JP2001189858A - Image processor, image processing method and a computer- readable recording medium recording program to allow computer to execute the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the performance for conversion processing of image data. SOLUTION: The image processor is provided with a dither processing section 301 that applies dither processing to each pixel of input image data with p- gradation to provide an output of matrix position information denoting a pixel value of each pixel and a growing direction of each pixel and with a resolution.gradation conversion section 302 that has a conversion table storing the matrix position information and a pixel pattern of m-gradation (n>m) or below in cross-reference with each other by each gradation which each pixel of the image data after the dither processing can take and replaces each pixel of the image data after the dither processing with a pixel pattern with the m-gradation or below based on the conversion table so as to apply the resolution conversion and the gradation transformation to the image data after the dither processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resolution conversion process for performing dither processing on p-gradation input image data read from an image reading section to generate n-gradation (p> n) image data and a gradation conversion process. More particularly, the present invention relates to an image processing apparatus, an image processing method, and a computer-readable recording medium storing a program for causing a computer to execute the method, which can optimize performance of image data conversion processing.

[0002]

2. Description of the Related Art Conventionally, digital copiers for processing digital image data from analog copiers have appeared, and digital copiers have not only functions as copiers, but also have the functions of copiers. There are digital multifunction peripherals that combine functions such as facsimile functions, printer functions, and scanner functions.

In such digital copiers and digital multifunction machines, the resolution of the scanner and the resolution of the printer may be different, and even in such a case, various density conversion processing techniques are required to output an image suitable for the resolution of the printer. Has been devised. For example, for an input image signal of n gradations per pixel, the number of pixels is converted to A × B times and the gradation is converted to m gradations (for example, see Japanese Patent Application Laid-Open No.
-37081).

[0004]

However, in the above-mentioned prior art, gradation conversion such as dither processing is performed on an input image signal, and dither processing is performed again using a threshold matrix of A × B times density. And so on. Therefore, there is a problem that it is necessary to prepare a large amount of threshold matrices, and it is necessary to provide a large-capacity memory for storing the threshold matrices.

Further, if tone conversion such as dither processing is performed again, many processing steps are required, so that there is a problem that the performance of image data conversion processing cannot be optimized.

[0006] In order to solve the above-mentioned problems of the prior art, the present invention provides an image processing apparatus, an image processing method, and a computer-readable storage medium capable of optimizing the performance of image data conversion processing. It is an object of the present invention to provide a computer-readable recording medium recording a program to be executed.

[0007]

Means for Solving the Problems To solve the above-mentioned problems,
In order to achieve the object, an image processing apparatus according to the present invention performs dither processing on input image data of p gradation read from an image reading unit and performs n dither processing (p> n).
An image processing apparatus for generating image data of
A dither processing unit that performs dither processing on each pixel of the input image data of the gradation, and outputs a pixel value of each pixel and matrix position information indicating a growth direction of the pixel; A conversion table that stores the matrix position information and a pixel pattern of m gradations (n> m) or less in association with each possible gradation of each pixel of the image data; A conversion unit for performing resolution conversion and gradation conversion of the image data after the dither processing by substituting the pixel pattern with the m or less gradation based on the conversion table.

According to the first aspect of the present invention, the performance of the image data conversion process can be optimized.

According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the converting means converts the image data of Ndpi and n gradation into N × 2dp.
It is characterized in that it is converted into image data of i and m gradations.

According to the second aspect of the present invention, it is possible to optimize the performance of the image data conversion process while suppressing the deterioration of the image quality of the output image.

According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect,
The conversion table stores a plurality of sets of pixel patterns for each gradation that can be taken by each pixel of the image data after the dither processing by the dither processing unit, and the conversion unit stores the pixel pattern based on an image quality mode of an output image. It is characterized in that a pattern group is selected.

According to the third aspect of the present invention, it is possible to perform a conversion process reflecting the image quality characteristics of a character or a photograph.

According to a fourth aspect of the present invention, in the image processing apparatus according to the first, second, or third aspect, the conversion means includes means for converting the image data on which the resolution conversion and the gradation conversion have been performed. The method is characterized in that the dot growth direction is switched so as to suppress the generation of the isolated point in (1).

According to the present invention, the generation of isolated points in the output image can be suppressed.

According to a fifth aspect of the present invention, in the image processing apparatus according to the fourth aspect, the conversion means stores information relating to a dot growth direction of the pixel having the m or less gradation. Storage means; and a growth direction determining means for determining the dot growth direction of the pixel based on the information on the dot growth direction stored in the storage means and updating the storage content of the storage means according to the dot growth direction. It is characterized by the following.

According to the fifth aspect of the present invention, generation of isolated points in an output image can be effectively suppressed.

According to a sixth aspect of the present invention, in the image processing apparatus according to the fifth aspect, the growth direction determining means is arranged so that the growth direction determining means determines the position of an adjacent pixel located at the upper left, right above, and upper right of the target pixel. The dot growth direction of the pixel of interest is determined so as to refer to the dot growth direction so that the dot is in contact with the referred adjacent pixel.

According to the invention described in claim 6, generation of isolated points in the output image can be effectively suppressed.

According to a seventh aspect of the present invention, in the image processing method, dither processing is performed on p-gradation input image data read from the image reading section to convert n-gradation (p> n) image data. A dither processing step of performing dither processing on each pixel of the input image data having the p gradation, and outputting a pixel value of each pixel and matrix position information indicating a growth direction of the pixel, Based on the matrix position information and the conversion table in which pixel patterns of m gradations (n> m) or less are stored in association with each possible gradation of each pixel of the image data after the dither processing in the dither processing step. Replacing each pixel of the image data after the dither processing with a pixel pattern of the m gradation or less,
And a conversion step of performing resolution conversion and gradation conversion of the image data after the dither processing.

According to the present invention, the performance of the image data conversion processing can be optimized.

