Image analysis – Histogram processing – For setting a threshold
Patent
1992-02-04
1994-10-25
Moore, David K.
Image analysis
Histogram processing
For setting a threshold
382 22, 382 24, G06K 966
Patent
active
053596722
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
The present invention relates to a line detecting method for use in image processing to detect the position of a rectilinear object, for example, a weld line or an edge of an object. More particularly, the present invention relates to a method which enables detection with high accuracy even in a case where the input image is not constant because of inferior surroundings or in a case where the object of detection is stained.
BACKGROUND OF THE INVENTION
As a known method of detecting a line by use of an image processing method, as described above, there is a method wherein an image is converted to binary form and a position that changes from black to white or from white to black is detected. Another method is known wherein differentiation is performed by use of a matrix of pixels arranged in 3 rows and 3 columns.
The method wherein a line or an edge is detected by converting the image to binary form requires that the ambient brightness and the work condition be fixed, since the binary image changes with a change in the ambient brightness.
The method that employs a 3.times.3 matrix is affected by a local change of the brightness and hence cannot provide a clear image, so that, if the brightness of the image changes gently, points where the brightness changes, that is, the periphery of the image, cannot be found. In addition, if the image has a stain or the like adjacent a rectilinear line to be detected, there is a strong possibility of inviting an erroneous detection. In addition, since a large number of arithmetic operations are required, the processing speed is low.
Accordingly, these methods can be applied in a case where the input image is constant and clear, but not in inferior surroundings such as those in which an articulated industrial robot performs an operation, for example, welding.
In view of the above-described problems, it is an object of the present invention to provide a method of detecting a line or an edge as an object of detection with high reliability even in an operation performed in surroundings where conditions are not constant and the work is extremely stained.
SUMMARY OF THE INVENTION
The present invention provides a method of detecting the position of a rectilinear object of detection from an image taken into an image processing apparatus by an imaging device, wherein a preparatory stage that comprises the steps (a) to (g) is first executed as follows:
(a) setting two parallel rectangular windows that cross a line to be detected at their long sides;
(b) adding image density values in each of the pixel rows in the direction of the short sides of the rectangular windows to obtain one-dimensional data comprising a row of the resulting added values for each rectangular window;
(c) obtaining at least one feature point for each of the one-dimensional data, which has a characteristic value based on the size, gradient, change in gradient, etc., of the one-dimensional data;
(d) combining the characteristic values at the feature points in one of the one-dimensional data with the characteristic values at the feature points in the other one-dimensional data, and obtaining a combination that has the maximum value as the sum of the characteristic values;
(e) storing in memory the inclination of a line connecting the two feature points that show the maximum value, together with the value of the sum;
(f) inclining each of the rectangular windows so that the short sides thereof are parallel to the line connecting the feature points, thereby forming a parallelogram-shaped window; and
(g) executing the steps (b) to (e) in regard to the parallelogram-shaped windows, thereby storing the inclination and the value of the sum.
To effect actual detection, the following step (h) is executed:
(h) executing the steps (b) to (e) again in regard to the parallelogram-shaped windows obtained in the preparatory stage, and comparing the inclination and the value of the sum, thus, obtained, with those obtained in the preparatory stage, thereby detecting the position of the line to be detected.
Acc
REFERENCES:
patent: 5073954 (1991-12-01), Van Tyne et al.
patent: 5228095 (1993-07-01), Abe
Hirakawa Kiyoshi
Nakazato Tatsumi
Nishikawa Seigo
Okumura Shinji
Johns Andrew W.
Kabushiki Kaisha Yaskawa Denki
Moore David K.
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