step, a third step of splitting the frequency spectrum of the low frequency band signal downsampled by the second step, using recursively a pre-set low-pass filter and a high-pass filter, for generating signals of a plurality of frequency bands, and a fourth step of encoding the signals of respective frequency bands obtained by the second step and the third step. The number of taps of the second-stage low-pass filter and the second-stage high-pass filter used in the third step is set so as to be smaller than the number of taps of the first-stage low-pass filter and the first-stage low-pass filter. In the case of splitting the frequency spectrum of a two-dimensional picture signal, the method may include high pass and low pass filtering at each stage in both horizontal and vertical directions, and the relationship involving the number of taps at each stage may be similar.