The present invention relates to an information extraction device for extracting information of a picture by means of mapping. The device according to the present invention can be used to obtain information concerning a picture, such as the existence of a straight line, the intersection of straight lines, and the three-dimensional direction of straight lines or parallel lines. Such information is useful for pattern recognition of an object, such as in the case of pattern recognition by an industrial robot.
In general, in order to obtain pattern information of an object article, an image of the object is taken by an imaging device, such as a TV camera, the image is processed electronically, and information is extracted from the result of the image processing.
One of the prior art methods of the information extraction is the Hough transformation method, in which the probability of extraction of a straight line or a line segment in the image from the object is enhanced.
In the Hough transformation method, the coordinates of a point (x.sub.i, y.sub.i) in the x-y plane of the image plane are transformed into a mapping function in the form of a sine wave: r=x.sub.i cos.theta.+y.sub.i sin.theta., in the .theta.-r plane of the parameter plane.
The sine waves, which correspond to points on a straight line in the picture plane, intersect at two points in the parameter plane. If only the positive value of .rho. is taken into consideration, the above-mentioned sine waves intersect at a single point. The angle .theta..sub.0 and the height r.sub.0 of the intersecting point in the parameter plane indicate the length of the vertical line from the original point to the straight line and the angle of the vertical line in the image plane. Hence, information of the straight line on the image plane can be extracted by using the obtained data of the angle .theta..sub.0 and the height r.sub.0. It is also possible to use such information extraction to reproduce a straight line having interruptions or distortions.
In the prior art Hough transformation method, however, it is necessary to obtain mapping functions corresponding to every point. The number of points for which the mapping functions are to be obtained is quite large. Hence, it takes a considerable length of time if such mapping functions are obtained by calculations in a point-by-point manner. Accordingly, it is difficult to extract information at a high speed.
Prior art technology for three-dimensional measurement of an object article includes a method for detecting the three-dimensional direction of a line or a plane existing in space, a method of using the vanishing point, and a method of binocular vision. However, these prior art methods may be used only under limited conditions of measurement.