A three-layer, two description image coder

Summary form only given. We propose a new DCT-based image coder that provides a balance in three areas: compression, progressive coding, and robustness. We design a unique form of progressive coding. The scheme is described as a three-layer, two description image coder because it provides three levels of progressive coding where the last two layers refine the image independent of each other. This is the first image (source) coder of this type. Our coding technique increases robustness to lost information when compared to traditional progressive coding methods, and it maintains progressivity. The proposed coding technique implements two levels of coefficient scaling. The goal of the first level of coefficient scaling is to obtain a coarse representation of the original DCT coefficients by using large quantization step sizes. Next, the coarse representation of each DCT block is subtracted from the original, producing a quantization error or residual, which is quantized with smaller step sizes. At this point, we have two quantized representations taken from the original DCT coefficients. To create two layers of image refinement, the residual data is divided into two descriptions such that adding either description to the coarse representation provides a significant improvement in image quality. Thus, the coding scheme creates three layers of successive refinement of image quality, where the first layer provides a coarse or base level of quality and the two following layers provide independent, full image descriptions for refinement. We show that the proposed layered image coding scheme provides good performance for practical packet erasure rates experienced in the two refinement layers