Two-stage multirate coding of color images

Abstract

Various procedures for coding color images have been described in the literature. Several of these have been based on subband coding, including some early results by the authors of this paper and Bruder, in which vector quantization and ADPCM were utilized effectively to encode the subband images. High quality coded images were achieved at bit-rates of approximately 0.6 bit/pixel for 512 x 512 color images. This paper introduces an improved system which evolved as an attempt to maintain the quality of the subband coder at lower bit-rates. The approach is based on a three component multirate representation of the image, composed of a chrominance sub-image pair, a medium-to-low frequency luminance image, and a high frequency luminance residual. Finite State Vector Quantization and Differential PCM are used to code these components. In addition, the paper discusses subband coding, vector quantization and predictive schemes, and provides some comparisons at low bit-rates. Simulation results indicate that noticeable subjective quality improvement can be achieved using the two-stage multirate scheme relative to the other coders that were considered.