An encoding/decoding technique and a computer architecture for progressive refinement of 3-D images is suggested. The method is based on a binary tree representation of grey-level images. A scheme to transform an N Ã N Ã N image array into a sequence of at most N Ã N Ã N elements is given. As more elements of the sequence are scanned finer resolution representations of the image are obtained. The proposed architecture, which is suitable for VLSI implementation, performs the transformations between the image and its encoding using O(log N) processors and in time and space proportional to the image size.