According to an eighth aspect of the present invention, in the image processing method according to the seventh aspect, the conversion step includes the step of converting the image data of Ndpi and n gradations into N × 2dp.
It is characterized in that it is converted into image data of i and m gradations.

According to the eighth aspect of the present invention, it is possible to optimize the performance of the image data conversion processing while suppressing the deterioration of the image quality of the output image.

The image processing method according to the ninth aspect of the present invention is the image processing method according to the seventh or eighth aspect.
The conversion table stores a plurality of sets of pixel patterns for each gradation that can be taken by each pixel of the image data after the dither processing by the dither processing means, and the conversion step performs the conversion based on an image quality mode of an output image. It is characterized in that a pattern group is selected.

According to the ninth aspect of the present invention, it is possible to perform a conversion process reflecting the image quality characteristics of a character or a photograph.

According to a tenth aspect of the present invention, in the image processing method according to any one of the seventh to ninth aspects, the conversion step includes performing the resolution conversion and the gradation conversion. It is characterized in that the direction of dot growth is switched so as to suppress generation of isolated points on image data.

According to the tenth aspect, it is possible to suppress generation of isolated points in an output image.

[0027] In the image processing method according to the eleventh aspect of the present invention, in the image processing method according to the tenth aspect, the conversion step may include: And determining the dot growth direction of the pixel based on the information, and updating the storage content of the storage unit according to the dot growth direction.

According to the eleventh aspect, generation of isolated points in an output image can be effectively suppressed.

According to a twelfth aspect of the present invention, in the image processing method according to the eleventh aspect, the conversion step includes the step of growing dots of adjacent pixels located at the upper left, right above, and upper right of the target pixel. The dot growth direction of the pixel of interest is determined so that the dot is in contact with the referred adjacent pixel by referring to the direction.

According to the twelfth aspect, the generation of isolated points in the output image can be effectively suppressed.

According to a thirteenth aspect of the present invention, there is provided a recording medium in which a program for causing a computer to execute the method according to any one of the seventh to twelfth aspects is recorded. This enables the operation of any one of claims 7 to 12 to be performed by a computer.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an image processing apparatus, an image processing method, and a computer-readable recording medium storing a program for causing a computer to execute the method will be described below with reference to the accompanying drawings. Will be described in detail.

First Embodiment (Outline of Processing of Image Processing Apparatus) First, the principle of the image processing apparatus according to the first embodiment will be described. FIG.
FIG. 2 is a block diagram functionally showing the configuration of the image processing apparatus according to the first embodiment of the present invention. In FIG. 1, the image processing apparatus has a configuration including the following five units.

Each of the above-described units includes an image data control unit 100, an image reading unit 101, an image memory control unit 102, and an image processing unit 103.
And the image writing unit 104 are connected to the image data control unit 100, respectively.

The processing performed by the image data control unit 100 is as follows.

For example, (1) data compression processing (primary compression) for improving data bus transfer efficiency, (2)
Transfer processing of primary compressed data to image data, (3) image synthesis processing (image data from a plurality of units can be synthesized, and also includes synthesis on a data bus), (4) image Shift processing (shifting of the image in the main scanning and sub-scanning directions), (5) image area expansion processing (the image area can be enlarged by an arbitrary amount to the periphery), and (6) image scaling processing (for example, 50% Or fixed magnification of 200%), (7) parallel bus interface processing,
(8) Serial bus interface processing (interface with process controller 211 described later), (9) format conversion processing of parallel data and serial data, (10) interface processing with image reading unit 101, (11) image processing Unit 10
3 and the like.

The processing performed by the image reading unit 101 is as follows.

For example, (1) read processing of the original reflected light by the optical system, (2) CCD (Charge Cou)
(3) digitization processing with an A / D converter, (4) shading correction processing (processing for correcting unevenness in illuminance distribution of a light source), (5) ) Scanner γ correction processing (processing for correcting the density characteristics of the reading system), and the like.

The processing performed by the image memory control unit 102 includes the following.

For example, (1) interface control processing with a system controller, (2) parallel bus control processing (interface control processing with a parallel bus), (3) network control processing, (4) serial bus control processing (a plurality of processes) External serial port control processing),
(5) Internal bus interface control processing (command control processing with the operation unit), (6) Local bus control processing (ROM and R for starting the system controller)
AM, font data access control processing), (7) memory module operation control processing (memory module write / read control processing, etc.), and (8) memory module access control processing (from a plurality of units). Arbitration of memory access requests), (9) data compression / expansion processing (processing to reduce the amount of data for effective use of memory), (10)
Image editing processing (clearing data in a memory area, rotating image data, synthesizing an image on a memory, and the like).

The processing performed by the image processing unit 103 is as follows.

For example, (1) shading correction processing (processing for correcting unevenness of the illuminance distribution of the light source), (2) scanner γ correction processing (processing for correcting the density characteristic of the reading process), (3) MTF correction processing, 4) smoothing, (5)
Arbitrary magnification processing in the main scanning direction, (6) density conversion (γ conversion processing: corresponding to density notch), (7) simple multi-value processing,
(8) Simple binarization processing, (9) Error diffusion processing, (10)
Dither processing, (11) dot arrangement phase control processing (rightward dot, leftward dot), (12) isolated point removal processing,
(13) Image area separation processing (color determination, attribute determination, adaptive processing), (14) density conversion processing, and the like.

The processing performed by the image writing unit 104 includes the following.

For example, (1) edge smoothing processing (jaggy correction processing), (2) correction processing for dot rearrangement,
(3) image signal pulse control processing, (4) parallel data and serial data format conversion processing, and the like.

(Hardware Configuration of Digital MFP)
Next, a hardware configuration when the image processing apparatus according to the first embodiment forms a digital multifunction peripheral will be described. FIG. 2 is a block diagram illustrating an example of a hardware configuration of the image processing apparatus according to the first embodiment.

