not a coincidence, but is the result of a carefully planned time of landing (sun elevation) and lander orientation (sun azimuth). * The picture was started 25 seconds after touchdown and took 15 seconds to acquire. The alternating bright and dark vertical striations at the left side of the image and the fine particles deposited on the footpad at the right side were caused by a turbulent cloud of dust raised by the lander's retrorockets. t *F. O. Huck and S. D. Wall, "Image quality prediction: An aid to the Viking Lander imaging investigation on Mars. " Appl. Opt. 15, 1748-1766 (1976). tT. A. Mutch, A. B. Binder, F. O. Huck, E. C. Levinthal, S. Liebes, Jr. , E. C. Morris, W. R. Patterson, J. B. Pollack, C. Sagan and G. R. Taylor, "The Surface of Mars: The view from the Viking 1 Lander. " Science 193, 791-801 (1976). VISUAL COMMUNICATION An Information Theory Approach Chapter 1 Introduction 1. 1 OBJECTIVE l The fundamental problem of communication, as Shannon stated it, is that of reproducing at one point either exactly or approximately a message selected at another point. In the classical model of communication (Fig. 1. 1), the infor­ mation source selects a desired message from a set of possible messages which the transmitter changes into the signal that is actually sent over the commu­ nication channel to the receiver. The receiver changes this signal back into a message, and hands this message to the destination.