This paper describes an image processing expert system for images of footprints used in criminal investigations, and user interface with this system. The purpose of this system is to increase the efficiency of footprint image processing through improved footprint image quality and automatic footprint pattern extraction. In footprint image processing, the most difficult issue is to carry through the complex processing sequence brought by the variety of pickup methods depending on the condition of pickup places, various patterns of footprints, noises and so on. Because this system constructs usable processing sequences for input images automatically by using knowledge of the image processing and has friendly user interface, not only police investigators but general police officers can deal with image processing easily. In the pattern extraction, a practical processing sequence for various footprint images is constructed through the simulation over 37 footprint images, and the usefulness of the expert system is ascertained experimentally.

The feasibility of using isodensity lines for a human face identification system is demonstrated through experi-mental investigation. Instead of using feature points extracted from the faces, as is done in the conventional matchingsystem, the technique presented uses gray level isodensity lines of the faces By comparing the shape of isodensitylines, people can be identified. The identification technique proposed has the following advantages over conventional

The multiple grid(MG) chain code which uses four different square grids is proposed to encode line drawings. The main processes adopted in the code are: 1) a grid selection algorithm which allocates quantization points only to the vicinity of the course of a line drawing, 2) labeling rule on quantization points which makes the frequency of some codes larger than that of other codes, and 3) quantization points allocation-not to the corners, but to the sides of a square which makes the straight line segments larger without increasing quantization error. A performance comparison of various chain codes is made from the viewpoints of the encoding efficiency, naturalness of the encoded lines, and the rate distortion measure. Also, the superiority of the MG chain code to other codes is shown. At last, application of the MG chain code to the electronic blackboard system is explained.