JPH0125072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compression method for character data, and more particularly to a data compression method that compresses data by storing its contour specifying information.

It is well known that binary data obtained by dividing characters into dots has extremely high redundancy.

Conventionally, various data compression methods have been proposed to reduce this redundancy.

One such data compression method is the so-called contour method, which compresses the amount of data by grasping the shape of a character using its outline and storing information specifying the outline.

As data compression methods based on the contour method, the vector approximation method as shown in FIG. 1 and the method of approximating the outline of a character using a polynomial as shown in FIG. 2 are known.

The vector approximation method shown in Figure 1 is
This is a method disclosed in Publication No. 149522, Japanese Unexamined Patent Publication No. 79154/1983, and the like. The outline of this vector approximation method is to approximate the contour 1 of an arbitrary character indicated by a dotted line with a set of two-dimensional vectors 2, and to obtain specific information for each vector (starting point position, length and inclination, or horizontal and vertical components). By using this as storage data, data compression is possible.

Furthermore, the method of approximating the outline of a character using the polynomial shown in FIG.
This is as shown in Publication No. 134745, Japanese Unexamined Patent Publication No. 134746/1983, and the like.

The outline of this method is as shown by the solid line in Fig. 2. First, a block B is created which is divided into functions with the character outline x as a variable, and within that block B, multiple sample points P _l are selected. and divide it into multiple segments S _l . After that, the entire contour is continuous.

The first derivative of the contour changes continuously.

This method calculates the coefficients of a polynomial that approximates a segment that satisfies the following conditions, and stores the coefficients.

These data compression methods using the contour method have the characteristic that they can handle character image reproduction at various magnifications by performing interpolation processing or vector magnification conversion processing when the compressed data is recalled and characters are reproduced. have.

However, on the other hand, the vector approximation method guarantees optimal results in terms of contour smoothness (continuity of contour slope) unless the approximation is performed based on character pixel data that has been decomposed into dots with a sufficiently large matrix size. However, the problem was that the roughness of the outline was noticeable especially when character images were reproduced at high magnification.

The present invention is based on the above points, and by using the same master font, small-sized characters can be reproduced by vector approximation, and large-sized characters can be reproduced by polynomial approximation, thereby improving the smoothness of character outlines. The object of the present invention is to provide a data compression method that can faithfully reproduce the text and obtain a sufficient data compression rate without reducing the reproduction speed of characters. Its feature is that in a character data compression method that compresses the amount of data by storing character outline specific information, the sample points used in the first approximation method to approximate the character outline are arranged in a matrix. A first step of extracting from the outline of the developed character; and at least utilizing the sample points extracted in the first step,
a second step of extracting sample points to be used in a second approximation method different from the approximation method from the outline of the character developed in a matrix;
Or, information identifying each segment divided by the sample points extracted in the second step,
The above-mentioned sample point is stored in the character data together with information identifying whether the sample point is used in the first or second approximation method.

The present invention will be explained in detail below using the drawings.

The method according to the present invention is applied to binary character data in the form of a matrix and dot matrix supplied from, for example, a scanner device. In yet another example,
It is applied to encoded character data using any method that can specify a matrix-like dot pattern.

That is, for example, by raster scanning with a scanner device, characters are dot-decomposed into a matrix of rows and columns;
The bit pattern data thus obtained is supplied as original character data to be processed by the method of the present invention.

The master font data created according to the present invention is divided into a plurality of blocks B ₁ to B ₄ divided by points P so that they can be expressed by a function whose variable is the character outline x as shown in FIG. 3, for example. Then, one character's worth of data is constructed as a set of each divided block information. One block is further divided into a plurality of segments at sample point P' (point P is also a sample point). For each sample point, an identification code that identifies whether the point is used for both vector approximation and polynomial approximation, or for only one, sample point coordinate information, and for each segment during polynomial approximation. It is equipped with coefficient information, etc.

