Image analysis – Pattern recognition – Feature extraction
Patent
1993-06-02
1996-12-17
Johns, Andrew
Image analysis
Pattern recognition
Feature extraction
382203, 382205, G06K 946
Patent
active
055861997
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for determining an orientation of a line segment in a contour in a local area of a binary contour image.
In the fields of image measurement and image recognition, when obtaining information on portions which correspond to characteristic features of an object, from an image stored in an image memory, a contour of the image is extracted, and then information on a characteristic feature such as a straight line is extracted. For extracting such information, it is necessary to obtain an orientation of the line segment in each area of the image.
BACKGROUND ART
FIGS. 1 and 2 are diagrams illustrating the Hough transform, which is conventionally used for extracting information on a straight line, from information on an image. According to the Hough transform, when a set of coordinates of a pixel the value of which corresponds to black (or white) of an original image is denoted by (xi, yi), curves expressed by the equations values of which correspond to black (or white). Since points on the same straight line on the original image (x-y plane) correspond to the same set of coordinates .rho., .theta. as indicated in FIG. 1, the above curves cross at a crossing point (.rho., .theta.) on the .rho.-.theta. plane (FIG. 2). Therefore, the straight line on the original image (x-y plane) can be obtained from the above crossing point of the curves on the .rho.-.theta. plane.
However, it is necessary to draw the curves as above for all of the points on each straight line, to obtain a straight line in accordance with the above method, and processing to obtain a crossing point is necessary for each straight line. Therefore, the amount of data processing becomes great. This great amount of data processing takes a large amount of software processing time, and large size hardware for the hardware processing.
Further, there is a drawback that only straight lines can be detected by the Hough transform, and it is impossible to detect a curve which can be locally deemed to be a line segment, but macroscopically has a curvature.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a method for determining an orientation of a line segment in a contour in a local area of a binary contour image whereby a local line segment in an image can be detected through a simple process.
A second object of the present invention is to provide a method and an apparatus for determining an orientation of a line segment in a contour in a local area of a binary contour image whereby a local line segment in an image can be detected through a simple process while suppressing an influence by noise.
A third object of the present invention is to provide a method and an apparatus for determining a macroscopic line segment from local line segments passing through respective contour points of an image.
A fourth object of the present invention is to provide a method and an apparatus for determining a connecting portion which connects between macroscopic line segments of contour points of an image.
A fifth object of the present invention is to provide a method and an apparatus for determining a position and an orientation of a corner formed in a contour of an image, based on orientations of line segments viewed from each of contour points of an image.
A sixth object of the present invention is to provide a method and an apparatus for determining a polygon formed in a contour of an image, based on positions and orientations of macroscopic line segments and corners formed in a contour of an image, which are obtained from the contour.
According to the first aspect of the present invention, there is provided a method for determining an orientation of a local line segment in a contour in a local area of a binary contour image. The method contains: a first step for obtaining the numbers of pixels each having a predetermined value and located in a plurality of orientations from one of pixel(s) located in the local area and having the above predetermined value; and a second step for d
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Kanda Shinji
Maruyama Tsugito
Morita Toshihiko
Wakitani Jun
Fujitsu Limited
Johns Andrew
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