JP2804347B2 - Image thinning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a thinning method for an image in which an outline of an image is tracked and a sequential thinning process is performed. In order to speed up the entire sequential thinning process, in the image thinning method in which the contour of the image is traced and the sequential thinning process is performed, the image is processed in an image portion where the thinning process is not completed. The thinning process is divided into thin line image portions that have already been thinned, and only the image portion that has not been thinned is subjected to thinning processing while tracking the outline of the image, and the remaining image portion that has been thinned is processed. , An area to be tracked for the next thinning process is reset.

[Industrial applications]

The present invention relates to an image thinning method for performing successive thinning by tracking the outline of an image.

[Conventional technology]

The thinning process is a method generally used in image processing, and is a process of extracting a center line having a width of one pixel by reducing the line width from given image data. This thinning process is also used when, for example, a drawing input device converts image data of an input image such as a figure into CAD data.

The image thinning process is performed by repeating a process of thinning an image such as a figure one pixel at a time, and the process of thinning one pixel is performed, for example, by an operation using a 3 × 3 mask. By preparing a 3 × 3 mask corresponding to the thinning processing in advance, it is possible to realize a processing of sequentially cutting off a portion having a line width of 2 pixels or more.

That is, by performing this mask operation once for the entire image, the line width in the image is reduced by one pixel. This processing is repeatedly performed on the entire screen until there are no pixels to be reduced, thereby performing the thinning processing of the image data.

FIG. 11 (a) shows a typical example of the thinning processing.
(B) and a sequential thinning process shown in FIG.

In the parallel type thinning processing, as shown in FIG.
This is a method of performing a mask operation on the entire screen while keeping the thinning method as described above. This parallel thinning process
Although the amount of calculation is larger than that of the following sequential thinning processing, the processing is simple, so that it is suitable for hardware implementation.

On the other hand, the sequential thinning process is a process in which a mask operation is not performed on the entire screen as in the parallel type, but only a portion of an image such as a figure is cut.

In other words, as shown in FIG. 11 (b), this is a method of performing a mask operation while tracing the outline of an image and cutting out the outline pixels of the image one by one. Next, the line width is reduced by one pixel.

The sequential thinning processing is more complicated than the parallel processing, but has a relatively small amount of calculation, and thus is suitable for execution on a general-purpose processor. The image thinning process itself can be performed in either a parallel thinning process or a sequential thinning process.
Almost the same results can be obtained, but in order to reduce hardware cost, a method using a general-purpose processor is preferable.

[Problems to be solved by the invention]

Since the parallel thinning process is simple, it is possible to speed up the thinning process by implementing hardware.

However, as described above, almost the same result can be obtained by the parallel thinning processing and the sequential thinning processing as described above, but in order to reduce hardware costs, a general-purpose processor is required. Is more advantageous in the sequential thinning process.

However, the sequential thinning processing is generally complicated in processing, and in particular, it takes time to trace the contour. Therefore, the thinning processing speed is generally slower than the parallel thinning processing realized by hardware. There was an inconvenience.

The present invention eliminates the need for the most time-consuming tracking processing in the sequential thinning processing, and speeds up the sequential thinning processing by tracking only the image portion for which the thinning processing has not been completed and performing the thinning processing. It is an object of the present invention to provide an image thinning method which is improved so as to perform the above.

[Means for solving the problem]

Means adopted by the present invention to solve the above-mentioned problem will be described with reference to FIG. FIG. 1 is a diagram illustrating the principle of the present invention.

1 (a) and 1 (b) show a sequential thinning process according to the present invention, and FIG. 1 (c) shows a conventional sequential thinning process.

In FIG. 1, P ₁₀ and P ₂₀ and P ₁₁ and P ₂₁ represents the images to be thinning process, L _0, L ₁₀ and L _20, L ₁₁ and L
Reference numeral ₂₁ denotes a tracking path when each image is subjected to sequential thinning processing, and C ₀ , C _10, and C ₁₁ indicate thin line images which have been thinned.

Also, SS ₁₀ and SS ₁₁ indicate the tracking start points of the images P ₁₀ and P ₁₁ , SE ₁₀ and SE ₁₁ indicate the tracking end points of the images P ₁₀ and P ₁₁ , and SS ₂₀ and SS ₂₁ indicate the images P ₂₀ and shows the tracking start point of the P _21, SE ₂₀ and SE ₂₁ shows the track end point of the image P ₂₀ and P _21.

The present invention is configured as follows to perform the sequential thinning processing shown in FIGS. 1 (a) and 1 (b). That is, in an image thinning method in which an outline of an image is tracked and a sequential thinning process is performed, (a) the image is divided into an image portion where the thinning process has not been completed and a thin line image portion which has been thinned (B) Only for the image portion for which the thinning process has not been completed,
A thinning process is performed while tracing the outline of the image. (C) For the remaining image portion subjected to the thinning process,
The tracking area for the next thinning process is reset.

