Combined VQ-DCT coding of images using interblock noiseless coding

Combined vector quantization (VQ) and two-dimensional discrete cosine transform (DCT) coding of images is discussed. An algorithm for bit allocation for a composite source is developed. This algorithm is used to vary the bit allocation of the transform encoder based on the VQ outputs. An important feature of the scheme is that the bit allocation map used for the scalar quantization of the 2D DCT coefficients varies according to the VQ output-one bit allocation map per VQ codevector. Thus, the VQ achieves two purposes: (1) it performs bit rate reduction, and (2) its output is used to determine the bit-allocation map for the 2D DCT coding. To exploit the interblock correlation, a two-dimensional interblock noiseless coding is used to encode the VQ outputs. Simulation results indicate that performance improvements over several other image-coding schemes can be obtained. The improvements are more noticeable at lower bit rates