Efficient Transmission Of "Most Important" Successive Image Approximations

Abstract

Swift recognition of grey scale images transmitted through low bandwidth channels has been demonstrated by various progressive techniques in which a series of gradually refined image approximations are received and displayed. A previous technique demonstrated non-homogeneous progressive transmission in which image content controls transmission priorities, resulting in a decrease of the time required to receive a usable image. The non-homogeneous technique utilized two simultaneous decompositions, a quad-tree based spatial and a subimage information measure. The concept of simultaneous decomposition is extended to include a third component: grey level approximation. Just as an undecomposed quad-subtree provides a spatial approximation, values of pixels used as quad-subtree representatives are initially approximated and later refined. The three simultaneous decompositions are integrated so as to achieve, for a given transmission time, a higher degree of received image usefulness. The receiver does not have a priori knowledge about which image areas are to receive preferential treatment, and the level of preference is the pixel. The total transmission time for the series of approximations concluding in lossless reception, including preferential decomposition overhead, is comparable to the time required by non-progressive lossless methods. The technique is computationally simple and intended for general purpose processor architectures.