(Operation)

The operation of the present invention will be described with reference to FIGS. 1 (a) and 1 (b).

First, each image to be processed, thinning processing is divided into the image P ₁₀ and P ₂₀ and thinning the processed thin line image C ₁₀ unterminated.

One then thinning processing is not completed image (and P ₁₀₎
Select for the image P _10, it performs the thinning process while tracking the outline. Specifically, until the process end point SE ₁₀ from the processing start point SS _10, while tracking along the track path L _10, the image P ₁₀ of first the sequential thinning processing.

Accordingly, the contour portion of the image P ₁₀ is being narrowed one pixel, as shown in Fig. 1 (b), the image P ₁₁ is formed.

Then, for the remaining images P ₁₁ subjected to this thinning, resetting the region to track for subsequent thinning process. Specifically, the processing start point SS ₁₁ and the processing end point SE ₁₁ of the image P ₁₁ is reset.

Similarly, the image (P ₂₀ ) to be subjected to the next thinning processing is searched, and the contour of the image P ₁₀ is tracked,
The first sequential thinning processing is performed. Specifically, from the processing start point SS ₂₀ to the processing end point SE ₂₀ , the tracking route L ₂₀
While tracking along, the image P _20, performs first successive thinning processing.

Accordingly, the contour portion of the image P ₂₀ is being narrowed one pixel, as shown in Fig. 1 (b), the image P ₂₁ is formed.

Then, for the remaining images P ₂₁ subjected to this thinning, resetting the region to track for subsequent thinning process. Specifically, the processing start point SS ₂₁ and the processing end point SE ₂₁ of the image P ₂₁ is reset.

In the case of the present invention, the thin line image C ₁₀ after the thinning process has been completed.
Is not tracked.

Similarly, run the images P ₁₁ and P ₂₁ the second round of sequential thinning processing for the remainder of the image portion subjected to thinning, resetting the region to track for subsequent thinning process I do. Also in this case, the thin line image after the thinning process is completed
For C ₁₁ is the tracking process is not performed.

In the same manner, the sequential thinning process is executed only for each image portion, and the process of resetting an area to be tracked for the next thinning process for the remaining image portions subjected to the thinning process is repeated. When all the images have been thinned, the thinning processing ends.

FIG. 1C shows a conventional sequential thinning process for comparison with the sequential thinning process of the present invention. In the conventional sequential thinning processing, the image P ₁₀ , the thin line image C ₀
And repeating that they would perform the thinning processing while the image P ₂₀ to week along track path L _0, go to process all thinning each image.

In sequential thinning process, although the tracking process of the contour is the most time-consuming process, in the conventional sequential thinning process, in order to perform each tracking processing for fine line image C ₀ thinning already, whole It has been difficult to improve the thinning processing speed.

On the other hand, according to the present invention, the thinning process is performed only on the image portion that has not been thinned while tracking the outline of the image, and the tracking process is not performed on the thin line image portion that has been thinned. To reduce the amount of processing,
The processing speed can be improved as compared with the conventional sequential thinning processing.

〔Example〕

One embodiment of the present invention will be described with reference to FIGS. FIG. 2 is an explanatory view of a system for implementing an embodiment of the present invention, FIG. 3 is an explanatory view of a thinned detection mask pattern used in the embodiment, and FIG. 4 is used in the embodiment. FIG. 5 is a flowchart showing the overall processing flow of the embodiment, FIG. 6 is a processing flowchart at the time of a closed loop of the embodiment, and FIG. 7 is a processing flow at the time of a closed loop of the embodiment. FIG. FIG. 8 is a flowchart of a process in the non-closed loop of the embodiment, FIG. 9 is an explanatory diagram of a process in the non-closed loop of the embodiment, and FIG. 10 is an explanatory diagram of a process in an overflow of the embodiment.

(A) Configuration of Implementation System In FIG. 2, reference numeral 11 denotes an image memory, which stores image data of each image to be subjected to thinning processing and thin line image data as a result of the thinning processing.

Reference numeral 12 denotes a mask table, which stores data of various mask patterns for mask calculation used when performing the thinning processing. As a mask pattern for thinning processing, for example, when a 3 × 3 image is given, all patterns for determining whether a central pixel should be a white pixel or a black pixel are stored.

The mask table 12 also stores information for determining whether or not the center image has been subjected to the thinning processing.

FIGS. 3A to 3C show, as this information, examples of 3 × 3 various mask patterns for determining that the center pixel has been thinned. These mask patterns are patterns for detecting an image having a line width of 1,
This makes it easy to determine that the center pixel has been subjected to the thinning processing.

Reference numeral 13 denotes a contour point table, which stores data of a tracking start point and a tracking end point of an area to be thinned.

