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An efficient subband coding method for encoding monochrome and color images is presented. In this method, the spectrum of the input image signal is decomposed nonuniformly into seven bands. In the coding process the lowest band is DPCM (differential pulse-code modulation)-coded while the higher bands are PCM-coded. The PCM quantizer is designed such that it reduces the subjective effect of quantization noise, and it also helps in an efficient transmission of higher band signals at low transmission rates. For encoding color images, the red (R), green (G), and blue (B) components of color images are first transferred to luminance (Y) and two chrominance components (I.Q). Each component is then decomposed separately into seven narrowbands. The higher-band signals corresponding to the luminance component are retained and coded separately, while the higher bands associated with I and Q components are discarded. The computer simulation results are presented in terms of average b/pixel and the quality of the reconstructured pictures. These results indicate that good quality reproduction can be achieved at high compression rates.>
Gharavi et al. (Fri,) studied this question.