JP2001078032A - Method and device for picture processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To save the memory capacity required for storage of a threshold matrix. SOLUTION: A threshold matrix selection part 13 selects one threshold matrix from a threshold matrix memory 12. A threshold matrix inversion part 14 inverts thresholds stored in the threshold matrix selected by the threshold matrix selection part 13 with a certain value as the center value to obtain an inverted threshold matrix. A binarizing part 15 performs binarization by using the threshold matrix selected by the threshold matrix selection part 13 or the inverted threshold matrix obtained by inverting thresholds by the threshold matrix inversion part 14. Binary data binarized by the binarizing part 15 are stored in a binary picture memory 16.

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 and an image processing method.

More specifically, the present invention particularly relates to an image processing apparatus and an image processing method for converting a multi-valued image into a binary image.

[0003]

2. Description of the Related Art Conventionally, as a method of converting a multi-valued image into a binary image, a method using a threshold matrix has been known. In this method, a threshold matrix of a predetermined size in which thresholds are stored is prepared in advance, and reference is made to
This is to make a value.

In the above method, when the same threshold matrix is applied to multi-value data of all ink colors,
When the multi-value data is the same, the dot generation patterns are synchronized, and there is a problem that the graininess is deteriorated.

[0005] On the other hand, there is a method of preparing a different threshold matrix for each ink color.

[0006]

However, in the latter known image processing method, it is necessary to prepare a different threshold matrix for each ink color, so that the memory required for binarization is required. There is a disadvantage that the capacity is significantly increased as compared with the former case using one type of threshold matrix. Therefore, if the free space of the memory for storing the threshold matrix is insufficient, there arises a problem that a different threshold matrix cannot be prepared for each ink color.

For example, when only two types of threshold matrices can be stored in the memory, different threshold matrices can be used for two different ink colors, cyan and magenta, but other ink colors, for example, yellow, can be used. , Cyan or magenta will be used. As a result, when the multi-value data is the same, the dot generation patterns of magenta and yellow are synchronized, and there is a problem that the graininess is deteriorated.

Accordingly, an object of the present invention is to provide
An object of the present invention is to provide an image processing apparatus and an image processing method that can save a memory capacity required for storing a threshold matrix.

[0009]

According to a first aspect of the present invention, there is provided an image processing apparatus for converting a multi-valued image into a binary image, wherein a predetermined threshold value is stored. Storage means having a threshold matrix, and a threshold value inversion means for obtaining an inversion threshold matrix obtained by inverting a predetermined value as a center value for the threshold values stored in the threshold matrix; and A binarizing means for performing binarization by reading a threshold value and comparing it with a multi-valued image.

According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the center value is a center value of a range in which multi-value data of a multi-value image can be taken.

According to a third aspect of the present invention, in the image processing apparatus according to the first aspect, the threshold value matrix is constituted by uniform random numbers within a predetermined range.

According to a fourth aspect of the present invention, in the image processing apparatus of the first aspect, the threshold matrix has a frequency characteristic of blue noise.

According to a fifth aspect of the present invention, in the image processing apparatus according to the first aspect, the binarizing means performs a binarizing process based on an organized dither method.

According to a sixth aspect of the present invention, in the image processing apparatus according to the first aspect, the binarizing means performs a binarizing process based on an error diffusion method.

According to a seventh aspect of the present invention, there is provided the image processing apparatus according to the first aspect, further comprising an image forming unit for forming an image based on the binary data binarized by the binarizing unit. .

According to an eighth aspect of the present invention, in the image processing apparatus according to the first aspect, the image processing apparatus further comprises a selecting means for selecting a desired threshold matrix from a plurality of threshold matrices.

According to a ninth aspect of the present invention, in the image processing apparatus of the first aspect, the threshold matrix and the inversion threshold matrix are applied to ink colors having different hues.