FIG. 4 shows an example of the configuration of the contour point table 13. Reference numerals 131 and 132 in FIG. 4A denote each contour point table created for each image.

FIG. 13B shows the respective contour point tables 131 and 132 of FIG.
And the like. The tracking start point area stores the coordinates (Xs, Ys) of the point at which tracking starts and the direction (Ds) at which tracking starts, and the tracking end area stores the coordinates (Xe, Ye) of the point at which tracking ends. And the direction (De) to start tracking are stored. The tracking start point shown in FIG. 3C and the tracking end point shown in FIG. 3D will be described in the section of the operation of the embodiment.

Reference numeral 14 denotes a microprocessor (hereinafter, referred to as an MPU), which controls and executes the entire thinning process such as the thinning process from the tracking start point to the tracking end point using the image memory 11, the mask table 12, and the contour point table 13. I do.

Reference numeral 15 denotes a control memory which stores a control program for the sequential thinning process performed by the MPU 14 and a thinning process flag area 151 which stores a thinning process flag (THINNED) for instructing execution of the thinning process. , Start flag (sta
rtflg), and a work area (not shown) for performing the thinning process.

The start flag (startflg) is a flag that indicates whether or not the search for the tracking start point and the tracking end point is being performed, and has the following meaning.

startflg = 1: During the search for the tracking start point, no candidate point (thinning point) has been found yet.

= 2: Candidate points are found during the search for the tracking start point.

 = -1: Searching for tracking end point.

(B) Operation of the embodiment FIGS. 4 to 10 show the sequential thinning processing according to the embodiment of the present invention.
With reference to the drawings, the overall flow of thinning processing, processing in a closed loop, processing in a non-closed loop, and the like will be described separately.

(B1) Overall Flow of Thinning Processing The overall flow of thinning processing will be described with reference to FIG. 5 and in the order of processing. The following processes are all performed by the MPU 14 unless otherwise specified.

Process S _{1 In} process S ₁ , a process of initializing the contour point table 13 is performed, all images in the image memory 11 are operated, and for all contours, a point serving as a start point of the tracking process is obtained.
It is registered in the tracking start point area of the contour point table of the image. This tracking start point may be any one point on the contour line of the image being scanned.

Process S _{2 The} THINNED flag is reset to “0” to indicate that the thinning process has not been executed. THINNED
Flag, if thinning process at least once among the processing loop of DO statement processing S ₃ described below is executed, "1" is set, if once even thinning process is performed, "0"
Is set.

If the thinning process has not been executed at all, it means that "all the outline point tables have completed the thinning process", and the thinning process ends.

Process S ₃ (DO sentence) Until the following process is completed, a process of extracting the contour point tables one by one from the beginning (contour point table 131) to the end of a plurality of contour point tables is performed.

Process S ₄ (IF sentence) It is determined whether the image of the contour point table extracted in process S ₃ has been subjected to the thinning process, or whether the thinning process is still possible.

If the thinning process has been, since the thinning process is not required, back to the top of the DO statement of processing S ₄ to skip the thinning process.

If thinning is possible, it is written below the IF statement
S ₅ the following process is performed.

For processable S ₅ thinning process (YES in the process S _4), thinning processing flag (THINNED flag) 151 is set to "1", execution of the thinning processing is instructed.

Processing S ₆ further thinning processing of image of the contour point table, whether the thinning process in the case of the closed loop is determined.

Processing S ₇ If the processing is a thinning processing in the case of a closed loop (in processing S ₆
YES), the thinning processing at the time of the closed loop is executed. In the thinning processing, thinning processing of one pixel is performed while tracking the outline of each image.

The thinning processing at the time of this closed loop is described in the following (B2)
This is explained in detail in the section.

Processing S ₈ If the processing is not a closed loop and the processing is thinning (processing
In S ₆ ELSE), thinning processing at the time of non-closed loop is executed.
Regarding the thinning processing at the time of the closed loop, the following (B3)
This is explained in detail in the section.

Process S _{9 It} is determined whether the THINNED flag is “1”, that is, whether or not the thinning process has been performed once.

When the process S ₁₀ thinning process has been performed once YE in (process S ₉
S), a contour point table newly created by the thinning process is additionally registered in the contour point table of the image.
The process of additionally registering the contour point table newly created by the thinning process in the contour point table of this image will be described in detail in the next section on closed loop and non-closed loop.

When the above processing is completed, if the THINNED flag is “1” and the thinning processing has been performed at least once, there is a possibility that the thinning processing can still be performed. Therefore, the processing jumps to a loop (Loop) and the processing is performed again. returning to S _2, the processing of S ₂ to S ₁₀ described above are repeated Kaee.

Thus, once the outline of each image for each thinning process ends went been narrowed by one pixel, to each image are thinned, continues around the loop of DO statements of the aforementioned process S _3.

