JPH01303581A - Border line tracking device for digital image - Google Patents

Abstract

PURPOSE:To extract a graphic form border line efficiently by generating a picture element state value that an aimed picture element has from the coordinate values of the aimed picture element on the border line and two picture elements which are before and behind the aimed picture element on the border line, detecting a tracking start candidate picture element previously, and marking only the picture element. CONSTITUTION:The aimed picture element is denoted as P, the picture element before it as P-, and the picture element behind it as P+. In this case, the direction CH1 from P- to P and the direction CH2 from P to PL are represented with Freeman chain codes (0-7). Then the picture element state value (0, 1) that the aimed picture element P has is determined in a table (a) according to the combination of the directions CH1 and CH2 and processing corresponding to this picture element state value is carried out. When the picture element state value is 1, a picture element value '1' is written at a corresponding position on a work memory and when the picture element value is '1', a tracking end picture element is decided and a next tracking start candidate picture element is searched for; when the picture element value is '0', an untracked picture element is decided and the border line begins to be tracked from this picture element. Consequently, the border line of a graphic form can be extracted efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an improvement of a digital image boundary tracing device in a digital graphic processing device.

<Prior Art> Extraction of figure boundaries in digital images is a basic method of image processing, and is important in applied fields such as figure recognition and data compression. Therefore, there is a need for a boundary line extraction method that can be processed at high speed with a simple hardware configuration.

As a typical method of conventional boundary edge extraction, for example, Ro
Senfeld4::Border pixel tracking (B orde
rPixel Following;Rosenfe
ld (translated by Nagao and others).

"Digital Image Processing" Kindai Kagakusha, 1978) is known.

This method starts from a suitable boundary pixel, traces adjacent boundary pixels in a fixed order, and finishes extracting one boundary line when it completes one round. Therefore, in order to extract all boundary lines included in the entire image without exception, it is necessary to add a "mark °°" to the boundary pixels for which tracking has been completely completed.

In particular, regarding marking, see FIG. 7(a).

As can be seen in the boundary line tracing extraction of the figure with a hole shown in (b), the boundary pixels that are exactly the same (Fig. 7 (a)) or mostly the same (Fig. 7 (b)) are placed on the outer boundary line. Alternatively, there may be cases where the pixel is tracked twice as a pixel on the inner boundary line, so it is not possible to simply use one mark to distinguish between a pixel that has finished tracking and a pixel that has not been tracked. It is necessary to distinguish between

<Problems to be Solved by the Invention> However, using two marks with different values when extracting a boundary line means that the original image is stored in advance in an original image memory having a capacity of normal 1 bit/1 pixel. In this case, a special memory of 2 bits/1 pixel, which is the same size as the original image memory but has a different configuration from normal memory, is provided as a work memory, which makes the hardware configuration more complicated. This is not desirable.

The present invention was made to solve the above problems, and uses a work memory with the same size and configuration as the original image memory, and efficiently extracts the boundary line of a figure using only one mark. The purpose is to obtain a device that can.

Means for Solving the Problems> The present invention, when a new boundary tracking start candidate pixel is detected, refers to the pixel value in the work memory to determine whether this candidate pixel is an untracked pixel or a tracking end pixel. It is characterized by performing the following, and its configuration is as follows.

That is, the present invention provides an image memory consisting of an original image memory that stores a digital image, a work memory that has the same capacity as the original image memory and is used as a working memory, and coordinates of boundary pixels on the original image memory. A pixel state value generation unit that sequentially inputs values and generates a pixel state value of the current pixel of interest from the coordinate values of the current pixel of interest and the coordinate values of the pixels before and after it; r! When the S value matches a predetermined value, a pixel value "1" is written to the position on the work memory corresponding to this pixel of interest, and when a new tracking start candidate pixel is detected, This is a digital image boundary tracking device comprising a controller that reads out a pixel value at a corresponding position and determines whether the pixel is a tracked pixel or an untracked pixel.

