JPH077616A - Inclination detection device - Google Patents

Abstract

PURPOSE:To provide an inclination detection device which can obtain an accurate inclination degree at high speed by obtaining an inclination angle including the error of a correction mark and converting it into the real inclination angle. CONSTITUTION:A mark position detection means 1 detects the correction mark from an original picture and obtains a minimum rectangle surrounding the correction mark. An inclination angle detection means 2 detects the inclination angle including the error between the correction marks based on the apex of the minimum rectangle. The detected inclination angle including the error is converted into the real inclination angle based on a known relation between the inclination angle including the error and the real inclination degree in an inclination angle correction means 3. The inclination angle correction means 3 can be constituted by a corresponding table.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt detecting device for detecting the tilt of a document image read by, for example, an image scanner or a fax, based on a positional relationship between tilt correction marks arranged in advance in the document image. Is.

[0002]

2. Description of the Related Art When a document is read by an image reading device such as an image scanner or a FAX, it may be read at an inclination depending on the set state of the document or an error of the image reading device. In order to detect and correct the tilt of such a document image, a plurality of marks for tilt correction are arranged in advance on the document to be read, and the positional relationship between the plurality of marks is detected to detect the document image. Detecting the inclination has been conventionally considered.

As one example thereof, a plurality of correction marks having different shapes are previously arranged on a document, and the mark shape such as width and height of these correction marks and the coordinate value of a reference point. We proposed an image processing device that detects and corrects. FIG. 2 is an explanatory diagram of an example of the correction marks arranged on the document, and FIG. 3 is an explanatory diagram of the positional relationship of the correction marks on the document. The correction marks having different shapes as shown in FIG. 2 are arranged at the four corners of the document, for example, as shown in FIG. Then, the document on which the correction marks are arranged is read by an image reading device to obtain a document image, and the correction marks are detected from the document image. Depending on the shape of the detected correction mark, the document image is rotated by 90 degrees or 180 degrees to be detected and corrected, and the coordinate value of the vertex of the correction mark is detected to determine the coordinate of the vertex. The tilt angle of the image can be obtained from the relationship between the values, and distortion such as tilt can be corrected.

As a method of obtaining the vertex of the correction mark, a method of using the vertex of the smallest rectangle surrounding the correction mark is used. According to this method, the correct result is obtained when the image has no inclination, that is, when the correction mark is not inclined at all, but when there is inclination, an error occurs. FIG. 4 is an explanatory diagram of an error in vertex coordinates when there is a tilt. As shown in FIG. 4, when the correction mark is inclined, the coordinates of the correct vertex of the correction mark are (x _t , y _t ), whereas the coordinates of the vertex of the smallest rectangle surrounding the mark are (x _{t f} , y _f ). Figure 4
In the case of the above, the coordinate value in the y-axis direction is erroneously obtained. Therefore, the tilt angle obtained based on the vertex coordinates including the error thus obtained also contains the error.

As described above, since the coordinates of the vertices of the correction mark are obtained as the coordinate values of the vertices of the smallest rectangle surrounding the correction mark, when the inclination of the image is large, that is, when the inclination of the correction mark is large. Has a problem that the coordinates of the vertices of the correction marks do not match the coordinates of the vertices of the minimum rectangle, and as a result, the inclination of the image calculated based on these coordinates cannot be accurately detected. In addition, if the shape of the correction mark and the coordinate values of the vertices of the correction mark are to be obtained accurately, more complicated processing such as recognizing the straight line portion of the correction mark and obtaining the inclination is required. There is a problem that it becomes longer.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and obtains a tilt angle including an error of a correction mark and converts it into a true tilt angle. Accordingly, it is an object of the present invention to provide a tilt detecting device that can obtain a correct tilt angle at high speed.

[0007]

According to the present invention, there is provided an inclination detecting device for detecting the inclination of a document image from the positional relationship between a plurality of inclination correction marks arranged in advance in the document image. Mark position detecting means for obtaining the coordinate values of the vertices of the smallest rectangle surrounding each of the inclination correcting marks, and the tilt angle for obtaining a tilt angle including an error from the coordinate values of the plurality of vertices obtained by the mark position detecting means. And a tilt angle correction means for obtaining a true tilt angle from the tilt angle including the error based on a known relationship between the tilt angle including the error and the true tilt angle. It is a feature.