According to a tenth aspect of the present invention, the multi-valued image is represented by two.
An image processing method for converting into a value image, wherein a threshold matrix in which a predetermined threshold is stored is obtained by inverting a threshold stored in the threshold matrix with a predetermined value as a center value. A threshold inversion step, and a binarization step of reading a threshold value from the threshold value matrix or the inversion threshold value matrix and comparing the threshold value with a multi-valued image to perform binarization.

According to an eleventh aspect of the present invention, in the image processing method of the tenth aspect, the center value is a center value of a range in which multi-value data of a multi-value image can be taken.

According to a twelfth aspect of the present invention, in the image processing method of the tenth aspect, the threshold matrix is:
It is composed of uniform random numbers in a predetermined range.

According to a thirteenth aspect of the present invention, in the image processing method according to the tenth aspect, the threshold matrix is:
It has frequency characteristics of blue noise.

According to a fourteenth aspect of the present invention, in the image processing method according to the tenth aspect, the binarizing step performs a binarizing process based on an organized dither method.

According to a fifteenth aspect of the present invention, in the image processing method of the tenth aspect, the binarizing step performs a binarizing process based on an error diffusion method.

The present invention according to claim 16 is the image processing method according to claim 10, further comprising an image forming step of forming an image based on the binary data binarized by the binarizing step. .

According to a seventeenth aspect of the present invention, there is provided the image processing method according to the tenth aspect, further comprising a selecting step of selecting a desired threshold matrix from a plurality of threshold matrices.

According to an eighteenth aspect of the present invention, in the image processing method according to the tenth aspect, the threshold matrix and the inversion threshold matrix are applied to ink colors having different hues.

According to a nineteenth aspect of the present invention, a multi-value image is represented by two
As an image processing method for converting into a value image, for a threshold matrix in which a predetermined threshold value is stored, a threshold value inversion obtained by inverting a threshold value stored in the threshold value matrix with a predetermined value as a center value is used. And a binarizing step of reading a threshold from the threshold matrix or the inversion threshold matrix and performing binarization by comparing the threshold with a multi-valued image in the form of a readable program. .

According to a twentieth aspect of the present invention, in the storage medium according to the nineteenth aspect, the center value is a center value of a range in which multi-value data of a multi-value image can be taken.

According to a twenty-first aspect of the present invention, in the storage medium according to the nineteenth aspect, the threshold value matrix is formed of uniform random numbers within a predetermined range.

According to a twenty-second aspect of the present invention, in the storage medium according to the nineteenth aspect, the threshold matrix has a frequency characteristic of blue noise.

According to a twenty-third aspect of the present invention, in the storage medium according to the nineteenth aspect, the binarizing step performs a binarizing process based on an organized dither method.

According to a twenty-fourth aspect of the present invention, in the storage medium according to the nineteenth aspect, the binarizing step performs a binarizing process based on an error diffusion method.

According to a twenty-fifth aspect of the present invention, the storage medium according to the nineteenth aspect further comprises an image forming step of forming an image based on the binary data binarized in the binarizing step.

The present invention according to claim 26 is the storage medium according to claim 19, further comprising a selecting step of selecting a desired threshold matrix from a plurality of threshold matrices.

According to a twenty-seventh aspect of the present invention, in the storage medium according to the nineteenth aspect, the threshold matrix and the inversion threshold matrix are applied to ink colors having different hues.

The present invention according to claim 28 is the invention according to claims 19 to
27, in the storage medium, a floppy disk, a hard disk, a magneto-optical disk storing a program readable by a server computer and a client computer as the storage medium,
An optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, and ROM are used.

The present invention according to claim 29 is the invention according to claims 19 to
27. The storage medium according to any one of 27, wherein the storage medium is detachable from a server computer and a client computer.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the overall configuration of the image processing apparatus according to the present embodiment. In FIG.
Reference numeral 1 denotes the entire image processing apparatus. The image processing apparatus 1 according to the present embodiment includes a multi-valued image memory 11, a threshold matrix 12, a threshold matrix selection unit 13, a threshold matrix inversion unit 14, a binarization unit 15, a binary image memory 16, an image output unit 17, The CPU 18 is included.