In the block diagram of FIG. 2, the image processing apparatus according to the first embodiment includes a reading unit 201, a sensor board unit 202, an image data control unit 203, an image processing processor 204, a video Data control unit 205 and image forming unit (engine) 206
And The image processing apparatus according to the first embodiment includes a process controller 211, a RAM 212, and a ROM 213 via a serial bus 210.

The image processing apparatus according to the first embodiment includes an image memory access control unit 221 and a facsimile control unit 224 via a parallel bus 220.
And an image memory access control unit 22
1, a memory module 222, a system controller 231, a RAM 232, and a ROM
233 and an operation panel 234.

Here, the relationship between each of the above components and each of the units 100 to 104 shown in FIG. 1 will be described. That is, the reading unit 201 and the sensor board
The function of the image reading unit 101 shown in FIG. 1 is realized by the unit 202. Similarly, the function of the image data control unit 100 is realized by the image data control unit 203. Similarly, the image processor 204
Realizes the function of the image processing unit 103.

Similarly, the video data control unit 205
The image writing unit 104 is realized by the image forming unit (engine) 206. Similarly, the image memory access control unit 221 and the memory module 2
The image memory control unit 102 is realized by 22.

Next, the contents of each component will be described. The reading unit 201 that optically reads a document includes a lamp, a mirror, and a lens, and condenses the reflected light of the lamp irradiation on the document to a light receiving element by the mirror and the lens.

A light receiving element, for example, a CCD is a sensor
The image data that is mounted on the board unit 202 and converted into an electric signal by the CCD is converted into a digital signal and then output (transmitted) from the sensor board unit 202.

The image data output (transmitted) from the sensor board unit 202 is transmitted to an image data control unit 203.
Is input (received). Functional device (processing unit)
The transmission of image data between the data buses is controlled entirely by the image data control unit 203.

The image data control unit 203 transfers data between the sensor board unit 202, the parallel bus 220, and the image processor 204, and processes the image data with the process controller 21 for the image data.
1 and a system controller 231 that controls the entire image processing apparatus. RAM2
Reference numeral 12 is used as a work area of the process controller 211, and the ROM 213 stores a boot program and the like of the process controller 211.

The image data output (transmitted) from the sensor board unit 202 is transmitted to the image data control unit 203.
(Transmit) to the image processor 204 via
Then, the signal deterioration due to the quantization into the optical system and the digital signal (referred to as the signal deterioration of the scanner system) is corrected and output (transmitted) to the image data control unit 203 again.

The image memory access control unit 221 comprises:
It controls writing / reading of image data to / from the memory module 222. In addition, the parallel bus 220
Controls the operation of each component connected to. Also, RAM
232 is used as a work area of the system controller 231, and the ROM 233 stores a boot program and the like of the system controller 231.

The operation panel 234 inputs the processing to be performed by the image processing apparatus. For example, the type of process (copying, facsimile transmission, image reading, printing, etc.), the number of processes, and the like are input. Thereby, the input of the image data control information can be performed. The contents of the facsimile control unit 224 will be described later.

Next, a job to be stored in the memory module 222 and reused for the read image data,
There are jobs that are not stored in the memory module 222, and each case will be described. As an example of storing in the memory module 222, when copying a plurality of sheets of one document, the reading unit 201 is operated only once, and the image data read by the reading unit 201 is stored in the memory module 222. There is a method of reading stored image data a plurality of times.

As an example in which the memory module 222 is not used, when only one document is copied, the read image data may be reproduced as it is, so that the memory module 222 by the image memory access control unit 221 is used. You do not need to access to.

First, when the memory module 222 is not used, the data transferred from the image processor 204 to the image data controller 203 is returned from the image data controller 203 to the image processor 204 again. The image processor 204 performs image quality processing for converting luminance data by the CCD in the sensor board unit 202 into area gradation.

The image data after the image quality processing is transferred from the image processing processor 204 to the video data control unit 205. The post-processing relating to the dot arrangement and the pulse control for reproducing the dots are performed on the signal changed to the area gradation, and then the reproduced image is formed on the transfer paper in the image forming unit 206.

Next, a description will be given of the flow of image data when additional processing such as rotation in the image direction and synthesis of images are performed at the time of reading out images stored in the memory module 222. The image data transferred from the image processor 204 to the image data control unit 203 is sent from the image data control unit 203 to the image memory access control unit 221 via the parallel bus 220.

Here, the system controller 23
1, control of access to image data and the memory module 222, expansion of print data of the external PC (personal computer) 223, and compression / expansion of image data for effective use of the memory module 222. .

The image data sent to the image memory access control unit 221 is stored in the memory module 222 after data compression, and the stored image data is read as needed. The read image data is decompressed, restored to the original image data, and returned from the image memory access control unit 221 to the image data control unit 203 via the parallel bus 220.

After the image data is transferred from the image data control unit 203 to the image processor 204, image quality processing and video / video processing are performed.
The data control unit 205 performs pulse control, and the image forming unit 206 forms a reproduced image on transfer paper.

In the flow of image data, the function of the digital multi-function peripheral is realized by the bus control by the parallel bus 220 and the image data control unit 203. The facsimile transmission function performs image processing on the read image data by the image processor 204, and executes the image data control unit 2.
03 and the facsimile control unit 224 via the parallel bus 220. The facsimile control unit 224 performs data conversion to a communication network, and transmits the data to a public line (PN) 225 as facsimile data.

On the other hand, the received facsimile data is
Line data from the public line (PN) 225 is converted into image data by the facsimile control unit 224 and transferred to the image processor 204 via the parallel bus 220 and the image data control unit 203. In this case, no special image quality processing is performed, the dot rearrangement and the pulse control are performed in the video data control unit 205, and the reproduced image is formed on the transfer paper in the image forming unit 206.

In a situation where a plurality of jobs, for example, a copy function, a facsimile transmission / reception function, and a printer output function operate in parallel, allocation of the right to use the reading unit 201, the imaging unit 206, and the parallel bus 220 to the job is performed by the system controller. 231 and the process controller 211.

