JPH04153889A - Line break part recognition device for line drawing - Google Patents

Abstract

PURPOSE:To automatically recognize the line break part of the line drawing by a computer by thinning the line drawing which is inputted as image data and recognizing end points, and recognizing the line break part according to the recognized end points. CONSTITUTION:A line thinning process is carried out for the inputted image data so that the line drawing part become as wide as a unit picture element. Picture elements which become end points P1 - P4 of the line drawing are recognized in the image data after the line thinning process. The recognized end points P1 - P4 are regarded as reference end points and the directions of the line drawing extending from the reference end points are recognized; and a specific range in the recognized directions is searched and when another end point or a segment which constitutes the line drawing is found in this specific range, it is recognized that there is the line break part between the reference end points and the found end point or segment. Consequently, the line break part of the line drawing which is inputted to the computer can automatically be recognized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a line drawing recognition device, and more particularly, to a line drawing recognition device for recognizing broken line parts, which may cause problems when coloring a line drawing using a computer. , relates to an automatic recognition device.

[Conventional technology]

With the spread of image processing technology using computers,
Increasingly, line drawings are imported into a computer as image data using a scanner, the line drawings are displayed on a display, and then computer processing is performed, such as coloring the closed area surrounded by the line drawings. For example, in the field of printing, a line drawing original drawn by a designer is scanned into a computer as image data, and C (cyan), M (magenta), and Y (yellow) are added to each closed area surrounded by the line drawing. , K (black), and performs coloring processing (so-called halftone filling processing) by specifying the dot densities of four colors.While looking at the display screen, the operator specifies the color for each closed area and applies the coloring. The results can be checked immediately on the display.Based on the thus obtained image data after the coloring process, a halftone plate for printing is created.

[Invention or problem to be solved]

As described above, the coloring process is performed by specifying a color for each closed area. However, if a line drawing that is supposed to be a closed area has a line break, it will not be treated as a closed area during computer processing, and the drawing will be colored against the operator's wishes (so-called color leakage). .

Such line breaks may exist in the line drawing manuscript itself drawn by the designer, but thin or blurred parts of the line drawing manuscript may appear after being input by a scanner. It is not recognized as a line during binarization processing,
In some cases, broken lines may appear.

As a countermeasure for the occurrence of such line breaks, methods are used such as adjusting the resolution at the time of scanner input or adjusting the threshold value at the time of binarization processing. There is also a method of correcting areas where line breaks are likely to occur in advance at the stage of the line drawing manuscript. However, in either method, it is difficult to completely suppress the occurrence of line breaks.

For this reason, for now, the operator gives instructions for coloring each closed area while looking at the display screen.
The current situation is that every time an unexpected coloring process is performed, the line breakage that causes the problem is identified and an operation is performed to correct it. As described above, finding broken lines on a display screen is a very labor-intensive and time-consuming task.

In particular, it is extremely difficult to see line breaks in the size of one pixel on the display screen with the naked eye, and the operator must perform operations such as enlarging the display as appropriate, which is a very complicated task. becomes.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a line drawing recognition device that can automatically recognize line breaks in a line drawing input to a computer.

[Means to solve the problem]

The present invention provides a line drawing recognition device that includes an image data input section that inputs a line drawing as image data made up of a set of pixels, and an image data input section that inputs a line drawing as image data consisting of a set of pixels; A thinning processing unit that performs line thinning processing, an endpoint recognition unit that recognizes pixels that are endpoints of line drawings on image data that has been subjected to line thinning processing, and a line drawing that sets the recognized endpoints as reference endpoints and that extends from the reference endpoints. , and searches within a predetermined range with respect to the recognized direction, and if other end points or line segments that make up the line drawing are found within this predetermined range, the reference end point and the found end point or line are searched. This includes a line break recognition unit that recognizes that a line break exists between the line and the line break.