In FIG. 1, reference numeral 11 denotes a multi-valued image memory for storing an input image. 12 is a multi-valued image memory 11
Is a threshold matrix in which predetermined threshold values required for binarizing the multi-value data stored in are stored. The threshold matrix 12 is composed of two types, a first threshold matrix 121 and a second threshold matrix 122. 13 is the threshold matrix 12 from 1
The threshold matrix selection unit selects one threshold matrix. Here, either the first threshold matrix 121 or the second threshold matrix 122 is selected.

Reference numeral 14 denotes a threshold matrix inverting unit that inverts a threshold stored in the threshold matrix selected by the threshold matrix selecting unit 13 with a certain value as a center value to obtain an inverted threshold matrix. Reference numeral 15 denotes binarization using the threshold matrix selected by the threshold matrix selection unit 13 or the inversion threshold matrix obtained by inverting the threshold by the threshold matrix inversion unit 14.
It is a value conversion unit. Reference numeral 16 denotes a binary image memory that stores the binary data binarized by the binarizing unit 15. 17
Is an image output unit that outputs a binary image. CPU18
Controls the entire image processing apparatus 1 according to the control procedure stored in the ROM.

In this embodiment, it is assumed that each pixel of a predetermined multi-valued image has an integer value in the range of 0 to 255 representing a pixel value and is stored in the multi-valued image memory 11.
In this state, the binarizing unit 15 reads out the image data stored in the multi-level image memory 11 and performs binarization.
The threshold matrix 12 includes two different threshold matrices 121 and 122. As a method of creating the threshold matrix 12, a threshold matrix or a blue noise matrix used for the dither method can be used. In the present embodiment, random numbers uniformly distributed in a predetermined range are used as the threshold matrix. Adopt as a matrix. That is, if random numbers are used for the threshold matrix, different random number sequences can be obtained only by changing parameters such as initial values given to a program or a device for generating random numbers, so that it is easy to create a plurality of threshold matrices. .

FIG. 2 shows an example of a threshold matrix using uniform random numbers generated in the range of 108 to 148.
In this figure, the matrix size is 4 × 4 for simplicity, but in practice, it is appropriate to use a matrix size of about 64 × 64.

FIG. 3 is a flowchart showing a process of converting a multi-valued image into a binary image using the threshold value matrix. In the figure, in step S1, initialization is performed.
In step S2, ink color information of a multivalued image to be processed is read. Here, the ink colors are four colors of cyan, magenta, yellow, and black.
One is read as ink color information. For example, when processing a cyan multivalued image, cyan is read as ink color information.

In step S3, one threshold matrix is selected from the plurality of threshold matrices by the threshold matrix selector 13 in FIG. This selection is made based on the ink color information read in step S2. That is, the correspondence between the ink color and the selected threshold matrix is stored in advance, and the threshold matrix is selected based on the stored relationship.

FIG. 4 shows the correspondence between the ink colors and the threshold matrix to be selected. In the figure, cyan and yellow indicate that the threshold matrix 1 is selected, and magenta and black indicate that the threshold matrix 2 is selected.
By using two threshold matrices in this way, it is possible to prevent, for example, the synchronization of the dot generation patterns of cyan and magenta.

Next, in step S4 of FIG. 3, it is determined whether or not the threshold matrix is inverted. In the present embodiment, the synchronization of the cyan and magenta dot generation patterns can be prevented. However, since the same threshold matrix is used for cyan and yellow, the synchronization of the dot generation patterns cannot be prevented as they are. Therefore,
Invert the threshold matrix corresponding to one ink color using the same threshold matrix. This step S
In No. 4, as shown in FIG. 4, the threshold matrix is inverted for two colors of yellow and black, and the inversion is not performed for cyan and magenta. That is, the process proceeds to step S5 for yellow and black, and proceeds to step S6 for cyan and magenta.