As explained at the process of IF statement processing S _4, finished fine line image portions of the thinning processing is skipped, the thinning processing is not performed.

When the thinning processing for each image is completed, processing S ₉
Since the state of the THINNED flag is maintained at "0" in step (3), it is detected that the thinning processing of each image has been completed, and the thinning processing ends.

Next, processing in a closed loop and a non-closed loop (when not a closed loop) will be described. Prior to the description of the processing at the time of the closed loop and the non-closed loop, the search processing of the tracking start point and the tracking end point will be described first with reference to FIGS. 4 (c) and 4 (d).

The tracking start point is, as shown in FIG. 4 (c), a boundary portion when a pixel (not shown) which has not been thinned is tracked from a pixel which has been thinned (shown by ●). Is a pixel (indicated by の) after the thinning process.

On the contrary, as shown in FIG. 4 (d), the tracking end point is defined as a pixel which has been subjected to thinning processing at a boundary portion when a thinned pixel has been tracked from a non-thinned pixel.示 す).

The above-mentioned tracking start point and tracking end point are used as the tracking start point and tracking end point when the loop is not closed. In the case of a closed loop, the tracking start point and the tracking end point are arbitrary points on the image outline, and both are common.
A tracking point that matches the coordinate point of the tracking start point is the tracking end point.

Finding the tracking start point and the tracking end point is nothing but searching for such a pattern while tracking the outline of the image. The tracking processing in the thinning processing at the time of the closed loop and at the time of the non-closed loop shown in FIG. 6 to FIG. 9 all shows processing for searching for this pattern.

Specifically, the tracking start point is determined by the following Articles (a) and (b)
Are obtained as pixels when the AND of the conditions 1 and 2 shown in FIG.

(A) Condition 1: The current pixel has been subjected to the thinning processing.

(B) Condition 2: startflg = 2 (the point before the currently tracked point is a point already subjected to thinning processing).

On the other hand, the tracking end point is obtained as a pixel when the AND of the conditions 3 and 4 shown in the following Articles (c) and (d) is satisfied.

(C) Condition 1: The current pixel has been subjected to the thinning processing.

(D) Condition 2: startflg = −1 (the point before the currently tracked point is a point that has not been thinned).

The tracking start point and tracking end point detection method is the same in the processing at the time of the closed loop and at the time of the non-closed loop. In the case of a non-closed loop, a search for a tracking start point is first performed by the above method. On the other hand, in the case of a closed loop, since the tracking start point is searched first, the tracking end point is detected earlier than the tracking start point.

(B2) Processing at the time of the closed loop The processing at the time of the closed loop is performed in the order of (1) to (5) shown in FIG. 7, and the processing of (1) to (5) is the procedure shown in the processing flowchart of FIG. It is performed according to. Hereinafter, the sixth
With reference to FIG. 7 and FIG. 7, the thinning processing at the time of the closed loop and the creation / update processing of the contour point table 13 will be described in accordance with the processing order of FIG.

The following processes are all MP
This is done by U14.

(1) Processing (1) The processing (1) in FIG. 7 is performed according to the following procedure shown in the processing flowchart in FIG.

It is assumed that the tracking start point has been registered in the contour point table of each image by the above-described initialization processing.

In the thinning process in the initial state, it is necessary to trace the outline of each image for one round, as in the ordinary sequential thinning process. Therefore, only the information of the tracking start point is stored in the outline point table. By registering and clearing the tracking end point to zero, it is indicated that the table is a table for tracking one round.

With reference to the contour point table 13, a contour point table of one figure is extracted. Now, it is a series of figures composed of a series of figure images P ₁₀ , thin line images C ₁₀ and images P ₂₀ shown in FIG. 7A, and the outline point table is a table 131 shown in FIG. 7A. Suppose there is. In the contour point table 131,
Tracking start point ST of the coordinates of the image _{P 10 (X 0, Y 0} ) and the direction of tracking (d ₀₎ is stored. Further, each data at the tracking end point has been requested to be all zero, indicating that the data is a closed loop process.

To search for the tracking end point, set startflg to "-1"
Is set to (see process S ₁ in FIG. 6, hereinafter, simply indicated by process Si processing Si of FIG. 6).

Note that startflg is a flag having the following contents as described above.

startflg = 1: During the search for the tracking start point, no candidate point (thinning point) has been found yet.

= 2: Candidate points are found during the search for the tracking start point.

 = -1: Searching for tracking end point.

Until the coordinates and directions of the tracking start point ST and the tracking end point also match, that is, the coordinate points and the tracking direction of the tracking end point
The following processes are performed until X ₀ , Y _0, and d ₀ (process S ₂ ). First, it is determined whether or not the currently focused pixel has been subjected to the thinning processing (processing S ₃ ).

Pixels that are currently of interest is not a thinning-treated (FIG. 6 ELSE), the process S ₁₁ is performed, Startflg is "2", i.e. the search of the tracking starting point whether the end is determined.

