JP2621810B2 - Figure detection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphic detecting method and apparatus for reading graphic data on a drawing and digitizing the drawing.

[0002]

2. Description of the Related Art Conventionally, a straight line and a curve drawn on a drawing are automatically detected and read by image processing technology and are digitized. Among them, Hough transform is known as a method resistant to noise. (See, for example, Pattern C by Richard O. Duda and Peter E. Hart.
lassification and Scene Analysis ”, John Wiley & S
ons1973, page 336) A straight line detection method using Hough transform will be described with reference to FIG. At an arbitrary point (x, y) on the straight line 11,

[0003]

The following holds. Therefore, it is necessary to obtain θ and ρ from the obtained image including the straight line.

In digital image processing, when a straight edge in an image is obtained, an edge extraction process is first performed on the image, and then a straight line is detected from the edge image.
In an actual image, the plurality of edge pixels 12 constituting the straight line 11 completely lie on the straight line 11 due to the characteristics of the edge extraction processing and noise due to image input, and the pixel 12 forms a straight line without interruption. I can't expect that.

In the Hough transform, this is solved in the form of accumulation in a parameter space. First, the (θ, ρ) space is divided into the accuracy and the range necessary for obtaining a straight line as shown in FIG. Each of the divided areas is called a cell 15. Each cell has a memory for counting. Next, for each pixel 12, its position coordinates (x, y) are substituted into equation (2),

[0007]

Ρ is calculated for 0 ≦ θ <2π to obtain a graph of a characteristic curve as shown in FIG. That is, the pixel 2 on one straight line limits the parameters (θ, ρ) of the equation of the straight line to the values on the characteristic curve 13 in FIG. The value of the memory of the cell of FIG.
increase. Characteristic curves 13a, 13b, 13c obtained from a plurality of pixels 12a, 12b, 12c (the diagram conceptually illustrates the principle, and the correspondence between the pixel position in FIG. 2 and the curve position in FIG. 3 is not accurate) , One point 14 on the (θ, ρ) plane
When this point intersects, this point is called an accumulation point, and the coordinates of this point (θ
₀ , ρ ₀ ) are the parameters of the straight line to be found,

[0009]

Is the equation of the straight line.

That is, in order to obtain the parameters (θ ₀ , ρ ₀ ) of a straight line, a characteristic curve is drawn for all “1” pixels in the area, and counting is performed for passing cells. Then, in order to detect the accumulation point 14, the count value of each cell in FIG. 3 is checked, and a straight line parameter (θ ₀ , ρ ₀ ) is obtained from the position of the cell having the maximum value. In this way, a straight line can be stably detected even when a pixel of the straight line is not correctly obtained in the course of image processing.

The above is the Hough transform usually used for detecting a straight line in an image. As described above, the detection of a certain figure can be performed by converting it into the accumulation in the parameter space with the parameters defining the figure as coordinate axes.
Attempts have been made to detect other figures. In particular, when a drawing is automatically read from an image, there are many demands for detecting a circle or an arc drawn frequently in the drawing. The above Hough transform is extended to the detection of a circle / arc as follows.
The extension method will be described with reference to FIG.

The circle 16 is represented by the coordinates (x ₀ , y ₀ ) of the center and the radius r ₀ , and is written as in equation (4).

[0014]

As described above, since a circle is represented by three parameters x ₀ , y ₀ , and r ₀ , the circle is represented by (x ₀ , y ₀ , r ₀ ) as shown in FIG. Consider a three-dimensional parameter space. This is divided into cells 17, and each cell has a memory for counting. "1" in the image
Equation (4) is modified for each pixel of the position (x _i , y _i ),

[0016]

Is calculated for each (x ₀ , y ₀ ):
(X ₀ , y ₀ , r ₀ ) The parameter range is represented as a curved surface 6 in a three-dimensional space. The plurality of pixels 18a, 18b, 18c. . . , A curved surface 19a, 1 indicating the existence range of the parameter as shown in FIG.
9b, 19c. . . (The correspondence between the position of the pixel in FIG. 5 and the curved surface in FIG. 7 is not accurate).
0, the parameters (x ₀ , y ₀ ,
r ₀ ) is required.

[0018]

However, in order to perform this in the same manner as in the case of detecting a straight line, the parameter space (x ₀ , y ₀ , r ₀ ) is discretized and divided into cells 17.
It is necessary to accumulate the number of times the curved surface 6 passes through the cell 19. In this case, the parameter space is a three-dimensional space,
Since the range of parameters is two-dimensional on a curved surface, the number of discretized cells becomes enormous, and the amount of processing for accumulating one pixel 18 becomes enormous. Therefore, this method was not very practical.

An object of the present invention is to provide a method and a method for easily detecting straight lines and arcs, which are important elements of a drawing, in a practical scene in which pixels through which a part of a figure passes are known in reading the drawing. To provide equipment.