In step S5, the threshold matrix is inverted by the threshold matrix inverting unit 14 in FIG. 1 to obtain an inverted threshold matrix. This threshold matrix inversion process will be described in detail with reference to the flowchart of FIG.

In FIG. 5, first, in step S51,
One threshold data TH is read from the threshold matrix.
In the next step S52, inversion processing of the threshold data TH is performed. Here, the center value is 128 because the multi-value data ranges from 0 to 255. The inversion process performed in step S52 is performed centering on the center value 128. When the threshold value after the inversion is expressed by an equation as INV_TH,

[0050]

## EQU1 ## INV_TH = 256-TH (1) For example, when TH = 130, INV_TH = 12
6, which indicates that the average value of TH and INV_TH always becomes the center value 128. In other words, the relationship between the threshold matrix and the inversion threshold matrix is a state where the phases are just opposite in terms of frequency characteristics.
That is, when the threshold matrix is considered globally, it can be said that the frequency characteristics of the two are the same, so that an image binarized using both can have similar characteristics.

On the other hand, since the threshold values stored in the two matrices are different, it is possible to prevent the synchronization of the dot generation patterns.

As described above, the point that the threshold matrix capable of preventing the synchronization of the dot generation pattern and capable of outputting a binary image having similar characteristics can be derived from one threshold matrix by a simple calculation. This is a major feature of the embodiment.

In the next step S53, it is determined whether or not there is a threshold value that has not been processed. If there is an unprocessed threshold, the process returns to step S51 to perform threshold inversion processing.
If there is no unprocessed threshold, the process ends.

With the above processing, it is possible to prevent the dot generation patterns of cyan and yellow and magenta and black from being synchronized. As a result, different threshold matrices are set for all the cyan, magenta, yellow and black ink colors. Can be applied.

Next, the process proceeds to step S6 in FIG. 3, and the multi-valued image data stored in the multi-valued image memory 11 in FIG. 1 to be binarized is read. As a reading method, all pixel data may be read at once, or may be read line by line. In step S7, 2 in FIG.
The binarization unit 15 performs binarization using a threshold matrix or an inverted threshold matrix.

Note that the present invention is not limited to the binarization method, and it is also possible to apply a systematic dither method or an error diffusion method.

FIG. 6 shows a method for binarizing multi-valued image data using a threshold matrix. As shown in the figure, the threshold value in the threshold value matrix is compared with the pixel value of the multi-valued image data at the same position, and if the pixel value is larger, the corresponding binary image dot is turned on, When the value is smaller or equal, the dot of the corresponding binary image is turned off. As described above, the matrix size is 4 × 4 for simplicity in the drawing, but it is preferable that the matrix size is actually about 64 × 64.

FIG. 7 shows an example of an error diffusion coefficient used when the error diffusion method is applied. This indicates that the error generated in the target pixel (*) is distributed to the right pixel by 、 and to the lower pixel by １ ／.

Next, in step S8 in FIG. 3, the binary data binarized in step S7 is stored in the binary image memory 16 in FIG. In step S9, it is determined whether there is any unprocessed multi-valued image data. If there is unprocessed multi-valued image data, the process returns to step S6 to read the multi-valued image data. If there is no unprocessed multi-valued image data, the process proceeds to step S10.

In step S10, it is determined whether there is an unprocessed ink color. If there is an unprocessed ink color, the process returns to step S2 to read the ink color information. If there is no unprocessed ink color, the process ends.

The image is binarized by repeating the above processing. Then, the binary image memory 16 of FIG.
Is transferred to the image output unit 17 of FIG. 1 to form an image.

The above-described processing configuration of FIG. 1 can be executed on a general information processing apparatus as shown in FIG. 8 based on software. 201 is a CPU (microprocessor). The CPU 201 controls each component connected to the bus 208 via the bus 208 in order to perform binarization, inversion of the threshold matrix, and the like, that is, to realize each functional configuration illustrated in FIG. Things. The bus 208 is an address bus,
It is a common bus composed of a control bus and a data bus. In other words, the bus 208 is used to transfer address signals, control signals, and various data between the devices connected to the bus 208.

