JP2000244734A - Image processor and multi-valuing processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate a multi-valuing processing and to simplify a structure. SOLUTION: Offset information set by a setting part 7 for setting offset information between one basic dither matrix value and a dither matrix is stored in an offset information storage memory 6, a multi-valuing table is prepared by a multi-valuing table preparation part 5 by the stored offset information and the prepared multi-valuing table is stored in a multi-valuing table storage memory 3. Then, by using a basic dither matrix and the stored multi-valuing table, input images are multi-valued by a multi-valuing part 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus capable of performing dither gradation processing, and to a multi-value processing method using dither.

[0002]

2. Description of the Related Art Generally, in a document image processing apparatus capable of handling not only code information but also image information, a document read by an image reading means such as a scanner is binarized by a pseudo gradation converting means such as a dither method. And output it with a printer having a small number of gradations. On the other hand, the dither binary method performs binarization by adding a periodic dither signal to an input pixel or a threshold.

Next, a binarization dither method using a periodic dither threshold will be described with reference to FIG. Input image (signal)
Is compared with the dither threshold by the comparator 52. If the input image is equal to or larger than the dither threshold, 1 is output.
Is output, and the result of binarization is output as an output image. The dither threshold is periodic, and in FIG.
An example of × 4 is shown.

In the case of multi-valued dither, for example, in the case of quaternary conversion, three planes P0, P1, and P2 are provided to determine an output value out with respect to an input value In.

An example shown in FIG. 7 will be described. Plane P0
The offset value of P1 and P1 is 15, and the offset value of P1 and P2 is 20. For a given input image data In, in the conventional multi-value processing, Value and P0, P1, P2
Are compared with the threshold values of the corresponding positions, respectively, and In <P
If 0, out = 0 is output, and P0 ≦ In <P1
, Out = 1 is output, if P1 ≦ In <P2, out = 2 is output, and if P2 ≦ In,
out = 3 is output.

As described above, P0, P
When the comparison is made in the order of 1, P2, it is necessary to perform the comparison calculation up to three times.

For example, as disclosed in Japanese Patent Laid-Open No. 6-253134, even if all dither patterns are generated from the basic dither pattern and the offset information, the capacity of the storage device for storing the dither pattern in advance is also required. However, when multi-valued, it is necessary to secure a storage device having the same capacity as that of the related art.

[0008]

In the conventional multi-value processing using the dither method, when the number of output gradations after the processing is small, the dither threshold value can be stored in a plurality of memories. As the number of gradations increases, more memories and registers for storing the dither threshold are required.

Further, the larger the number of output gradations, the greater the number of comparisons, so that processing time is required and the processing speed is reduced.

An object of the present invention is to provide an image processing apparatus and a multi-value processing method capable of solving the above problems, increasing the speed of the multi-value processing, and simplifying the structure. It is in.

[0011]

According to a first aspect of the present invention, there is provided an image processing apparatus for performing multi-value processing using dither, setting means for setting offset information between one basic dither matrix value and dither matrix, Offset information storage means for storing offset information set by the setting means; multivalued table creation means for creating a multivalued table based on the offset information stored by the offset information means; Means for storing a multivalued table prepared by the means, a basic dither matrix, and a multivalued table stored by the multivalued table storage means. And a multivalued means for performing a value conversion.

In the first aspect, a basic dither offset matrix can be used instead of the basic dither matrix.

According to a third aspect of the present invention, in the multi-value processing method using dither, when offset information between one basic dither matrix value and the dither matrix is set, the offset information storage for storing the set offset information. A multi-level quantization table creating step of creating a multi-level quantization table based on the offset information stored in the offset information step; a multi-level quantization table storing step of storing the created multi-level quantization table; The image processing apparatus further includes a multi-level conversion step of performing multi-level conversion on the input image using the matrix and the multi-level conversion table stored in the multi-level conversion table storage step.

In the present invention, a basic dither offset matrix can be used instead of the basic dither matrix.

The control program recorded on the computer-readable recording medium causes the computer to store the set offset information when the offset information between one basic dither matrix value and the dither matrix is set. A multi-valued table is created based on the offset information, and the created multi-valued table is stored.
The input image can be multi-valued using the basic dither matrix and the stored multi-value conversion table.

In the present invention, a basic dither offset matrix can be used instead of the basic dither matrix.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<First Embodiment> FIG. 1 shows a first embodiment of the present invention.
An embodiment will be described. This is an example of an image processing apparatus. This image processing apparatus reads input image information by, for example, one image reading device such as an image scanner.
The digital data is input as 8-bit data per pixel, and the input pixel value is subjected to gradation processing by a dither multi-value conversion method using this device. This image processing apparatus includes a multi-level conversion unit 1, a basic dither matrix storage memory 2, a multi-level conversion table storage memory 3, a selection unit 4, a multi-level conversion table generation unit 5, an offset information storage memory 6, And an information setting unit 7.