Since the search of the tracing starting point is the observed completion, thinning processing of S ₁₄ is performed. In the process S14, the MPU ₁₄ starts tracking along the route in the direction do using the mask table 12 and the contour point table 131, and starts the image starting from the tracking start point ST.
Thinning the first one pixel of the P _10.

When the first 1 pixel thinning processing of image P ₁₀ is completed, the process returns to S _2, is repeated Work with the foregoing,
Thinning processing of the next 1 pixel of the image P ₁₀ is performed. Hereinafter similarly, thinning processing on the image P ₁₀ along the contour line direction do is repeatedly executed.

(2) Process (2) The process (1) in FIG. 7 is performed according to the following procedure shown in the process flowchart in FIG. The number of each procedure is indicated by a continuation number of the above-described process (1).

Continue to perform the thinning processing, the coordinate point Xm, reaches the pixel of Ym, in the process S _3, the pixel currently focused is detected to be a thinning processed. This detection processing is performed using the mask pattern for detection of the completion of the thinning processing described with reference to FIG.

When a thinned pixel is detected (processing S ₃
In YES), startflg is "1", i.e. whether it is during the search of the tracking start point is determined (process S _4). Since it is in search of the tracking termination point, the next process S ₆ is carried out.

In process S _6, startflg is "-1", ie, whether it is during the search of the tracking end point is determined. Since it is in search of the tracking end point is determined YES, and the next process S ₇ is performed.

In process S _7, whether the contour point table that is already registered tracking start point is determined. Since contour point table tracking start point is registered not, it is determined that ELSE, the next process S ₉ is performed.

In step S _9, the newly contour point table 132 as shown in FIG. 7 (2) is created, X of alive pixel point, Y-coordinate and direction, i.e. the coordinate Xm: Ym and direction dm is the track end point Is stored. Note that the “−” mark of the tracking start point in the contour point table 132 is information indicating that the data is not data relating to the coordinates and the direction.

When tracking endpoint registration processing S ₉ is completed, the next process S
_{In step 10} , the startflg is updated to "1" to indicate that no candidate point (thinning point) has been found during the search for the tracking start point of the next image.

The process returns to S _3, by using the thinning processed detection mask in the mask table 12, the pixel that is currently of interest is whether the thinning already or not.

Since the thinning processing has been completed, YES is determined and the next S
The process of ₅ is performed, and the startflg is "2", that is, it is instructed that the candidate point is found during the search for the tracking start point.

The following treatment of the aforementioned processes S ₃ to S ₅ is repeated, the tracking is performed along the fine line image C _10.

Tracking start point of the image P ₂₀ (coordinates Xn, Yn) is reached, the
Since the current pixel of interest has not been thinned,
In process S ₃ is judged ELSE, the process of step S ₁₁ is performed.

In the process S _11, whether startflg is "2", i.e. the search of the tracking starting point whether the end is determined.

Since startflg is "2", the following S ₁₂ is performed, as shown in FIG. 7 (3), a new contour point table
133 is created, and the X and Y coordinates of the pixel point immediately before the current pixel point, that is, Xn _-1 and Yn _-1 and the tracking direction dn _-1 are newly registered at the tracking start point.

A registration process of the tracking starting point and ending process S ₁₃ is performed, Startflg is "-1", ie it is indicated is in the search of the tracking termination point.

(4) processing (4) processing (4) is a creation / update process of the thinning processing and contour point table for the image P _20.

The image P _20, the process of searching the tracking termination point while performing the thinning process, as shown in FIG. 7 (4) (4) is executed.

The process (4) Since carried out in the same manner as the process of searching the tracking termination point of the image P ₁₀ in FIG. (1) described in the above processing (1), the detailed description is omitted,
The point will be described.

Thinning processing of the processing S ₁₄ along the contour line of the image P ₂₀ is performed, the tracking termination point of the image P ₂₀ (Xk, Yk and tracking directions dk)
Through the first pixel of the fine line image C ₁₀ again, the processing S
_{In 3} , it is determined that the pixel of interest is already thinned.

Then in the process S _6, "-1" startflg, ie after it has been determined is in search of the tracking end point,
In process S _7, whether the contour point table that is already registered tracking start point is determined.

Since there is a contour point table 133 in which the tracking start points (Xn _-1 , Yn _-1 , dn _-1 ) are registered, the determination is YES and the next processing is performed.
S ₈ is performed, as shown in FIG. 4, the contour point table 133
, The X and Y coordinates Xk and Yk of the current pixel point and the tracking direction dk are registered as tracking end points.

When tracking endpoint registration process S ₈ is completed, the next process S
_{In step 10} , the startflg is updated to "1" to indicate that no candidate point (thinning point) has been found during the search for the next image tracking start point.

