Understanding Image Intensities

Traditionally, image intensities have been processed to segment an image into regions or to find edge-fragments. Image intensities carry a great deal more information about three-dimensional shape, however. To exploit this information, it is necessary to understand how images are formed and what determines the observed intensity in the image. The gradient space, popularized by Huffman and Mackworth in a slightly different context, is a helpful tool in the development of new methods. 0. Introduction and Motivation The purpose of this paper is to explore some of the puzzling phenomena observed by researchers in computer vision. They range from the effects of mutual illumination to the characteristic appearance of metallic surfaces—subjects which at first glance may seem to take us away from the central issues of artificial intelligence. But surely if artificial intelligence research is to claim victory over the vision problem, then it has to embrace the whole domain, understanding not only the problem solving aspects, but also the physical laws that underlie image formation and the corresponding symbolic constraints that enable the problem solving. One reason for previous neglect of the image itself was the supposition that the work must surely already have been done by researchers in image processing, pattern recognition, signal processing and allied fields. There are several reasons why this attitude was misadvised: Image processing deals with the conversion of images into new images, usually for human viewing. Computer image understanding systems, on the other hand, must work toward symbolic descriptions, not new images. 1 This report describes research done at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology. Support for the laboratory's research is provided in part by the Advanced Research Projects Agency of the Department of Defence under Office of Naval Research contract N00014-75-C-0643. Artificial Intelligence 8 (1977), 201-231 Copyright © 1977 by North-Holland Publishing Company UNDERSTANDING IMAGE INTENSITIES ')C\-1