Patent US 5,109,451

An orthogonal transform coding system for images which orthogonally transforms image data to spatial frequencies and divides the domain of the spatial frequencies into low and high frequency domains using a plurality of domain patterns prepared in advance. This system quantizes and encodes the high and low frequency domains of the orthogonally transformed data by different methods. Coding of the data in the low frequency domain is preformed based on bits which are allocated to those data in accordance with their energies. The data in the high frequency domain are decomposed into bit planes and run-length coding is performed for each bit plane, whereby a small number of bits are allocated to those data in the low frequency domain in the coding and an efficient coding of images is accomplished.