<Operation> The principle of operation of the digital image boundary line tracking device according to the present invention will be described below.

In advance, the work memory, which is a working memory, is all cleared (pixel tii 'OJ is written).

One boundary line on the original image memory is traced, and the pixel of interest is set as P for the coordinate values of each consecutive pixel on the boundary line each time.
, when the previous pixel is P-1 and the subsequent pixel is P0,
The P-→P direction CHI and the P→P+ direction CH2 are represented by Freeman chain codes (0 to 7) shown in FIG.

Figure 4 (a) from the combination of direction CHI and direction CH2
According to the table, the pixel state value (0, 1) of the pixel of interest P is
is determined, and processing corresponding to this pixel state value is performed.

When the pixel status value is 0, nothing is done to the work memory.

When the pixel status value is 1, the pixel of interest changes from pixel value "0" to "1".
”, and since it is a tracking start candidate pixel, the pixel value “1” (
mark).

When a new tracking start candidate pixel is detected, the pixel value (mark) of the coordinate value on the work memory corresponding to that candidate pixel is checked, and if the pixel value is "1" (marked), it is determined that it is the tracking end pixel. and searches for the next tracking start candidate pixel.
When the pixel value is "0" (no mark), boundary line tracking is started from this pixel as an untracked pixel.

<Embodiment> FIG. 1 shows a block diagram of the configuration of a digital image boundary line tracking device embodying the present invention.

Reference numeral 1 denotes an image memory, which consists of an original image memory 11 and a work memory 12. The original image memory 11 is a memory for storing a digital image read from an image input device such as an image scanner, and the work memory 12 distinguishes between tracked pixels and untracked pixels during a boundary line tracking operation. This is a working memory in which marks are set for Both memories are normal pixel memories with a capacity of 1 bit/pixel. In the original image memory 11, pixel (art, + is a figure part, pixel fM r OJ
is the background part.

Reference numeral 2 denotes a buffer memory that stores the boundary line extraction results, that is, a coordinate list of boundary pixels.

Reference numeral 3 denotes a pixel state value generation unit which sequentially inputs the coordinate values of pixels on the original image memory 11 and generates a current state value of the pixel from the coordinate values of the current pixel of interest and the coordinate values of the pixels before and after it.

4 is a controller that executes overall control and boundary line tracing processing procedures. The controller 4 stores the original image memory 1
1, reads and accesses the pixel to be processed and its surrounding pixels, sequentially determines the coordinate values of the boundary pixels to be tracked, writes them to the buffer memory 2, and transfers the original image to the pixel state value generation unit 3. The coordinate values on the memory 11 are sent, the work memory 12 is marked according to the pixel state value calculated by the pixel state value generation unit 3 (the pixel value "11" is written), and the coordinate values on the work memory 12 are marked. Pixels that have finished tracking and pixels that have not been tracked are distinguished by referring to the mark.

FIG. 2 shows a block diagram of the I=ul path of the pixel state value generation section 3.

The pixel coordinate values (X, Y) from the controller 4 are taken into the j1! quaternary register 31P+) by the synchronization clock cL, and the contents are stored in the register 32 (P) and register 3.
Transferred to 3(P-). The first code generation unit 34 generates the direction CHI (3 bits) determined from the coordinate values of the current pixel P and the coordinate values of the previous pixel P−, and the second code generation unit 35 generates A direction CH2 (3 bits) determined from the coordinate values of pixel P and the next pixel P, FIA&1, is generated. The ROM 36 has a direction C111 (R
A 1 ; 3 bits'), CH2 (RA2; 3 bits) 6-bit address A5. ..., according to AO, 6 as shown in FIG. 4(b) corresponding to FIG. 4(a>)
Four pixel state values Y+0, 1) are predetermined.

Now, the operation of the device of the present invention configured as described above will be explained in the fifth section.
This will be explained using the flowchart shown in the figure.