[For production]

Since the input image data is thinned, it becomes possible to recognize the end points of the line drawing. The end points approved in this way are
There are two cases: a line drawing is an original endpoint, and a line break constitutes an endpoint even though it was not originally an endpoint. Therefore, the work of recognizing which case is occurring is performed by the line break recognition unit. The basic principle of the work carried out by this line break recognition unit is that when an end point is formed by a line break, if you search for the direction in which the line drawing is extended from one end point, you will find the other end point (or based on the idea that the number of minutes) will be discovered. Therefore, one end point is set as a reference end point, and if the other end point (or line segment) is found, a line break between the two is detected. This can be recognized as a broken line.

[Examples] Hereinafter, examples illustrating the present invention will be described. FIG. 1 is a block diagram showing the basic configuration of a line break recognition device according to the present invention. On the right side of each block are model diagrams 11 to 14 that explain the processing in that block.
is shown. The image data input unit 1 is a device that inputs line drawings as image data consisting of a set of pixels, and is specifically configured by, for example, a scanner device.

This device captures a line drawing drawn by a designer as a set of pixels, and binarizes it by determining whether the density value of each pixel exceeds a predetermined threshold. That is, the pixels are divided into pixels that make up the line drawing part and pixels that make up the background part. However, the line drawing at this stage is not composed of lines in a geometric sense with no width, but rather is composed of lines with thickness, as shown in model diagram 11. Become. In the model shown here, a broken line X exists near the center of the line drawing. Note that it is also possible to create line drawings using a CAD system, etc., and in this case, the image data input section 1 may be configured not by a scanner device but by an interface device for inputting image data from the CAD system. Become.

The line thinning processing unit 2 is a device that performs line thinning processing on the input image data so that the width of the line drawing part becomes the unit pixel. realized by In the apparatus of this embodiment, image data of a line drawing having a thickness as shown in the model diagram 11 or image data of a line drawing having a width of one pixel as shown in the model diagram 12 is converted. Since various methods are known for such thinning processing, detailed explanation of the processing contents will be omitted in this specification. for example,"
The basic principles and algorithms are disclosed on pages 53 to 65 of ``Digital Image Processing for Image Understanding'' (published by Shokodo in 1988), and ``Digital Image Processing Engineering (Nikkan Kogyo Shimbun Publishing)''. Published in 1985) J 138-14
Since specific calculation methods are disclosed on page 2, please refer to these documents for details.

The endpoint recognition unit 3 is a device that performs processing to recognize pixels that become endpoints of line drawings for image pigs that have been subjected to line thinning processing, and is specifically realized by a computer and software installed therein. . Through this end point recognition process, for example, for thinned image data as shown in model diagram 12, end point P as shown in model diagram 13 is obtained.
1 to P4 are recognized. There are cases where such endpoints are the original endpoints of the line drawing, and cases where the endpoints are formed by line breaks even though they are not originally endpoints.
There are two cases. In the example of model diagram 13, the end point P1. P4 is the original end point of the line drawing, but the end point P2
．． P3 is an end point caused by the occurrence of line break portion X. In this way, the endpoints recognized by the endpoint recognition unit 3 include the two types of endpoints described above. Note that details of this endpoint recognition processing will be described later.

The line break recognition unit 4 performs the work of separating the two types of end points described above, and also performs the work of finding the other end point (or line segment) for the end point due to a line break.

In other words, one end point is set as a reference end point, the direction of the line drawing extending from this reference end point is recognized, a predetermined range is searched in the recognized direction, and other end points or line segments that make up the line drawing are searched within this predetermined range. If found, a task is performed to recognize that a line break exists between the reference end point and the found end point or line segment. This device is also specifically realized by a computer and software installed therein. In the example of the line drawing shown in the model diagram 13, a line break is recognized between the end points P2 and P3 indicated by arrows in the model diagram 14. The details of the line break recognition process will be described later.