[0020]

According to a first aspect of the present invention, when the position of a part of a figure forming a straight line or an arc on a drawing is known, this position is used as an origin and the position of another pixel forming the figure is determined. To (x _i , y _i ) (i = 1, 2,..., N; n is 0
The number of pixels with non-pixel values) in the (ω, φ) space discretized into multiple cells

[0021]

The accumulated pixel values in a cell which satisfies, The peak of the accumulated value accumulation point (ω _{0, φ 0)} as, phi ₀ ≠ 0
In the case of, r figure from the origin in the direction of the angle of ω _{0 0} =
1/2 [phi ₀ is detected as an arc of radius r ₀ centered at a remote location, in the case of phi ₀ = 0, the figure through the origin,
This is a figure detection method for detecting a straight line in the direction of an angle of ω ₀ + π / 2.

According to a second aspect of the present invention, there is provided an image memory for holding a drawing as an image, starting point searching means for scanning the image and detecting a part of a figure as a starting point, and discretely dividing the (ω, φ) space into a plurality of cells. a cumulative memory turned into the a position of the start point as the origin, the positions of pixels having a pixel value non-zero that is regarded as forming the figure _{(x i, y i) (} i = 1,2, ... ,,
n; n is the number of pixels having a non-zero pixel value)
With respect to the cell position (ω, φ) of the accumulation memory,

[0024]

A characteristic curve accumulating means for accumulating pixel values in cells satisfying the following conditions; peak detecting means for obtaining a peak of the accumulated value of the accumulating memory as an accumulation point (ω ₀ , φ ₀ ); From the position (ω ₀ , φ ₀ ), if φ ₀ ≠ 0, the figure is r ₀ = １ ／ in the direction of the angle ω ₀ from the origin.
An output is an arc with a radius r ₀ centered at a position φ ₀ away. If φ ₀ = 0, the figure passes through the origin and ω ₀ + π
And a circle / straight line calculating means for outputting a straight line in the direction of the angle of / 2.

[0026]

The present invention is directed to a case where the starting point 22 of the figure 21 is determined on the image by a known method as shown in FIG. For example, when a straight edge portion is obtained as a binary image having “1” and the background is “0” by a process such as edge extraction, the entire image is scanned in the scanning direction 2 from the upper left.
3 is scanned, and the found “1” pixel is the starting point 22.
It is.

If this point is the origin, the coordinates of the center 24 of the figure 21 which is the arc to be detected are (x ₀ , y ₀ ), and the radius is r ₀ ,

[0028]

Holds, and any point (x, y) on this circle
By substituting into equation (4),

[0030]

When it is transformed,

[0032]

[0033]

Equation (8), like equation (1), comprises coordinates (x, y) of each point on the figure and two parameters ω and φ representing the figure. Therefore, the pixels 25a, 25b,. . . Is calculated for the position (x _i , y _i ) of equation (8) with respect to 0 ≦ ω <2π, a graph 26 on the ω-φ plane as shown in FIG.
a, 26b,. . . Is obtained.

[0035]

Therefore, the ω-φ plane is divided into cells, and FIG.
The curves 26a, 26b,. . . The coordinates (ω ₀ , φ ₀ ) of the accumulation point 27 can be obtained by accumulating the number of times of passing through and detecting the peak. The angle ω ₀ from the origin to the center 24 of the arc in FIG.
From the obtained φ ₀ , the distance (radius of the arc) r ₀ is

[0037]

[0038]

In the present invention, a straight line is obtained similarly. Since the straight line corresponds to r ₀ = ∞, φ ₀ = 0. Therefore, as shown in FIG. 10, a straight line 29 passing through the starting point 28 has a direction 30 perpendicular to the straight line 29 determined as ω ₀ of the accumulation point 27.

[0040]

An embodiment of the present invention will be described with reference to FIG.
The image memory 1 stores a binary image including a figure, and the starting point searching means 2 scans the image memory 1 in a certain direction to search for a "1" pixel which is a starting point of the figure. For example, when the starting point searching means 2 scans the image memory 1 from the upper left in the direction of the scanning direction 7 like a television, a pixel which is a part of a circle is found. This pixel is set to a starting point 8 (X _s ,
Y _s ).

The accumulating memory 4 is a counting memory which divides the ω-φ space into cells as required as shown in FIG. 11, and each cell has an accuracy capable of counting up to the number of pixels occupied by the detection range 9 described below. . All counting memories constituting the accumulating memory 4 are all cleared to 0 when the starting point 8 is searched. In FIG. 11, the accumulative memory includes only the area of φ ≧ 0. According to equation (9), a calculation result of φ <0 also appears, and this can also be accumulated, but (ω,
If an accumulation point appears at (φ) = (ω ₁ , φ ₁ ), an accumulation point always appears at (ω, φ) = (ω ₁ + π, −φ ₁ ) in principle. Configuration.

In this embodiment, since a circle and a straight line having a radius equal to or less than a predetermined radius are detected, the characteristic curve accumulating means 3 sets a detection range 9 in the image memory 1,
The following processing is performed for each “1” pixel within this range.

