Analysis of a 2-D DCT image coding scheme with motion compensation and vector quantization

A new effective adaptive coding scheme for data compression of images is presented. It is based on a reduction of the spatial, temporal and statistical redundancy. Inter-frame motion compensation technique was used to take advantage of the image temporal correlation. A unitary 2D-DCT was performed on each (8x 8) pixel block in order to exploit spatial correlation and in order to decorrelate the block elements and to make the relative quantization error subjectively less disturbing. The Rate Distortion Function of a Laplacian source was used as a classification strategy by relating a block to a coding bit rate in accordance with its energy. The a.c. transform coefficients were vector quantized by using the pyramidal vector quantizer based on the cubic lattice. Compression ratios in the 8 — 12 range give a distribution quality for colour image sequences according to the CCIR Rec. 601 (12-20 Mbit/sec) or HDTV sequences (50-70 Mbit/sec). Experimental results obtained by computer simulations are presented and the influence of the motion compensation and the vector quantization on the objective error are analysed.