[0008]

According to the present invention, in the tilt angle correcting means,
Based on the known relationship between the tilt angle including the error and the true tilt angle, the true tilt angle is found from the tilt angle including the error found from the coordinate values of the vertices of the smallest rectangle surrounding the tilt correction mark. A more accurate tilt angle to be corrected can be obtained.
At this time, the known relationship between the tilt angle including the error and the true tilt angle is made into a correspondence table, and the value of the true tilt angle with respect to the value of the tilt angle including the error is obtained by using this correspondence table. A high-speed, accurate tilt angle to be corrected can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of a tilt detecting device of the present invention. In the figure, 1 is a mark position detecting means, 2 is an inclination angle detecting means, and 3 is an inclination angle correcting means. The mark position detecting means 1 cuts out an area in which a correction mark can exist from the document image, and from the cut-out area,
Detect the correction mark. The document image may be an image read from the image reading device or an image sent via a communication line or the like. From the detected correction mark, a minimum rectangle surrounding the correction mark is obtained. The method of obtaining this minimum rectangle is arbitrary, but for example, when detecting the correction mark, the contour of the correction mark is traced and the maximum and minimum values of the coordinate values in the x-axis and y-axis directions at that time are calculated. It can be obtained by sequentially updating. Thus, for example, as compared with the case where the straight line portion of the correction mark is recognized and the vertex of the correction mark is obtained, the vertex of the smallest rectangle surrounding the correction mark can be obtained easily and at high speed. . From the obtained minimum rectangle, the coordinates of the vertex of the minimum rectangle corresponding to the vertex of the correction mark are obtained.
For example, when the coordinate values of the upper left correction mark as shown in FIG. 4 are obtained from the document image shown in FIG. 3, the coordinates (x _f , y _f ) of the upper left vertex of the minimum rectangle are obtained.

For example, as shown in FIGS. 2 and 3, when the correction marks have different shapes, when the minimum rectangle surrounding the correction marks is obtained, the direction of the document, for example, rotated by 90 degrees. It is possible to detect the case where it is rotating or rotating 180 degrees. When such a case is detected, the document image can be rotated by ± 90 degrees or 180 degrees.

The tilt angle detecting means 2 is based on the coordinates of the vertices of the minimum rectangle surrounding the correction mark obtained by the mark position detecting means 1, and for example, the tilt angle including an error between the two correction marks. To detect. When there are three or more correction marks, the tilt angle can be detected for each set of correction marks. For example, when four correction marks are arranged as in the document image shown in FIG. 3, six tilt angles can be detected.
Of course, the inclination angle may be detected only for some combinations.

The tilt angle correction means 3 corrects the tilt angle including the error calculated by the tilt angle detection means 2 to a true tilt angle. The tilt angle correction means 3 can be configured by, for example, a table in which a tilt angle including an error and a true tilt angle are associated with each other. Of course, it is also possible to obtain it by calculation, but when using a table, conversion to a true tilt angle can be performed at high speed.

The principle of the tilt angle correction performed by the tilt angle correction means 3 will be described. FIG. 5 is an explanatory diagram of the relationship between the true inclination angle and the inclination angle including an error, and FIG. 6 is an explanatory view of the relationship between the correction mark size and the distance. In FIG. 5, when the vertices of the correction mark are A and B, and the vertices of the smallest rectangle surrounding the correction mark are A ′ and B ′, the inclination angle detecting means 2 is a straight line connecting the vertices A ′ and B ′. Detects the inclination of. _Let this inclination be θ _f . As shown in FIG.
Correct tilt angle θ obtained from the vertices A and B of the correction mark
_An error occurs between _t and the tilt angle θ _f calculated from the vertex coordinates of the minimum rectangle surrounding the correction mark.

If the tilt angle θ _{t of the} image is known in advance, the vertex coordinates of the minimum rectangle surrounding the above-mentioned correction mark are
It can be obtained from the length of the correction mark, and the inclination angle θ _f including an error can be obtained by calculation using the obtained vertex coordinates of the minimum rectangle. That is, the true tilt angle θ ^t can be obtained by performing the reverse calculation from the tilt angle θ _f including the error. Further, if θ _f is obtained in advance for various θ _t and a correspondence table is created, conversely, θ _t can be obtained from θ _f from the correspondence.

As shown in FIG. 6, the length of each side of the correction mark is d ₁ , d ₂ , d ₃ , and d _4, and the distance between the vertices of the correction mark is D. These values are information known in advance. Further, in FIG. 5, the coordinate axes are x-axis facing right and y-axis facing up, and the vertex A of the left correction mark is the origin (0,0). At this time, the coordinates of the vertex B of the correction mark are (Dcos θ _t , Dsin θ _t ). At this time the minimum rectangle vertices A surrounding each correction mark 'coordinates _{of, (0, d 2 sinθ t} ) , and the vertex B' are _{coordinates, (Dcosθ t + d 4 sinθ} t, Ds
in θ _t ). From the coordinates of the vertices A ′ and B ′, the tilt angle θ _{f including} an error is expressed by the following equation. _{tanθ f = (Dsinθ t -d 2} sinθ t) / (Dcosθ t + d 4 s inθ t) molecule on the right side of this equation, the denominator is divided by cos [theta] _t, theta _t
Solving for, we get θ _t = tan ⁻¹ (D tan θ _f / (D−d ₂ −d ₄ tan θ _f ))