(5) Processing (5) In processing (5) shown in FIG.
Tracking process to C ₁₀ and the image P ₁₀ is performed. Each of these processes
Since carried out in the same manner as the tracking process of the aforementioned processes (3) and the fine line image C ₁₀ and the image P ₂₀ in (4), a detailed description of its operation will be described for their processing results are omitted.

Process of the aforementioned processing S ₃ to S ₅ is repeated, thin line image C
Tracking is performed along ₁₀ . New tracking start point of the image P ₁₀ (coordinates Xl, Yl) is reached, since the pixels that are currently of interest is not the line thinning processed, is determined ELSE in the process S _3, the processing of step S ₁₁ rows Will be

In the process S _11, Startflg is "2", ie, it is determined that the search of the tracking starting point is the end, the next process S
₁₂ is done.

In the process S _12, as shown in FIG. 7 (5), newly contour point table 134 is created one, X pixel point immediately preceding the current pixel point on the trace start point, Y-coordinate, i.e. Xl _-1 ,
Y1 _-1 and tracking direction dl _-1 are newly registered.

A registration process of the tracking starting point and ending process S ₁₃ is performed, Startflg is "-1", ie it is indicated is in the search of the tracking termination point.

The image P _10, the process of searching the tracking termination point while performing the thinning process, as shown in FIG. 7 (5) is executed.

This tracking process is so carried out in the same manner as the process of searching the tracking termination point of the image P ₂₀ in FIG. (4) described in the above processing (4), a detailed description thereof will be omitted.

Thinning processing of the processing S ₁₄ along the contour lines of the image P ₁₀ is performed to match the pixel points to the currently targeted tracking start point of the image P ₁₀ and (X _0, Y ₀ and tracking directions d ₀₎ If it is detected, it ends the process S _2, the following process S ₁₅ is performed.

In process S _15, whether the contour point table is not registered in the tracking start point is determined. The contour point table 132 is determined as YES because the tracking start point is not registered,
Next process S ₁₆ is performed.

In process ₁₆ , as shown in FIG. 7 (5), the tracking end point (Xm, Ym, d
m) is registered as the tracking end point of the contour point table 134.

When the process of registering the tracking end point in the contour point table 134 is completed, a process of deleting the contour point table 131 in which the original tracking start point is registered and the contour point table 132 in which the tracking start point is not registered is performed.

As described above, the thinning process and the contour point table updating process in the closed loop are completed.

Note that the thinned point (coordinate point Xm, Ym in FIG. 7)
Is returned to the original tracking start point XST (X ₀ , Y ₀ ) without finding, the contour point table is not updated, and the contour point table without the tracking start point is not added. Therefore, in this case, the thinning processing ends without performing the deletion processing of the contour point table.

(B3) Unclosed Loop Processing Unclosed loop processing is shown in FIG. 9 (1) to (5).
The processing of (1) to (5) is performed according to the procedure shown in the processing flowchart of FIG. Hereinafter, the thinning processing at the time of the non-closed loop will be described with reference to FIGS. 8 and 9 in accordance with the processing order of FIG.

In addition, the following processing is performed by the MPU14 unless otherwise specified.
Is to be performed by

(1) Processing (1) The processing (1) shown in (1) of FIG. 9 is performed according to the following procedures shown in the processing flowchart of FIG.

With reference to the contour point table 13, a contour point table of one figure is extracted. Now, a series of thin line image C ₀₀ , graphic image P ₁₀ , thin line image C ₁₁ and image P ₂₀ shown in (1) of FIG.
It is assumed that the outline point table is a table 131 shown in FIG. 9 (1).

The tracking start point of the contour point table 131, the tracking start point ST of the coordinates of the fine line image C ₀₀ (Xs, Ys) and has a direction (ds) is stored in the tracking Its tracking end point, the image P ₂₀ , The coordinates (Xe, Ye) of the tracking end point and the tracking direction (de) are stored. In this case, since the data at the tracking end point has not been cleared to all zeros, it indicates that the process is a non-closed loop process.

To search for tracking start point, Startflg is set to "1" (process S ₁ in Figure 8).

(2) Processing (2) The processing (2) shown in (2) of FIG. 9 is performed according to the following procedure shown in the processing flowchart of FIG. In addition,
The processing number of the processing (2) is indicated by a continuation number of the processing (1).

Until the coordinates and directions of the tracking start point ST and the tracking end point also match, that is, the coordinate points and the tracking direction of the tracking end point
The following processes are performed until Xs, Ys, and ds are reached (process S
₂ ).

First, it is determined whether or not the currently focused pixel has been subjected to the thinning processing (processing S ₃ ).

The pixel currently focused is thinning processed (YES in the process S _3), followed by treatment S ₄ is performed, Startflg is "1", i.e. whether it is during the search of the tracking starting point Is determined.