Now, the nature of general line breaks that occur in line drawings will be briefly described with reference to FIG. In the line drawing shown in Figure 2, area A is a closed area surrounded by two circular arcs, and if this part is colored, only this closed area will be colored as shown by diagonal hatching in the figure. It is possible to do this. However, one of the two arcs constituting area B has a broken line X1.
Therefore, region B is not a closed region.

For this reason, when coloring is applied to area B, the coloring will also be applied to the adjacent area C, as shown by the dotted hatching in the figure, resulting in so-called color leakage, resulting in coloring that is not as intended by the operator. become unable to do so. In particular, as described above, if the line break portion X1 is a minute line break of about one pixel, it is very difficult to find it on the display. In this way, when a portion of the line segment is missing and a broken line portion X1 occurs, two end points will occur on both sides of the broken line portion X1. In addition, there are also line breaks that occur when the connection is incomplete at a location where another line segment is connected in the middle of a line segment, such as the line break portion X2. In this case, one end point separate from the line segment will occur at the line break. In any case, line breaks will be seen around the end points. However, a broken line does not necessarily exist around the end point. For example, on the left side of the line drawing shown in Figure 2, a pattern consisting of three circular arcs is drawn, and although there are three end points each at both ends Y1 and Y2 of this circular arc, none of them are line breaks. is irrelevant. The processing in the endpoint recognition unit 3 described above is a task of recognizing all the endpoints of a line drawing, and the processing in the line break recognition unit 4 is a task of finding endpoints related to the line break from among the recognized endpoints. It can be said that there is. Below, these operations will be explained in order.

The endpoint recognition unit 3 is a device that recognizes endpoints based on the image data that has been subjected to the thinning process. Specifically, this process is performed as follows. Now, an example will be described in which end point recognition processing is performed on a line drawing as shown in FIG.

Each small square shown in FIG. 3 represents one pixel, and this line drawing is composed of 17 pixels from pixel a to pixel q. Since line thinning processing has already been performed, all line widths are in units of one pixel. The end point recognition unit 3 in this embodiment performs processing to determine whether each of the 17 pixels forming a line drawing is an end point or not using the following method. In other words, as shown in Fig. 4, a line drawing is constructed within eight pixels (pixels numbered 1 to 8 in the figure) surrounding the pixel to be judged (the hatched pixel in the figure). The number of pixels included is counted, and if only one pixel among the eight pixels constitutes a line drawing, the pixel to be determined is recognized as an end point. Applying this to the specific line drawing shown in Figure 3, we get
It will look like this: For example, if pixel a is selected as the pixel to be determined, there are only one pixel, that is, only one pixel, surrounding it that constitutes a line drawing. Therefore, pixel a can be determined to be an end point. Similarly, pixel m
, pixel q also have only one surrounding pixel, pixel β and pixel p, which constitute the line drawing, so these can also be determined to be end points.

For all other pixels, it is determined that they are not endpoints because there are two or more surrounding pixels that make up the line drawing. For example, around pixel 2, pixels a and c are
There is a pixel, and around the pixel there are 3 pixels i, n,
Since there are pixels, none of them are endpoints. In this way, in the example of FIG. 3, three pixels, a, m, and q, are recognized as end points.

Note that the above-mentioned endpoint recognition method is shown as an example, and the apparatus of the present invention may use any other method for endpoint recognition.

Next, the line break recognition process in the line break recognition section 4, which is an important feature of the present invention, will be described in detail based on the flowchart of FIG. Here, a description will be given of a line drawing as shown in FIG. 6, taking as an example a case where end points P1 to P6 are recognized. First, in step S1, reference end points are extracted. This is a task of extracting an arbitrary end point as a reference end point, and it does not matter which end point is extracted as the reference end point. For example, in the example of FIG. 6, any one of the endpoints P1 to P6 is extracted as the reference endpoint. Then, the following process is a process of finding another end point or line segment that is the counterpart of this reference end point.