The information setting section 7 is constituted by a keyboard or the like, and sets the size, contents and offset information of the dither matrix to be used. The selection unit 4 sends an address and a read signal to the basic dither matrix storage memory 2 and the offset information storage memory 6 according to the settings obtained from the information setting unit 7. The basic dither matrix storage memory 2 selects and stores basic dither information to be used from a large number of basic dither information in the memory based on the address and read signal supplied from the selection unit 4, and outputs the basic dither information to the multi-value conversion unit 1. is there. The offset information storage memory 6 previously stores offset information corresponding to information such as the type of printer, etc., the number of gradations, the medium, the output resolution, and the like. The offset information is output to the unit 5.

The multivalued table creation section 5 creates a multivalued table according to the offset information output from the offset information storage memory 6 and outputs the created multivalued table to the multivalued table storage memory 3. is there. The multivalued table storage memory 3 stores the multivalued table supplied from the multivalued table creation unit 5 and outputs the table to the multivalued unit 1. The multi-level conversion unit 1 performs multi-level conversion of an input image (signal) based on the basic dither information supplied from the basic dither matrix storage memory 2 and the multi-level conversion table supplied from the multi-level table storage memory 3. Then, the multivalued information is output as an output image (signal) to a printer (not shown) or the like.

Next, the operation of the multi-value conversion section 1 will be described with reference to FIG. In the multi-level conversion unit 1, a threshold value (in this case, 21
3) is obtained, and the obtained threshold value is subtracted from, for example, 255 by the subtracter 21, and the subtraction result (42 in this case) is obtained.
Is added to the pixel value of the input image data by the adder 22 to generate data Value. The obtained data Value is sent to the multi-value quantization table, where the input value Va
The value out is output from lue as output image data.

The multi-value table stored in the multi-value table generation unit 5 has a pixel value of input image data of 8 bits.
Has 512 indexes. For example, 4
In the case of binarization, dither threshold values of three dither matrices are used. However, the difference value of the dither threshold value between each plane is constant, and plane k and plane k + 1 at this time are constant.
The difference value of (k = 0, 1, 2, 3,...) Is defined as D (k). Index values 0 to 254 of the table are filled with 0.

Next, from 255 to 254 + D (0) is filled with 1. Hereinafter, until the index value reaches 511,
Similarly, the value is incremented by one within the width of D (k) to fill the multi-value quantization table. The multi-value table may be set in advance and stored, or may be created based on the settings input from the information setting unit.

Next, the theory of the multi-value conversion unit of the present invention will be described. For example, when the input image data is quaternized, it is necessary to use dither thresholds of three dither matrices. When the dither thresholds of the respective dither matrices are P0, P1, and P2, the offset values between the planes are dl and d2, and the threshold of the basic dither matrix is d0,

[0025]

P0 = d0, P1 = d0 + dl, P2 = d0 + dl + d2 In this case, the relationship between the input value In and the output value out is as follows.

[0026]

## EQU2 ## When In <P0, out = 0, when P0 ≦ In <P1, out = 1, when P1 ≦ In <P2, out = 2, when P2 ≦ In, out = 3.

Then, rewriting equation 2 using equation 1 gives

[0028]

When In <d0, out = 0, when d0 ≦ In <(d0 + dl), out = 1, when d0 + dl ≦ In <(d0 + dl + d2), and when out = 2 d0 + dl + d2 ≦ In, out = 3. . Then, subtracting d0 from both sides of Equation 3 gives

[0029]

## EQU4 ## When In-d0 <0, out = 0, when 0.ltoreq.In-d0 <dl, out = 1, when dl.ltoreq.In-d0 <dl + d2, and when out = 2 dl + d2.ltoreq.In-d0, out. = 3.

When the input image data is 8 bits, Valu
If e = In−d0, both In and d0 are from 0 to 25.
Since any value of 5 can be taken independently, Value
Is in a range from -255 to 255.
To calculate with a positive number,

[0031]

Equation 5 Value = In−d0 + 255 = In + (255−d0) Therefore, 0 ≦ Value ≦ 510.

It is also possible to proceed with the calculation while including a negative number without performing this operation. Using this Value,
Is

[0033]

[Formula 6] When Value <255, out = 0 255 ≦ Value <255 + d1, when out = 1 255 + d1 ≦ Value <255 + d1 + d2, o
When ut = 2 255 + dl + d2 ≦ Value, out = 3. Since values other than Value are fixed values, a table is created using Equation 6. FIG. 3 shows a multivalued table in this case. The threshold value d0 is obtained from the basic dither matrix for the input image In, and the value obtained by calculating In + 255-d0 is subtracted from the multivalue table to perform the multivalue processing without performing the comparison calculation. be able to.

