Making Progressive Transmission Adaptive

Progressive transmission hierarchically reorganizes the information in an image with the aim of increasing transmission efficiency on a low bandwidth channel. We have developed methods for adaptively choosing initial and successive approximations to be sent when the end user is a human telebrowsing through a database to find particular desired images. Because of progressive transmission overhead, it is desirable to send in one step the approximation which is just good enough to allow a user to make a positive decision (e.g., want/don´t want). During past and present sessions of telebrowsing, positive response times are recorded and used to estimate the actual positive response time probability mass function. This estimate is used with a previously calculated overhead function to choose the best initial and successive approximations. We discuss the application of two-channel coding to progressive transmission and conclude that little is gained by further coding of the initial lowresolution approximation. However, the interpretation of these lowresolution images is enhanced if the displayed size is a function of image resolution. We present a method for determination of the best displayed image size which is based on the modulation transfer function of the human visual system.