An improved SBC/VQ scheme for color image coding

The authors had previously proposed a subband coding method for color images that used vector quantization and AD-PCM (pulse code modulation) (see C.S. Kim et al., Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing, p.753-6, Apr. 1988). High-quality coded images were achieved at bit rates of 0.6 bits/pixel for 512×512 color images. In the present work, the authors discuss an improved system that enables further reduction in the bit rate. The proposed approach is no longer a subband coder in the true sense, but rather a multirate VQ/DPCM (differential pulse code modulation) system. The approach is based on a three-component multirate representation of the image, composed of a chrominance subimage pair, a medium- to low-frequency luminance image, and a high-frequency luminance residual. FSVQ (finite-state VQ) and DPCM are used strategically in coding these components, with noticeable improvement over previous results