Edge detection analyzer

#In the field of pattern recognition it is necessary or advantageous in some application to detect the presence of straight lines. In such applications not only is the presence of the line significant, but also its orientation and exclusivity within the field-of-interest, and the contrast level along its edge. One such application is in the military arena wherein the field-of-interest may be a geographical area. Straight lines detected therein identify man-made objects. The present invention not only has such military application but also may be used anywhere that it is desirable to identify straight line signatures. One such other application may be in the medical field wherein the present invention can be employed as a diagnostic tool. This invention must be used in conjunction with a computer to determine the presence of straight lines, corners, or other geometrical configuration.

#Typically, a field-of-interest is imaged by an electronic video means. Thereafter, the image is interrogated by any of a number of means, one such means is by systematically scanning the image in discrete steps under the direction of a computer a full raster pattern. The scan may also contain circular components in that at least one small circular scan is conducted at each discrete point along the raster pattern. That is, at, say position X.sub.6, Y.sub.2, a series of concentric circular scans of a small portion of the entire image is conducted. Then, the computer driven scan is moved to the next discrete point (X.sub.7, Y.sub.2) and the series of circular scans are again conducted, until each discrete point throughout the entire raster pattern has been interrogated. Thereby, the entire image of the field-of-interest is systematically investigated.

#The present invention is designed to be employed in conjunction with a computer driven scanning technique as described above wherein multiple circular scans are taken at each of a plurality of discrete points within the computer raster pattern. The present invention processes the information obtained during the scan at each such discrete point to detect the presence of contrast edges. Each edge occuring within the scan image is sensed, but if more than one edge is detected the information will be rejected. That is, the present invention is interested only in processing one-edge signatures and will reject false information resulting from, such as, noise. The present invention then determines the orientation of the angle of the edge at which the contrast of the image changes. Additionally, circuitry that is disclosed within the specification as a preferred embodiment of the present invention also includes as an option, means for rejecting contrast edges that are too far from the center of the scan circle, since such edges have a greater likelihood of false readings.

#FIG. 1 is a block diagram of the present invention;

#FIG. 2 is a schematic diagram, partially in block form of a preferred embodiment of the present invention; and

#FIG. 3 is a waveform diagram of representative waveforms appearing within the circuit of FIG. 2.

#FIG. 1 is a block diagram showing the technique of the present invention on an input 10 of video data that is coupled to common mode rejection circuit (CMR) 12 through timing circuit 22. CMR 12 processes the video input to determine whether a contrast edge exists with the circularly scanned portion of the image. CMR 12 may also include a contrast threshold that is adjustable. The threshold provides a level that must be exceeded by the level of contrast before the video can be processed any further.

#CMR 12 provides a digitized output of detected video to edge validity circuit 14. Circuit 14 determines if more than one distinct edge exists during the scan revolution. If more than one edge is indicated the information is rejected as being inconsistent with data required for a straight line signature. When it is verified that only a single edge is present, a "valid" signal is coupled from circuit 14 to NAND 20.

#Angle counter 16 is initiated at the start of each even scan revolution. Thereby, a reference datum line is established from which the measured angle of the contrast edge can be calculated. When the scan crosses the contrast edge the first time the counter's pace is reduced by one-half. And, when it crosses the edge the second time the then value of the count is available for a computer when it receives a "start read" flag. It identifies the angle of the edge by defining the point on the circumferance of the scan circle that is half-way between the first intersection and the second. Thereby, a single numerical value identifies the angle of orientation of the contrast edge.