Reference numeral 203 denotes an input device, which includes a keyboard, a mouse, and the like, and is provided with a switch having a selection function for instructing an operation relating to image formation of the image processing apparatus. Reference numeral 202 denotes a ROM, that is, a read-only memory. The ROM 202 has a CPU
The control procedure 201 is stored, whereby various processes according to the present embodiment such as binarization and inversion of a threshold matrix can be performed. Reference numeral 205 denotes a RAM (random access memory), which is used as a work memory for the CPU 201 to execute various processes such as binarization and inversion of a threshold matrix, and a temporary storage for controlling each component.

Reference numeral 206 denotes an external storage device, which provides a storage area for storing a multi-valued image and a threshold matrix. 20
Reference numeral 7 denotes a display, which includes a cathode ray tube, liquid crystal, and the like. Reference numeral 204 denotes a printer, which is an image processing apparatus 1 shown in FIG.
Corresponding to

With the above configuration, it is possible to save the memory capacity required for storing the threshold matrix.

The present invention may be applied to a system constituted by a plurality of devices or to an apparatus constituted by a single device. Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to store the storage medium in a computer (or CPU or MPU) of the system or the apparatus. Needless to say, the present invention can also be achieved by reading and executing the program code stored in the medium. In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and as a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, Magneto-optical disk,
A CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like can be used. When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. Performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

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 included 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.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the above-described flowcharts. However, in brief, an example of the memory map in FIG. Each module shown will be stored in a storage medium. That is, at least a threshold matrix inversion processing module corresponding to the threshold matrix inversion unit in FIG. 1, a binarization processing module corresponding to the processing in the binarization unit and the threshold matrix selection unit in FIG. 1, and a binary image memory The binary data stored in the storage unit 105 may be sequentially transferred to the image output unit 107 (printer 204), and the program code of each module of the image forming processing module for forming an image may be stored in a storage medium.

As described above, according to the present embodiment, it is possible to save the memory capacity required for storing the threshold matrix.

[0070]

As described above, according to the present invention, a remarkable effect that the memory capacity required for storing the threshold matrix used for the binarization processing can be saved can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a threshold matrix using uniform random numbers generated in a range from 108 to 148.

FIG. 3 is a flowchart illustrating a processing operation for converting a multivalued image into a binary image using a threshold matrix.

FIG. 4 is a diagram illustrating a correspondence relationship between an ink color and a threshold matrix to be selected, and whether to invert the threshold matrix.

FIG. 5 is a flowchart illustrating a threshold matrix inversion process.

FIG. 6 shows multivalued image data 2 using a threshold matrix.
It is a figure which shows a quantification method.

FIG. 7 is a diagram showing an example of an error diffusion coefficient used in the error diffusion method.

FIG. 8 is a configuration diagram of an information processing apparatus according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of a layout on a predetermined storage medium of a program module for executing image processing according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image processing apparatus 11 Multi-valued image memory 12 Threshold matrix 13 Threshold matrix selection unit 14 Threshold matrix inversion unit 15 Binarization unit 16 Binary image memory 17 Image output unit 18 CPU 201 CPU 202 ROM 203 Input device 204 Printer 205 RAM 206 External memory 207 Display

Claims (29)