An embodiment of the master font data creation method according to the present invention will be described below. FIG. 41 is a diagram schematically showing one block of the outline of an original character.
First, the outline is developed into a matrix size of, for example, N×N dots, corresponding to the size of small characters that are most frequently used (FIG. 4, 2). The curved line indicated by the dotted line is the developed contour.
Sample points used for vector approximation are extracted using an arbitrary method on this matrix size. Fourth
The points marked with ● in FIG. 2 are sample points used for vector approximation.

After extracting sample points by vector approximation from a small matrix in the first step as described above, in the next second step, it is expanded into a large-sized matrix. FIG. 43 is an enlarged view of FIG. 42 (for example, 5N×5N dots), and the ● marks correspond to the sample points in FIG. 42. Also, the outline of the original characters in Figure 4 1 is shown in Figure 4 3.
, and superimpose it on the matrix of sample points enlarged to the larger size. The part indicated by the dotted line is the enlarged outline.
Next, sample points used for polynomial approximation are additionally extracted by reusing at least the sample points (marked with ●) used for vector approximation. Regarding the extraction of sample points, for example, Japanese Patent Application Laid-Open No. 1983-1981 by the present applicant
This is carried out by the method disclosed in Publication No. 134747, etc. The points marked with ▲ in FIG. 4 are additionally extracted sample points. When reproducing in polynomial approximation, ●
The points marked with marks and the points marked with ▲ are used as sample points.

Finally, the coefficients of each term of the approximate polynomial for each segment S ₁ to _{S 9} divided by sample points are determined.
For example, the calculation of this coefficient was published in Japanese Patent Application Laid-open No. 58
It can be determined by the method described in Japanese Patent No. 134745. In this way, by the second step,
Obtain memory data using polynomial approximation from a large matrix.

FIG. 5 is a diagram showing the basic structure of master font data created according to the present invention. As shown in the figure, one character of data consists of a plurality of pieces of block information.
The format of one block of information has the structure shown by B.

First, the block header stores information about the entire block. Firstly, the X coordinate information of the end point of the block; secondly, information identifying whether the block shows the outline of the character changing from OFF to ON or the outline changing from ON to OFF when the character is played; Third, information about the number of segments of the block is stored. Following the block header is an information section regarding each segment indicated by A ₁ , A ₂ , . . . . The segment header of the segment information section stores the coordinates of the sample point, the degree of the polynomial, and a code for identifying whether the sample point is used for vector approximation. If we now set the identification codes as 0: not a sample point used for vector approximation and 1: sample point used for vector approximation, point P ₁ in Figure 4, 3 is used for vector approximation, so it becomes "1" ( Note that all sample points are used for polynomial approximation). Point _P2 is not used for vector approximation, so it becomes "0".

The segment information section stores coefficients of each term in polynomial approximation.

In this way, one block information is constructed from as many segment information as the number of segments stored in the block header.

A plurality of pieces of one block information constitute one character of master font data.

Next, a case will be described in which a character image is reproduced based on the stored data using the character data compression method described above.

[Small-sized characters] Since the contours of small-sized characters are reproduced by vector approximation, extract only the segment information with the identification code "1" used for vector approximation from the 1 block information in Figure 5. Interpolated values are calculated for each segment, and vector approximation for one block is performed.
Note that no coefficient information is necessary at this time. The above operations are performed for one character block.

[Large-sized characters] Since the contours of large-sized characters are reproduced by polynomial approximation, the identification codes "1" and "0" used for polynomial approximation, that is, all segment information, are extracted from one block of information in Figure 5. Polynomial approximation is performed by calculating interpolated values using The above operations are performed for one character block.

Next, another embodiment of the present invention will be described.

FIG. 6 is a diagram illustrating a method for creating master font data according to another embodiment of the present invention. The procedure will be explained below.

First, the outline of the character is developed into a medium matrix size as shown in FIG. 61. The curve in FIG. 61 represents one block of the contour. Next, sample points used for polynomial approximation are extracted. The points marked with ● are sample points. Then, the coefficients of each term in the polynomial approximation for each segment are determined. The above is the first step. As a second step, additional sample points to be used for vector approximation are extracted using the same matrix size. At this time, the sample points used for the polymorphic approximation that have already been extracted are always used and extracted. The points marked with ■ in FIG. 6 are additionally extracted sample points used for vector approximation.