(A) Each pixel coordinate (X _i , Y _i ) is translated in parallel to a coordinate system whose origin is the starting point coordinate (X _s , Y _s ), and the normalized coordinate (x _i , y _i ) is calculated. obtain.

[0044]

(B) For each (x _i , y _i ), φ is calculated for each ω (0 ≦ ω <2π) by equation (9),
1 is added to the value of the cell (ω, φ) of the accumulation memory.

The above processing is performed for all “1” s in the detection range 9.
Is executed for the pixel of.

When this is completed, the peak search means 5 is started. The peak searching means 5 scans all the cells of the accumulation memory 4 and obtains (ω, φ) of the cell having the largest count value as (ω ₀ , φ ₀ ). The circle / straight line calculating means 6 first checks whether φ ₀ is 0, and in this case, outputs ω ₀ + π / 2 as the direction of the straight line. Straight start (X _s, Y _s)
From this result, an external device (not shown) draws the resulting straight line, for example,

[0048]

Can be obtained as follows.

If φ ₀ is not ₀ , r ₀ = １ ／ φ
Gives the distance from the starting point to the center of the circle, and equation (6)
, The center coordinate becomes (x ₀ , y ₀ ). Again external device start point of coordinates (X _s, Y _s) is also read out,
The coordinates of the center of the circle

[0051]

Can be obtained as follows.

In the embodiment, straight lines and circular arcs are obtained as binarized figures as shown in FIG. 1. However, when the figure is an image with shading, each pixel is either "1" or "1". An intermediate value other than “0” indicating the likeness of a figure can be taken.
Even in such a case, the present invention can cope with the situation. By accumulating the pixel values in the accumulation memory 4 and finding an accumulation point, it is possible to detect a straight line or an arc in the same manner.

[0054]

As described above, by adopting the configuration of the present invention, a straight line or an arc on the drawing can be stably detected from an image under the condition that some of its pixels have been obtained. You can do it. As a feature of the present invention, it is not necessary that the direct and circular arcs are completely connected, and even if there are a few noise pixels, they can be obtained by peak detection. Another great effect is that a straight line and a circular arc can be detected simultaneously with one configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a Hough transform for detecting a straight line according to a conventional technique.

FIG. 3 is an explanatory diagram of a Hough transform for detecting a straight line according to the related art.

FIG. 4 is an explanatory diagram of a Hough transform for detecting a straight line according to a conventional technique.

FIG. 5 is an explanatory diagram of a method for detecting a circular arc according to the related art.

FIG. 6 is an explanatory diagram of a method for detecting a circular arc according to the related art.

FIG. 7 is an explanatory diagram of a method for detecting a circular arc according to the related art.

FIG. 8 is an explanatory diagram of the principle of the present invention.

FIG. 9 is an explanatory diagram of the principle of the present invention.

FIG. 10 is an explanatory diagram of the principle of the present invention.

FIG. 11 is an explanatory diagram showing a configuration of a cumulative memory of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image memory 2 Starting point searching means 3 Characteristic curve accumulating means 4 Accumulating memory 5 Peak detecting means 6 Circle / straight line calculating means

Claims (2)

(57) [Claims] 1. When the position of a part of a figure forming a straight line or an arc on a drawing is known, this position is used as an origin, and other pixel positions forming the figure are defined as (x _i , y _i ) (i = 1
2,. . . , N; n is the number of pixels having a pixel value other than 0)
In the (ω, φ) space discretized into a plurality of cells, Is accumulated in a cell satisfying the following equation, and the peak of the accumulated value is obtained as an accumulation point (ω ₀ , φ ₀ ). When φ ₀ ≠ 0,
R ₀ = 1 / (2 figure is from the origin in the direction of the angle of ω ₀
φ ₀ ) An arc with a radius r ₀ having a center at a distant position is detected. When φ ₀ = 0, the figure passes through the origin and ω ₀ + π
A figure detecting method for detecting a straight line in the direction of the angle of / 2. 2. An image memory for holding a drawing as an image, a starting point searching means for scanning the image and detecting a part of a figure as a starting point, and a cumulative memory for discretizing (ω, φ) space into a plurality of cells. And the position of a pixel having a non-zero pixel value regarded as constituting a figure as (x _i , y _i )
(I = 1, 2,..., N; n is the number of pixels having a pixel value other than 0), and the cell position (ω, φ) of the accumulation memory is A characteristic curve accumulating means for accumulating the pixel values in a cell that satisfies the peak of the accumulated value of the cumulative memory integrated point (omega _0,
a peak detection means for determining as a phi _0), the integrated point (ω _{0, φ} from the position of _0), .phi.0 the case of ≠ 0 is, r from figure origin in the direction of the angle ω _{0 0} = 1 /
(2φ ₀ ) An arc with a radius r ₀ whose center is located at a distance is output. When φ ₀ = 0, the figure passes through the origin and ω ₀ +
and a circle / straight line calculating means for outputting a straight line in the direction of the angle of π / 2.