Further, in the above example, the tilt angle is 0 ° or more (the counterclockwise direction is the positive direction), but when the tilt angle is 0 ° or less, the same calculation is performed as follows. The formula is derived. ^{_{θ f = tan -1 (Dsinθ t}} -d 3 sinθ t) / (Dcosθ t + d 1 sinθ t) Similarly, solving for theta _t, the following equation is obtained. θ _t = tan ⁻¹ (D tan θ _f / (D−d ₃ + d ₁ tan θ _f )) By using this equation, the tilt angle θ _{f including} an error
From this, the true tilt angle θt can be calculated.

By performing the tilt correction on the basis of the tilt angle thus obtained, compared to the case where the tilt angle is simply found based on the coordinates of the vertex of the smallest rectangle surrounding the correction mark, The tilt can be detected more accurately.

FIG. 7 is an explanatory diagram of an example of a correspondence table between the tilt angle θ _{f including} an error and the true tilt angle θ _t . From the above equation, the inclination angle θ _f including the error is converted to the true inclination angle θ
_{Although t} can be obtained by calculation, in order to obtain the true tilt angle θ _t at higher speed, a conversion method using a correspondence table can be used. In FIG. 7, as an example, D
= 800, d ₂ = 10, and d ₄ = 10 are given, the correspondence table of the inclination angle θ _{f including} the error and the true inclination angle θ _t is shown. By subtracting this table from the tilt angle θ _{f including an} error, the corresponding true tilt angle θ _t is obtained as the true tilt angle with less error. According to this correspondence table, the true tilt angle θ _t can be obtained faster than the calculation of the true tilt angle θ _t each time the tilt angle θ _{f including an} error is actually given. . For example, when the tilt angle θ _{f including} the error detected by the tilt angle detecting means 2 is 1.0 degree, the true tilt angle θ _t is 1.012879 degree according to the correspondence table shown in FIG. .
This correspondence table shows that the lengths d ₁ , d ₂ ,
It can be created for each of d ₃ , d ₄ and the distance D between the vertices of the correction mark. For example, in the document shown in FIG. 3, the correspondence table used for the inclinations of the upper left correction mark and the upper right correction mark, the correspondence table used for the inclinations of the upper left and lower left correction marks, and the upper left and lower right It is possible to prepare a correspondence table used for the inclination of the correction mark.
These correspondence tables may be switched and used according to the correction mark used for detection in the tilt angle detection means 2.

As described above, the corrected tilt angle can be obtained at a higher speed by using the correspondence table of the true tilt angle with respect to the tilt angle including the error which is obtained in advance.

[0020]

As is apparent from the above description, according to the present invention, a tilt angle including an error is obtained from the vertices of the minimum rectangle surrounding the correction mark, and the tilt angle including the error and the true tilt are included. Since the true tilt angle is obtained from the relationship with the angle, it is not necessary to recognize the straight line portion of the correction mark, and the accurate tilt angle can be detected at high speed. By correcting the tilt of the image based on this detection result, it becomes possible to perform more accurate tilt correction, and it is possible to obtain a good corrected image.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a tilt detecting device of the present invention.

FIG. 2 is an explanatory diagram of an example of correction marks arranged on a document.

FIG. 3 is an explanatory diagram of a positional relationship of correction marks on a document.

FIG. 4 is an explanatory diagram of an error in vertex coordinates when there is a tilt.

FIG. 5 is an explanatory diagram of a relationship between a true tilt angle and a tilt angle including an error.

FIG. 6 is an explanatory diagram of a relationship between a size of a correction mark and a distance.

FIG. 7 shows a tilt angle θ _{f including an} error and a true tilt angle θ
It is explanatory drawing of an example of the correspondence table of _t .

[Explanation of symbols]

1 mark position detecting means, 2 tilt angle detecting means, 3
Inclination angle correction means.

Claims (1)

[Claims] 1. A tilt detection device for detecting the tilt of a document image from the positional relationship between a plurality of tilt correction marks arranged in advance in the document image, wherein each of the plurality of tilt correction marks is detected from the document image. A mark position detecting means for obtaining coordinate values of vertices of the surrounding minimum rectangle, a tilt angle detecting means for obtaining a tilt angle including an error from coordinate values of the plurality of vertices obtained by the mark position detecting means, and an error. A tilt detecting device comprising tilt angle correcting means for obtaining a true tilt angle from a tilt angle including the error based on a known relationship between the tilt angle and the true tilt angle.