Low-bit-rate lossless image coding using classified vector quantization with orthogonal polynomials transform

In this paper, a low bit-rate lossless image coding scheme based on Classified Vector Quantization with Orthogonal Polynomials Transform (OPT) has been proposed. In this work, two vector quantization codebooks VQ1 and VQ2 are used to encode the smooth and edge blocks separately. The proposed scheme divides each input image to be encoded into small blocks and classifies them in spatial domain since it reduces the classification complexity. The smooth blocks are encoded using VQ1 codebook and Adaptive Differential Pulse Code Modulation (ADPCM), so as to provide good response to the non-stationarity of the input data. The edge blocks are vector quantized using VQ2, the OPT is applied on the code vector of edge blocks to obtain transformed coefficient matrix and are encoded with code vector index. The Orthogonal Polynomials Transform maximizes the Energy Packing Efficiency (EPE) which is equivalent to minimizing the Mean Square Error (MSE) in terms of step response. The proposed lossless coding scheme gives better results when compared with existing lossless encoders.