JPS633387A - Encoding method for digital border line - Google Patents

Abstract

PURPOSE:To improve an encoding efficiency if a digital border line does not need to be faithfully stated by deciding an extraction point according to a set interval for extracting picture elements and obtaining a difference vector between a current extraction point and its previous one. CONSTITUTION:Graphic data on a digital image read out of an input device is stored in an image memory part 1, and the output of a digital border line, encoding algorithm and encoded results are stored in a main memory part 2. A processor 31 scans the image memory part 1, extracts one point in a digital graphic and temporarily stores coordinates components X and Y not only in a register group 32 but also in the main memory part 2. The processor 31 sequentially tracks picture elements at a start point, decides the extraction point according to the preset interval for extracting picture elements obtains the difference vector between the current extraction point and its previous one, and stores the components X and Y in the register group 32 and the memory part 2. The processor 31 takes the components X and Y stored in the memory part 2 for information on encoded digital border lines.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for encoding digital contour lines in digital solid image data read from an input device such as a facsimile.

<Prior art> Extracting the outline, which is the outermost part of the black pixel area, of a digital figure read from a facsimile or the like is two-dimensional information that is extremely important for describing the characteristics of the digital figure. Become. At this time, a large amount of digital contour data is stored on a limited storage device,
Alternatively, in order to transmit it, it is necessary to encode the digital contour data to compress the amount of data.

Figure 8 (
Freeman's chain encoding methods shown in a) and (b) are conventionally known.

This method focuses on one pixel of the digital contour line,
Pixels are tracked and encoded in eight directions indicated by arrows O to 7 shown in FIG. 8(a). In this chain code, one pixel constituting a digital contour line is represented by eight symbols, so the number of encoded bits per link (a set of two connected pixels) is three bits.

For example, when encoding a digital contour line as shown in FIG. 8(b), the starting point coordinate ps is
56545442332212''.

However, in such a chain encoding method, when it is not necessary to faithfully describe a digital contour line, such as when describing a contour line with few small bends, the digital contour line is encoded pixel by pixel (3 Since the number of bits per link is wasted, the coding efficiency cannot be improved to 3 bits or less per link.

<Problems to be Solved by the Invention> The problems to be solved by the present invention are to improve encoding efficiency when it is not necessary to faithfully describe digital contours; The purpose of this paper is to realize a digital contour encoding method that is more effective than the chain encoding method.

<Means for Solving the Problems> The outline of the present invention for solving the above problems is as follows.

It has an image memory section in which image data of a digital figure is stored, a main memory section in which an algorithm for contour extraction and encoding of this digital figure and the results of this encoding are stored, and a group of registers. a processor unit that executes a conversion algorithm and a numerical calculation; and a step of sequentially tracking pixel by pixel starting from one point of the digital figure; The method is characterized by comprising a step of determining an extraction point, and a step of finding a difference vector between the current extraction point and the previous extraction point and using its X and Y components as encoded information of the digital contour line. This is a method for encoding digital contours.

Effect> The digital contour encoding method of the present invention sequentially tracks each pixel, determines the extraction point based on a preset pixel extraction interval, and compares the current extraction point and the previous extraction point. A difference vector with respect to the point is obtained and its X and Y components are used as encoded information of the digital contour line.

<Embodiment> FIG. 1 shows a configuration block diagram of an example of a device suitable for implementing the method of the present invention.

In this figure, 1 is an image memory unit that stores graphic data of digital images read from an input device such as a facsimile, and 2 is a main memory unit that stores digital contour extraction/encoding algorithms and their encoding results. ,3
is a processor section consisting of a processor 31 that executes numerical calculations and digital contour extraction/encoding algorithms, and a register group 32 that temporarily stores the results; the image memory section 1, the main memory section 2, and the processor section 3 are the system - They are mutually connected to the path SS, and the processor section 3 can access the image memory section 1 and the main memory section 2.

The object handled by the present invention is the digital contour line of the digital image in the image memory unit 1 as shown in FIG. component (0≦Y≦N), and each pixel has coordinates (X
, Y). However, X, Y, M, N
is a non-negative m number.

Next, the principle of the encoding method of the present invention will be explained using FIGS. 5(a) and 5(b).

As shown in FIGS. 8(a) and 8(b), the conventional encoding method traces the digital contour line pixel by pixel, extracts it, and encodes it, but the method of the present invention is as shown in FIG. (a), (b)
As shown in , pixel tracking is performed pixel by pixel, but extraction is performed based on a preset pixel extraction interval (P
s＊PH□.

