Key points are not available for this paper at this time.
This study revisits simple methods, subsampling and modulo differentiation, to combine them in a system suitable for operation in ISDN as well as non-ISDN environments with good overall performance. The modulo difference of selected pairs of pixels in a digital image enables the design of a hierarchal code which represents the original digital image without any information loss. The pixels are selected by pairing together consecutive non-overlapping pixels in the original image and then in successive subsampled versions of it. The subsampling is 2:1 and, as the pairing, is alternated horizontally and vertically. This algorithm uniquely combines hierarchal and parallel processing. Further processing of the hierarchal code through an entropy coder achieves good compression. If a Huffman code is used, default tables can be designed with minimum penalty. Parallel processing allows the coder to operate at various speeds, up to real time, and the hierarchal data structure enables operations in a progressive transmission mode. The algorithm's inherent simplicity and the use of the modulo difference operation make this coding scheme computationally simple and robust to noise and errors in coding or transmission. The system can be implemented economically in software as well as in hardware. Coder and decoder are symmetrical. Compression results can be slightly improved by using 2-D prediction but at the cost of an increase in system complexity and sensitivity to noise.
Torbey et al. (Wed,) studied this question.