The process controller 211 controls the flow of image data, and the system controller 231
Controls the entire system and manages the activation of each resource. In addition, the function selection of the digital multi-function peripheral is selectively inputted on the operation panel (operation unit) 234, and the processing contents such as the copy function and the facsimile function are set.

The system controller 231 and the process controller 211 communicate with each other via the parallel bus 220, the image data control unit 203, and the serial bus 210. Specifically, communication between the system controller 231 and the process controller 211 is performed by performing data format conversion for the data interface between the parallel bus 220 and the serial bus 210 in the image data control unit 203.

(Resolution Conversion Processing and Gradation Conversion Processing) Next, the outline of the resolution conversion processing and gradation conversion processing of the image processor 204 constituting the image processing unit 103 will be described. FIG. 3 is a block diagram illustrating an outline of resolution conversion processing and gradation conversion processing of the image processor 204 of the image processing apparatus according to the first embodiment. FIG. 4 is an image processing according to the first embodiment. 6 is a flowchart illustrating a sequence of a series of processes in the device.

As shown in FIG. 3, the image processor 204 includes a dither processing section 301 as dither processing means.
And a resolution / gradation conversion unit 302 as conversion means having a conversion table. And roughly,
As shown in FIG. 4, first, dither processing is performed (step S401), and each pixel of the input image signal is replaced with a pixel pattern having a predetermined gradation or less based on the conversion table, thereby performing resolution conversion processing and gradation conversion. Processing is performed (step S402).

In the following description, an input image signal having 256 gradations is subjected to dither processing to generate an image signal having 9 gradations, and the resolution is doubled based on the conversion table. A case where the gradation is converted into three gradations will be described. However, this does not limit the present invention.

The dither processing section 301 shown in FIG. 3 receives the input image signal (Ndp) input from the image data control section 203.
i, 256 gradations) based on the dither threshold matrix to generate a 9-gradation (Ndpi) image signal after dither processing. Then, matrix position information corresponding to the dither threshold matrix used for the dither processing is output to the resolution / gradation conversion unit 302 together with the generated image signal after the dither processing.

Here, the dither threshold value matrix in the dither processing unit 301 is associated with the dither threshold value for converting the gradation from 256 gradations to 9 gradations and the dither threshold value. It has matrix position information. FIG. 5 is an explanatory diagram showing an example of the correspondence between the dither threshold and the matrix position information in the dither threshold matrix, and FIG. 6 is a diagram showing the correspondence between the pixel growth direction and the assignment code in the matrix position information. It is explanatory drawing which shows an example.

As shown in FIG. 5, the dither threshold matrix (3 × 3) has a dither threshold and matrix position information, and this matrix position information is associated with the dither threshold. . For example, the dither threshold matrix 1 shown in FIG.
, The pixels (gradations) grow in a spiral around the center, and the corresponding matrix position information also shows the spiral pixel growth direction.

In this case, since the dither processing section 301 converts the gradation from 256 gradations to 9 gradations, nine dither threshold value matrices are prepared as shown in FIG. All of the nine dither threshold matrixes have matrix position information having the same configuration.

Since such matrix position information can indicate eight pixel growth directions, eight patterns of matrix position information to which codes corresponding to the pixel growth directions are assigned can be obtained as shown in FIG. For example, the matrix position information indicating the downward pixel growth direction is assigned a code (000b) as matrix position information 1, and the matrix position information indicating the upward pixel growth direction is defined as matrix position information 2. Code (001
b) is assigned.

The matrix position information to which codes are assigned according to the correspondence shown in FIG.
Along with the image signal after dither processing converted to gradation,
Output to the resolution / gradation conversion unit 302.

The resolution / gradation conversion unit 302 shown in FIG.
A conversion table is provided for storing the three gradation pixel patterns in association with the nine gradations that the image signal after dither processing can take. Then, based on the conversion table, each pixel of the image signal after dither processing is replaced with a corresponding pixel pattern,
The replaced pixel pattern is output to the image data control unit 203 or the video data control unit 205 as an output image signal.

FIG. 7 is an explanatory diagram showing an example of the configuration of the conversion table. As shown in FIG. 7, the corresponding pixel pattern is selected based on the matrix position information and the gradation of the image signal after dither processing. Here, in the 2 × 2 pixel pattern shown in FIG. 7, no mark indicates 0 gradation (00b), Δ indicates 1 gradation (01b), and ○ indicates 2 gradation (11b). As a result, the resolution is doubled, and the gray scale is converted from 9 gray scales to 3 gray scales.

For example, when the matrix position information input from dither processing section 301 is matrix position information 1, the matrix position information of the dither threshold matrix used for dither processing indicates the downward pixel growth direction. Therefore, the pixel pattern to be selected also has a pattern arrangement in which pixels grow downward, as shown in FIG.

As described above, in the image processing apparatus according to the first embodiment, since the dither threshold matrix has matrix position information indicating the pixel growth direction, the dither threshold matrix is used to perform the dither process again. Resolution conversion and gradation conversion can be performed without a large-capacity memory for storing a dither threshold matrix.

Further, the image processing apparatus according to the first embodiment can perform resolution conversion and gradation conversion based on the conversion table, thereby optimizing the performance of the image data conversion processing. Becomes possible.

[Second Embodiment] The first embodiment is now described.
In the description, the case where the output image is not distinguished whether it is text or a photograph is described, but the present invention is not limited to this, and the output image is text,
Resolution conversion and gradation conversion can be performed by distinguishing between a photograph and a mixture of characters and photographs. Thus, in a second embodiment, an image processing apparatus that performs resolution conversion and gradation conversion based on the image quality mode of an output image will be described.

FIG. 8 is a block diagram showing an outline of resolution conversion processing and gradation conversion processing of the image processor 204 of the image processing apparatus according to the second embodiment. It is to be noted that the same reference numerals are given to the portions having the same functions as the respective portions described in the first embodiment, and the detailed description thereof will be omitted.