P2TL, ...+PR-+π), current extraction point PJT
Difference vector aj between L and the previous extraction point PJ-ITL
(al, a2..., ai) and this X.

Y component (ΔXJ, ΔYJ) (1≦J≦1.PoTL
=Ps) is used as encoded information.

Below, the process steps (algorithm) of the digital contour encoding method of the present invention will be explained in detail using the flowchart of FIG.

(1) First, the image memory section 1 is scanned, and the top row and leftmost black pixel point is extracted as one point on the contour line of the digital figure, and is set as the starting point Ps.

(2) The coordinate values (Xs, Ys) of the starting point Ps are stored in the registers RXs and RYs, respectively, and also in the main memory section 2.

(3) When the pixel extraction interval of the digital contour is n (≧2), find a positive integer k that satisfies 2"-'≦n×2, and store it in the main memory section 2 as +1 to the segment length d-. do.

(4) Transfer the contents of registers RXs and RY6 to register RXa
, RYa, respectively.

(5) Set the initial value 0 to register 1.

(6) Register to count the number of segments! Set the initial value to 0.

(7) Set the initial value n-1 to register CNTR.

The value of n is the tracking point (pixel) extraction interval.

(8) When point Pi (X, Y() is the current tracking point on the contour line, find the next tracking point P, +1, and set its coordinates Ml (XL++, Y+,) as a register, RX ,
Each is stored in RY. This contour extraction method includes a conventional method using a 3×3 mask, a method using a 2×2 mask, etc., but here it is assumed that contour lines are extracted in the form of 8-connection.

(9) Add 1 to the contents of register 1.

(10), Register RX from the contents of registers RX and RY
By subtracting the contents of s and RY6, the tracking point Pt
The distances DX and DY between ++ and the starting point Ps are determined, respectively.

(11) Check the values of DX and DY, DX-DY-0
In case (Y), proceed to step (17) and DX-DY-
If it is not 0 (N), proceed to step (12).

(12) Subtract 1 from the contents of register CNTR.

(13) Check the contents of register CNTR, and
If it is not R-0 (N), repeat the operation from step (8), and if it is CNTR-0 (Y), execute step (14).

(14) Register RX'a that stores the coordinate value of the previous extraction point from the contents of registers RX and RY that store the coordinate value of the current extraction point PL++.

The contents of RYa are subtracted to obtain a difference vector at (ΔX, ΔY) between the current extraction point and the previous extraction point, and the difference vector at (ΔX, ΔY) is stored in the main memory section 2.

(15) The contents of registers RX and RY, which store the current extraction point locus 1ff*Pt++, are stored in register RXa,
Set each to RYa.

(16) Register! Add 1 to the contents of and perform step (7
) Repeat the operations from ).

On the other hand, in (11), in the case of DX-DY-0, (Y
) means that the digital contour is closed, and (17
) step.

(17) Register RX in which the starting point coordinate value Ps is stored
By subtracting the contents of registers RXa and RYa, which store the coordinate values of the final extraction point, from the contents of s and RYs, respectively, the difference vector with respect to the last extraction point, X,
Each Y component is determined and stored in the main memory section 1. However, at this time, RX=RXs, RY-RYs.

(18) Add 1 to the contents of register l.

(19) Register! The contents of are stored in the main memory unit 2 as the number of segments.

(20> End of operation (END).

The method of the present invention is executed according to the above zero procedure.

In this way, the data format of the encoded string obtained by the method of the present invention is as shown in FIG.

The encoded sequence is the starting point coordinate value Ps (
Xs, Ys'), segment a! , segment length d(
− to +1) and from the first to the first! The difference vector (ΔX
J, ΔYJ) (j-1, 2,...

It is composed of the following values. Also, the difference vector (ΔXJ
, ΔYJ ) are expressed in two's complement format.

Here, the number of encoded bits representing the starting point coordinate value Ps is CS % number of segments! Cn is the number of encoding bits representing .

If the number of encoded bits representing the segment length d is Cd and the number of encoded bits representing the difference vector (ΔXJIΔYJ) of each segment is CΔ, then the number of encoded bits of a digital contour line consisting of two segments by the method of the present invention is C is C=C5+
It is expressed as C1+Ca+Ca.l.