That is, first in step S2, direction recognition regarding this reference end point is performed. This is a task of recognizing the direction of the line drawing extending from this reference end point, and in other words, it can be said to be a task of predicting which direction the line drawing is likely to have extended from the end point. For example, in the example shown in FIG. 6, if the end points P1 to P6 are each selected as the reference end points, the directions recognized for each reference end point are the directions shown by the arrows D1 to D6, respectively. Note that a specific method for performing this direction recognition will be described later.

When direction recognition is completed, the scope angle and scope length are set in step S3.

Here, the scope is a figure that defines a predetermined range with respect to the recognized direction with respect to the reference end point, and in this embodiment, a fan-shaped figure with the reference end point as the focal point is used as the scope. This scope is used to find out whether there is another end point or line segment that is the counterpart of the reference end point. Let us explain the function of this scope using the model shown in Figure 7. In this model, it is assumed that an end point P and an end point Q are recognized as the end points of a certain line segment, and another line segment R crosses the end points in the vicinity thereof.

Here, the end point P is selected as the reference end point, and step S2
It is assumed that the direction indicated by the dashed line is recognized by the direction recognition in . In this case, in step S3, if the scope angle is set to θ1 and the scope length is set to Ll, the scope S as shown by the dashed line in the diagram jN7
C1 is set.

The scope SCI is a fan-shaped figure with a radius L1 centered on the reference end point P, and forms an area extending at an angle θ1 on both sides of the arrow. In step S3, appropriate values for the scope angle and scope length are determined in advance, taking into consideration the type of line drawing to be handled, the size and type of line breaks that occur, and the like.

In this way, once the predetermined scope is set, step S
4, an endpoint search within the scope is performed. That is, in the example shown in FIG. 7, it is searched whether or not there are other endpoints within the area of scope SCI. If another end point is found through this search, the process advances to step S6 via step S5, and line break bear recognition processing is performed. Here, the line break pair refers to a pair of end points consisting of a reference end point and another found end point, and the process in step s6 treats these end points as bare end points constituting the line break part. This is a recognition process. If no end point is found within the scope, the process advances to step s7, and a search for a line segment within the same scope is performed. If a line segment is found through this search, the process proceeds to step s6 via step S8, and line break pair recognition processing is performed. In this case, a line break pair refers to a pair consisting of a reference end point and a discovered line segment, and the process in step S6 is a process for recognizing this pair as a bare line constituting a line break portion.

If no other end point or line segment is found within the scope, the process advances to step S9, where it is determined whether the current scope angle and scope length are within a predetermined range. If it is within the predetermined range, the process returns to step S3 and the scope angle and scope length are reset, but in the reset, settings are made larger than the previous settings. This may be set so that only the scope angle becomes larger, or may be set so that only the scope length becomes larger.

In this embodiment, both the scope angle and the scope length are reset to slightly larger values.

Once a new scope is thus set in step S3, the procedures from step s4 onwards are repeated again. The reconfigured scope expands the area a little, so there is a possibility that new endpoints or line segments that were not discovered with the previous scope may be discovered. For example, in the example shown in FIG. 7, scope angle θ1. Nothing was found in the scope SCI with scope length L1, but with scope angle θ2. If the scope SC2 with the scope length L2 is reset, another end point Q will be found within the scope, and the scope angle θ3. If scope SC3 with scope length L3 is reset, another line segment R will be discovered within the scope. In this way, until 2 endpoints or line segments are found, the process of resetting the scope in step S3 is repeated, and when 5 endpoints or line segments are found, the broken line bear C recognition process is performed in step S6. You will be killed. In this way, by gradually increasing the size of the cope and repeating the search, it is possible to first find an end point or a line segment that is closer to the reference end point P. It is possible to form a line-broken bear first. For example, in the example in Figure 7, scope S
Although nothing was discovered in CI, end point Q was discovered in scope SC2, and line segment R was discovered in summer in scope SC3, but when end point Q was discovered in scope SC2, step S6 ( Since the recognition process of a broken bear is performed, scope SC3 is not actually set in this case.In other words, the reference end point P and the end point Q are recognized as a broken bear. Note that if neither endpoints nor line segments are found, the size of the scope is gradually increased and the search operation is repeated, but in step S9, if the scope angle or scope length exceeds a predetermined range. If it is determined that there is, the process returns to step S3 and proceeds to step 510.In other words, if neither endpoints nor line segments are found even though the scope has reached a predetermined size, the search is terminated at this point, and this criterion is used. Regarding the end point, it is determined that there is no other party to form a bear.