As shown in FIG. 8, the image processor 204 includes a dither processing section 301 as dither processing means.
And a resolution / gradation conversion unit 801 as conversion means having a conversion table for each image quality mode. Schematically, as shown in FIG. 8, after performing dither processing, each pixel of the input image signal is replaced with a pixel pattern having a predetermined gradation or less based on the conversion table, thereby achieving resolution conversion processing and gradation processing. Performs tone conversion processing.

In the following description, an input image signal of 256 gradations is subjected to dither processing to generate an image signal of 9 gradations, and the resolution is doubled based on a conversion table. A case where the gradation is converted into three gradations will be described. However, this does not limit the present invention.

The resolution / gradation conversion unit 801 shown in FIG.
A conversion table is provided for each image quality mode, in which a pixel pattern of three gradations is stored in association with every nine gradations that can be taken by the image signal after dither processing. Then, the image data control unit 203
, A pixel pattern group corresponding to the image quality mode is selected from the conversion table based on the image quality mode information input from the CPU, and resolution conversion and gradation conversion are performed based on the selected pixel pattern group.

FIG. 9 is an explanatory diagram showing an example of the structure of the conversion table when the image quality mode is the character mode.
FIG. 10 is an explanatory diagram showing an example of the configuration of the conversion table when the image quality mode is the photograph mode.
FIG. 9 is an explanatory diagram illustrating an example of a configuration of a conversion table when an image quality mode is a text / photo mixed mode. Here, a case where three image quality modes are provided will be described. However, other modes can be provided.

Here, when it is desired to output an image composed of characters (character mode), it is desirable to reproduce and output sharp character edges. Output can be suppressed. Therefore, in the character mode, a conversion table having a pixel pattern that makes extensive use of two gradations with high contrast as shown in FIG. 9 is used.

When it is desired to output an image composed of photographs (photo mode), it is desired to reproduce intermediate gradations. Therefore, by using a pixel pattern that frequently uses one gradation with low contrast, It is possible to output with the deterioration of the image quality suppressed. Therefore, in the photograph mode, a conversion table having a pixel pattern that makes extensive use of one gradation with low contrast as shown in FIG. 10 is used.

If it is desired to output an image in which characters and photographs are mixed (character / photo mixed mode), a conversion table having a pixel pattern intermediate between the character mode and the photo mode as shown in FIG. Is used.

As described above, the image processing apparatus according to the second embodiment can perform resolution conversion and gradation conversion based on the image quality mode of the output image and the conversion table. It is possible to perform a conversion process reflecting the image quality characteristics of the image.

[Third Embodiment] Now, the first embodiment will be described.
In cases 2 and 3, the case where resolution conversion and gradation conversion are performed by referring to a conversion table based on matrix position information indicating a dot growth direction in a dither threshold matrix used for dither processing is described. The present invention is not limited to this. The dot growth direction can be switched, and resolution conversion and gradation conversion can be performed by referring to a conversion table based on the switched dot growth direction information. Therefore, in the third embodiment,
An image processing apparatus that switches the dot growth direction and performs resolution conversion and gradation conversion based on the switched dot growth direction information will be described.

FIG. 12 is a block diagram showing an outline of resolution conversion processing and gradation conversion processing of the image processor 204 of the image processing apparatus according to the third embodiment. 9 is a flowchart illustrating a procedure of a series of processes in the image processing apparatus. In addition,
The same reference numerals are given to the portions having the same functions as the respective portions described in the first and second embodiments, and the detailed description thereof will be omitted.

As shown in FIG. 12, the image processor 204 includes a dither processing unit 30 as dither processing means.
1, conversion table and dot growth direction switching unit 120
2 and a resolution / gradation conversion unit 1201 having the same. And roughly, after performing dither processing,
As shown in FIG. 13, first, the dot growth direction information is determined (step S1301), the dot growth direction information is updated (step S1302), and resolution conversion and gradation conversion are performed based on the conversion table (step S1302). Step S1303).

In the following description, an input image signal having 256 gradations is subjected to dither processing to generate an image signal having 9 gradations, and the resolution is doubled based on a conversion table. A case where the gradation is converted into three gradations will be described. However, this does not limit the present invention.

A resolution / gradation converter 1201 shown in FIG.
Includes a conversion table that stores pixel patterns of three gradations in association with nine possible gradations of an image signal after dither processing, and a dot growth direction switching unit 1202 that switches a dot growth direction. Then, resolution conversion and gradation conversion are performed with reference to the conversion table based on the dot growth direction information determined by the dot growth direction switching unit 1202.

The dot growth direction switching unit 1202 includes:
The dot growth direction information is stored, and the dot growth direction switching unit 1202 refers to the stored dot growth direction information of the adjacent pixels located at the upper left, immediately above, and upper right of the pixel of interest to determine the adjacent pixel. While determining the dot growth direction information of the target pixel so that the dots touch,
The stored dot growth direction information of the target pixel is updated to the determined dot growth direction information.

Here, a case will be described in which the dot growth direction information of the adjacent pixels located at the upper left, right above, and upper right of the target pixel is referred to. However, the present invention is not limited to this. It is also possible to refer to eight adjacent pixels.

FIG. 14 is a block diagram showing an outline of the processing for determining the dot growth direction information of the target pixel.
FIG. 16 is an explanatory diagram showing a positional relationship between a target pixel and an adjacent pixel, and FIG. 16 is an explanatory diagram showing an example of a correspondence relationship between a dot growth direction and an assignment code in dot growth direction information.

FIG. 17 is an explanatory diagram showing an example of the correspondence between the dot growth direction information of the adjacent pixel and the dot growth direction instruction code for the pixel of interest. FIG. FIG. 9 is an explanatory diagram showing an example of a correspondence relationship between dot growth direction determination codes and dot growth direction information determined based on these codes. Hereinafter, a process of determining and updating the dot growth direction information of the target pixel by the dot growth direction switching unit 1202 will be described with reference to these accompanying drawings.