FIG. 8 shows an example of the digital image that is the subject of this explanation, and shows the original image memory 1 operated by the apparatus of the present invention.
6 shows the states of the original image memory 11 and the work memory 12.
The above changes are shown in Figure 6<a>-(2) to (g)-
(2) represents a change in the work memory 12.

(a) The controller 4 completely clears the work memory 12 (writes the pixel value roJ).

(b) The controller 4 scans the original image memory 11 from the upper left, examines the pixels in the horizontal scanning line direction, and selects the pixel value r1 located at the leftmost position. The presence or absence of a pixel or a pixel whose pixel value changes from pixel value r□ to pixel value "1" is checked.

(c) If there is a corresponding pixel (pixel A in FIG. 6(a)-(1)), the work memory 12 corresponding to the corresponding pixel
The upper coordinate position is the pixel position AO in Figure 6 (a)-(2))
Check the pixel value of.

(d) If the pixel value is "0" on the work memory 12, this pixel (A) is determined to be an untracked pixel (no mark), and the 8 pixels surrounding the corresponding pixel <A) on the original image memory 11 are Examine the value.

(Po) If the pixel values of the surrounding eight pixels on the original image memory 12 are all "0", the corresponding pixel is an isolated pixel, and its locus m value is stored in the buffer memory 2.

(F) If there is a pixel value "1" in the 8 pixels surrounding the corresponding pixel, the corresponding pixel (A) is set as the tracking start pixel and its coordinates are
Store the value in buffer memory 2.

(g) One boundary line is traced with the corresponding pixel (A) as the tracing start pixel, and the coordinate values of the traced pixel are sequentially stored in the buffer memory 2, and at the same time, these coordinate values are sequentially sent to the pixel state value generation unit 3. give.

The pixel state value generation unit 3 sequentially generates a pixel state value (0 or 1) of the pixel of interest from the coordinate values of the pixel of interest on the boundary line and the two pixels before and after the boundary line, and sends the pixel state value (0 or 1) to the controller 4.

(H) If the pixel status value is 1, write the pixel value "]" at the coordinate position on the work memory 12 corresponding to the pixel P of interest (add a mark).

(W) If the pixel status value is 0, no access is made to the work memory 12.

For example, in FIG. 6(b)-(1), when Pl is the pixel of interest, Pl- is the previous pixel, and P1+ is the next pixel, from FIG. 4(a), direction CH1=4. CH2=5, the address for the ROM 36 is #25, and the pixel state value of the pixel P of interest is calculated as 1 according to FIG. 4(b). Then, as shown in FIG. 6(b)-(2),
Corresponding location y in work memory 12! , writes the pixel value "1" (ward) to P10.

In addition, in FIG. 6(b)-(1), if P2 is the pixel of interest, the pixel state value becomes O by the same operation, and no access is made to the work memory 12 (FIG. 6(b) )-(2)).

(n) Processing procedure (g), (ch) (or (su))
Repeat, extract one boundary line, work memory 12
Perform the above marking (write the pixel value "1").

Figure 6(b)-(1) shows the state of tracking of boundary line #1, and Figure 6(b)-(2) shows the marked result for boundary line #1 (symbols (figures) are pixel values. represents "1").

(l) If processing for all scanning lines has not been completed, return to step c).

Next, the controller 4 tracks the new boundary line by
As shown in FIG. 6(c)-<1), the rask operation is restarted from pixel B to the right of pixel A, and the leftmost pixel value is "1".
” or a pixel that changes from pixel value “0” to pixel value “l” and has pixel value “0” on work memory 12
(Pixel CO on FIG. 6(C)=(2): No mark) is detected.

The state of the tracking operation for boundary line #2 with pixel C as the tracking start pixel is shown in Fig. 6(d)-(1), and Fig. 6(d)-(
In 2), the mark at the time of tracking boundary line #2 indicates the result.