Also, since CΔ-2d, C=C5+Ci+Cd+2d-1 becomes. -Generally, Cs　10C1+Cd(2d-1 Because it is, 2d- in C! becomes.

On the other hand, if the total number of pixels constituting the digital contour is CL, and the number of encoded bits representing L is CL, then the number CI of encoded bits in the conventional chain encoding method is Ct = Cs + CL
It is expressed as +3L, and -generally, since C8+0L (3L), it becomes SL in Ct.

Here, 1:L/n (1 to 2≦n<2', +1 to d-)
Therefore, the ratio C/Cr of the number of bits encoded by the chain encoding method and the method of the present invention is 26-1 in C/Cf.
/3L −26/3n = 2 (k+ 1 ＞/3n).

For example, in the case of n-3, it is d-3, so C/Ct
-2/3, and when comparing the chain encoding method and the encoding method according to the present invention, the number of encoding bits can be compressed to about 2/3.

That is, the number of encoding bits per link can be compressed from the conventionally required 3 bits to about 2 bits.

FIGS. 6(a) and 6(b) show examples of extraction of difference vectors obtained by actually using the method of the present invention.

FIG. 6(a) shows the starting point Ps for the digital contour line.
From (Xs, Ys), the extraction interval is set to n-3, the extraction points P1 + P2, .

This is an example of finding a+2.

The values of the components of each difference vector determined in FIG. 6(a) are stored in the main memory section 2 in the data format shown in FIG. 6(b).

That is, starting point coordinate value Ps (Xs, Ys), number of segments 1-12, segment length d-3, difference vector ai
It is composed of the values of the X and Y components of (j-1, 2, -, 12). However, the value of each component of the difference vector is expressed in two's complement format.

Next, FIG. 7 shows the result of decoding according to this encoded information.

Decoding starts from the starting point coordinates P s (X s * Y s ) and calculates the X of the difference vector aJ from the segment length d.
.

Y component is the number of segments! It is only necessary to sequentially cut out the vector, calculate an approximate vector from the difference vector each time, and reproduce the line figure corresponding to this approximate vector as a contour line.

In FIG. 7, each block is reproduced as a contour line, the blocks indicated by dotted lines represent pixels of the original figure, and the blocks marked with diagonal lines represent pixels shifted from the original figure.

As described above, according to the method of the present invention, the number of encoding bits can be reduced when it is not necessary to faithfully describe a digital contour.

<Effects of the Invention> The digital contour encoding method of the present invention sequentially tracks each pixel, determines an extraction point based on a preset pixel extraction interval, and compares the current extraction point with the previous one. Since the difference vector with the extraction point is determined and its X and Y components are used as encoding information of the digital contour, encoding efficiency can be improved when it is not necessary to faithfully describe the digital contour.

For example, if the pixel extraction interval when tracking pixels is set to 3, the number of bits per link (a set of two connected pixels) can be compressed from 3 bits to about 2 pits.

Further, decoding can be easily performed by reproducing a line figure corresponding to the approximate vector from information on the starting point coordinates, number of segments, segment length, and difference vector.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an apparatus for implementing the digital contour encoding method of the present invention, FIG. 2 is a flowchart showing the process steps (algorithm) of the digital contour encoding method of the present invention, Figure 3 is a diagram showing the format of data obtained by the method of the present invention, Figure 4 is a diagram showing the figures targeted by the method of the present invention, and Figure 5 (
a). (b) is a diagram for explaining the principle of the method of the present invention, No. 6
Figures (a) and (b) are diagrams when the method of the present invention is applied to an actual figure, Figure 7 is a diagram showing the result of decoding using the data obtained by the method of the present invention, and Figure 8 (a)
, (b') are diagrams for explaining the conventional chain encoding method. 1... Image memory section, 2... Main memory section, 3...
Processor section, 31... processor, 32... register group. Figure 1 Figure 5 (CI) s (b) M7 Figure 1) c: Leather Figure 8

Claims (1)

[Scope of Claims] An image memory unit that stores image data of a digital figure, a main memory unit that stores an algorithm for extracting and encoding contours of the digital figure, and the results of this encoding, and a group of registers. a processor unit that executes the contour extraction/encoding algorithm and numerical calculation; (c) determining the extraction point based on a preset pixel extraction interval, and (c) finding the difference vector between the current extraction point and the previous extraction point and converting its X and Y components into a digital contour line. 1. A method for encoding a digital contour line, comprising the step of converting the contour line into encoded information.