Since it is in search of a tracking start point (YES), does the following: processing S _5, startflg is "2", that is, during the search of the tracking starting point, the candidate point is indicated that has yet been found.

The process returns to S _3, the process of ~ the above until the thinning processed pixel points is repeated.

Work with the foregoing is repeated, beginning at pixel point of the image P _10, that is, the pixel point not thinning processed (coordinate points Xa, Ya) to reach, in the process S _3, the pixels that are currently targeted It is determined that the thinning process has not been completed. This detection processing is performed using the mask pattern for detection of the completion of the thinning processing described with reference to FIG.

When the pixel is not the line thinning processed is detected (in the process S ₃ ELSE), the process S ₉ is performed, Startflg is "2", i.e. whether or not the search end of the tracing starting point is determined) . Since the search of the tracing starting point is the end (YE in processing S ₉
S), the following processing S ₁₀ is performed.

In process S _10, as shown in the FIG. 9 (2), a new contour point table 132 is created one, X pixel point immediately preceding the current pixel point on the trace start point, Y-coordinate, i.e. Xa
_-1 , Ya _-1 and the tracking direction da _-1 are newly registered.

A registration process of the tracking starting point and ending process S ₁₁ is performed, Startflg is "-1", ie it is indicated is in the search of the tracking termination point.

(3) Process (3) The process (3) shown in (3) of FIG. 9 is performed according to the following procedures shown in the process flowchart of FIG.

Returning to process S _3, pixels that are currently of interest is determined whether thinning processed.

Pixels that are currently of interest is not a thinning-treated (ELSE treated S _3), are performed in the same way as described above the process S _9, st
It is determined whether artflg is “2”, that is, whether or not the search for the tracking start point has been completed.

Because it is being searched for tracking the end point, since the course search tracking start point is not finished, processing of the next S ₁₂ is performed. In the process S _12, MPU 14 may use the mask table 12 and the contour point table 13, and start tracking along the path of the direction dn _-1, thinning the first 1 pixel starting from the tracking start point of the image P ₁₀ I do.

When the first 1 pixel thinning processing of image P ₁₀ is completed, the process returns to S _2, is repeated Work with the foregoing,
Thinning processing of the next 1 pixel of the image P ₁₀ is performed. In the same manner, thinning processing on the image P ₁₀ is repeated along the outline direction dn _-1.

Thinning processing of the processing S ₁₂ along the contour lines of the image P ₁₀ is performed, the tracking termination point of the image P ₁₀ (Xb, Yb and tracking directions db)
Once in the first pixel of the fine line image C ₁₀ through, that pixel currently focused in the process S ₃ is thinning processed is determined.

Next, in process ₆ , when it is determined that startflg is “−1”, that is, the search for the tracking end point is being performed,
The following processing S ₇ is carried out.

In process S _7, as shown in the FIG. 9 (3), to track the end point of the contour point table 132, the current pixel point X, Y coordinates X
b, Yb and the tracking direction db are registered as tracking end points.

When tracking endpoint registration processing S ₇ is completed, the next process S ₈
To update the startflg to "1", indicating that no candidate point (thinning point) has been found during the search for the tracking start point of the next figure.

(4) In the process (4) the process shown in (4) of FIG. 9 (4), the tracking process of the fine line image C ₁₀ and the image P ₂₀ is performed. Each process, so is the how as the tracking process of the thin line image C ₀₀ and the image P ₁₀ in the process described above (1) to (3), for their processing results are omitted the detailed description of the operation explain.

Process of the aforementioned processing S ₃ to S ₅ is repeated, thin line image C
Tracking is performed along ₁₀ . Upon reaching the first pixel point in a tracking start point of the image P ₂₀ (coordinates Xc, Yc), the pixel currently attention is not a thinning processed, it is determined that ELS in the process S _3, step S ₉ Is performed.

In step S _9, startflg is "2", ie, it is determined that the search of the tracking starting point is the end, the next process S ₁₀
Is performed.

In process S _10, as shown in the FIG. 9 (4), a new contour point table 133 is created one, X pixel point immediately preceding the current pixel point on the trace start point, Y-coordinate, i.e. Xc
_-1 , Yc _-1 and the tracking direction dc _-1 are newly registered.

A registration process of the tracking starting point and ending process S ₁₁ is performed, Startflg is "-1", ie it is indicated is in the search of the tracking termination point.

The image P _20, as shown in the FIG. 9 (4),
A process of searching for the tracking end point while performing the thinning process is executed.

This tracking process is so carried out in the same manner as the process of searching the tracking termination point of the image P ₁₀ in FIG. (3) described in the above processing (3), a detailed description thereof will be omitted.

Thinning processing of the processing S ₁₂ along the contour line of the image P ₂₀ is performed, the tracking termination point of the current designated pixel point image P ₁₀ (Xe, Ye and tracking direction de) and it is detected that matches Once, it terminates the process S _2, the following process S ₁₃ is performed.