<Second Embodiment> FIG. 4 shows a second embodiment of the present invention.
An embodiment will be described. This embodiment uses a basic dither offset matrix storage memory 42 instead of the basic dither matrix storage memory 2 of the first embodiment, and calculates 255-d0 as in the first embodiment. The multi-value processing is performed by the multi-value processing unit 41 using the basic dither offset matrix created by performing the calculation of d0 '= 255-d0 in advance without performing the calculation every time.

The basic dither offset matrix storage memory 42 selects and stores basic dither information to be used from a large number of basic dither offset information in the memory, based on the address and the read signal supplied from the selection unit 4, Output to The basic dither offset information used here holds the matrix d0 'of the multi-value processing method of the first embodiment. Multi-value conversion section 41
Sends the offset value obtained from the basic dither offset pattern according to the coordinate value of the input image data to the adder, and the adder adds this value to the pixel value of the input image data to generate data Value. Data Value is sent to the multi-value table, and output image data is obtained from the table according to the value of Value. A specific example will be described with reference to FIG. 5. The offset value 42 obtained from the basic dither offset matrix is supplied to the adder 52 according to the coordinates of the input image data, and the adder 52 simultaneously receives the pixel value of the input image data. Supplied,
The value obtained by adding these two numerical values is supplied to the multi-value conversion table. In multi-valued table, input value Value to value o
ut is output as output image data.

Therefore, in the multi-value processing using the dither method, one basic dither matrix value and offset information between the dither matrices are stored or input, a multi-value table is generated from the offset information, and the basic dither matrix is multiplied. By using the binarization table, input image data can be multi-valued without comparison operation.

Thus, in the multi-value processing using the dither method, the input image data can be multi-valued using the basic dither matrix information and the multi-value conversion table created from the offset information. Compared with the conventional method, the storage device can be simplified, and the processing speed can be increased.

As described above, the storage medium storing the program codes of the software for realizing the functions of the above-described embodiments is supplied to the system or the apparatus, and the computer (or CPU or MP) of the system or the apparatus is supplied.
It goes without saying that the object of the present invention is also achieved when U) reads out and executes the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM (com
pactdisk ROM), CD-R (compact disk recordable)
, Magnetic tape, nonvolatile memory card, ROM (rea
d only memory), and so on.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the operating system (OS) running on the computer based on the instruction of the program code.
Needless to say, a case in which the functions of the above-described embodiments are realized by performing part or all of the actual processing by a ting system or the like is also included.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instructions of the program code, It goes without saying that the CPU provided in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0043]

As described above, according to the present invention,
With the configuration as described above, in the multi-value processing using the dither method, by using the basic dither matrix information and the multi-value table, the input image data is multi-valued without performing a comparison operation. It is possible to speed up the multi-value processing and simplify the storage device for storing the dither matrix.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing a first embodiment.

FIG. 3 is a diagram illustrating an example of a multi-value quantization table.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining a second embodiment.

FIG. 6 is an explanatory diagram for explaining the principle of binarization using conventional dither.

FIG. 7 is an explanatory diagram for explaining a conventional multilevel dither pattern.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multi-value part 2 Basic dither matrix storage memory 3 Multi-value table storage memory 4 Selection part 5 Multi-value table preparation part 6 Offset information storage memory 7 Information setting part

Claims (6)

[Claims] 1. An image processing apparatus for performing multi-value processing using dither, a setting means for setting offset information between one basic dither matrix value and a dither matrix, and storing the offset information set by the setting means. Offset information storage means, a multi-valued table creation means for creating a multi-valued table based on the offset information stored by the offset information means, and a multi-valued table created by the multi-valued table creation means are stored. Multivalued table storage means, and a multivalued means for multivalued an input image using the basic dither matrix and the multivalued table stored by the multivalued table storage means. An image processing apparatus comprising: 2. The image processing apparatus according to claim 1, wherein a basic dither offset matrix is used instead of the basic dither matrix. 3. A multi-value processing method using dither, wherein when offset information between one basic dither matrix value and a dither matrix is set, an offset information storing step of storing the set offset information; A multi-level quantization table creating step of creating a multi-level quantization table based on the offset information stored in the information step; a multi-level quantization table storing step of storing the created multi-level quantization table; the basic dither matrix; A multi-value processing step of performing multi-value processing on the input image using the multi-value table stored in the value table storage step. 4. The multivalue processing method according to claim 3, wherein a basic dither offset matrix is used instead of the basic dither matrix. 5. When a computer sets offset information between one basic dither matrix value and a dither matrix, the set offset information is stored, and a multi-value table is created based on the stored offset information. A computer-readable recording that stores a created multi-level quantization table, and that records a control program that can perform multi-level quantization of an input image using the basic dither matrix and the stored multi-level quantization table. Medium. 6. The computer-readable recording medium according to claim 5, wherein a control program that uses a basic dither offset matrix instead of the basic dither matrix is recorded.