As shown in FIG. 14, first, dot growth direction information of adjacent pixels (three reference pixels shown in FIG. 15) located at the upper left, immediately above, and upper right of the target pixel is stored. Based on the dot growth direction information, a dot growth direction instruction code for the target pixel is selected. Next, the dot growth direction determining code for the target pixel is calculated by calculating the logical sum of the selected dot growth instruction codes. Then, the dot growth direction information of the target pixel is determined based on the calculated dot growth direction determination code and the gradation after the dither processing.

Here, as the dot growth direction information, as shown in FIG. 16, four patterns of dot growth direction information to which codes corresponding to the dot growth directions can be taken. For example, a code (00b) is assigned to the dot growth direction information indicating the dot growth direction from the lower right to the upper left as dot growth direction information 1, and the dot growth direction indicates the dot growth direction from the lower left to the upper right. As the direction information, a code (01b) is assigned as the dot growth direction information 2.

As shown in FIG. 17, the dot growth direction designating code for the target pixel is uniquely selected based on the positional relationship between the reference pixel and the target pixel and the dot growth direction information of the reference pixel. For example, if the reference pixel located at the upper left of the target pixel has dot growth direction information 1, it means that the dot of the reference pixel has grown from the lower right to the upper left. By growing from the upper left to the lower right, the dot of the reference pixel and the dot of the target pixel come into contact. Therefore, in this case, as shown in FIG. 17, the dot growth direction instruction code (10b) for growing the dots from the upper left to the lower right is selected.

On the other hand, if the reference pixel located directly above the pixel of interest has dot growth direction information 1, it means that the dot of the reference pixel has grown from lower right to upper left, and If the dot of the pixel is grown from the lower left to the upper right, the dot of the reference pixel and the dot of the target pixel come into contact. If the reference pixel located at the upper right of the target pixel has dot growth direction information 2, it means that the dot of the reference pixel is growing from the lower left to the upper right. If you grow from the top right
The dot of the reference pixel and the dot of the target pixel come into contact.

As described above, according to the purpose of selecting the dot growth direction instruction code so that the reference pixel and the dot of the target pixel are in contact with each other, the dot growth direction instruction code for the target pixel is changed as shown in FIG. And the dot growth direction information of the reference pixel.

In FIG. 17, the dot growth direction instruction code (10b) is a code for instructing the dot growth from upper left to lower right, and the dot growth direction instruction code (01b) is from upper right to lower left. The dot growth direction instruction code (00b) is a code that does not instruct dot growth in any direction. The dot growth direction determining code of the pixel of interest is calculated by taking the logical sum of the three dot growth direction instruction codes selected based on the correspondence shown in FIG.

Next, as shown in FIG. 18, the dot growth direction information of the target pixel is uniquely determined based on the dot growth direction determination code calculated from the dot growth direction instruction code and the gradation after dither processing. It is determined. For example, if the tone after the dither processing is 0 tone, it means that no dot is to be printed. Therefore, regardless of the dot growth direction determination code, the tone is located directly above the target pixel. The dot growth direction information of the reference pixel is determined as the dot growth direction information of the target pixel.

On the other hand, the gradation after the dither processing is changed from 1 gradation to 8 gradations.
If it is a gradation and the dot growth direction determination code is (00b), it means that all of the reference pixels have dot growth direction information 3 or 4, and the dots of the target pixel and the reference pixel are in contact with each other. Is not possible, so 1
In order to make contact with the reference pixel after the line, the dot growth direction information of the reference pixel located immediately above the pixel of interest and X
The axially symmetric dot growth direction information is determined as the dot growth direction information of the target pixel.

Further, the gradation after the dither processing is changed from 1 gradation to 8 gradations.
Gradation, and the dot growth direction determination code is (01b)
In the case of (10b) or (11b), FIG.
As shown in (1), the dot growth direction information of the target pixel is determined.

Then, based on the determined dot growth direction information of the target pixel, the previously stored dot growth direction information of the target pixel is updated to the determined dot growth direction information. Further, based on the determined dot growth direction information of the target pixel and the gradation after dither processing, resolution conversion and gradation conversion are performed by referring to a conversion table. FIG. 19 is an explanatory diagram illustrating an example of the configuration of the conversion table according to the third embodiment.

As described above, the image processing apparatus according to the third embodiment can appropriately switch the dot growth direction of the target pixel, thereby suppressing the generation of isolated points in the output image. Becomes

Further, the image processing apparatus according to the third embodiment can switch the dot growth direction information of the target pixel by referring to the dot growth direction information of the pixel adjacent to the target pixel. , It is possible to effectively suppress the generation of isolated points.

The image processing apparatus according to the third embodiment updates the dot growth direction information of the target pixel stored in advance by referring to the dot growth direction information of the pixel adjacent to the target pixel. Accordingly, generation of isolated points in the output image can be more effectively suppressed.

[0116]

As described above, according to the first aspect of the present invention, the dither processing means performs dither processing on each pixel of the input image data of the p-gradation to obtain the pixel value of each pixel. Matrix position information indicating the growth direction of the pixel is output, and the conversion table stores the matrix position information and m gradations (n> n) for each possible gradation of each pixel of the image data after the dither processing by the dither processing means. m) The following pixel patterns are stored in association with each other, and the conversion means replaces each pixel of the image data after the dither processing with a pixel pattern of the m or less gradation based on the conversion table. Since the resolution conversion and the gradation conversion of the image data are performed, it is possible to obtain an image processing apparatus capable of optimizing the performance of the conversion processing of the image data.