Next, the rask operation is restarted from the pixel to the right of pixel C to detect the tracking start candidate pixel E. Figure 6 (,e)-(1)
), it is confirmed that there is no mark at the corresponding position EO on the work memory 12 (FIG. 6(e)-(2)), and the boundary line tracing operation is performed using this point E as the tracing start pixel.

The state of the tracking operation for boundary line #3 with pixel E as the tracking start pixel is shown in Fig. 6(f)-(1).
In 2), the mark at the time of tracking boundary line #3 indicates the result.

Furthermore, as shown in FIG. 6(g)-(1), the rask operation is restarted from the pixel F to the right of the pixel E, and the isolated pixel G (sixth
In Figure (g)-(2), the GO pixel value "O") is detected and all operations are completed.

Through the above procedure, from the digital image shown in FIG. 8, the outer till boundary line #l (solid arrow) and the inner boundary line #2 as shown in FIG. 9 are created. #3 (dotted arrow) and isolated pixel G are extracted.

In this way, when searching for a boundary line tracing start pixel, the work area of the boundary line tracing candidate pixel obtained by the rask operation is
The mark on the memory is checked and the boundary line tracing operation is started only when there is no mark, so the boundary line of the figure can be efficiently traced using only one mark, using a work memory with the same size and configuration as the original image memory. Can be extracted well.

<Effects of the Invention> The digital image boundary tracing device of the present invention traces one boundary line on the original image memory, and calculates the target pixel from the coordinate values of the target pixel on the boundary line and the two pixels before and after the boundary line. The tracking start candidate pixel (pixel that changes from pixel "fli ro" to [1]) is generated by this.
is detected in advance and marked only at that pixel, so even if the shape includes an overlap between the outer and inner boundaries, only one mark, that is, the size and configuration of the original image memory, can be used. Figure boundaries can be efficiently extracted simply by providing the same work memory.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a block diagram of the configuration of the digital image boundary line tracking device of the present invention, Fig. 2 is a detailed circuit diagram of the pixel state value generation section of the device of the present invention, and Fig. 3 is the Freeman's A diagram representing a chain code, FIG. 4(a). (b) is a table showing the coordinate value of the pixel of interest and the pixel state value determined from the coordinate values of the pixels before and after it, FIG. 5 is a flowchart showing the operation of the device of the present invention, and FIGS. 6(a)-(1)
),..., Fig. 6(g)-(2> is a diagram showing the state of the original image memory and work memory during the boundary line tracing operation of the device of the present invention, Fig. 7(a), (b) is a diagram showing a digital image in which the outer boundary line and the inner boundary line are exactly the same or mostly the same, FIG. 8 is a diagram showing a digital image targeted by the device of the present invention, and FIG. It is a diagram showing the obtained boundary line.l...Image memory, 11...Original image memory, 12.
...Work memory, 2...Buffer memory, 3.
... Pixel state value generation unit, 31.32.33...Register, 34...First code generation unit, 35...Second code generation unit, 36...ROM, 4.
··controller. Agent Patent Attorney Shinsuke Ozawa 77 Figure 2 (b-(1) (C)-(1) Figure ((1)-(2) (b)-(2) (C)-(2) (d>I,) Ki2 (f”4- (1); Figure td)-(2) Figure 8 Figure 9 ↓° No.

Claims (1)

[Claims] (1) An image memory consisting of an original image memory that stores a digital image, a work memory that has the same capacity as the original image memory and is used as a working memory, and coordinate values of boundary pixels on the original image memory are sequentially stored. A pixel state value generation unit that generates a pixel state value of the pixel of interest from the input coordinate values of the current pixel of interest and the coordinate values of the pixels before and after it; A pixel value "1" is written at a position on the work memory corresponding to the pixel of interest. When a new tracking start candidate pixel is detected, the pixel value at the corresponding position on the work memory is read out and this pixel is tracked. A digital image boundary line tracing device comprising a controller that determines whether a pixel is an end pixel or an untracked end pixel.