After performing the above process with one endpoint as the reference endpoint,
After step SIO, the process returns to step SIO, and the end point is extracted as another end point or a reference end point. At this time, endpoints that have already been extracted in the past or endpoints that have already been paired with a bear are excluded from the extraction targets. In this way, when there are no more endpoints to be extracted, this process is completed via step 510. As a result, it is recognized that a line break exists between the end points where the bare lines are set, or between the end points where the bare lines are set and the line.

Let us consider a case where the above procedure is performed on the example of a line drawing shown in FIG. 6, for example. First, in step S1, reference end points are extracted. For example, end points P1 to P
6, the end point P1 is first extracted as the reference end point, and the direction of the arrow D1 is recognized in step S2. A scope of a predetermined size is defined in this direction and a search is performed, but even if the scope is enlarged to a predetermined limit, no end point or line segment is found, and step S9
．． After going through SIO, the process returns to step s1. Next, the end point P
2 is extracted as a reference end point, and the direction of arrow D2 is recognized in step S2.

When a scope of a predetermined size is defined in this direction and a search is performed, the end point P3 is eventually discovered. Therefore, in step S6, the reference end point P2 and the discovered end point P3 are recognized as line-broken bears. Returning to step S1 again, since the end point P3, which was scheduled to be extracted next, has already been marked bare, the end point P4 is extracted as the reference end point.

However, for the end point P4, no other party to form a bear is found, and after going through steps S9 and 510, step S
Return to 1. Here, the end point P5 is extracted as the reference end point, and as a result of a search using the scope, the line segment R is discovered, and the end point P5 and the line segment R are recognized as a bare line break. Finally, a search is performed using the endpoint P6 as the reference endpoint, or no effort is found (to form a bear). Thus, in the example of the line drawing shown in FIG.
Another line break portion is recognized due to the line break bear. In this way, automatic recognition of broken lines by a computer becomes possible.

By informing the operator of the recognized line break portion, the burden of correction work on the operator can be reduced. It is also possible to automatically correct line breaks.

That is, if there is a line break between end points, it is sufficient to perform a process of forming line segments at these breaks and connecting them. Furthermore, if there is a line break between an end point and a line segment, a process may be performed to form and connect a line segment between one point on the line segment and the end point. For example, in FIG. 7, to connect end point P and line segment R,
A line segment connecting the point Ql on the line segment R (in this example, you can take the intersection of the arrow and the line segment R, or the point closest to the end point P) and the end point P. All you have to do is process it.

Now, as mentioned above, recognizing a broken line requires the work of recognizing the direction of the line drawing extending from the reference end point, and a specific example of this work will be explained using FIG. 8. now,
As shown in FIG. 8, it is assumed that there is an end of a line drawing composed of pixels a to n, and pixel a is recognized as the end point. In this embodiment, the direction extending from the end point a of this line drawing is determined by the following method. First, the fifth pixel e and the tenth pixel j counting from the end point a are identified. Generally, the Xth pixel counting from the end point pixel and y
It is only necessary to specify the pixel. Here, appropriate values for x and y are determined by considering the type of line drawing to be handled and the resolution at the time of input. After identifying the two pixels in this way, consider the direction from the y-th pixel to the X-th pixel, and take the direction that passes through the end point pixel and parallel to this direction as the direction to be found. In the specific example shown in FIG. 8, consider a direction D1 from the 10th pixel j to the 5th pixel e, find the direction D2 that passes through the end point pixel a, and parallel to the direction D1, and calculate this direction D.
2 is the direction to be recognized.