According to a second aspect of the present invention, in the first aspect of the present invention, the conversion means includes Ndp.
Since the image data of i and n gradations is converted into image data of N × 2 dpi and m gradations, it is possible to optimize the performance of the conversion processing of the image data while suppressing the deterioration of the image quality of the output image. This provides an effect that a simple image processing device can be obtained.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the conversion table may include a level which can be taken by each pixel of the image data after the dither processing by the dither processing means. A plurality of sets of pixel patterns for each key are stored, and the conversion means selects the pixel pattern group based on the image quality mode of the output image, so that it is possible to perform a conversion process reflecting the image quality characteristics of characters or photographs. This provides an effect that a simple image processing device can be obtained.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the conversion means includes an isolated image on the image data subjected to the resolution conversion and the gradation conversion. Since the dot growth direction is switched so as to suppress the generation of points, an effect is obtained that an image processing apparatus capable of suppressing the generation of isolated points in the output image can be obtained.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the conversion means includes the m
Storage means for storing information relating to the dot growth direction of a pixel having a gradation or less, and determining the dot growth direction of the pixel based on the information relating to the dot growth direction stored in the storage means; Since the apparatus includes the growth direction determining means for updating the storage contents of the means, it is possible to obtain an image processing apparatus capable of effectively suppressing generation of isolated points in an output image.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the growth direction determining means determines a dot growth direction of an adjacent pixel located at the upper left, right above, and upper right of the target pixel. , And the dot growth direction of the pixel of interest is determined such that the dot is in contact with the referenced adjacent pixel, so that an image processing apparatus capable of effectively suppressing the generation of isolated points in the output image can be obtained. This has the effect.

According to the seventh aspect of the present invention, in the dithering step, dithering is performed on each pixel of the input image data of the p-gradation to obtain a pixel value of each pixel and a growth direction of the pixel. And converting the matrix position information and m gradations (n> m) or less for each possible gradation of each pixel of the image data after the dither processing in the dither processing step. Based on the conversion table in which the pixel patterns are stored in association with each other, each pixel of the image data after the dither processing is replaced with a pixel pattern having the m or less gradation and the resolution conversion and the gradation of the image data after the dither processing are performed. Since tone conversion is performed, an effect is obtained that an image processing method capable of optimizing the performance of image data conversion processing can be obtained.

Further, according to the invention described in claim 8, in the invention described in claim 7, the conversion step is performed using Ndp.
Since the image data of i and n gradations is converted into image data of N × 2 dpi and m gradations, it is possible to optimize the performance of the conversion processing of the image data while suppressing the deterioration of the image quality of the output image. This provides an effect that a simple image processing method can be obtained.

According to the ninth aspect of the present invention, in the seventh or eighth aspect of the present invention, the conversion table may include a level that can be taken by each pixel of the image data after the dither processing by the dither processing means. A plurality of sets of pixel patterns for each key are stored, and the conversion step selects the pixel patterns based on the image quality mode of the output image, so that a conversion process that reflects the image quality characteristics of characters or photographs can be performed. This provides an effect that a simple image processing method can be obtained.

According to the tenth aspect of the present invention,
The invention according to any one of claims 7 to 9, wherein the conversion step includes changing a dot growth direction so as to suppress generation of an isolated point on the image data subjected to the resolution conversion and the gradation conversion. Since the switching is performed, an effect is obtained that an image processing method capable of suppressing generation of isolated points in the output image can be obtained.

According to the eleventh aspect of the present invention,
11. The dot growth direction according to claim 10, wherein the conversion step determines the dot growth direction of the pixel based on information on the dot growth direction of the pixel of m or less gradation stored in a predetermined storage unit. Accordingly, since the storage content of the storage unit is updated, it is possible to obtain an image processing method capable of effectively suppressing generation of an isolated point in an output image.

According to the twelfth aspect of the present invention,
12. The invention according to claim 11, wherein the conversion step refers to a dot growth direction of an adjacent pixel located at the upper left, right above, and upper right of the pixel of interest, and the pixel of interest is arranged such that the referenced adjacent pixel is in contact with the dot. Since the dot growth direction is determined, it is possible to obtain an image processing method capable of effectively suppressing generation of isolated points in an output image.

According to the thirteenth aspect of the present invention,
By recording a program for causing a computer to execute the method according to any one of claims 7 to 12, the program can be machine-readable, whereby the operation of any one of claims 7 to 12 can be performed. There is an effect that a recording medium that can be executed by a computer is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram functionally showing a configuration of an image processing apparatus according to a first embodiment of the present invention;

FIG. 2 is a block diagram illustrating an example of a hardware configuration of the image processing apparatus according to the first embodiment;

FIG. 3 is a block diagram illustrating an outline of resolution conversion processing and gradation conversion processing of an image processor 204 of the image processing apparatus according to the first embodiment.

FIG. 4 is a flowchart illustrating a procedure of a series of processes in the image processing apparatus according to the first embodiment;

FIG. 5 is an explanatory diagram showing an example of a correspondence relationship between a dither threshold value and matrix position information in a dither threshold value matrix.

FIG. 6 is an explanatory diagram showing an example of a correspondence relationship between pixel growth directions and assignment codes in matrix position information.

FIG. 7 is an explanatory diagram illustrating an example of a configuration of a conversion table.

FIG. 8 is a block diagram illustrating an outline of a resolution conversion process and a gradation conversion process of an image processor 204 of the image processing apparatus according to the second embodiment.

FIG. 9 is an explanatory diagram illustrating an example of a configuration of a conversion table when an image quality mode is a character mode.

FIG. 10 is an explanatory diagram illustrating an example of a configuration of a conversion table when an image quality mode is a photograph mode.

FIG. 11 is an explanatory diagram showing an example of the configuration of a conversion table when the image quality mode is a mixed text / photo mode.

FIG. 12 is a block diagram illustrating an outline of resolution conversion processing and gradation conversion processing of an image processor 204 of the image processing apparatus according to the third embodiment.