In step S _13, since the original contour point table 131 is no longer needed, performs processing to cancel the contour point table 131.

As described above, the thinning processing and the creation / update processing of the contour point table in the non-closed loop are completed.

(B4) Thinning processing The thinning is performed by referring to the tracking start point and tracking end point of each image registered in the contour point table for closed loop and the contour point table for non-closed loop created as described above. The thinning process can be performed only on each of the images P ₁₀ , P _20, etc. without performing the tracking process on each of the processed thin line images.

Since the tracking processing for the thin line image portion that does not require the thinning processing is not required, the entire thinning processing time can be reduced, and the processing speed can be improved.

The thinning processing of each image itself can be performed by various known methods, and a description thereof will be omitted.

Further, when the thinning processing is performed on one image, the image generates a plurality of small images and a plurality of thin line images connecting them. In that case,
By the processing at the time of the closed loop described in 2) and the processing at the time of the non-closed loop described in (B3), a contour point table in which the tracking start point and the tracking end point of each newly generated image are registered is newly created. Thereafter, thinning processing for each new image is performed by using this new contour point table.

(B5) Overflow Processing When the thinning processing is performed by the method described above, the number of contour point tables gradually increases as the thinning processing proceeds.

However, since the memory capacity of the contour point table 13 is limited, the contour point table 13 may overflow as the thinning process proceeds. If the contour point table 13 overflows, a new contour point table 13 cannot be generated, and the subsequent thinning processing will fail.

FIG. 10 shows an example of a method for avoiding such a failure due to overflow.

The MPU 14 collects an unnecessary contour point table after the thinning process. For example, when the contour point tables 131 and 132 are deleted in FIG. 7 (5), the collection is performed.

In this case, it is necessary to quickly find an unused contour point table. As the method, for example, FIG. 10 (a)
As shown in (1), if a pointer to the next table is provided in the contour point table, the used part and the vacant part of the contour point table can be managed by the two pointers, the empty pointer and the in-use pointer. “NEXT” indicates the address of the table to be connected next, and “NULL” indicates that there is no table to be connected next.

The contour point table that is no longer used due to erasure etc.
By updating the pointers of the unused contour point table and the contour point table immediately before it, as shown in FIG.

By linking the used tables and the empty tables in this manner, both the used tables and the empty tables can be quickly searched by referring to the pointer.

Further, when such a process of linking the in-use table and the empty table is performed, an overflow occurs only when all the contour point tables 13 are in use. Therefore, the contour point table 13 is effectively used, and the overflow is performed. Can be reduced.

If an overflow has occurred, the division process of the tracking start point and the tracking end point ends at that point. In this case, subsequent thinning processing is performed in the same manner as in the conventional thinning processing method. However, since the thinning processing of the present invention has progressed before that, even in such a case, the conventional thinning processing is performed. The thinning processing can be performed at a higher speed than the processing method.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various modifications in accordance with the gist of the invention are possible.

(Effect)

As described above, the present invention performs thinning processing while tracking the outline of an image only for an image part for which thinning has not been completed, and does not perform tracking processing for a thin line image part after thinning processing. As a result, the processing amount is reduced, and the processing speed can be improved as compared with the conventional sequential thinning processing.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is an explanatory diagram of an embodiment system of an embodiment of the present invention, FIG. 3 is an explanatory diagram of a thinning-processed detection mask pattern used in the embodiment, FIG. 4 is an explanatory diagram of a contour point table and a start point and a tracking end point used in the embodiment. FIG. 5 is a flowchart showing the flow of the entire processing of the embodiment. FIG. 6 is a closed loop of the embodiment. FIG. 7 is an explanatory diagram of a process in a closed loop of the embodiment, FIG. 8 is a flowchart of a process in a non-closed loop of the embodiment, and FIG. 9 is a diagram of a process in a non-closed loop of the embodiment. FIG. 10 is an explanatory diagram of a process at the time of overflow of the embodiment, and FIG. 11 is an explanatory diagram of a conventional thinning processing method. In FIG. 2, 11 ... image memory, 12 ... mask table, 13 ... contour point table, 14 ... processor (MPU), 15 ... control memory.

Claims (2)

(57) [Claims] 1. An image thinning method in which an outline of an image is tracked and a sequential thinning process is performed, wherein: (a) an image is divided into an image portion which has not been thinned and a thin line image which has been thinned; (B) Only the image portion for which the thinning process has not been completed,
A thinning process is performed while tracing the outline of the image. (C) For the remaining image portion subjected to the thinning process,
A thinning method for an image, wherein a tracking area for the next thinning processing is reset. 2. An image portion area to be subjected to a successive thinning process is:
2. The method for thinning an image according to claim 1, wherein the tracking start point and the tracking end point are set.