Apparatus for quantizing classified vectors of image signals using

Abstract

An apparatus for vector-quantizing an image signal having a low transmission rate which includes a four-band linear filter para-unitary (LPPU) filter group for transforming an input image signal into transform coefficients which are represented by 4.times.4 frequency bands. A code modulator differential-pulse-code-modulates a direct current (DC) component among the transform coefficients output from the four-band LPPU filter group. A coefficient extractor extracts a predetermined number of low-frequency alternating current (AC) component coefficients from the transform coefficients output from the four-band LPPU filter group. A classifier determines a corresponding class, from a plurality of predetermined classes, using the low-frequency AC component coefficients extracted by the coefficient extractor, and outputs class information representing the determined class. A classified vector quantizer quantizes classified vectors of corresponding AC component coefficients input from the coefficient extractor according to the class information output from the classifier and outputs block position information, corresponding to an image block having a predetermined size, of a block matching the transform coefficients transformed by the four-band LPPU filter group, together with the classified-vector-quantized image data and the corresponding class information when the class information does not represent a particular class among the plurality of the predetermined classes, and outputs the classified-vector-quantized image data and the corresponding class information when the class information represents the particular class.