[Claims] 1. An image processing apparatus for converting a multi-valued image into a binary image, comprising: a storage unit having a threshold matrix in which a predetermined threshold is stored;
Threshold inversion means for obtaining an inversion threshold matrix obtained by inverting a predetermined value as a center value, and by reading a threshold value from the threshold matrix or the inversion threshold matrix and comparing with a multi-value image,
An image processing apparatus comprising: a binarizing unit for performing binarization. 2. The image processing apparatus according to claim 1, wherein the center value is a center value of a range in which multi-value data of a multi-value image can be taken. 3. The image processing apparatus according to claim 1, wherein the threshold matrix is configured by a uniform random number in a predetermined range. 4. The image processing apparatus according to claim 1, wherein the threshold matrix has a frequency characteristic of blue noise. 5. The image processing apparatus according to claim 1, wherein said binarization means performs binarization processing based on an organized dither method. 6. The image processing apparatus according to claim 1, wherein said binarization means performs binarization processing based on an error diffusion method. 7. The image processing apparatus according to claim 1, further comprising: an image forming unit that forms an image based on the binary data binarized by the binarizing unit. Image processing device. 8. The image processing apparatus according to claim 1, further comprising a selection unit for selecting a desired threshold matrix from a plurality of threshold matrices. 9. The image processing apparatus according to claim 1, wherein the threshold matrix and the inversion threshold matrix are:
An image processing apparatus which is applied to ink colors of different hues. 10. An image processing method for converting a multi-valued image into a binary image, wherein, for a threshold matrix in which a predetermined threshold is stored, a threshold stored in the threshold matrix is centered on a predetermined value. A threshold inversion step of obtaining an inversion threshold matrix inverted as a value, and a binarization step of reading a threshold from the threshold matrix or the inversion threshold matrix and performing binarization by comparing with a multi-value image. An image processing method comprising: 11. The image processing method according to claim 10, wherein the center value is a center value of a range in which multi-value data of a multi-value image can be taken. 12. The image processing method according to claim 10, wherein said threshold value matrix is constituted by a uniform random number within a predetermined range. 13. The image processing method according to claim 10, wherein the threshold matrix has a frequency characteristic of blue noise. 14. The image processing method according to claim 10, wherein the binarizing step performs a binarizing process based on a systematic dither method. 15. The image processing method according to claim 10, wherein the binarizing step performs a binarizing process based on an error diffusion method. 16. The image processing method according to claim 10, further comprising an image forming step of forming an image based on the binary data binarized by said binarizing step. Image processing method. 17. The image processing method according to claim 10, further comprising a selection step of selecting a desired threshold matrix from a plurality of threshold matrices. 18. The image processing method according to claim 10, wherein the threshold matrix and the inversion threshold matrix are:
An image processing method which is applied to ink colors of different hues. 19. An image processing method for converting a multi-valued image into a binary image, wherein a threshold value matrix storing a predetermined threshold value is determined by setting a threshold value stored in the threshold value matrix to a predetermined value as a center value. A threshold inversion step of obtaining an inverted inversion threshold matrix, and a binarization step of reading a threshold from the threshold matrix or the inversion threshold matrix and performing binarization by comparing the threshold with a multi-valued image, are readable. A storage medium characterized by being stored in the form of a program. 20. The storage medium according to claim 19, wherein the center value is a center value of a range in which multi-value data of a multi-value image can be taken. 21. The storage medium according to claim 19, wherein said threshold value matrix is composed of a uniform random number in a predetermined range. 22. The storage medium according to claim 19, wherein said threshold matrix has frequency characteristics of blue noise. 23. The storage medium according to claim 19, wherein said binarization step performs binarization processing based on an organized dither method. 24. The storage medium according to claim 19, wherein said binarization step performs a binarization process based on an error diffusion method. 25. The storage medium according to claim 19, further comprising an image forming step of forming an image based on the binary data binarized by said binarizing step. Medium. 26. The storage medium according to claim 19, further comprising a selecting step of selecting a desired threshold matrix from a plurality of threshold matrices. 27. The storage medium according to claim 19, wherein the threshold matrix and the inversion threshold matrix are:
A storage medium characterized by being applied to ink colors of different hues. 28. The storage medium according to claim 19, wherein the storage medium stores a program readable by a server computer and a client computer, a hard disk, a magneto-optical disk, A storage medium using an optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, and a ROM. 29. The storage medium according to claim 19, wherein said storage medium is detachable from a server computer and a client computer.