The scope SC will be defined along this direction D2 from the pixel a. The feature of this method is that it ignores the directional information of pixels near the end points (pixels a, b, cd in the example of FIG. 8). This method is based on the empirical rule that pixel positions near end points often deviate from the original appearance of the line drawing, and is one of the simple methods that can yield meaningful results in practice. In the above method, the direction is determined by connecting two pixels, or the direction can also be determined by applying the method of least squares to the position coordinates of each pixel. for example,
In the example shown in Figure 8, the method of least squares is applied to the coordinate values of six pixels from pixel e to pixel j, the most appropriate straight line passing through these six pixel positions is found, and the direction is determined based on the direction of this straight line. All you have to do is recognize it.

The present invention has been described above based on the illustrated embodiments, but
The present invention is not limited to this embodiment, and can be implemented in various other ways. For example, in addition to the direction recognition method described above, there may be various other methods. In short, any method can be used as long as the direction in which the line drawing is expected to grow further from the end point can be recognized.

In addition, in the above embodiment, a fan-shaped scope was used, but
Other shapes of scopes such as triangles, diamonds, etc. may also be used. In short, any graphic scope may be used as long as it can define an area within a predetermined range regarding the direction recognized from the reference end point.

Furthermore, in the above-described embodiment, when the other end point is found within the scope defined from one reference end point, line break pair recognition processing is performed unconditionally for both end points. However, we also define a scope from the discovered endpoint of the other party, check whether a reference endpoint is found within this scope, and recognize a broken line pair only when both endpoints are within the scope of the other party. You may also do so. For example, as shown in FIG. 9, if a scope Sep is defined in the direction Dp with respect to the reference end point P, and another end point Q is found within this scope SCp, a scope SCq is defined in the direction Dq with respect to this end point Q, and the scope S.C.
Only when the reference end point P is found within q, it is also possible to recognize the end point P and the end point Q as a pair of broken lines.

〔Effect of the invention〕

As described above, according to the line drawing recognition device according to the present invention, the line drawing input as image data is thinned, the end points are recognized, and the line break parts are recognized based on the recognized end points. This makes it possible to automatically recognize broken lines in line drawings.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a line break recognition device according to the present invention, FIG. 2 is a diagram explaining the properties of general line break parts that occur in line drawings, and FIGS. 1 is a diagram explaining the processing of the end point recognition section in the apparatus shown in FIG. 1, FIG. 5 is a flow chart showing the processing procedure of the line break recognition section in the apparatus shown in FIG. Figure 7 shows the line drawing model to be applied.
8 is a diagram illustrating a specific example of direction recognition processing in the procedure shown in FIG. 5, and FIG. 9 is a diagram illustrating another embodiment of the present invention. It is a figure explaining search processing using such a scope. 11-14...Model diagram, D, DI-D6. DpDq
...Direction, P, PI~P6・End point, Q, Ql・End point,
R... Line segment, SC, 5CI-5C3, SCp. SCq... Scope, X, XI, X2... Line break, Yl, Y2... End. Patent applicant Dai Nippon Printing Co., Ltd. Applicant's agent Patent attorney Hiro Shimura

Claims (1)

[Claims] An image data input unit that inputs a line drawing as image data consisting of a set of pixels, and a line thinning unit that performs line thinning processing on the input image data so that the width of the line drawing portion becomes a unit pixel. A processing unit, an endpoint recognition unit that recognizes pixels that are endpoints of line drawings for image data that has been subjected to line thinning processing, and an endpoint recognition unit that recognizes the recognized endpoints as reference endpoints and recognizes and recognizes the direction of the linework extending from this reference endpoint. If another end point or line segment constituting the line drawing is found within this predetermined range, a line is inserted between the reference end point and the found end point or line segment. A line break recognition device for a line drawing, comprising: a line break recognition unit that recognizes the presence of a break.