The master font data created in the first and second steps as described above is stored in the format shown in FIG. 5, as in the previous embodiment. However, in this embodiment, the identification code is a code for identifying whether a sample point is a sample point used for polynomial approximation. Here, the identification codes are set as follows: 0: Sample points not used for polynomial approximation 1: Sample points used for polynomial approximation (all sample points are used for vector approximation). Therefore, since the point _R1 in FIG. 62 is used for polynomial approximation, the identification code is "1". point
R ₂ is “0” because it is not used for polynomial approximation.

The other difference from the previous embodiment is that in the previous embodiment, all the sample points found were used for polynomial approximation, so the coefficient information is always placed after the sample point coordinate information stored in the segment header in FIG. The remembered segment information section continued.

However, in this embodiment, not all of the obtained sample points are used for polynomial approximation, so there is always a segment information section following the segment header that does not have coefficient information.

For character reproduction, [Small-sized characters] For small-sized characters, vector approximation is performed using all sample points.

[Large size characters] Polynomial approximation is performed using only segment information with an identification code of "1".

As explained above, according to the present invention, using the same master font data, an approximation method suitable for reproduction of each character size is used, that is, vector approximation is used for small-sized characters, and polynomial approximation is used for large-sized characters. Since the master font data is configured in such a way that the contours of characters can be reproduced using a single method of vector approximation or polynomial approximation, this method compensates for the shortcomings of both methods. The effect is remarkable.

Specifically, it is sufficient to display small-sized characters that are frequently used in the main text, etc., in a correspondingly small dot matrix. Since it is necessary to output a large number of characters in the main text, etc., an approximation method with a high output speed is desirable. In this respect, in the present invention, since the algorithm for reproduction is simple,
It is possible to increase the output speed by using vector approximation with a high output speed.

On the other hand, large-sized characters do not appear frequently but are large, so they can be reproduced using vector approximation.
If the character quality is even slightly poor, it will stand out. Therefore, polynomial approximation can be used, which provides good quality of reproduced characters, although there is a slight decrease in output speed compared to vector approximation. Normally, large-sized characters appear much less frequently than small-sized characters, so they have little effect on the overall character output speed.

Furthermore, it is already well known from the above-mentioned publications that both vector approximation and polynomial approximation have high data compression rates, and even if the master font data is configured to use these two approximation methods separately, it is easy to distinguish between the two. The data compression ratio is still high even in the method according to the present invention, since the number of codes to be processed is only increased.

The present invention has remarkable effects as described above.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining vector approximation, Figure 2 is a diagram for explaining polynomial approximation, Figure 3 is a diagram for explaining master font data, and Figure 4 is a diagram for creating a master font according to an embodiment of the present invention. Figure 5 showing
The figure shows the basic structure of master font data.
FIG. 6 is a diagram showing a method for creating a master font according to another embodiment of the present invention.

Claims (1)

[Claims] 1. In a character data compression method that compresses the amount of data by storing character contour specifying information, sample points used in a first approximation method for approximating the character contour are arranged in a matrix. a first step of extracting from the outline of the expanded character; and a second approximation method that is different from the first approximation method by reusing at least the sample points extracted in the first step. a second step of extracting sample points from the contours of the characters developed in a matrix, and combining the extracted sample point information with the first or second
information identifying each segment divided by the sample points extracted in step 1, along with information identifying whether the sample point is to be used in the first or second approximation method, as character data. A character data compression method characterized by storing data inside. 2. A vector approximation method is used as the first approximation method, a polynomial approximation method is used as the second approximation method, and in the second step, a matrix larger in size than the matrix from which the first sample points are extracted is used. 2. The character data compression method according to claim 1, wherein sample points are extracted using the method. 3. A polynomial approximation method is used as the first approximation method,
Claim 1, wherein the vector approximation method is the second approximation method, and the sample points used in the first and second approximation methods are extracted using matrices of the same size. Character data compression method described.