FIG. 13 is a flowchart illustrating a procedure of a series of processes in the image processing apparatus according to the third embodiment;

FIG. 14 is a block diagram illustrating an outline of a process of determining dot growth direction information of a target pixel.

FIG. 15 is an explanatory diagram illustrating a positional relationship between a target pixel and an adjacent pixel.

FIG. 16 is an explanatory diagram showing an example of a correspondence relationship between dot growth directions and assignment codes in dot growth direction information.

FIG. 17 is an explanatory diagram showing an example of a correspondence relationship between dot growth direction information of an adjacent pixel and a dot growth direction instruction code for a target pixel.

FIG. 18 is an explanatory diagram showing an example of a correspondence relationship between a tone after dither processing, a dot growth direction determination code, and dot growth direction information determined based on these.

FIG. 19 is an explanatory diagram illustrating an example of a configuration of a conversion table according to the third embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Image data control unit 101 Image reading unit 102 Image memory control unit 103 Image processing unit 104 Image writing unit 201 Reading unit 202 Sensor board unit 203 Image data control unit 204 Image processing processor 205 Video data control unit 206 Image formation Unit (engine) 210 Serial bus 211 Process controller 212,232 RAM 213,233 ROM 220 Parallel bus 221 Image memory access control unit 222 Memory module 223 Personal computer (PC) 224 Facsimile control unit 225 Public line 231 System Controller 234 Operation panel 301 Dither processing unit 302,801,1201 Resolution / gradation conversion unit 1202 dot growth direction switching unit

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yuji Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Hiroyuki Kawamoto 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Ricoh Co., Ltd. (72) Inventor: Sugiko Shikigi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Ishii (72) Rie Ishii 1-3-6, Nakamagome, Ota-ku, Tokyo Stock Company (72) Inventor Hideto Miyazaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Yoshiyuki 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72 Inventor Shinya Miyazaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Goji Tone 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Association Ricoh Co., Ltd. (72) Inventor Fumio Yoshizawa 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. 5B057 CA08 CA12 CA16 CB07 CB12 CB16 CD05 CE13 CH01 CH07 CH11 5C076 AA21 BA07 BB04 BB44 5C077 LL06 LL19 MP01 NN08 NN19 NP01 PP15 PP20 PQ08 PQ12 PQ22 PQ23 RR09

Claims (13)

[Claims] 1. A dither process is performed on input image data of p gradation read from an image reading unit to perform n dither processing (p> n).
An image processing apparatus that generates dither processing for each pixel of the input image data of the p-gradation, and outputs a pixel value of each pixel and matrix position information indicating a growth direction of the pixel. A conversion table for storing, in association with the matrix position information and a pixel pattern of m or less gradations (n> m), for each possible gradation of each pixel of the image data after the dither processing by the dither processing means A conversion unit that replaces each pixel of the image data after the dither processing with a pixel pattern having the m or less gradation based on the conversion table, and performs resolution conversion and gradation conversion of the image data after the dither processing. An image processing apparatus comprising: 2. The image processing apparatus according to claim 1, wherein the conversion unit converts the image data of Ndpi, n gradations into image data of N × 2 dpi, m gradations. 3. The conversion table stores a plurality of sets of pixel patterns for each gradation that can be taken by each pixel of the image data after the dither processing by the dither processing means. The image processing apparatus according to claim 1, wherein the pixel pattern group is selected based on the following. 4. The apparatus according to claim 1, wherein said conversion means switches a dot growth direction so as to suppress generation of an isolated point on the image data subjected to the resolution conversion and the gradation conversion. Or the image processing apparatus according to 3. 5. A storage means for storing information relating to a dot growth direction of a pixel having m or less gradations,
Growth direction determining means for determining the dot growth direction of the pixel based on the information on the dot growth direction stored in the storage means and updating the storage content of the storage means according to the dot growth direction. The image processing device according to claim 4. 6. The growth direction determining means refers to a dot growth direction of an adjacent pixel located at the upper left, right above, and upper right of the target pixel, and determines a dot of the target pixel such that the referenced adjacent pixel is in contact with the dot. The image processing apparatus according to claim 5, wherein a growth direction is determined. 7. A dithering process is performed on input image data of p gradation read from an image reading unit to obtain n gradation (p> n).
In the image processing method for generating the image data, dither processing is performed on each pixel of the input image data of the p-gradation to output a pixel value of each pixel and matrix position information indicating a growth direction of the pixel. A conversion table in which the matrix position information and a pixel pattern of m or less gradations (n> m) are associated with each other for each gradation that can be taken by each pixel of the image data after the dither processing in the dither processing step And converting each pixel of the image data after the dither processing to a pixel pattern having the m or less gradation and performing resolution conversion and gradation conversion of the image data after the dither processing. An image processing method characterized in that: 8. The image processing method according to claim 7, wherein said converting step converts the image data of Ndpi, n gradations into image data of N × 2 dpi, m gradations. 9. The conversion table stores a plurality of sets of pixel patterns for each gradation that can be taken by each pixel of the image data after the dither processing by the dither processing means. The image processing method according to claim 7, wherein the pixel pattern group is selected based on: 10. The method according to claim 7, wherein in the conversion step, a dot growth direction is switched so as to suppress generation of an isolated point on the image data on which the resolution conversion and the gradation conversion have been performed. Or the image processing method according to 9. 11. The conversion step includes determining a dot growth direction of a pixel based on information on a dot growth direction of a pixel having m or less gradations stored in a predetermined storage unit and determining the dot growth direction of the pixel based on the dot growth direction. 11. The image processing method according to claim 10, wherein the storage content of the image is updated. 12. The conversion step refers to a dot growth direction of an adjacent pixel located at the upper left, right above, and upper right of the target pixel, and determines a dot growth direction of the target pixel such that the referred adjacent pixel is in contact with the dot. 12. The image processing method according to claim 11, wherein is determined. 13. A computer-readable recording medium on which a program for causing a computer to execute the method according to claim 7 is recorded.