A comparison of vector quantization techniques in transform and subband coding of imagery

摘要

Transform image coding is considered using scalar quantization, pyramid vector quantization (PVQ), weighted pyramid vector quantization (WPVQ) and generalized Lloyd algorithm vector quantization (VQ). Subband image coding is considered using scalar quantization and pyramid vector quantization. A modification to the PVQ encoding algorithm is described and shown to provide improvement in encoded image peak signal-to-noise ratio (PSNR) of 0.5 to 1.0 dB. The WPVQ encoding algorithm is described and an adaptive WPVQ image coder is developed which provides improvements of up to 1.5 dB over the PVQ coder. In a simulation study, at low bit-rates (0.5 bit/pel) the transform VQ coder generally provided the largest PSNR, although the PVQ subband coder was superior for some images, and th was competitive for most images. At larger encoding rates (for which, because of complexity, the generalized Lloyd algorithm VQ was not considered) the scalar quantizer subband coder generally yielded larger PSNR than did the scalar quantizer transform coder. The PVQ transform and subband coders provided similar values of PSNR, but the subband coded image had less blockiness than the transform coded image. At an encoding rate of 0.5 bit/pel, the subband coders and the full search VQ and adaptive WPVQ transform coders are roughly an order of magnitude more complex than the PVQ and tree-searched VQ transform coders.